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<!DOCTYPE html> <html lang="en"> <head> <meta content="text/html; charset=utf-8" http-equiv="content-type"/> <title>From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface</title>  <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport"/> <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/css/bootstrap.min.css" rel="stylesheet" type="text/css"/> <link href="/static/browse/0.3.4/css/ar5iv.0.7.9.min.css" rel="stylesheet" type="text/css"/> <link href="/static/browse/0.3.4/css/ar5iv-fonts.0.7.9.min.css" rel="stylesheet" type="text/css"/> <link href="/static/browse/0.3.4/css/latexml_styles.css" rel="stylesheet" type="text/css"/> <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/js/bootstrap.bundle.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/1.3.3/html2canvas.min.js"></script> <script src="/static/browse/0.3.4/js/addons_new.js"></script> <script src="/static/browse/0.3.4/js/feedbackOverlay.js"></script> <meta content=" 5G Positioning, TDoA, OpenAirInterface, NRPPA, LMF. " lang="en" name="keywords"/> <base href="/html/2409.05217v3/"/></head> <body> <nav class="ltx_page_navbar"> <nav class="ltx_TOC"> <ol class="ltx_toclist"> <li class="ltx_tocentry ltx_tocentry_section"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S1" title="In From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref">I </span><span class="ltx_text ltx_font_smallcaps">Introduction</span></span></a></li> <li class="ltx_tocentry ltx_tocentry_section"> <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S2" title="In From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref">II </span><span class="ltx_text ltx_font_smallcaps">3GPP’s framework for UL-TDOA based positioning </span></span></a> <ol class="ltx_toclist ltx_toclist_section"> <li class="ltx_tocentry ltx_tocentry_subsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S2.SS1" title="In II 3GPP’s framework for UL-TDOA based positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">II-A</span> </span><span class="ltx_text ltx_font_italic">Protocol Required for UL-TDoA Positioning Method in OAI</span></span></a></li> </ol> </li> <li class="ltx_tocentry ltx_tocentry_section"> <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3" title="In From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref">III </span><span class="ltx_text ltx_font_smallcaps">Contribution to the OAI and Implementation Status of UL-TDoA</span></span></a> <ol class="ltx_toclist ltx_toclist_section"> <li class="ltx_tocentry ltx_tocentry_subsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.SS1" title="In III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">III-A</span> </span><span class="ltx_text ltx_font_italic">UL-TDoA Positioning Procedure in OAI</span></span></a></li> <li class="ltx_tocentry ltx_tocentry_subsection"> <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.SS2" title="In III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">III-B</span> </span><span class="ltx_text ltx_font_italic">Enabling ToA estimation in OAI’s gNB</span></span></a> <ol class="ltx_toclist ltx_toclist_subsection"> <li class="ltx_tocentry ltx_tocentry_subsubsection"> <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.SS2.SSS1" title="In III-B Enabling ToA estimation in OAI’s gNB ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">III-B</span>1 </span>gNB-PHY</span></a> <ol class="ltx_toclist ltx_toclist_subsubsection"> <li class="ltx_tocentry ltx_tocentry_paragraph"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.SS2.SSS1.Px1" title="In III-B1 gNB-PHY ‣ III-B Enabling ToA estimation in OAI’s gNB ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title">FAPI interface</span></a></li> </ol> </li> <li class="ltx_tocentry ltx_tocentry_subsubsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.SS2.SSS2" title="In III-B Enabling ToA estimation in OAI’s gNB ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">III-B</span>2 </span>gNB-MAC</span></a></li> </ol> </li> </ol> </li> <li class="ltx_tocentry ltx_tocentry_section"> <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4" title="In From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref">IV </span><span class="ltx_text ltx_font_smallcaps">Validation of our Open-Source UL-TDoA positioning</span></span></a> <ol class="ltx_toclist ltx_toclist_section"> <li class="ltx_tocentry ltx_tocentry_subsection"> <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS1" title="In IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-A</span> </span><span class="ltx_text ltx_font_italic">OAI-rfsimulator based setup</span></span></a> <ol class="ltx_toclist ltx_toclist_subsection"> <li class="ltx_tocentry ltx_tocentry_subsubsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS1.SSS1" title="In IV-A OAI-rfsimulator based setup ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-A</span>1 </span>Preparing the Setup</span></a></li> </ol> </li> <li class="ltx_tocentry ltx_tocentry_subsection"> <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS2" title="In IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-B</span> </span><span class="ltx_text ltx_font_italic">O-RAN based Localization Testbed at EURECOM</span></span></a> <ol class="ltx_toclist ltx_toclist_subsection"> <li class="ltx_tocentry ltx_tocentry_subsubsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS2.SSS1" title="In IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-B</span>1 </span>Deployment</span></a></li> <li class="ltx_tocentry ltx_tocentry_subsubsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS2.SSS2" title="In IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-B</span>2 </span>Logical Architecture</span></a></li> <li class="ltx_tocentry ltx_tocentry_subsubsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS2.SSS3" title="In IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-B</span>3 </span>Ground truth measurements</span></a></li> </ol> </li> <li class="ltx_tocentry ltx_tocentry_subsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS3" title="In IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-C</span> </span><span class="ltx_text ltx_font_italic">Preprocessing and Position Estimation</span></span></a></li> <li class="ltx_tocentry ltx_tocentry_subsection"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.SS4" title="In IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref"><span class="ltx_text">IV-D</span> </span><span class="ltx_text ltx_font_italic">Results</span></span></a></li> </ol> </li> <li class="ltx_tocentry ltx_tocentry_section"><a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S5" title="In From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_title"><span class="ltx_tag ltx_tag_ref">V </span><span class="ltx_text ltx_font_smallcaps">Conclusions</span></span></a></li> </ol></nav> </nav> <div class="ltx_page_main"> <div class="ltx_page_content"> <article class="ltx_document ltx_authors_1line"> <h1 class="ltx_title ltx_title_document">From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface</h1> <div class="ltx_authors"> <span class="ltx_creator ltx_role_author"> <span class="ltx_personname">Adeel Malik1, Mohsen Ahadi2, Florian Kaltenberger26, Klaus Warnke3, Nguyen Tien Thinh2, <br class="ltx_break"/>Nada Bouknana2, Cedric Thienot1, Godswill Onche2, Sagar Arora5 <br class="ltx_break"/> </span><span class="ltx_author_notes">The work included in this paper has been supported by the ”France 2030” investment program through the projects 5G-OPERA and GEO-5G. <span class="ltx_contact ltx_role_affiliation">1<span class="ltx_text ltx_font_italic" id="id1.1.id1">Firecell</span>, Nice, France </span> <span class="ltx_contact ltx_role_affiliation">2<span class="ltx_text ltx_font_italic" id="id2.2.id1">EURECOM</span>, Sophia Antipolis, France </span> <span class="ltx_contact ltx_role_affiliation">3<span class="ltx_text ltx_font_italic" id="id3.3.id1">TU Dresden</span>, Dresden, Germany </span> <span class="ltx_contact ltx_role_affiliation">5<span class="ltx_text ltx_font_italic" id="id4.4.id1">OpenAirInterface Software Alliance</span>, Sophia-Antipolis, France </span> <span class="ltx_contact ltx_role_affiliation">6<span class="ltx_text ltx_font_italic" id="id5.5.id1">Northeastern University</span>, Boston (MA), USA </span></span></span> </div> <div class="ltx_abstract"> <h6 class="ltx_title ltx_title_abstract">Abstract</h6> <p class="ltx_p" id="id6.id1">This paper presents, for the first time, an open-source implementation of the 3GPP Uplink Time Difference of Arrival (UL-TDoA) positioning method using the OpenAirInterface (OAI) framework. UL-TDoA is a critical positioning technique in 5G networks, leveraging the time differences of signal arrival at multiple base stations to determine the precise location of User Equipment (UE). This implementation aims to democratize access to advanced positioning technology by integrating UL-TDoA capabilities into both the Radio Access Network (RAN) and Core Network (CN) components of OAI, providing a comprehensive and 3GPP-compliant solution.</p> <p class="ltx_p" id="id7.id2">The development includes the incorporation of essential protocol procedures, message flows, and interfaces as defined by 3GPP standards. Validation is conducted using two distinct methods: an OAI-RF simulator-based setup for controlled testing and an O-RAN-based Localization Testbed at EURECOM in real-world conditions. The results demonstrate the viability of this open-source UL-TDoA implementation, enabling precise positioning in various environments. By making this implementation publicly available, the study paves the way for widespread research, development, and innovation in the field of 5G positioning technologies, fostering collaboration and accelerating the advancement of cellular network positioning.</p> </div> <div class="ltx_keywords"> <h6 class="ltx_title ltx_title_keywords">Index Terms: </h6> 5G Positioning, TDoA, OpenAirInterface, NRPPA, LMF. </div> <section class="ltx_section" id="S1"> <h2 class="ltx_title ltx_title_section"> <span class="ltx_tag ltx_tag_section">I </span><span class="ltx_text ltx_font_smallcaps" id="S1.1.1">Introduction</span> </h2> <div class="ltx_para" id="S1.p1"> <p class="ltx_p" id="S1.p1.1">5G new radio (NR) represents a major leap in wireless communications, significantly improving speed, connectivity, and latency. Beyond enhancing mobile broadband (eMBB), 5G NR enables ultra-reliable low-latency communication (URLLC) and massive machine-type communications (mMTC). A key innovation within the 5G framework is precise positioning and localization, which is anticipated to create new opportunities across sectors such as automotive, healthcare, logistics, and smart city development.</p> </div> <div class="ltx_para" id="S1.p2"> <p class="ltx_p" id="S1.p2.1">Traditional positioning methods like GPS, Wi-Fi, and Bluetooth Low Energy (BLE) beacons, while commonly used, suffer from limitations regarding accuracy, latency, and reliability. GPS, for instance, provides reliable outdoor coverage but often struggles with accuracy and performance in indoor and densely urban environments, along with high power consumption. Wi-Fi and BLE perform better indoors, but their accuracy can be affected by network density and environmental factors. In contrast, 5G positioning technologies offer superior accuracy, low latency, and consistent performance in both indoor and outdoor scenarios. 5G NR positioning leverages advanced signal characteristics and infrastructure improvements introduced by the new standard. Techniques such as Time Difference of Arrival (TDoA), Angle of Arrival (AoA), and multi-cell Round Trip Time (RTT) are enhanced by 5G’s higher frequency bands, massive multiple-input multiple-output (MIMO) technology, and beamforming capabilities. These advancements enable highly accurate and reliable positioning, even in challenging environments like urban canyons and indoor spaces.</p> </div> <div class="ltx_para" id="S1.p3"> <p class="ltx_p" id="S1.p3.1">Among the various positioning techniques standardized by the 3rd Generation Partnership Project (3GPP) <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib1" title="">1</a>]</cite>, this paper focuses on the Uplink Time Difference of Arrival (UL-TDoA) method. UL-TDoA determines the location of a User Equipment (UE) by analyzing the time differences in the arrival of uplink signals at multiple base stations. However, the practical implementation of UL-TDoA positioning presents several challenges, including the need for precise synchronization between base stations, advanced signal processing, and robust algorithms to manage multipath propagation and non-line-of-sight conditions. Moreover, proprietary solutions can be costly and rigid, potentially hindering innovation and customization for specific needs.</p> </div> <div class="ltx_para" id="S1.p4"> <p class="ltx_p" id="S1.p4.1">In this context, open-source software emerges as a vital tool in democratizing access to advanced technologies, promoting innovation, and supporting collaborative development. OpenAirInterface (OAI) is a notable open-source project that offers a comprehensive, 3GPP-compliant implementation of LTE and 5G Radio Access Network (RAN) and Core Network (CN) components. OAI provides a flexible and effective platform for researchers, developers, and network operators to experiment with and deploy advanced communication technologies <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib2" title="">2</a>]</cite>.</p> </div> <section class="ltx_paragraph" id="S1.SS0.SSS0.Px1"> <h5 class="ltx_title ltx_title_paragraph">Related work</h5> <div class="ltx_para" id="S1.SS0.SSS0.Px1.p1"> <p class="ltx_p" id="S1.SS0.SSS0.Px1.p1.1">There are several examples where OAI is used as a basis for positioning. In <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib3" title="">3</a>]</cite>, OAI is combined with a multi-channel SDR and a custom 2x2 patch antenna array for enhanced cell-ID (E-CID) positioning in indoor scenarios, by using RTT and AoA estimates based on the demodulation reference signal (DM-RS). The HOP-5G project <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib4" title="">4</a>, <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib5" title="">5</a>]</cite> sponsored the development of the PRS in OAI for DL-TDoA positioning for FR1 and FR2 and demonstrated the feasibility of this techniques. Based on this work, <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib6" title="">6</a>]</cite> built a testbed with three OAI base stations or gNBs and a OAI user equipment exploiting the PRS transmissions for DL-TDoA positioning. More recently, a novel framework is presented in <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib7" title="">7</a>]</cite> to estimate the RTT between a UE and a base station (gNB) with existing 5G NR transmissions.</p> </div> <div class="ltx_para" id="S1.SS0.SSS0.Px1.p2"> <p class="ltx_p" id="S1.SS0.SSS0.Px1.p2.1">This paper presents a comprehensive open-source implementation of the 3GPP Uplink Time Difference of Arrival (UL-TDoA) positioning method using the OpenAirInterface (OAI) framework. The primary goal of this work is to integrate UL-TDoA capabilities into both the RAN and CN components of OAI, thereby enabling precise UE positioning within 5G networks. Our implementation enables end-to-end testing of UL-TDoA positioning by incorporating the necessary 3GPP-defined protocol procedures and message exchanges. Key Contributions of this Paper:</p> </div> <div class="ltx_para" id="S1.SS0.SSS0.Px1.p3"> <ul class="ltx_itemize" id="S1.I1"> <li class="ltx_item" id="S1.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S1.I1.i1.p1"> <p class="ltx_p" id="S1.I1.i1.p1.1">Integration of UL-TDoA Support in OAI: We have integrated the UL-TDoA positioning procedure into the OAI framework, enhancing its RAN and CN components to support accurate positioning by implementing the necessary protocol procedures, message flows, and interfaces.</p> </div> </li> <li class="ltx_item" id="S1.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S1.I1.i2.p1"> <p class="ltx_p" id="S1.I1.i2.p1.1">Design and Architecture Insights: We offer detailed insights into integrating UL-TDoA procedures into the OAI architecture, including protocol choices and strategies for 3GPP standards compatibility.</p> </div> </li> <li class="ltx_item" id="S1.I1.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S1.I1.i3.p1"> <p class="ltx_p" id="S1.I1.i3.p1.1">Validation of Implementation: We validate our UL-TDoA implementation using two distinct setups: the OAI-RF simulator-based setup and the O-RAN-based Localization Testbed at EURECOM. These validation methods allow us to demonstrate the functionality and reliability of our implementation under both controlled, simulated conditions and realistic operational scenarios.</p> </div> </li> <li class="ltx_item" id="S1.I1.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S1.I1.i4.p1"> <p class="ltx_p" id="S1.I1.i4.p1.1">Documentation and Tutorial for Implementation: We provide comprehensive documentation and tutorials on how to set up and use the UL-TDoA implementation within the OAI framework. This includes detailed steps for deploying the 5G core and RAN components, configuring the RF simulator, and initiating the positioning procedures.</p> </div> </li> </ul> </div> <div class="ltx_para" id="S1.SS0.SSS0.Px1.p4"> <p class="ltx_p" id="S1.SS0.SSS0.Px1.p4.1">By making this implementation openly available, we aim to provide a valuable resource for the research community and network operators. Our work encourages further exploration and development of UL-TDoA positioning, fostering innovation and collaboration in the field of cellular network positioning technologies.</p> </div> <div class="ltx_para" id="S1.SS0.SSS0.Px1.p5"> <p class="ltx_p" id="S1.SS0.SSS0.Px1.p5.1">The following sections will review the technical background of the UL-TDoA positioning framework, highlighting key network entities and protocols. We will then discuss the capabilities of the OpenAirInterface platform and detail the implementation of UL-TDoA positioning within the OAI framework. Next, we will present the validation of our implementation. Finally, we will conclude with a discussion of the implications of our work and future research directions.</p> </div> </section> </section> <section class="ltx_section" id="S2"> <h2 class="ltx_title ltx_title_section"> <span class="ltx_tag ltx_tag_section">II </span><span class="ltx_text ltx_font_smallcaps" id="S2.1.1">3GPP’s framework for UL-TDOA based positioning </span> </h2> <div class="ltx_para" id="S2.p1"> <p class="ltx_p" id="S2.p1.1">The 3GPP framework for positioning in 5G networks involves a combination of network components, interfaces, and positioning methods to provide accurate and reliable location information for User Equipment (UE). The 3GPP standards supporting UL-TDOA positioning are detailed in technical specification TS 38.305<cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib1" title="">1</a>]</cite>, which outline the technical requirements for all location services, including UL-TDOA. The framework defined by 3GPP for UL-TDOA-based positioning of a target UE, as well as the delivery of location assistance data to a UE with NG-RAN access in 5G systems, is illustrated in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S2.F1" title="Figure 1 ‣ II 3GPP’s framework for UL-TDOA based positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">1</span></a>. The key network components include the UE, Next Generation Radio Access Network (NG-RAN), the Access and Mobility Management Function (AMF), the Location Management Function (LMF), and the Location service LCS entity. These network components are defined as:</p> <ul class="ltx_itemize" id="S2.I1"> <li class="ltx_item" id="S2.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I1.i1.p1"> <p class="ltx_p" id="S2.I1.i1.p1.1">UE: The UE is the mobile device enabled with 5G services (5GS) whose location is being determined.</p> </div> </li> <li class="ltx_item" id="S2.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I1.i2.p1"> <p class="ltx_p" id="S2.I1.i2.p1.1">NG-RAN: The NG-RAN is comprised of at least one Next Generation Node B (gNB). The gNB serves as the base station in 5G networks, facilitating the radio connection between user equipment (UE) and the 5G core network. Each gNB is linked to one or more Transmission Reception Points (TRPs), which are individual antennas or groups of antennas responsible for transmitting and receiving wireless signals. </p> </div> </li> <li class="ltx_item" id="S2.I1.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I1.i3.p1"> <p class="ltx_p" id="S2.I1.i3.p1.1">AMF: The Access and Mobility Management Function (AMF) is an essential part of the 5G core network, tasked with managing access and mobility functions. It oversees UE registration, session management, and ensures seamless mobility across various cells and networks.</p> </div> </li> <li class="ltx_item" id="S2.I1.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I1.i4.p1"> <p class="ltx_p" id="S2.I1.i4.p1.1">LMF: The Location Management Function (LMF) is a central entity within the 5G core network that oversees location services. It coordinates the collection of TDOA measurements and is responsible for calculating the final position of the UE.</p> </div> </li> <li class="ltx_item" id="S2.I1.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I1.i5.p1"> <p class="ltx_p" id="S2.I1.i5.p1.1">LCS entity: The Location Services (LCS) entity manages the delivery of location-based services by processing positioning requests from LCS clients. It coordinates with various network elements to ascertain the user equipment’s (UE) location. LCS clients can include applications installed on the UE or external systems that require the UE’s location data. </p> </div> </li> </ul> </div> <figure class="ltx_figure" id="S2.F1"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="214" id="S2.F1.g1" src="extracted/6285822/fig/Positioning_Architecture.png" width="509"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 1: </span>UE Positioning Architecture applicable to NG-RAN <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib1" title="">1</a>, Section 5.1]</cite></figcaption> </figure> <div class="ltx_para" id="S2.p2"> <p class="ltx_p" id="S2.p2.1">The interface defined by the 3GPP that can be used among different network components in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S2.F1" title="Figure 1 ‣ II 3GPP’s framework for UL-TDOA based positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">1</span></a> is defined as</p> <ul class="ltx_itemize" id="S2.I2"> <li class="ltx_item" id="S2.I2.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I2.i1.p1"> <p class="ltx_p" id="S2.I2.i1.p1.1">NR-Uu: The NR-Uu interface is the radio interface in 5G networks, connecting the User Equipment (UE) to the gNodeB (gNB). It is responsible for the transmission of data, control signals, and user information between the UE and the 5G network. The NR-Uu interface supports various functionalities, including signaling, data transfer, and radio resource management, ensuring efficient communication between the UE and the network.</p> </div> </li> <li class="ltx_item" id="S2.I2.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I2.i2.p1"> <p class="ltx_p" id="S2.I2.i2.p1.1">NG-C: The NG-C interface in 5G networks connects the gNodeB (gNB) to the Access and Mobility Management Function (AMF). It handles control plane tasks like session and mobility management, ensuring efficient communication between the radio access network and the core network. The NG-C interface is transparent to all UE positioning-related procedures, serving only as a transport link for the NR positioning protocols involved in these processes. In positioning procedures involving the gNB, the NG-C interface transparently transfers positioning requests from the LMF to the gNB and delivers positioning results from the gNB to the LMF.</p> </div> </li> <li class="ltx_item" id="S2.I2.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S2.I2.i3.p1"> <p class="ltx_p" id="S2.I2.i3.p1.1">NLs: The NLs interface connects the Location Management Function (LMF) and the Access and Mobility Management Function (AMF) and is transparent to all UE and gNB positioning procedures. It serves as a transport link for the LTE Positioning Protocol (LPP) and NR Positioning Protocol (NRPPa).</p> </div> </li> </ul> </div> <figure class="ltx_figure" id="S2.F2"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_square" height="489" id="S2.F2.g1" src="extracted/6285822/fig/UL_TDOA_procedure.jpg" width="509"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 2: </span>UL-TDoA Positioning Procedure (3GPP) <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib1" title="">1</a>, 8.13.3.4]</cite>.</figcaption> </figure> <section class="ltx_subsection" id="S2.SS1"> <h3 class="ltx_title ltx_title_subsection"> <span class="ltx_tag ltx_tag_subsection"><span class="ltx_text" id="S2.SS1.5.1.1">II-A</span> </span><span class="ltx_text ltx_font_italic" id="S2.SS1.6.2">Protocol Required for UL-TDoA Positioning Method in OAI</span> </h3> <div class="ltx_para" id="S2.SS1.p1"> <p class="ltx_p" id="S2.SS1.p1.1">The 3GPP specifies various positioning methods in its technical report <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib1" title="">1</a>, Section 8]</cite>, this paper focuses specifically on the UL-TDoA positioning method and its open-source implementation within the OpenAirInterface framework.</p> </div> <div class="ltx_para" id="S2.SS1.p2"> <p class="ltx_p" id="S2.SS1.p2.1">In the UL-TDoA positioning method, the UE location is estimated based on UL-RToA measurements gathered at various gNBs/TRPs for uplink signals from the UE, along with other configuration details. To perform these uplink measurements, participating gNBs/TRPs need to be informed about the characteristics of the SRS signal transmitted by the UE for the required measurement period. These characteristics must remain consistent across the periodic SRS transmissions. The LMF directs the serving gNB to instruct the UE to transmit SRS signals for positioning. The serving gNB then decides on the necessary resources and communicates the SRS configuration to the LMF, which in turn relays this information to the neighboring gNBs/TRPs participating in the UE positioning procedure.</p> </div> <div class="ltx_para" id="S2.SS1.p3"> <p class="ltx_p" id="S2.SS1.p3.1">Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S2.F2" title="Figure 2 ‣ II 3GPP’s framework for UL-TDOA based positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">2</span></a> defines the UL-TDoA positioning procedure as per 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib1" title="">1</a>, Section 8.13]</cite>. As illustrated in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S2.F2" title="Figure 2 ‣ II 3GPP’s framework for UL-TDOA based positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">2</span></a>, the NRPPa protocol is integral to the UL-TDoA positioning procedure, facilitating communication between the LMF and gNB. The NRPPa protocol data units (PDUs) enable the exchange of positioning-related information, including configuration settings, measurement requests, and results. This communication allows the gNBs to precisely measure the TDoA of uplink signals from the UE at various TRPs. The measurements obtained are then utilized by the localization algorithm within the LMF to determine the UE’s exact position.</p> </div> <div class="ltx_para" id="S2.SS1.p4"> <p class="ltx_p" id="S2.SS1.p4.1">It is important to note that there is no direct connection between the gNB and the LMF; all NRPPa-related messages must pass through the AMF. Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S2.F3" title="Figure 3 ‣ II-A Protocol Required for UL-TDoA Positioning Method in OAI ‣ II 3GPP’s framework for UL-TDOA based positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">3</span></a> demonstrates the protocol layering required for transferring NRPPa messages between the LMF and gNB. In the next section, we present in detail the messages exchanged by each network element during the NRPPa PDU Transfer process between gNB and LMF.</p> </div> <figure class="ltx_figure" id="S2.F3"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="240" id="S2.F3.g1" src="extracted/6285822/fig/Protocol_Layering_NG-RAN.png" width="349"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 3: </span>Protocol Layering for LMF to NG-RAN Signalling <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib1" title="">1</a>, Section 6.5]</cite></figcaption> </figure> </section> </section> <section class="ltx_section" id="S3"> <h2 class="ltx_title ltx_title_section"> <span class="ltx_tag ltx_tag_section">III </span><span class="ltx_text ltx_font_smallcaps" id="S3.1.1">Contribution to the OAI and Implementation Status of UL-TDoA</span> </h2> <div class="ltx_para" id="S3.p1"> <p class="ltx_p" id="S3.p1.1">In this section, we outline the essential components needed within OAI’s 5G RAN and 5G Core to facilitate the implementation of the UL-TDoA positioning procedure. A summary of our contributions to OAI’s open-source platform is detailed below:</p> <ul class="ltx_itemize" id="S3.I1"> <li class="ltx_item" id="S3.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I1.i1.p1"> <p class="ltx_p" id="S3.I1.i1.p1.1">Contributions to OAI 5G RAN:</p> <ul class="ltx_itemize" id="S3.I1.i1.I1"> <li class="ltx_item" id="S3.I1.i1.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i1.I1.i1.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i1.I1.i1.p1"> <p class="ltx_p" id="S3.I1.i1.I1.i1.p1.1">Implementation of ToA estimation from SRS</p> </div> </li> <li class="ltx_item" id="S3.I1.i1.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i1.I1.i2.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i1.I1.i2.p1"> <p class="ltx_p" id="S3.I1.i1.I1.i2.p1.1">Integration of NRPPa functionalities <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>]</cite></p> </div> </li> <li class="ltx_item" id="S3.I1.i1.I1.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i1.I1.i3.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i1.I1.i3.p1"> <p class="ltx_p" id="S3.I1.i1.I1.i3.p1.1">Development of NRPPa PDU Transfer protocol between AMF and gNB <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib9" title="">9</a>]</cite></p> </div> </li> </ul> </div> </li> <li class="ltx_item" id="S3.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I1.i2.p1"> <p class="ltx_p" id="S3.I1.i2.p1.1">Contributions to OAI 5G Core (LMF):</p> <ul class="ltx_itemize" id="S3.I1.i2.I1"> <li class="ltx_item" id="S3.I1.i2.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i2.I1.i1.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i2.I1.i1.p1"> <p class="ltx_p" id="S3.I1.i2.I1.i1.p1.1">Implementation of LMF-specific procedures <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>]</cite></p> </div> </li> <li class="ltx_item" id="S3.I1.i2.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i2.I1.i2.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i2.I1.i2.p1"> <p class="ltx_p" id="S3.I1.i2.I1.i2.p1.1">Integration of NRPPa functionalities <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>]</cite></p> </div> </li> <li class="ltx_item" id="S3.I1.i2.I1.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i2.I1.i3.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i2.I1.i3.p1"> <p class="ltx_p" id="S3.I1.i2.I1.i3.p1.1">Development of NRPPa PDU transfer protocol between AMF and LMF <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib11" title="">11</a>]</cite></p> </div> </li> </ul> <p class="ltx_p" id="S3.I1.i2.p1.2">Contributions to OAI 5G Core (AMF):</p> <ul class="ltx_itemize" id="S3.I1.i2.I2"> <li class="ltx_item" id="S3.I1.i2.I2.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i2.I2.i1.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i2.I2.i1.p1"> <p class="ltx_p" id="S3.I1.i2.I2.i1.p1.1">Implementation of NRPPa PDU Transfer protocol between AMF and LMF <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib11" title="">11</a>]</cite></p> </div> </li> <li class="ltx_item" id="S3.I1.i2.I2.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I1.i2.I2.i2.1.1.1">–</span></span> <div class="ltx_para" id="S3.I1.i2.I2.i2.p1"> <p class="ltx_p" id="S3.I1.i2.I2.i2.p1.1">Development of NRPPa PDU Transfer protocol between AMF and gNB <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib9" title="">9</a>]</cite></p> </div> </li> </ul> </div> </li> </ul> </div> <div class="ltx_para" id="S3.p2"> <p class="ltx_p" id="S3.p2.1">These contributions significantly enhance the OAI open-source 5G platform’s ability to support precise positioning and location-based services. The following subsection details the specific developments implemented in the OAI codebase to enable the UL-TDoA positioning procedure, which are essential for integrating UL-TDoA functionality within the OAI framework.</p> </div> <figure class="ltx_figure" id="S3.F4"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="607" id="S3.F4.g1" src="x1.png" width="830"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 4: </span>End-to-End Implementation of UL-TDoA Positioning Procedure in OAI.</figcaption> </figure> <section class="ltx_subsection" id="S3.SS1"> <h3 class="ltx_title ltx_title_subsection"> <span class="ltx_tag ltx_tag_subsection"><span class="ltx_text" id="S3.SS1.5.1.1">III-A</span> </span><span class="ltx_text ltx_font_italic" id="S3.SS1.6.2">UL-TDoA Positioning Procedure in OAI</span> </h3> <div class="ltx_para" id="S3.SS1.p1"> <p class="ltx_p" id="S3.SS1.p1.1">Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.F4" title="Figure 4 ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">4</span></a> provides an overview of our end-to-end implementation of the UL-TDoA positioning procedure in OAI. We will now examine each message exchange in this procedure, highlighting the specific developments we contributed to the OAI framework.</p> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p2"> <p class="ltx_p" id="S3.SS1.p2.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p2.1.1">Message 1 Initiation of Location Request:</span></p> </div> <div class="ltx_para" id="S3.SS1.p3"> <p class="ltx_p" id="S3.SS1.p3.1">The UL-TDoA positioning procedure begins with an external API generating a location information request for a target UE for the LMF. As shown in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.F5" title="Figure 5 ‣ III-A UL-TDoA Positioning Procedure in OAI ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">5</span></a> to initiate the location procedure, the external API (which can be an advanced API or a simple one-line command) sends the HTTP post request to <span class="ltx_text ltx_font_italic" id="S3.SS1.p3.1.1">determine-location</span> API of LMF, where the request contains a data structure of type <span class="ltx_text ltx_font_italic" id="S3.SS1.p3.1.2">InputData</span> <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>, Section 6.1.6.2.2]</cite>. To enable the exchange of this message, we first developed the 3gpp-compliant LMF framework and integrated it into OAI’s core network framework<cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib12" title="">12</a>]</cite>. Then within that LMF framework, we develop the determine-location API <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>, Section 6]</cite> to handle the positioning request following the 3gpp standard.</p> </div> <figure class="ltx_figure" id="S3.F5"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="89" id="S3.F5.g1" src="extracted/6285822/fig/DetermineLoc.png" width="349"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 5: </span>Determine Location Request <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>, Figure 5.2.2.2.2-1]</cite></figcaption> </figure> <div class="ltx_para" id="S3.SS1.p4"> <p class="ltx_p" id="S3.SS1.p4.1">The 3GPP outlines multiple identification methods <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>, Section 6.1.6.2.2]</cite> for initiating the positioning of a target UE. In our implementation, we utilized the <span class="ltx_text ltx_font_italic" id="S3.SS1.p4.1.1">Subscription Permanent Identifier</span> (SUPI) to identify the target UE. The SUPI functions as a permanent identifier for subscribers within the network, supporting various authentication, authorization, and identification tasks in 5G networks. Specifically, in our implementation, the SUPI is represented by the International Mobile Subscriber Identity (IMSI), a commonly used identifier in mobile networks. The key information elements included in the InputData to initiate the location request for our implementation are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p5"> <ul class="ltx_itemize" id="S3.I2"> <li class="ltx_item" id="S3.I2.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I2.i1.p1"> <p class="ltx_p" id="S3.I2.i1.p1.1">SUPI</p> </div> </li> <li class="ltx_item" id="S3.I2.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I2.i2.p1"> <p class="ltx_p" id="S3.I2.i2.p1.1">NR Cell Global Identifier (NCGI)</p> </div> </li> <li class="ltx_item" id="S3.I2.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I2.i3.p1"> <p class="ltx_p" id="S3.I2.i3.p1.1">Periodic Event Info</p> </div> </li> </ul> <p class="ltx_p" id="S3.SS1.p5.1">Once the LMF receives the determine-location request for a specific UE it initiates the procedure to retrieve all the required information from gNBs for the UL-TDOA positioning method. The procedure consists of several NRPPA messages (Messages 2-9 of Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.F4" title="Figure 4 ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">4</span></a>) exchanged between LMF and gNB(s).</p> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p6"> <p class="ltx_p" id="S3.SS1.p6.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p6.1.1">Message 2 TRP Information Request:</span></p> </div> <div class="ltx_para" id="S3.SS1.p7"> <p class="ltx_p" id="S3.SS1.p7.1">The LMF initiates the UL-TDOA positioning method by sending a TRP information request <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.1.14]</cite> to obtain the necessary TRP information for UE positioning. The key information elements included in our implementation of the TRP information request, based on the list provided by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.1.14]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p8"> <ul class="ltx_itemize" id="S3.I3"> <li class="ltx_item" id="S3.I3.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I3.i1.p1"> <p class="ltx_p" id="S3.I3.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I3.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I3.i2.p1"> <p class="ltx_p" id="S3.I3.i2.p1.1">NRPPa Transection ID</p> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p9"> <p class="ltx_p" id="S3.SS1.p9.1">The TRP information request is part of the non-UE-associated NRPPa procedures. In our implementation, the AMF forwards this non-UE-associated message to all the gNBs connected to it. The TRP information request message terminates in the MAC handler of the gNB. We have added processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, and gNB-MAC of OAI’s open-source 5G framework.</p> </div> <div class="ltx_para" id="S3.SS1.p10"> <ol class="ltx_enumerate" id="S3.I4"> <li class="ltx_item" id="S3.I4.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I4.i1.1.1.1">Message 2.a.</span></span> <div class="ltx_para" id="S3.I4.i1.p1"> <p class="ltx_p" id="S3.I4.i1.p1.1">The LMF creates an NRPPa PDU for the TRP Information Request and forwards it to the AMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I4.i1.p1.1.1">Namf Communication Non-UE N2 Message Transfer</span> procedure, carrying the NRPPa PDU.</p> </div> </li> <li class="ltx_item" id="S3.I4.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I4.i2.1.1.1">Message 2.b.</span></span> <div class="ltx_para" id="S3.I4.i2.p1"> <p class="ltx_p" id="S3.I4.i2.p1.1">The AMF then initiates the <span class="ltx_text ltx_font_italic" id="S3.I4.i2.p1.1.1">NGAP Downlink Non-UE Associated NRPPa Transport</span> procedure, carrying the NRPPa PDU, and sends it to all the gNBs connected to the AMF.</p> </div> </li> <li class="ltx_item" id="S3.I4.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I4.i3.1.1.1">Message 2.c.</span></span> <div class="ltx_para" id="S3.I4.i3.p1"> <p class="ltx_p" id="S3.I4.i3.p1.1">Upon receiving the message from the AMF, each gNB processes the NGAP message and forwards the NRPPa PDU to the <span class="ltx_text ltx_font_italic" id="S3.I4.i3.p1.1.1">Downlink Non-UE Associated NRPPa Transport</span> handler in the gNB-NRPPa thread.</p> </div> </li> <li class="ltx_item" id="S3.I4.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I4.i4.1.1.1">Message 2.d.</span></span> <div class="ltx_para" id="S3.I4.i4.p1"> <p class="ltx_p" id="S3.I4.i4.p1.1">The gNB-NRPPa thread decodes the NRPPa PDU and forwards an <span class="ltx_text ltx_font_italic" id="S3.I4.i4.p1.1.1">F1AP: TRP Information Request<span class="ltx_note ltx_role_footnote" id="footnote1"><sup class="ltx_note_mark">1</sup><span class="ltx_note_outer"><span class="ltx_note_content"><sup class="ltx_note_mark">1</sup><span class="ltx_tag ltx_tag_note"><span class="ltx_text ltx_font_upright" id="footnote1.1.1.1">1</span></span><span class="ltx_text ltx_font_upright" id="footnote1.5">The F1 Application Protocol (F1AP) is used to manage and control the interaction between the gNB Central Unit (gNB-CU) and the gNB Distributed Unit (gNB-DU) in 5G NR architecture when the gNB is operating in split mode. We have added the basic framework for all positioning messages 2-9 of Figure </span><a class="ltx_ref ltx_font_upright" href="https://arxiv.org/html/2409.05217v3#S3.F4" title="Figure 4 ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">4</span></a><span class="ltx_text ltx_font_upright" id="footnote1.6"> in OAI’s framework to support split mode; however, the complete processing of these messages has only been implemented for monolithic mode. Our goal is to extend our work to support the positioning procedure in split mode.</span></span></span></span></span> message to the gNB-RRC.</p> </div> </li> <li class="ltx_item" id="S3.I4.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I4.i5.1.1.1">Message 2.e.</span></span> <div class="ltx_para" id="S3.I4.i5.p1"> <p class="ltx_p" id="S3.I4.i5.p1.1">The gNB-RRC thread processes the request and forwards the <span class="ltx_text ltx_font_italic" id="S3.I4.i5.p1.1.1">F1AP: TRP Information Request</span> to the gNB-MAC.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p11"> <p class="ltx_p" id="S3.SS1.p11.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p11.1.1">Message 3 TRP Information Response:</span></p> </div> <div class="ltx_para" id="S3.SS1.p12"> <p class="ltx_p" id="S3.SS1.p12.1">All gNBs participating in the positioning procedure prepare a TRP information response and send it to the LMF, providing essential data such as configuration and location, which are crucial for accurate UE positioning. The key information elements included in our implementation of the TRP information response, based on the list provided by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.1.15]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p13"> <ul class="ltx_itemize" id="S3.I5"> <li class="ltx_item" id="S3.I5.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I5.i1.p1"> <p class="ltx_p" id="S3.I5.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I5.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I5.i2.p1"> <p class="ltx_p" id="S3.I5.i2.p1.1">NRPPa Transection ID</p> </div> </li> <li class="ltx_item" id="S3.I5.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I5.i3.p1"> <p class="ltx_p" id="S3.I5.i3.p1.1">TRP Information</p> <ul class="ltx_itemize" id="S3.I5.i3.I1"> <li class="ltx_item" id="S3.I5.i3.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I5.i3.I1.i1.1.1.1">–</span></span> <div class="ltx_para" id="S3.I5.i3.I1.i1.p1"> <p class="ltx_p" id="S3.I5.i3.I1.i1.p1.1">TRP ID</p> </div> </li> <li class="ltx_item" id="S3.I5.i3.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I5.i3.I1.i2.1.1.1">–</span></span> <div class="ltx_para" id="S3.I5.i3.I1.i2.p1"> <p class="ltx_p" id="S3.I5.i3.I1.i2.p1.1">NG-RAN CGI</p> <ul class="ltx_itemize" id="S3.I5.i3.I1.i2.I1"> <li class="ltx_item" id="S3.I5.i3.I1.i2.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">*</span> <div class="ltx_para" id="S3.I5.i3.I1.i2.I1.i1.p1"> <p class="ltx_p" id="S3.I5.i3.I1.i2.I1.i1.p1.1">PLMN Identity</p> </div> </li> </ul> </div> </li> <li class="ltx_item" id="S3.I5.i3.I1.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I5.i3.I1.i3.1.1.1">–</span></span> <div class="ltx_para" id="S3.I5.i3.I1.i3.p1"> <p class="ltx_p" id="S3.I5.i3.I1.i3.p1.1">Geographical Coordinates</p> <ul class="ltx_itemize" id="S3.I5.i3.I1.i3.I1"> <li class="ltx_item" id="S3.I5.i3.I1.i3.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">*</span> <div class="ltx_para" id="S3.I5.i3.I1.i3.I1.i1.p1"> <p class="ltx_p" id="S3.I5.i3.I1.i3.I1.i1.p1.1">Relative Cartesian Location</p> </div> </li> <li class="ltx_item" id="S3.I5.i3.I1.i3.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">*</span> <div class="ltx_para" id="S3.I5.i3.I1.i3.I1.i2.p1"> <p class="ltx_p" id="S3.I5.i3.I1.i3.I1.i2.p1.1">Location Uncertainty</p> </div> </li> </ul> </div> </li> </ul> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p14"> <p class="ltx_p" id="S3.SS1.p14.1">The TRP Information Response message terminates at the LMF, and we have implemented processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, and gNB-MAC components of OAI’s open-source 5G framework.</p> </div> <div class="ltx_para" id="S3.SS1.p15"> <ol class="ltx_enumerate" id="S3.I6"> <li class="ltx_item" id="S3.I6.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I6.i1.1.1.1">Message 3.a.</span></span> <div class="ltx_para" id="S3.I6.i1.p1"> <p class="ltx_p" id="S3.I6.i1.p1.1">The gNB-MAC handler processes the TRP Information Request, creates an <span class="ltx_text ltx_font_italic" id="S3.I6.i1.p1.1.1">F1AP: TRP Information Response</span> containing the relevant TRP information, and forwards it to the gNB-RRC for further processing.</p> </div> </li> <li class="ltx_item" id="S3.I6.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I6.i2.1.1.1">Message 3.b.</span></span> <div class="ltx_para" id="S3.I6.i2.p1"> <p class="ltx_p" id="S3.I6.i2.p1.1">The gNB-RRC handler processes the <span class="ltx_text ltx_font_italic" id="S3.I6.i2.p1.1.1">F1AP: TRP Information Response</span> received from the gNB-MAC and forwards it to the gNB-NRPPa handler.</p> </div> </li> <li class="ltx_item" id="S3.I6.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I6.i3.1.1.1">Message 3.c.</span></span> <div class="ltx_para" id="S3.I6.i3.p1"> <p class="ltx_p" id="S3.I6.i3.p1.1">The gNB-NRPPa handler processes the <span class="ltx_text ltx_font_italic" id="S3.I6.i3.p1.1.1">F1AP: TRP Information Response</span>, extracts key information, creates an NRPPa PDU, and sends it to the gNB-NGAP handler by initiating the <span class="ltx_text ltx_font_italic" id="S3.I6.i3.p1.1.2">Uplink Non-UE Associated NRPPa Transport</span> procedure.</p> </div> </li> <li class="ltx_item" id="S3.I6.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I6.i4.1.1.1">Message 3.d.</span></span> <div class="ltx_para" id="S3.I6.i4.p1"> <p class="ltx_p" id="S3.I6.i4.p1.1">The gNB-NGAP then initiates the <span class="ltx_text ltx_font_italic" id="S3.I6.i4.p1.1.1">NGAP Uplink Non-UE Associated NRPPa Transport</span> procedure and forwards the NRPPa PDU to the AMF.</p> </div> </li> <li class="ltx_item" id="S3.I6.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I6.i5.1.1.1">Message 3.e.</span></span> <div class="ltx_para" id="S3.I6.i5.p1"> <p class="ltx_p" id="S3.I6.i5.p1.1">The AMF forwards the NRPPa PDU to the LMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I6.i5.p1.1.1">Namf Communication Non-UE N2 Info Notify</span> procedure.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p16"> <p class="ltx_p" id="S3.SS1.p16.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p16.1.1">Message 4 Positioning Information Request:</span> After receiving the TRP Information Responses from all gNBs involved in the positioning process, the LMF initiates the retrieval of UL-SRS configuration details for the target UE. It then sends a Positioning Information Request message to the serving gNB. In response, the serving gNB allocates the necessary resources for UL-SRS and configures the target device with the appropriate UL-SRS resource sets. The key information elements included in our implementation of the Positioning Information Request, as outlined by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.1.10]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p17"> <ul class="ltx_itemize" id="S3.I7"> <li class="ltx_item" id="S3.I7.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I7.i1.p1"> <p class="ltx_p" id="S3.I7.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I7.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I7.i2.p1"> <p class="ltx_p" id="S3.I7.i2.p1.1">NRPPa Transaction ID</p> </div> </li> <li class="ltx_item" id="S3.I7.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I7.i3.p1"> <p class="ltx_p" id="S3.I7.i3.p1.1">Requested SRS Transmission Characteristics </p> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p18"> <p class="ltx_p" id="S3.SS1.p18.1">The Positioning Information Request is part of the UE-associated NRPPa procedures. Therefore, the AMF will forward this message only to the gNB that is serving the UE. The Positioning information request message terminates in the MAC handler of the gNB. We have added processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, and gNB-MAC of OAI’s open-source 5G framework.</p> </div> <div class="ltx_para" id="S3.SS1.p19"> <ol class="ltx_enumerate" id="S3.I8"> <li class="ltx_item" id="S3.I8.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I8.i1.1.1.1">Message 4.a.</span></span> <div class="ltx_para" id="S3.I8.i1.p1"> <p class="ltx_p" id="S3.I8.i1.p1.1">The LMF creates an NRPPa PDU for the Positioning Information Request and forwards it to the AMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I8.i1.p1.1.1">Namf Communication N1N2 Message Transfer</span> procedure, carrying the NRPPa PDU.</p> </div> </li> <li class="ltx_item" id="S3.I8.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I8.i2.1.1.1">Message 4.b.</span></span> <div class="ltx_para" id="S3.I8.i2.p1"> <p class="ltx_p" id="S3.I8.i2.p1.1">The AMF then initiates the <span class="ltx_text ltx_font_italic" id="S3.I8.i2.p1.1.1">NGAP Downlink UE Associated NRPPa Transport</span> procedure, carrying the NRPPa PDU, and sends it to the serving gNB.</p> </div> </li> <li class="ltx_item" id="S3.I8.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I8.i3.1.1.1">Message 4.c.</span></span> <div class="ltx_para" id="S3.I8.i3.p1"> <p class="ltx_p" id="S3.I8.i3.p1.1">Upon receiving the message from the AMF, the gNB processes the NGAP message and forwards the NRPPa PDU to the <span class="ltx_text ltx_font_italic" id="S3.I8.i3.p1.1.1">Downlink UE Associated NRPPa Transport</span> handler in the gNB-NRPPa thread.</p> </div> </li> <li class="ltx_item" id="S3.I8.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I8.i4.1.1.1">Message 4.d.</span></span> <div class="ltx_para" id="S3.I8.i4.p1"> <p class="ltx_p" id="S3.I8.i4.p1.1">The gNB-NRPPa thread decodes the NRPPa PDU and forwards a <span class="ltx_text ltx_font_italic" id="S3.I8.i4.p1.1.1">F1AP: Positioning Information Request</span> message to the gNB-RRC.</p> </div> </li> <li class="ltx_item" id="S3.I8.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I8.i5.1.1.1">Message 4.e.</span></span> <div class="ltx_para" id="S3.I8.i5.p1"> <p class="ltx_p" id="S3.I8.i5.p1.1">The gNB-RRC thread processes the request and forwards the <span class="ltx_text ltx_font_italic" id="S3.I8.i5.p1.1.1">F1AP: Positioning Information Request</span> to the gNB-MAC.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p20"> <p class="ltx_p" id="S3.SS1.p20.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p20.1.1">Message 5 Positioning Information Response:</span> After processing the Positioning Information Request, the serving gNB prepares a Positioning Information Response that includes the UL SRS configuration for the target UE. In the current OAI RAN framework, the SRS configuration is predefined in the gNB settings and does not allow for dynamic adjustments for individual UEs. Consequently, when the serving gNB receives the Positioning Information Request, it disregards the specific configuration requested by the LMF and instead returns the existing UL SRS configuration that has already been applied to the target UE. The key information elements included in our implementation of the Positioning Information response, as outlined by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.1.11]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p21"> <ul class="ltx_itemize" id="S3.I9"> <li class="ltx_item" id="S3.I9.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I9.i1.p1"> <p class="ltx_p" id="S3.I9.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I9.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I9.i2.p1"> <p class="ltx_p" id="S3.I9.i2.p1.1">NRPPa Transaction ID</p> </div> </li> <li class="ltx_item" id="S3.I9.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I9.i3.p1"> <p class="ltx_p" id="S3.I9.i3.p1.1">SRS Configuration </p> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p22"> <p class="ltx_p" id="S3.SS1.p22.1">The Positioning Information Response message terminates at the LMF, and we have implemented processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, and gNB-MAC components of OAI’s open-source 5G framework.</p> </div> <div class="ltx_para" id="S3.SS1.p23"> <ol class="ltx_enumerate" id="S3.I10"> <li class="ltx_item" id="S3.I10.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I10.i1.1.1.1">Message 5.a.</span></span> <div class="ltx_para" id="S3.I10.i1.p1"> <p class="ltx_p" id="S3.I10.i1.p1.1">The gNB-MAC handler processes the Positioning Information Request, creates an <span class="ltx_text ltx_font_italic" id="S3.I10.i1.p1.1.1">F1AP: Positioning Information Response</span> containing the SRS configuration, and forwards it to the gNB-RRC for further processing.</p> </div> </li> <li class="ltx_item" id="S3.I10.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I10.i2.1.1.1">Message 5.b.</span></span> <div class="ltx_para" id="S3.I10.i2.p1"> <p class="ltx_p" id="S3.I10.i2.p1.1">The gNB-RRC handler processes the <span class="ltx_text ltx_font_italic" id="S3.I10.i2.p1.1.1">F1AP: Positioning Information Response</span> received from the gNB-MAC and forwards it to the gNB-NRPPa handler.</p> </div> </li> <li class="ltx_item" id="S3.I10.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I10.i3.1.1.1">Message 5.c.</span></span> <div class="ltx_para" id="S3.I10.i3.p1"> <p class="ltx_p" id="S3.I10.i3.p1.1">The gNB-NRPPa handler processes the <span class="ltx_text ltx_font_italic" id="S3.I10.i3.p1.1.1">F1AP: Positioning Information Response</span>, extracts key information, creates an NRPPa PDU, and sends it to the gNB-NGAP handler by initiating the <span class="ltx_text ltx_font_italic" id="S3.I10.i3.p1.1.2">Uplink UE Associated NRPPa Transport</span> procedure.</p> </div> </li> <li class="ltx_item" id="S3.I10.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I10.i4.1.1.1">Message 5.d.</span></span> <div class="ltx_para" id="S3.I10.i4.p1"> <p class="ltx_p" id="S3.I10.i4.p1.1">The gNB-NGAP then initiates the <span class="ltx_text ltx_font_italic" id="S3.I10.i4.p1.1.1">NGAP Uplink UE Associated NRPPa Transport</span> procedure and forwards the NRPPa PDU to the AMF.</p> </div> </li> <li class="ltx_item" id="S3.I10.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I10.i5.1.1.1">Message 5.e.</span></span> <div class="ltx_para" id="S3.I10.i5.p1"> <p class="ltx_p" id="S3.I10.i5.p1.1">The AMF forwards the NRPPa PDU to the LMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I10.i5.p1.1.1">Namf Communication N2 Info Notify</span> procedure.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p24"> <p class="ltx_p" id="S3.SS1.p24.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p24.1.1">Message 6 Positioning Activation Request:</span></p> </div> <div class="ltx_para" id="S3.SS1.p25"> <p class="ltx_p" id="S3.SS1.p25.1">Once the LMF is informed of the SRS configuration for the target UE, it initiates the activation of UE SRS transmission by sending an NRPPa Positioning Activation Request message to the serving gNB. The key information elements included in our implementation of the Positioning Activation Request, as outlined by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.1.12]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p26"> <ul class="ltx_itemize" id="S3.I11"> <li class="ltx_item" id="S3.I11.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I11.i1.p1"> <p class="ltx_p" id="S3.I11.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I11.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I11.i2.p1"> <p class="ltx_p" id="S3.I11.i2.p1.1">NRPPa Transection ID</p> </div> </li> <li class="ltx_item" id="S3.I11.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I11.i3.p1"> <p class="ltx_p" id="S3.I11.i3.p1.1">SRS Resource Set ID</p> </div> </li> <li class="ltx_item" id="S3.I11.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I11.i4.p1"> <p class="ltx_p" id="S3.I11.i4.p1.1">SRS Resource Trigger</p> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p27"> <p class="ltx_p" id="S3.SS1.p27.1">The Positioning Activation Request is part of the UE-associated NRPPa procedures. Therefore, the AMF will forward this message only to the gNB that is currently serving the UE. The Positioning Activation request message terminates in the MAC handler of the gNB. We have added processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, and gNB-MAC of OAI’s open-source 5G framework.</p> </div> <div class="ltx_para" id="S3.SS1.p28"> <ol class="ltx_enumerate" id="S3.I12"> <li class="ltx_item" id="S3.I12.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I12.i1.1.1.1">Message 6.a.</span></span> <div class="ltx_para" id="S3.I12.i1.p1"> <p class="ltx_p" id="S3.I12.i1.p1.1">The LMF creates an NRPPa PDU for the Positioning Activation Request and forwards it to the AMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I12.i1.p1.1.1">Namf Communication N1N2 Message Transfer</span> procedure, carrying the NRPPa PDU.</p> </div> </li> <li class="ltx_item" id="S3.I12.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I12.i2.1.1.1">Message 6.b.</span></span> <div class="ltx_para" id="S3.I12.i2.p1"> <p class="ltx_p" id="S3.I12.i2.p1.1">The AMF then initiates the <span class="ltx_text ltx_font_italic" id="S3.I12.i2.p1.1.1">NGAP: Downlink UE-associated NRPPa Transport</span> procedure, carrying the NRPPa PDU, and sends it to the serving gNB.</p> </div> </li> <li class="ltx_item" id="S3.I12.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I12.i3.1.1.1">Message 6.c.</span></span> <div class="ltx_para" id="S3.I12.i3.p1"> <p class="ltx_p" id="S3.I12.i3.p1.1">Upon receiving the message from the AMF, the gNB processes the NGAP message and forwards the NRPPa PDU to the <span class="ltx_text ltx_font_italic" id="S3.I12.i3.p1.1.1">Downlink UE-associated NRPPa Transport</span> handler in the gNB-NRPPa thread.</p> </div> </li> <li class="ltx_item" id="S3.I12.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I12.i4.1.1.1">Message 6.d.</span></span> <div class="ltx_para" id="S3.I12.i4.p1"> <p class="ltx_p" id="S3.I12.i4.p1.1">The gNB-NRPPa thread decodes the NRPPa PDU and forwards a <span class="ltx_text ltx_font_italic" id="S3.I12.i4.p1.1.1">F1AP: Positioning Activation Request</span> message to the gNB-RRC.</p> </div> </li> <li class="ltx_item" id="S3.I12.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I12.i5.1.1.1">Message 6.e.</span></span> <div class="ltx_para" id="S3.I12.i5.p1"> <p class="ltx_p" id="S3.I12.i5.p1.1">The gNB-RRC thread processes the request and forwards the <span class="ltx_text ltx_font_italic" id="S3.I12.i5.p1.1.1">F1AP: Positioning Activation Request</span> to the gNB-MAC.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p29"> <p class="ltx_p" id="S3.SS1.p29.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p29.1.1">Message 7 Positioning Activation Response:</span> In the current OAI RAN framework, UE SRS transmission is preactivated, and real-time modifications to a UE’s SRS transmission are not supported. As a result, when the gNB receives the request, it generates a Positioning Activation Response and sends it back to the LMF, indicating that the target device is transmitting the SRS. The key information elements included in our implementation of the Positioning Activation Response, as outlined by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.1.18]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p30"> <ul class="ltx_itemize" id="S3.I13"> <li class="ltx_item" id="S3.I13.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I13.i1.p1"> <p class="ltx_p" id="S3.I13.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I13.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I13.i2.p1"> <p class="ltx_p" id="S3.I13.i2.p1.1">NRPPa Transaction ID</p> </div> </li> <li class="ltx_item" id="S3.I13.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I13.i3.p1"> <p class="ltx_p" id="S3.I13.i3.p1.1">Criticality Diagnostics</p> </div> </li> <li class="ltx_item" id="S3.I13.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I13.i4.p1"> <p class="ltx_p" id="S3.I13.i4.p1.1">System Frame Number</p> </div> </li> <li class="ltx_item" id="S3.I13.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I13.i5.p1"> <p class="ltx_p" id="S3.I13.i5.p1.1">Slot Number</p> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p31"> <p class="ltx_p" id="S3.SS1.p31.1">The Positioning Activation Response message terminates at the LMF, and we have implemented processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, and gNB-MAC components of OAI’s open-source 5G framework. Although UE SRS transmission is preactivated, allowing the Positioning Activation Request to be handled entirely at the gNB-NRPPa with a response generated there, we have included the processing of this message in both the gNB-RRC and gNB-MAC for completeness. This approach ensures future compatibility with potential OAI code developments that may support on-the-fly SRS activation.</p> </div> <div class="ltx_para" id="S3.SS1.p32"> <ol class="ltx_enumerate" id="S3.I14"> <li class="ltx_item" id="S3.I14.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I14.i1.1.1.1">Message 7.a.</span></span> <div class="ltx_para" id="S3.I14.i1.p1"> <p class="ltx_p" id="S3.I14.i1.p1.1">The gNB-MAC handler processes the Positioning Activation Request, creates an <span class="ltx_text ltx_font_italic" id="S3.I14.i1.p1.1.1">F1AP: Positioning Activation Response</span>, and forwards it to the gNB-RRC for further processing.</p> </div> </li> <li class="ltx_item" id="S3.I14.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I14.i2.1.1.1">Message 7.b.</span></span> <div class="ltx_para" id="S3.I14.i2.p1"> <p class="ltx_p" id="S3.I14.i2.p1.1">The gNB-RRC handler processes the <span class="ltx_text ltx_font_italic" id="S3.I14.i2.p1.1.1">F1AP: Positioning Activation Response</span> received from the gNB-MAC and forwards it to the gNB-NRPPa handler.</p> </div> </li> <li class="ltx_item" id="S3.I14.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I14.i3.1.1.1">Message 7.c.</span></span> <div class="ltx_para" id="S3.I14.i3.p1"> <p class="ltx_p" id="S3.I14.i3.p1.1">The gNB-NRPPa handler processes the <span class="ltx_text ltx_font_italic" id="S3.I14.i3.p1.1.1">F1AP: Positioning Activation Response</span>, extracts key information, creates an NRPPa PDU, and sends it to the gNB-NGAP handler by initiating the <span class="ltx_text ltx_font_italic" id="S3.I14.i3.p1.1.2">Uplink UE-associated NRPPa Transport</span> procedure.</p> </div> </li> <li class="ltx_item" id="S3.I14.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I14.i4.1.1.1">Message 7.d.</span></span> <div class="ltx_para" id="S3.I14.i4.p1"> <p class="ltx_p" id="S3.I14.i4.p1.1">The gNB-NGAP initiates the <span class="ltx_text ltx_font_italic" id="S3.I14.i4.p1.1.1">NGAP: Uplink UE-associated NRPPa Transport</span> procedure and forwards the NRPPa PDU to the AMF.</p> </div> </li> <li class="ltx_item" id="S3.I14.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I14.i5.1.1.1">Message 7.e.</span></span> <div class="ltx_para" id="S3.I14.i5.p1"> <p class="ltx_p" id="S3.I14.i5.p1.1">The AMF forwards the NRPPa PDU to the LMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I14.i5.p1.1.1">Namf Communication N2 Information Notify</span> procedure.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p33"> <p class="ltx_p" id="S3.SS1.p33.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p33.1.1">Message 8 Measurement Request:</span></p> </div> <div class="ltx_para" id="S3.SS1.p34"> <p class="ltx_p" id="S3.SS1.p34.1">Once the Positioning Activation Response is received by the LMF, it initiates the retrieval of ToA measurements from all the gNBs/TRPs involved in the positioning of the target UE. The LMF sends a Measurement Request to each participating gNB, which includes the SRS configuration previously received from the serving gNB in the Positioning Information Response for the target UE. The participating gNBs then use this configuration to perform the ToA measurements and send the results back to the LMF. The key information elements included in our implementation of the measurement Request, as outlined by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.4.1]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p35"> <ul class="ltx_itemize" id="S3.I15"> <li class="ltx_item" id="S3.I15.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I15.i1.p1"> <p class="ltx_p" id="S3.I15.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I15.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I15.i2.p1"> <p class="ltx_p" id="S3.I15.i2.p1.1">NRPPa Transection ID</p> </div> </li> <li class="ltx_item" id="S3.I15.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I15.i3.p1"> <p class="ltx_p" id="S3.I15.i3.p1.1">ITRP ID </p> </div> </li> <li class="ltx_item" id="S3.I15.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I15.i4.p1"> <p class="ltx_p" id="S3.I15.i4.p1.1">SRS Configuration </p> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p36"> <p class="ltx_p" id="S3.SS1.p36.1">The measurement request is part of the non-UE-associated NRPPa procedures. In our implementation, the AMF forwards this non-UE-associated message to all the gNBs connected to it<span class="ltx_note ltx_role_footnote" id="footnote2"><sup class="ltx_note_mark">2</sup><span class="ltx_note_outer"><span class="ltx_note_content"><sup class="ltx_note_mark">2</sup><span class="ltx_tag ltx_tag_note">2</span>In future work, we plan to enable the LMF and AMF to send Measurement Requests to specific gNBs. This approach allows for the selection of a targeted subset of gNBs to participate in the positioning process and provide measurements, optimizing resource usage and potentially improving accuracy.</span></span></span>. The measurement request message terminates in the PHY handler of the gNB. We have added processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, gNB-MAC, and gNB-PHY of OAI’s open-source 5G framework.</p> </div> <div class="ltx_para" id="S3.SS1.p37"> <ol class="ltx_enumerate" id="S3.I16"> <li class="ltx_item" id="S3.I16.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I16.i1.1.1.1">Message 8.a.</span></span> <div class="ltx_para" id="S3.I16.i1.p1"> <p class="ltx_p" id="S3.I16.i1.p1.1">The LMF creates an NRPPa PDU for the Measurement Request and forwards it to the AMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I16.i1.p1.1.1">Namf Communication Non-UE N2 Message Transfer</span> procedure, which carries the NRPPa PDU.</p> </div> </li> <li class="ltx_item" id="S3.I16.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I16.i2.1.1.1">Message 8.b.</span></span> <div class="ltx_para" id="S3.I16.i2.p1"> <p class="ltx_p" id="S3.I16.i2.p1.1">The AMF then initiates the <span class="ltx_text ltx_font_italic" id="S3.I16.i2.p1.1.1">NGAP Downlink Non-UE Associated NRPPa Transport</span> procedure, carrying the NRPPa PDU, and sends it to all the gNBs connected to the AMF.</p> </div> </li> <li class="ltx_item" id="S3.I16.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I16.i3.1.1.1">Message 8.c.</span></span> <div class="ltx_para" id="S3.I16.i3.p1"> <p class="ltx_p" id="S3.I16.i3.p1.1">Upon receiving the message from the AMF, each gNB processes the NGAP message and forwards the NRPPa PDU to the <span class="ltx_text ltx_font_italic" id="S3.I16.i3.p1.1.1">Downlink Non-UE Associated NRPPa Transport</span> handler in the gNB-NRPPa thread.</p> </div> </li> <li class="ltx_item" id="S3.I16.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I16.i4.1.1.1">Message 8.d.</span></span> <div class="ltx_para" id="S3.I16.i4.p1"> <p class="ltx_p" id="S3.I16.i4.p1.1">The gNB-NRPPa thread decodes the NRPPa PDU and forwards an <span class="ltx_text ltx_font_italic" id="S3.I16.i4.p1.1.1">F1AP: Measurement Request</span> message to the gNB-RRC.</p> </div> </li> <li class="ltx_item" id="S3.I16.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I16.i5.1.1.1">Message 8.e.</span></span> <div class="ltx_para" id="S3.I16.i5.p1"> <p class="ltx_p" id="S3.I16.i5.p1.1">The gNB-RRC thread processes the request and forwards the <span class="ltx_text ltx_font_italic" id="S3.I16.i5.p1.1.1">F1AP: Measurement Request</span> to the gNB-MAC.</p> </div> </li> <li class="ltx_item" id="S3.I16.i6" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I16.i6.1.1.1">Message 8.f.</span></span> <div class="ltx_para" id="S3.I16.i6.p1"> <p class="ltx_p" id="S3.I16.i6.p1.1">The gNB-MAC thread processes the request and forwards the <span class="ltx_text ltx_font_italic" id="S3.I16.i6.p1.1.1">FAPI: Measurement Request</span> to the gNB-PHY.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p38"> <p class="ltx_p" id="S3.SS1.p38.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p38.1.1">Message 9 Measurement Response:</span></p> </div> <div class="ltx_para" id="S3.SS1.p39"> <p class="ltx_p" id="S3.SS1.p39.1">All gNBs that have received the Measurement Request and are involved in the positioning procedure generate a Measurement Response and send it to the LMF, providing crucial ToA measurements necessary for accurate UE positioning. The precision and resolution of these ToA measurements are essential for achieving high positioning accuracy, as any errors in the ToA measurements can significantly affect the overall accuracy. To enhance measurement precision, we have integrated a state-of-the-art channel estimation and ToA estimation procedure into the gNB. A detailed overview of this integration is provided in Section <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.SS2" title="III-B Enabling ToA estimation in OAI’s gNB ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag"><span class="ltx_text">III-B</span></span></a>. The key information elements included in our implementation of the measurement response, based on the list provided by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib8" title="">8</a>, Section 9.1.4.2]</cite>, are as follows:</p> </div> <div class="ltx_para" id="S3.SS1.p40"> <ul class="ltx_itemize" id="S3.I17"> <li class="ltx_item" id="S3.I17.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I17.i1.p1"> <p class="ltx_p" id="S3.I17.i1.p1.1">Message Type</p> </div> </li> <li class="ltx_item" id="S3.I17.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I17.i2.p1"> <p class="ltx_p" id="S3.I17.i2.p1.1">NRPPa Transection ID</p> </div> </li> <li class="ltx_item" id="S3.I17.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I17.i3.p1"> <p class="ltx_p" id="S3.I17.i3.p1.1">TRP ID</p> </div> </li> <li class="ltx_item" id="S3.I17.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I17.i4.p1"> <p class="ltx_p" id="S3.I17.i4.p1.1">Measurement Result</p> <ul class="ltx_itemize" id="S3.I17.i4.I1"> <li class="ltx_item" id="S3.I17.i4.I1.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I17.i4.I1.i1.1.1.1">–</span></span> <div class="ltx_para" id="S3.I17.i4.I1.i1.p1"> <p class="ltx_p" id="S3.I17.i4.I1.i1.p1.1">UL RTOA Measurement</p> </div> </li> <li class="ltx_item" id="S3.I17.i4.I1.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I17.i4.I1.i2.1.1.1">–</span></span> <div class="ltx_para" id="S3.I17.i4.I1.i2.p1"> <p class="ltx_p" id="S3.I17.i4.I1.i2.p1.1">gNB Rx-Tx Time Difference </p> </div> </li> </ul> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p41"> <p class="ltx_p" id="S3.SS1.p41.1">The measurement Response message terminates at the LMF, and we have implemented processing for this message in the LMF, AMF, gNB-NGAP, gNB-NRPPA, gNB-RRC, gNB-MAC, and gNB-PHY components of OAI’s open-source 5G framework.</p> </div> <div class="ltx_para" id="S3.SS1.p42"> <ol class="ltx_enumerate" id="S3.I18"> <li class="ltx_item" id="S3.I18.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I18.i1.1.1.1">Message 9.a.</span></span> <div class="ltx_para" id="S3.I18.i1.p1"> <p class="ltx_p" id="S3.I18.i1.p1.1">The gNB-PHY handler processes the Request, creates an <span class="ltx_text ltx_font_italic" id="S3.I18.i1.p1.1.1">FAPI: Measurement Response</span> containing the ToA measuement and corresponding TRP information, and forwards it to the gNB-MAC for further processing.</p> </div> </li> <li class="ltx_item" id="S3.I18.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I18.i2.1.1.1">Message 9.b.</span></span> <div class="ltx_para" id="S3.I18.i2.p1"> <p class="ltx_p" id="S3.I18.i2.p1.1">The gNB-MAC handler processes the Response, creates an <span class="ltx_text ltx_font_italic" id="S3.I18.i2.p1.1.1">F1AP: Measurement Response</span> containing the relevant TRP information, and forwards it to the gNB-RRC for further processing.</p> </div> </li> <li class="ltx_item" id="S3.I18.i3" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I18.i3.1.1.1">Message 9.c.</span></span> <div class="ltx_para" id="S3.I18.i3.p1"> <p class="ltx_p" id="S3.I18.i3.p1.1">The gNB-RRC handler processes the <span class="ltx_text ltx_font_italic" id="S3.I18.i3.p1.1.1">F1AP: Measurement Response</span> received from the gNB-MAC and forwards it to the gNB-NRPPa handler.</p> </div> </li> <li class="ltx_item" id="S3.I18.i4" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I18.i4.1.1.1">Message 9.d.</span></span> <div class="ltx_para" id="S3.I18.i4.p1"> <p class="ltx_p" id="S3.I18.i4.p1.1">The gNB-NRPPa handler processes the <span class="ltx_text ltx_font_italic" id="S3.I18.i4.p1.1.1">F1AP: Measurement Response</span>, extracts key information, creates an NRPPa PDU, and sends it to the gNB-NGAP handler by initiating the <span class="ltx_text ltx_font_italic" id="S3.I18.i4.p1.1.2">Uplink Non-UE Associated NRPPa Transport</span> procedure.</p> </div> </li> <li class="ltx_item" id="S3.I18.i5" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I18.i5.1.1.1">Message 9.e.</span></span> <div class="ltx_para" id="S3.I18.i5.p1"> <p class="ltx_p" id="S3.I18.i5.p1.1">The gNB-NGAP then initiates the <span class="ltx_text ltx_font_italic" id="S3.I18.i5.p1.1.1">NGAP Uplink Non-UE Associated NRPPa Transport</span> procedure and forwards the NRPPa PDU to the AMF.</p> </div> </li> <li class="ltx_item" id="S3.I18.i6" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item"><span class="ltx_text ltx_font_bold" id="S3.I18.i6.1.1.1">Message 9.f.</span></span> <div class="ltx_para" id="S3.I18.i6.p1"> <p class="ltx_p" id="S3.I18.i6.p1.1">The AMF forwards the NRPPa PDU to the LMF by initiating the <span class="ltx_text ltx_font_italic" id="S3.I18.i6.p1.1.1">Namf Communication Non-UE N2 Info Notify</span> procedure.</p> </div> </li> </ol> </div> <div class="ltx_para ltx_noindent" id="S3.SS1.p43"> <p class="ltx_p" id="S3.SS1.p43.1"><span class="ltx_text ltx_font_bold ltx_font_italic" id="S3.SS1.p43.1.1">Message 10 Location Response:</span></p> </div> <div class="ltx_para" id="S3.SS1.p44"> <p class="ltx_p" id="S3.SS1.p44.1">The Location Management Function (LMF) receives Time of Arrival (ToA) measurements (uLRTOAmeas) from each gNB and TRP, along with the TRP information response containing the relative Cartesian coordinates (x, y, z) of each TRP, which are essential for computing the user’s position. Before using these ToA measurements, the LMF must map the reported uLRTOAmeas from the gNB to actual measured values using predefined tables from ETSI TS 138 133. For each location determination request, the LMF converts the array of ToA values into Time Difference of Arrival (TDoA) values, referencing the TRP with the strongest Received Signal Received Power (RSRP). Using the known TRP locations, a localization algorithm within the LMF—currently utilizing linear and nonlinear least squares solutions—calculates the user’s location and returns it to the determine-location API. This localization function is designed to accept TDoA values and TRP positions as input, producing an estimated user position as output, allowing for the integration of any localization algorithm that follows this input-output format into the LMF.</p> </div> <div class="ltx_para" id="S3.SS1.p45"> <p class="ltx_p" id="S3.SS1.p45.1">Once the LMF has calculated the position of the target UE, it initiates the process to provide a response to the External API that initiated the positioning request, as illustrated in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.F5" title="Figure 5 ‣ III-A UL-TDoA Positioning Procedure in OAI ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">5</span></a>. This response includes a data structure of type <span class="ltx_text ltx_font_italic" id="S3.SS1.p45.1.1">LocationData</span> <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>, Section 6.1.6.2.3]</cite>. The key information elements included in our implementation of the positioning response (i.e., LocationData), based on the list provided by 3GPP <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>, Section 6.1.6.2.3]</cite>, are as follows:</p> <ul class="ltx_itemize" id="S3.I19"> <li class="ltx_item" id="S3.I19.i1" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I19.i1.p1"> <p class="ltx_p" id="S3.I19.i1.p1.1">Geographical coordinates</p> </div> </li> <li class="ltx_item" id="S3.I19.i2" style="list-style-type:none;"> <span class="ltx_tag ltx_tag_item">•</span> <div class="ltx_para" id="S3.I19.i2.p1"> <p class="ltx_p" id="S3.I19.i2.p1.1">Relative Cartesian Location</p> </div> </li> </ul> </div> <div class="ltx_para" id="S3.SS1.p46"> <p class="ltx_p" id="S3.SS1.p46.1">This concludes our explanation of the end-to-end implementation of the UL-TDoA positioning procedure in OAI, as illustrated in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S3.F4" title="Figure 4 ‣ III Contribution to the OAI and Implementation Status of UL-TDoA ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">4</span></a>. In the following section, we introduce our state-of-the-art ToA estimation procedure, which has been integrated into OAI’s gNB.</p> </div> </section> <section class="ltx_subsection" id="S3.SS2"> <h3 class="ltx_title ltx_title_subsection"> <span class="ltx_tag ltx_tag_subsection"><span class="ltx_text" id="S3.SS2.5.1.1">III-B</span> </span><span class="ltx_text ltx_font_italic" id="S3.SS2.6.2">Enabling ToA estimation in OAI’s gNB</span> </h3> <section class="ltx_subsubsection" id="S3.SS2.SSS1"> <h4 class="ltx_title ltx_title_subsubsection"> <span class="ltx_tag ltx_tag_subsubsection"><span class="ltx_text" id="S3.SS2.SSS1.5.1.1">III-B</span>1 </span>gNB-PHY</h4> <div class="ltx_para" id="S3.SS2.SSS1.p1"> <p class="ltx_p" id="S3.SS2.SSS1.p1.9">The PHY layer involves two primary processes: channel estimation and subsequent Time of Arrival (ToA) estimation based on the pilot symbols of the Sounding Reference Signal (SRS). The SRS is a wide-band reference signal transmitted by the UE in the uplink. The SRS for positioning is generated using the Zadoff-Chu sequence <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib13" title="">13</a>]</cite>, similar to the SRS for communication, although they can be configured differently. 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id="S3.SS2.SSS1.p1.8.m8.2.3.1.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.3">subscript</csymbol><ci id="S3.SS2.SSS1.p1.8.m8.2.3.2.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.3.2">𝐗</ci><apply id="S3.SS2.SSS1.p1.8.m8.2.2.2.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2"><times id="S3.SS2.SSS1.p1.8.m8.2.2.2.3.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.3"></times><ci id="S3.SS2.SSS1.p1.8.m8.2.2.2.4.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.4">𝑆</ci><ci id="S3.SS2.SSS1.p1.8.m8.2.2.2.5.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.5">𝑅</ci><apply id="S3.SS2.SSS1.p1.8.m8.2.2.2.6.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.6"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p1.8.m8.2.2.2.6.1.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.6">subscript</csymbol><ci id="S3.SS2.SSS1.p1.8.m8.2.2.2.6.2.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.6.2">𝑆</ci><list id="S3.SS2.SSS1.p1.8.m8.2.2.2.2.2.3.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.2.2.4"><ci id="S3.SS2.SSS1.p1.8.m8.1.1.1.1.1.1.cmml" xref="S3.SS2.SSS1.p1.8.m8.1.1.1.1.1.1">𝑛</ci><ci id="S3.SS2.SSS1.p1.8.m8.2.2.2.2.2.2.cmml" xref="S3.SS2.SSS1.p1.8.m8.2.2.2.2.2.2">𝑝</ci></list></apply></apply></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.8.m8.2c">\mathbf{X}_{SRS_{n,p}}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.8.m8.2d">bold_X start_POSTSUBSCRIPT italic_S italic_R italic_S start_POSTSUBSCRIPT italic_n , italic_p end_POSTSUBSCRIPT end_POSTSUBSCRIPT</annotation></semantics></math> to estimate the channel <math alttext="\hat{\mathbf{H}}_{{n,p,l}}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.9.m9.3"><semantics id="S3.SS2.SSS1.p1.9.m9.3a"><msub id="S3.SS2.SSS1.p1.9.m9.3.4" xref="S3.SS2.SSS1.p1.9.m9.3.4.cmml"><mover accent="true" id="S3.SS2.SSS1.p1.9.m9.3.4.2" xref="S3.SS2.SSS1.p1.9.m9.3.4.2.cmml"><mi id="S3.SS2.SSS1.p1.9.m9.3.4.2.2" xref="S3.SS2.SSS1.p1.9.m9.3.4.2.2.cmml">𝐇</mi><mo id="S3.SS2.SSS1.p1.9.m9.3.4.2.1" xref="S3.SS2.SSS1.p1.9.m9.3.4.2.1.cmml">^</mo></mover><mrow 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xref="S3.SS2.SSS1.p1.9.m9.3.4.2.2">𝐇</ci></apply><list id="S3.SS2.SSS1.p1.9.m9.3.3.3.4.cmml" xref="S3.SS2.SSS1.p1.9.m9.3.3.3.5"><ci id="S3.SS2.SSS1.p1.9.m9.1.1.1.1.cmml" xref="S3.SS2.SSS1.p1.9.m9.1.1.1.1">𝑛</ci><ci id="S3.SS2.SSS1.p1.9.m9.2.2.2.2.cmml" xref="S3.SS2.SSS1.p1.9.m9.2.2.2.2">𝑝</ci><ci id="S3.SS2.SSS1.p1.9.m9.3.3.3.3.cmml" xref="S3.SS2.SSS1.p1.9.m9.3.3.3.3">𝑙</ci></list></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.9.m9.3c">\hat{\mathbf{H}}_{{n,p,l}}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.9.m9.3d">over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT</annotation></semantics></math>:</p> <table class="ltx_equation ltx_eqn_table" id="S3.E1"> <tbody><tr class="ltx_equation ltx_eqn_row ltx_align_baseline"> <td class="ltx_eqn_cell ltx_eqn_center_padleft"></td> <td class="ltx_eqn_cell ltx_align_center"><math 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ltx_align_right">(1)</span></td> </tr></tbody> </table> <p class="ltx_p" id="S3.SS2.SSS1.p1.13">Since the SRS can be mapped to multiple consecutive OFDM symbols <math alttext="l\in\{1,\dots,N_{symb}^{SRS}\}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.10.m1.3"><semantics id="S3.SS2.SSS1.p1.10.m1.3a"><mrow id="S3.SS2.SSS1.p1.10.m1.3.3" xref="S3.SS2.SSS1.p1.10.m1.3.3.cmml"><mi id="S3.SS2.SSS1.p1.10.m1.3.3.3" xref="S3.SS2.SSS1.p1.10.m1.3.3.3.cmml">l</mi><mo id="S3.SS2.SSS1.p1.10.m1.3.3.2" xref="S3.SS2.SSS1.p1.10.m1.3.3.2.cmml">∈</mo><mrow id="S3.SS2.SSS1.p1.10.m1.3.3.1.1" xref="S3.SS2.SSS1.p1.10.m1.3.3.1.2.cmml"><mo id="S3.SS2.SSS1.p1.10.m1.3.3.1.1.2" stretchy="false" xref="S3.SS2.SSS1.p1.10.m1.3.3.1.2.cmml">{</mo><mn id="S3.SS2.SSS1.p1.10.m1.1.1" xref="S3.SS2.SSS1.p1.10.m1.1.1.cmml">1</mn><mo id="S3.SS2.SSS1.p1.10.m1.3.3.1.1.3" xref="S3.SS2.SSS1.p1.10.m1.3.3.1.2.cmml">,</mo><mi id="S3.SS2.SSS1.p1.10.m1.2.2" mathvariant="normal" xref="S3.SS2.SSS1.p1.10.m1.2.2.cmml">…</mi><mo 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xref="S3.SS2.SSS1.p1.10.m1.3.3.1.1.1.3.4">𝑆</ci></apply></apply></set></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.10.m1.3c">l\in\{1,\dots,N_{symb}^{SRS}\}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.10.m1.3d">italic_l ∈ { 1 , … , italic_N start_POSTSUBSCRIPT italic_s italic_y italic_m italic_b end_POSTSUBSCRIPT start_POSTSUPERSCRIPT italic_S italic_R italic_S end_POSTSUPERSCRIPT }</annotation></semantics></math>, during the channel estimation process, the SRS channel is estimated over all the symbols. <br class="ltx_break"/>The channel estimate is then interpolated to refine the estimates obtained from the LS estimation process using filter vectors <math alttext="\mathbf{F}_{\text{start}}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.11.m2.1"><semantics id="S3.SS2.SSS1.p1.11.m2.1a"><msub id="S3.SS2.SSS1.p1.11.m2.1.1" xref="S3.SS2.SSS1.p1.11.m2.1.1.cmml"><mi id="S3.SS2.SSS1.p1.11.m2.1.1.2" 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id="S3.SS2.SSS1.p1.13.m4.1.1.3a.cmml" xref="S3.SS2.SSS1.p1.13.m4.1.1.3"><mtext id="S3.SS2.SSS1.p1.13.m4.1.1.3.cmml" mathsize="70%" xref="S3.SS2.SSS1.p1.13.m4.1.1.3">end</mtext></ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.13.m4.1c">\mathbf{F}_{\text{end}}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.13.m4.1d">bold_F start_POSTSUBSCRIPT end end_POSTSUBSCRIPT</annotation></semantics></math>, depending on the position within the OFDM symbol, as follows:</p> <table class="ltx_equation ltx_eqn_table" id="S3.E2"> <tbody><tr class="ltx_equation ltx_eqn_row ltx_align_baseline"> <td class="ltx_eqn_cell ltx_eqn_center_padleft"></td> <td class="ltx_eqn_cell ltx_align_center"><math alttext="\hat{\mathbf{H}}_{n,p,l}^{\text{interp}}[k]\!\!=\!\!\begin{cases}\!\mathbf{F}_% {\text{start}}\cdot\hat{\mathbf{H}}_{n,p,l}[k]&\!\!\!\!\text{if }\!k=0\text{ % or }k<K_{\text{TC}}\\ \!\mathbf{F}_{\text{middle}}\cdot\hat{\mathbf{H}}_{n,p,l}[k]&\!\!\!\!\text{if % }\!k\neq 0\text{ and }(k+K_{\text{TC}})<N_{\text{sc}}\\ \!\mathbf{F}_{\text{end}}\cdot\hat{\mathbf{H}}_{n,p,l}[k]&\!\!\!\!\text{if }\!% (k+K_{\text{TC}})\!\geq\!N_{\text{sc}}\!\text{ or }\!k\!=\!M_{\text{sc}}\!-\!1% \end{cases}" class="ltx_Math" display="block" id="S3.E2.m1.10"><semantics id="S3.E2.m1.10a"><mrow id="S3.E2.m1.10.11" xref="S3.E2.m1.10.11.cmml"><mrow id="S3.E2.m1.10.11.2" xref="S3.E2.m1.10.11.2.cmml"><msubsup id="S3.E2.m1.10.11.2.2" xref="S3.E2.m1.10.11.2.2.cmml"><mover accent="true" id="S3.E2.m1.10.11.2.2.2.2" xref="S3.E2.m1.10.11.2.2.2.2.cmml"><mi id="S3.E2.m1.10.11.2.2.2.2.2" xref="S3.E2.m1.10.11.2.2.2.2.2.cmml">𝐇</mi><mo id="S3.E2.m1.10.11.2.2.2.2.1" xref="S3.E2.m1.10.11.2.2.2.2.1.cmml">^</mo></mover><mrow id="S3.E2.m1.9.9.3.5" xref="S3.E2.m1.9.9.3.4.cmml"><mi id="S3.E2.m1.7.7.1.1" xref="S3.E2.m1.7.7.1.1.cmml">n</mi><mo id="S3.E2.m1.9.9.3.5.1" xref="S3.E2.m1.9.9.3.4.cmml">,</mo><mi 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\!\mathbf{F}_{\text{end}}\cdot\hat{\mathbf{H}}_{n,p,l}[k]&\!\!\!\!\text{if }\!% (k+K_{\text{TC}})\!\geq\!N_{\text{sc}}\!\text{ or }\!k\!=\!M_{\text{sc}}\!-\!1% \end{cases}</annotation><annotation encoding="application/x-llamapun" id="S3.E2.m1.10d">over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT start_POSTSUPERSCRIPT interp end_POSTSUPERSCRIPT [ italic_k ] = { start_ROW start_CELL bold_F start_POSTSUBSCRIPT start end_POSTSUBSCRIPT ⋅ over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT [ italic_k ] end_CELL start_CELL if italic_k = 0 or italic_k < italic_K start_POSTSUBSCRIPT TC end_POSTSUBSCRIPT end_CELL end_ROW start_ROW start_CELL bold_F start_POSTSUBSCRIPT middle end_POSTSUBSCRIPT ⋅ over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT [ italic_k ] end_CELL start_CELL if italic_k ≠ 0 and ( italic_k + italic_K start_POSTSUBSCRIPT TC end_POSTSUBSCRIPT ) < italic_N start_POSTSUBSCRIPT sc end_POSTSUBSCRIPT end_CELL end_ROW start_ROW start_CELL bold_F start_POSTSUBSCRIPT end end_POSTSUBSCRIPT ⋅ over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT [ italic_k ] end_CELL start_CELL if ( italic_k + italic_K start_POSTSUBSCRIPT TC end_POSTSUBSCRIPT ) ≥ italic_N start_POSTSUBSCRIPT sc end_POSTSUBSCRIPT or italic_k = italic_M start_POSTSUBSCRIPT sc end_POSTSUBSCRIPT - 1 end_CELL end_ROW</annotation></semantics></math></td> <td class="ltx_eqn_cell ltx_eqn_center_padright"></td> <td class="ltx_eqn_cell ltx_eqn_eqno ltx_align_middle ltx_align_right" rowspan="1"><span class="ltx_tag ltx_tag_equation ltx_align_right">(2)</span></td> </tr></tbody> </table> <p class="ltx_p" id="S3.SS2.SSS1.p1.16">where <math alttext="K_{\text{TC}}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.14.m1.1"><semantics id="S3.SS2.SSS1.p1.14.m1.1a"><msub id="S3.SS2.SSS1.p1.14.m1.1.1" xref="S3.SS2.SSS1.p1.14.m1.1.1.cmml"><mi id="S3.SS2.SSS1.p1.14.m1.1.1.2" xref="S3.SS2.SSS1.p1.14.m1.1.1.2.cmml">K</mi><mtext id="S3.SS2.SSS1.p1.14.m1.1.1.3" xref="S3.SS2.SSS1.p1.14.m1.1.1.3a.cmml">TC</mtext></msub><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p1.14.m1.1b"><apply id="S3.SS2.SSS1.p1.14.m1.1.1.cmml" xref="S3.SS2.SSS1.p1.14.m1.1.1"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p1.14.m1.1.1.1.cmml" xref="S3.SS2.SSS1.p1.14.m1.1.1">subscript</csymbol><ci id="S3.SS2.SSS1.p1.14.m1.1.1.2.cmml" xref="S3.SS2.SSS1.p1.14.m1.1.1.2">𝐾</ci><ci id="S3.SS2.SSS1.p1.14.m1.1.1.3a.cmml" xref="S3.SS2.SSS1.p1.14.m1.1.1.3"><mtext id="S3.SS2.SSS1.p1.14.m1.1.1.3.cmml" mathsize="70%" xref="S3.SS2.SSS1.p1.14.m1.1.1.3">TC</mtext></ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.14.m1.1c">K_{\text{TC}}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.14.m1.1d">italic_K start_POSTSUBSCRIPT TC end_POSTSUBSCRIPT</annotation></semantics></math> is the comb size parameter, <math alttext="M_{\text{sc}}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.15.m2.1"><semantics id="S3.SS2.SSS1.p1.15.m2.1a"><msub id="S3.SS2.SSS1.p1.15.m2.1.1" xref="S3.SS2.SSS1.p1.15.m2.1.1.cmml"><mi id="S3.SS2.SSS1.p1.15.m2.1.1.2" xref="S3.SS2.SSS1.p1.15.m2.1.1.2.cmml">M</mi><mtext id="S3.SS2.SSS1.p1.15.m2.1.1.3" xref="S3.SS2.SSS1.p1.15.m2.1.1.3a.cmml">sc</mtext></msub><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p1.15.m2.1b"><apply id="S3.SS2.SSS1.p1.15.m2.1.1.cmml" xref="S3.SS2.SSS1.p1.15.m2.1.1"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p1.15.m2.1.1.1.cmml" xref="S3.SS2.SSS1.p1.15.m2.1.1">subscript</csymbol><ci id="S3.SS2.SSS1.p1.15.m2.1.1.2.cmml" xref="S3.SS2.SSS1.p1.15.m2.1.1.2">𝑀</ci><ci id="S3.SS2.SSS1.p1.15.m2.1.1.3a.cmml" xref="S3.SS2.SSS1.p1.15.m2.1.1.3"><mtext id="S3.SS2.SSS1.p1.15.m2.1.1.3.cmml" mathsize="70%" xref="S3.SS2.SSS1.p1.15.m2.1.1.3">sc</mtext></ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.15.m2.1c">M_{\text{sc}}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.15.m2.1d">italic_M start_POSTSUBSCRIPT sc end_POSTSUBSCRIPT</annotation></semantics></math> is the number of subcarriers in an SRS sequence, and <math alttext="N_{\text{sc}}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.16.m3.1"><semantics id="S3.SS2.SSS1.p1.16.m3.1a"><msub id="S3.SS2.SSS1.p1.16.m3.1.1" xref="S3.SS2.SSS1.p1.16.m3.1.1.cmml"><mi id="S3.SS2.SSS1.p1.16.m3.1.1.2" xref="S3.SS2.SSS1.p1.16.m3.1.1.2.cmml">N</mi><mtext id="S3.SS2.SSS1.p1.16.m3.1.1.3" xref="S3.SS2.SSS1.p1.16.m3.1.1.3a.cmml">sc</mtext></msub><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p1.16.m3.1b"><apply id="S3.SS2.SSS1.p1.16.m3.1.1.cmml" xref="S3.SS2.SSS1.p1.16.m3.1.1"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p1.16.m3.1.1.1.cmml" xref="S3.SS2.SSS1.p1.16.m3.1.1">subscript</csymbol><ci id="S3.SS2.SSS1.p1.16.m3.1.1.2.cmml" xref="S3.SS2.SSS1.p1.16.m3.1.1.2">𝑁</ci><ci id="S3.SS2.SSS1.p1.16.m3.1.1.3a.cmml" xref="S3.SS2.SSS1.p1.16.m3.1.1.3"><mtext id="S3.SS2.SSS1.p1.16.m3.1.1.3.cmml" mathsize="70%" xref="S3.SS2.SSS1.p1.16.m3.1.1.3">sc</mtext></ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.16.m3.1c">N_{\text{sc}}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.16.m3.1d">italic_N start_POSTSUBSCRIPT sc end_POSTSUBSCRIPT</annotation></semantics></math> is the total number of subcarriers in an OFDM symbol. <br class="ltx_break"/>Next, frequency domain channel oversampling and conversion of the estimated channel from the frequency domain to the time domain are performed using an Inverse Fast Fourier Transform (IFFT):</p> <table class="ltx_equationgroup ltx_eqn_gather ltx_eqn_table" id="S5.EGx1"> <tbody id="S3.E3"><tr class="ltx_equation ltx_eqn_row ltx_align_baseline"> <td class="ltx_eqn_cell ltx_eqn_center_padleft"></td> <td class="ltx_eqn_cell ltx_align_center"><math alttext="\displaystyle\hat{\mathbf{H}}_{n,p,l}^{\text{oversamp}}=\begin{bmatrix}\hat{% \mathbf{H}}_{n,p,l}^{\text{interp}}(1:N_{\text{fft}}/2),\\ \mathbf{zeros}(1,L\times N_{\text{fft}}-N_{\text{fft}}),\\ \hat{\mathbf{H}}_{n,p,l}^{\text{interp}}(N_{\text{fft}}/2+1:\text{end})\end{bmatrix}" class="ltx_math_unparsed" display="block" id="S3.E3.m1.4"><semantics id="S3.E3.m1.4a"><mrow id="S3.E3.m1.4.5"><msubsup id="S3.E3.m1.4.5.2"><mover accent="true" id="S3.E3.m1.4.5.2.2.2"><mi id="S3.E3.m1.4.5.2.2.2.2">𝐇</mi><mo id="S3.E3.m1.4.5.2.2.2.1">^</mo></mover><mrow id="S3.E3.m1.4.4.3.5"><mi id="S3.E3.m1.2.2.1.1">n</mi><mo id="S3.E3.m1.4.4.3.5.1">,</mo><mi id="S3.E3.m1.3.3.2.2">p</mi><mo id="S3.E3.m1.4.4.3.5.2">,</mo><mi id="S3.E3.m1.4.4.3.3">l</mi></mrow><mtext id="S3.E3.m1.4.5.2.3">oversamp</mtext></msubsup><mo id="S3.E3.m1.4.5.1">=</mo><mrow id="S3.E3.m1.1.1.3"><mo 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id="S3.E3.m1.1.1.1.1.3.3.3.3.5.4"><mi id="S3.E3.m1.1.1.1.1.3.3.3.3.5.4.2">N</mi><mtext id="S3.E3.m1.1.1.1.1.3.3.3.3.5.4.3">fft</mtext></msub><mo id="S3.E3.m1.1.1.1.1.3.3.3.3.5.5">/</mo><mn id="S3.E3.m1.1.1.1.1.3.3.3.3.5.6">2</mn><mo id="S3.E3.m1.1.1.1.1.3.3.3.3.5.7" stretchy="false">)</mo></mrow><mo id="S3.E3.m1.1.1.1.1.3.3.3.3.6">,</mo></mrow></mtd></mtr><mtr id="S3.E3.m1.1.1.1.1c"><mtd id="S3.E3.m1.1.1.1.1d"><mrow id="S3.E3.m1.1.1.1.1.5.5.2.2.2"><mrow id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1"><mi id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.3">𝐳𝐞𝐫𝐨𝐬</mi><mo id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.2">⁢</mo><mrow id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1"><mo id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.2" stretchy="false">(</mo><mn id="S3.E3.m1.1.1.1.1.4.4.1.1.1">1</mn><mo id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.3">,</mo><mrow id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1"><mrow id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.2"><mi id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.2.2">L</mi><mo id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.2.1" lspace="0.222em" rspace="0.222em">×</mo><msub id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.2.3"><mi id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.2.3.2">N</mi><mtext id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.2.3.3">fft</mtext></msub></mrow><mo id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.1">−</mo><msub id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.3"><mi id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.3.2">N</mi><mtext id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.1.3.3">fft</mtext></msub></mrow><mo id="S3.E3.m1.1.1.1.1.5.5.2.2.2.1.1.1.4" stretchy="false">)</mo></mrow></mrow><mo id="S3.E3.m1.1.1.1.1.5.5.2.2.2.2">,</mo></mrow></mtd></mtr><mtr id="S3.E3.m1.1.1.1.1e"><mtd id="S3.E3.m1.1.1.1.1f"><mrow id="S3.E3.m1.1.1.1.1.8.8.3.3"><msubsup id="S3.E3.m1.1.1.1.1.8.8.3.3.4"><mover accent="true" id="S3.E3.m1.1.1.1.1.8.8.3.3.4.2.2"><mi id="S3.E3.m1.1.1.1.1.8.8.3.3.4.2.2.2">𝐇</mi><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.4.2.2.1">^</mo></mover><mrow id="S3.E3.m1.1.1.1.1.8.8.3.3.3.3.5"><mi id="S3.E3.m1.1.1.1.1.6.6.1.1.1.1.1">n</mi><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.3.3.5.1">,</mo><mi id="S3.E3.m1.1.1.1.1.7.7.2.2.2.2.2">p</mi><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.3.3.5.2">,</mo><mi id="S3.E3.m1.1.1.1.1.8.8.3.3.3.3.3">l</mi></mrow><mtext id="S3.E3.m1.1.1.1.1.8.8.3.3.4.3">interp</mtext></msubsup><mrow id="S3.E3.m1.1.1.1.1.8.8.3.3.5"><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.5.1" stretchy="false">(</mo><msub id="S3.E3.m1.1.1.1.1.8.8.3.3.5.2"><mi id="S3.E3.m1.1.1.1.1.8.8.3.3.5.2.2">N</mi><mtext id="S3.E3.m1.1.1.1.1.8.8.3.3.5.2.3">fft</mtext></msub><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.5.3">/</mo><mn id="S3.E3.m1.1.1.1.1.8.8.3.3.5.4">2</mn><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.5.5">+</mo><mn id="S3.E3.m1.1.1.1.1.8.8.3.3.5.6">1</mn><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.5.7" lspace="0.278em" rspace="0.278em">:</mo><mtext id="S3.E3.m1.1.1.1.1.8.8.3.3.5.8">end</mtext><mo id="S3.E3.m1.1.1.1.1.8.8.3.3.5.9" stretchy="false">)</mo></mrow></mrow></mtd></mtr></mtable><mo id="S3.E3.m1.1.1.3.2">]</mo></mrow></mrow><annotation encoding="application/x-tex" id="S3.E3.m1.4b">\displaystyle\hat{\mathbf{H}}_{n,p,l}^{\text{oversamp}}=\begin{bmatrix}\hat{% \mathbf{H}}_{n,p,l}^{\text{interp}}(1:N_{\text{fft}}/2),\\ \mathbf{zeros}(1,L\times N_{\text{fft}}-N_{\text{fft}}),\\ \hat{\mathbf{H}}_{n,p,l}^{\text{interp}}(N_{\text{fft}}/2+1:\text{end})\end{bmatrix}</annotation><annotation encoding="application/x-llamapun" id="S3.E3.m1.4c">over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT start_POSTSUPERSCRIPT oversamp end_POSTSUPERSCRIPT = [ start_ARG start_ROW start_CELL over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT start_POSTSUPERSCRIPT interp end_POSTSUPERSCRIPT ( 1 : italic_N start_POSTSUBSCRIPT fft end_POSTSUBSCRIPT / 2 ) , end_CELL end_ROW start_ROW start_CELL bold_zeros ( 1 , italic_L × italic_N start_POSTSUBSCRIPT fft end_POSTSUBSCRIPT - italic_N start_POSTSUBSCRIPT fft end_POSTSUBSCRIPT ) , end_CELL end_ROW start_ROW start_CELL over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT start_POSTSUPERSCRIPT interp end_POSTSUPERSCRIPT ( italic_N start_POSTSUBSCRIPT fft end_POSTSUBSCRIPT / 2 + 1 : end ) end_CELL end_ROW end_ARG ]</annotation></semantics></math></td> <td class="ltx_eqn_cell ltx_eqn_center_padright"></td> <td class="ltx_eqn_cell ltx_eqn_eqno ltx_align_middle ltx_align_right" rowspan="1"><span class="ltx_tag ltx_tag_equation ltx_align_right">(3)</span></td> </tr></tbody> </table> <p class="ltx_p" id="S3.SS2.SSS1.p1.18">where <math alttext="L" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.17.m1.1"><semantics id="S3.SS2.SSS1.p1.17.m1.1a"><mi id="S3.SS2.SSS1.p1.17.m1.1.1" xref="S3.SS2.SSS1.p1.17.m1.1.1.cmml">L</mi><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p1.17.m1.1b"><ci id="S3.SS2.SSS1.p1.17.m1.1.1.cmml" xref="S3.SS2.SSS1.p1.17.m1.1.1">𝐿</ci></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.17.m1.1c">L</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.17.m1.1d">italic_L</annotation></semantics></math> is the oversampling factor, and <math alttext="N_{\text{fft}}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.18.m2.1"><semantics id="S3.SS2.SSS1.p1.18.m2.1a"><msub id="S3.SS2.SSS1.p1.18.m2.1.1" xref="S3.SS2.SSS1.p1.18.m2.1.1.cmml"><mi id="S3.SS2.SSS1.p1.18.m2.1.1.2" xref="S3.SS2.SSS1.p1.18.m2.1.1.2.cmml">N</mi><mtext id="S3.SS2.SSS1.p1.18.m2.1.1.3" xref="S3.SS2.SSS1.p1.18.m2.1.1.3a.cmml">fft</mtext></msub><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p1.18.m2.1b"><apply id="S3.SS2.SSS1.p1.18.m2.1.1.cmml" xref="S3.SS2.SSS1.p1.18.m2.1.1"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p1.18.m2.1.1.1.cmml" xref="S3.SS2.SSS1.p1.18.m2.1.1">subscript</csymbol><ci id="S3.SS2.SSS1.p1.18.m2.1.1.2.cmml" xref="S3.SS2.SSS1.p1.18.m2.1.1.2">𝑁</ci><ci id="S3.SS2.SSS1.p1.18.m2.1.1.3a.cmml" xref="S3.SS2.SSS1.p1.18.m2.1.1.3"><mtext id="S3.SS2.SSS1.p1.18.m2.1.1.3.cmml" mathsize="70%" xref="S3.SS2.SSS1.p1.18.m2.1.1.3">fft</mtext></ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p1.18.m2.1c">N_{\text{fft}}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p1.18.m2.1d">italic_N start_POSTSUBSCRIPT fft end_POSTSUBSCRIPT</annotation></semantics></math> is the IFFT length. The IFFT operation is defined as:</p> <table class="ltx_equation ltx_eqn_table" id="S3.E4"> <tbody><tr class="ltx_equation ltx_eqn_row ltx_align_baseline"> <td class="ltx_eqn_cell ltx_eqn_center_padleft"></td> <td class="ltx_eqn_cell ltx_align_center"><math alttext="\hat{\mathbf{h}}^{\text{oversamp}}_{n,p,l}(t)=\frac{1}{L\times N_{\text{fft}}}% \sum_{k=0}^{L\times N_{\text{fft}}-1}\hat{\mathbf{H}}_{n,p,l}^{\text{oversamp}% }[k]e^{i2\pi kt/(L\times N_{\text{fft}})}" class="ltx_Math" display="block" id="S3.E4.m1.9"><semantics id="S3.E4.m1.9a"><mrow id="S3.E4.m1.9.10" xref="S3.E4.m1.9.10.cmml"><mrow id="S3.E4.m1.9.10.2" xref="S3.E4.m1.9.10.2.cmml"><msubsup id="S3.E4.m1.9.10.2.2" xref="S3.E4.m1.9.10.2.2.cmml"><mover accent="true" id="S3.E4.m1.9.10.2.2.2.2" xref="S3.E4.m1.9.10.2.2.2.2.cmml"><mi id="S3.E4.m1.9.10.2.2.2.2.2" xref="S3.E4.m1.9.10.2.2.2.2.2.cmml">𝐡</mi><mo id="S3.E4.m1.9.10.2.2.2.2.1" xref="S3.E4.m1.9.10.2.2.2.2.1.cmml">^</mo></mover><mrow id="S3.E4.m1.3.3.3.5" xref="S3.E4.m1.3.3.3.4.cmml"><mi id="S3.E4.m1.1.1.1.1" xref="S3.E4.m1.1.1.1.1.cmml">n</mi><mo id="S3.E4.m1.3.3.3.5.1" xref="S3.E4.m1.3.3.3.4.cmml">,</mo><mi id="S3.E4.m1.2.2.2.2" xref="S3.E4.m1.2.2.2.2.cmml">p</mi><mo id="S3.E4.m1.3.3.3.5.2" xref="S3.E4.m1.3.3.3.4.cmml">,</mo><mi id="S3.E4.m1.3.3.3.3" xref="S3.E4.m1.3.3.3.3.cmml">l</mi></mrow><mtext id="S3.E4.m1.9.10.2.2.2.3" xref="S3.E4.m1.9.10.2.2.2.3a.cmml">oversamp</mtext></msubsup><mo id="S3.E4.m1.9.10.2.1" xref="S3.E4.m1.9.10.2.1.cmml">⁢</mo><mrow id="S3.E4.m1.9.10.2.3.2" xref="S3.E4.m1.9.10.2.cmml"><mo id="S3.E4.m1.9.10.2.3.2.1" stretchy="false" xref="S3.E4.m1.9.10.2.cmml">(</mo><mi id="S3.E4.m1.8.8" xref="S3.E4.m1.8.8.cmml">t</mi><mo id="S3.E4.m1.9.10.2.3.2.2" stretchy="false" xref="S3.E4.m1.9.10.2.cmml">)</mo></mrow></mrow><mo id="S3.E4.m1.9.10.1" xref="S3.E4.m1.9.10.1.cmml">=</mo><mrow id="S3.E4.m1.9.10.3" xref="S3.E4.m1.9.10.3.cmml"><mfrac id="S3.E4.m1.9.10.3.2" xref="S3.E4.m1.9.10.3.2.cmml"><mn id="S3.E4.m1.9.10.3.2.2" 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1 end_POSTSUPERSCRIPT over^ start_ARG bold_H end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT start_POSTSUPERSCRIPT oversamp end_POSTSUPERSCRIPT [ italic_k ] italic_e start_POSTSUPERSCRIPT italic_i 2 italic_π italic_k italic_t / ( italic_L × italic_N start_POSTSUBSCRIPT fft end_POSTSUBSCRIPT ) end_POSTSUPERSCRIPT</annotation></semantics></math></td> <td class="ltx_eqn_cell ltx_eqn_center_padright"></td> <td class="ltx_eqn_cell ltx_eqn_eqno ltx_align_middle ltx_align_right" rowspan="1"><span class="ltx_tag ltx_tag_equation ltx_align_right">(4)</span></td> </tr></tbody> </table> <p class="ltx_p" id="S3.SS2.SSS1.p1.20">where <math alttext="t" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.19.m1.1"><semantics id="S3.SS2.SSS1.p1.19.m1.1a"><mi id="S3.SS2.SSS1.p1.19.m1.1.1" xref="S3.SS2.SSS1.p1.19.m1.1.1.cmml">t</mi><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p1.19.m1.1b"><ci id="S3.SS2.SSS1.p1.19.m1.1.1.cmml" 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The ToA is estimated by identifying the index <math alttext="\tau_{n}^{\text{peak}}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p1.20.m2.1"><semantics id="S3.SS2.SSS1.p1.20.m2.1a"><msubsup id="S3.SS2.SSS1.p1.20.m2.1.1" xref="S3.SS2.SSS1.p1.20.m2.1.1.cmml"><mi id="S3.SS2.SSS1.p1.20.m2.1.1.2.2" xref="S3.SS2.SSS1.p1.20.m2.1.1.2.2.cmml">τ</mi><mi id="S3.SS2.SSS1.p1.20.m2.1.1.2.3" xref="S3.SS2.SSS1.p1.20.m2.1.1.2.3.cmml">n</mi><mtext id="S3.SS2.SSS1.p1.20.m2.1.1.3" xref="S3.SS2.SSS1.p1.20.m2.1.1.3a.cmml">peak</mtext></msubsup><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p1.20.m2.1b"><apply id="S3.SS2.SSS1.p1.20.m2.1.1.cmml" xref="S3.SS2.SSS1.p1.20.m2.1.1"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p1.20.m2.1.1.1.cmml" xref="S3.SS2.SSS1.p1.20.m2.1.1">superscript</csymbol><apply id="S3.SS2.SSS1.p1.20.m2.1.1.2.cmml" xref="S3.SS2.SSS1.p1.20.m2.1.1"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p1.20.m2.1.1.2.1.cmml" xref="S3.SS2.SSS1.p1.20.m2.1.1">subscript</csymbol><ci 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id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.2.1.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.2"></abs><apply id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1"><times id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.1.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.1"></times><apply id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2"><csymbol cd="ambiguous" id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.1.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2">subscript</csymbol><apply id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.2.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.2"><ci id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.2.1.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.2.1">^</ci><ci id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.2.2.cmml" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.1.1.1.2.2.2">ℎ</ci></apply><list id="S3.E5.m1.3.3.3.4.cmml" xref="S3.E5.m1.3.3.3.5"><ci id="S3.E5.m1.1.1.1.1.cmml" xref="S3.E5.m1.1.1.1.1">𝑛</ci><ci id="S3.E5.m1.2.2.2.2.cmml" xref="S3.E5.m1.2.2.2.2">𝑝</ci><ci id="S3.E5.m1.3.3.3.3.cmml" xref="S3.E5.m1.3.3.3.3">𝑙</ci></list></apply><ci id="S3.E5.m1.4.4.cmml" xref="S3.E5.m1.4.4">𝑡</ci></apply></apply><cn id="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.3.cmml" type="integer" xref="S3.E5.m1.6.6.2.2.2.2.1.1.1.1.3">2</cn></apply></apply></apply></apply></apply></apply></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.E5.m1.6c">\tau_{n}^{\text{peak}}=\arg\max_{t}\{\frac{1}{N_{\text{symb}}^{\text{SRS}}}% \sum_{l=1}^{N_{symb}^{SRS}}\sum_{p=1}^{P_{RX}}\left|\hat{h}_{n,p,l}(t)\right|^% {2}\}</annotation><annotation encoding="application/x-llamapun" id="S3.E5.m1.6d">italic_τ start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT start_POSTSUPERSCRIPT peak end_POSTSUPERSCRIPT = roman_arg roman_max start_POSTSUBSCRIPT italic_t end_POSTSUBSCRIPT { divide start_ARG 1 end_ARG start_ARG italic_N start_POSTSUBSCRIPT symb end_POSTSUBSCRIPT start_POSTSUPERSCRIPT SRS end_POSTSUPERSCRIPT end_ARG ∑ start_POSTSUBSCRIPT italic_l = 1 end_POSTSUBSCRIPT start_POSTSUPERSCRIPT italic_N start_POSTSUBSCRIPT italic_s italic_y italic_m italic_b end_POSTSUBSCRIPT start_POSTSUPERSCRIPT italic_S italic_R italic_S end_POSTSUPERSCRIPT end_POSTSUPERSCRIPT ∑ start_POSTSUBSCRIPT italic_p = 1 end_POSTSUBSCRIPT start_POSTSUPERSCRIPT italic_P start_POSTSUBSCRIPT italic_R italic_X end_POSTSUBSCRIPT end_POSTSUPERSCRIPT | over^ start_ARG italic_h end_ARG start_POSTSUBSCRIPT italic_n , italic_p , italic_l end_POSTSUBSCRIPT ( italic_t ) | start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT }</annotation></semantics></math></td> <td class="ltx_eqn_cell ltx_eqn_center_padright"></td> <td class="ltx_eqn_cell ltx_eqn_eqno ltx_align_middle ltx_align_right" rowspan="1"><span class="ltx_tag ltx_tag_equation ltx_align_right">(5)</span></td> </tr></tbody> </table> </div> <div class="ltx_para" id="S3.SS2.SSS1.p2"> <p class="ltx_p" id="S3.SS2.SSS1.p2.1">The ToA in seconds can be calculated as:</p> </div> <div class="ltx_para" id="S3.SS2.SSS1.p3"> <table class="ltx_equation ltx_eqn_table" id="S3.E6"> <tbody><tr class="ltx_equation ltx_eqn_row ltx_align_baseline"> <td class="ltx_eqn_cell ltx_eqn_center_padleft"></td> <td class="ltx_eqn_cell ltx_align_center"><math alttext="\text{ToA}_{n}=\left(\frac{\tau_{n}^{\text{peak}}}{L}\right)\cdot T_{s}" class="ltx_Math" display="block" id="S3.E6.m1.1"><semantics id="S3.E6.m1.1a"><mrow id="S3.E6.m1.1.2" xref="S3.E6.m1.1.2.cmml"><msub id="S3.E6.m1.1.2.2" xref="S3.E6.m1.1.2.2.cmml"><mtext id="S3.E6.m1.1.2.2.2" xref="S3.E6.m1.1.2.2.2a.cmml">ToA</mtext><mi id="S3.E6.m1.1.2.2.3" xref="S3.E6.m1.1.2.2.3.cmml">n</mi></msub><mo id="S3.E6.m1.1.2.1" xref="S3.E6.m1.1.2.1.cmml">=</mo><mrow id="S3.E6.m1.1.2.3" xref="S3.E6.m1.1.2.3.cmml"><mrow id="S3.E6.m1.1.2.3.2.2" xref="S3.E6.m1.1.1.cmml"><mo id="S3.E6.m1.1.2.3.2.2.1" xref="S3.E6.m1.1.1.cmml">(</mo><mfrac id="S3.E6.m1.1.1" xref="S3.E6.m1.1.1.cmml"><msubsup id="S3.E6.m1.1.1.2" xref="S3.E6.m1.1.1.2.cmml"><mi id="S3.E6.m1.1.1.2.2.2" xref="S3.E6.m1.1.1.2.2.2.cmml">τ</mi><mi id="S3.E6.m1.1.1.2.2.3" xref="S3.E6.m1.1.1.2.2.3.cmml">n</mi><mtext id="S3.E6.m1.1.1.2.3" xref="S3.E6.m1.1.1.2.3a.cmml">peak</mtext></msubsup><mi id="S3.E6.m1.1.1.3" xref="S3.E6.m1.1.1.3.cmml">L</mi></mfrac><mo id="S3.E6.m1.1.2.3.2.2.2" rspace="0.055em" xref="S3.E6.m1.1.1.cmml">)</mo></mrow><mo id="S3.E6.m1.1.2.3.1" rspace="0.222em" xref="S3.E6.m1.1.2.3.1.cmml">⋅</mo><msub id="S3.E6.m1.1.2.3.3" xref="S3.E6.m1.1.2.3.3.cmml"><mi id="S3.E6.m1.1.2.3.3.2" xref="S3.E6.m1.1.2.3.3.2.cmml">T</mi><mi id="S3.E6.m1.1.2.3.3.3" xref="S3.E6.m1.1.2.3.3.3.cmml">s</mi></msub></mrow></mrow><annotation-xml encoding="MathML-Content" id="S3.E6.m1.1b"><apply id="S3.E6.m1.1.2.cmml" xref="S3.E6.m1.1.2"><eq id="S3.E6.m1.1.2.1.cmml" xref="S3.E6.m1.1.2.1"></eq><apply id="S3.E6.m1.1.2.2.cmml" xref="S3.E6.m1.1.2.2"><csymbol cd="ambiguous" id="S3.E6.m1.1.2.2.1.cmml" xref="S3.E6.m1.1.2.2">subscript</csymbol><ci id="S3.E6.m1.1.2.2.2a.cmml" xref="S3.E6.m1.1.2.2.2"><mtext id="S3.E6.m1.1.2.2.2.cmml" xref="S3.E6.m1.1.2.2.2">ToA</mtext></ci><ci id="S3.E6.m1.1.2.2.3.cmml" xref="S3.E6.m1.1.2.2.3">𝑛</ci></apply><apply id="S3.E6.m1.1.2.3.cmml" xref="S3.E6.m1.1.2.3"><ci id="S3.E6.m1.1.2.3.1.cmml" xref="S3.E6.m1.1.2.3.1">⋅</ci><apply id="S3.E6.m1.1.1.cmml" xref="S3.E6.m1.1.2.3.2.2"><divide id="S3.E6.m1.1.1.1.cmml" xref="S3.E6.m1.1.2.3.2.2"></divide><apply id="S3.E6.m1.1.1.2.cmml" xref="S3.E6.m1.1.1.2"><csymbol cd="ambiguous" id="S3.E6.m1.1.1.2.1.cmml" xref="S3.E6.m1.1.1.2">superscript</csymbol><apply id="S3.E6.m1.1.1.2.2.cmml" xref="S3.E6.m1.1.1.2"><csymbol cd="ambiguous" id="S3.E6.m1.1.1.2.2.1.cmml" xref="S3.E6.m1.1.1.2">subscript</csymbol><ci id="S3.E6.m1.1.1.2.2.2.cmml" xref="S3.E6.m1.1.1.2.2.2">𝜏</ci><ci id="S3.E6.m1.1.1.2.2.3.cmml" xref="S3.E6.m1.1.1.2.2.3">𝑛</ci></apply><ci id="S3.E6.m1.1.1.2.3a.cmml" xref="S3.E6.m1.1.1.2.3"><mtext id="S3.E6.m1.1.1.2.3.cmml" mathsize="70%" xref="S3.E6.m1.1.1.2.3">peak</mtext></ci></apply><ci id="S3.E6.m1.1.1.3.cmml" xref="S3.E6.m1.1.1.3">𝐿</ci></apply><apply id="S3.E6.m1.1.2.3.3.cmml" xref="S3.E6.m1.1.2.3.3"><csymbol cd="ambiguous" id="S3.E6.m1.1.2.3.3.1.cmml" xref="S3.E6.m1.1.2.3.3">subscript</csymbol><ci id="S3.E6.m1.1.2.3.3.2.cmml" xref="S3.E6.m1.1.2.3.3.2">𝑇</ci><ci id="S3.E6.m1.1.2.3.3.3.cmml" xref="S3.E6.m1.1.2.3.3.3">𝑠</ci></apply></apply></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.E6.m1.1c">\text{ToA}_{n}=\left(\frac{\tau_{n}^{\text{peak}}}{L}\right)\cdot T_{s}</annotation><annotation encoding="application/x-llamapun" id="S3.E6.m1.1d">ToA start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT = ( divide start_ARG italic_τ start_POSTSUBSCRIPT italic_n end_POSTSUBSCRIPT start_POSTSUPERSCRIPT peak end_POSTSUPERSCRIPT end_ARG start_ARG italic_L end_ARG ) ⋅ italic_T start_POSTSUBSCRIPT italic_s end_POSTSUBSCRIPT</annotation></semantics></math></td> <td class="ltx_eqn_cell ltx_eqn_center_padright"></td> <td class="ltx_eqn_cell ltx_eqn_eqno ltx_align_middle ltx_align_right" rowspan="1"><span class="ltx_tag ltx_tag_equation ltx_align_right">(6)</span></td> </tr></tbody> </table> </div> <div class="ltx_para" id="S3.SS2.SSS1.p4"> <p class="ltx_p" id="S3.SS2.SSS1.p4.1">Where <math alttext="T_{s}" class="ltx_Math" display="inline" id="S3.SS2.SSS1.p4.1.m1.1"><semantics id="S3.SS2.SSS1.p4.1.m1.1a"><msub id="S3.SS2.SSS1.p4.1.m1.1.1" xref="S3.SS2.SSS1.p4.1.m1.1.1.cmml"><mi id="S3.SS2.SSS1.p4.1.m1.1.1.2" xref="S3.SS2.SSS1.p4.1.m1.1.1.2.cmml">T</mi><mi id="S3.SS2.SSS1.p4.1.m1.1.1.3" xref="S3.SS2.SSS1.p4.1.m1.1.1.3.cmml">s</mi></msub><annotation-xml encoding="MathML-Content" id="S3.SS2.SSS1.p4.1.m1.1b"><apply id="S3.SS2.SSS1.p4.1.m1.1.1.cmml" xref="S3.SS2.SSS1.p4.1.m1.1.1"><csymbol cd="ambiguous" id="S3.SS2.SSS1.p4.1.m1.1.1.1.cmml" xref="S3.SS2.SSS1.p4.1.m1.1.1">subscript</csymbol><ci id="S3.SS2.SSS1.p4.1.m1.1.1.2.cmml" xref="S3.SS2.SSS1.p4.1.m1.1.1.2">𝑇</ci><ci id="S3.SS2.SSS1.p4.1.m1.1.1.3.cmml" xref="S3.SS2.SSS1.p4.1.m1.1.1.3">𝑠</ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S3.SS2.SSS1.p4.1.m1.1c">T_{s}</annotation><annotation encoding="application/x-llamapun" id="S3.SS2.SSS1.p4.1.m1.1d">italic_T start_POSTSUBSCRIPT italic_s end_POSTSUBSCRIPT</annotation></semantics></math> is the sampling period.</p> </div> <section class="ltx_paragraph" id="S3.SS2.SSS1.Px1"> <h5 class="ltx_title ltx_title_paragraph">FAPI interface</h5> <div class="ltx_para" id="S3.SS2.SSS1.Px1.p1"> <p class="ltx_p" id="S3.SS2.SSS1.Px1.p1.1">The FAPI interface is a standardized interface between the PHY and the MAC specified by the small cell forum <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib14" title="">14</a>]</cite>. The SRS measurements are sent from PHY to the MAC via the SRS.indication message. This message includes a field called “Timing advance offset in nanoseconds,” which is meant to be used for UL TDoA positioning measurements. However, the standard does not foresee that there can be multiple such measurements from multiple TRPs connected to the same DU. We solved this issue by adding a new value for SRS type (5) and a new report type (“Localization”) to the SRS indication message. These additions are allowed in the current specification and do not break the compatibility with implementations that do not support this report type. The actual values of the Timing advance offsets in ns from the multiple TRPs are sent in the report-tagged list value (TLV) directly as an array in the value field, where each value uses 16bit.</p> </div> </section> </section> <section class="ltx_subsubsection" id="S3.SS2.SSS2"> <h4 class="ltx_title ltx_title_subsubsection"> <span class="ltx_tag ltx_tag_subsubsection"><span class="ltx_text" id="S3.SS2.SSS2.5.1.1">III-B</span>2 </span>gNB-MAC</h4> <div class="ltx_para" id="S3.SS2.SSS2.p1"> <p class="ltx_p" id="S3.SS2.SSS2.p1.1">The MAC is responsible for scheduling the SRS and for handling the SRS indication messages from the PHY.</p> </div> <div class="ltx_para" id="S3.SS2.SSS2.p2"> <p class="ltx_p" id="S3.SS2.SSS2.p2.1">The scheduling is different depending if the UE is connected to the same MAC (serving cell measurements) or to a different MAC (neighbor cell measurements).</p> </div> <div class="ltx_para" id="S3.SS2.SSS2.p3"> <p class="ltx_p" id="S3.SS2.SSS2.p3.1">The serving cell measurements are straightforward as the SRS scheduling is already activated at the PDU session establishment during the connection procedure. Upon reception of an F1 positioning measurement request, the MAC simply takes the latest ToA measurement it received from the PHY and generates the F1 positioning measurement response.</p> </div> <div class="ltx_para" id="S3.SS2.SSS2.p4"> <p class="ltx_p" id="S3.SS2.SSS2.p4.1">In the case of a neighbor cell measurement, the MAC first has to activate the SRS measurements. For this kind of measurement we have also had to slightly modify the usage of the FAPI interface as the current interface does not support this usage. We have introduced a special RNTI reserved for this usage. The RNTI is used in the SRS PDU of the UL_TTI request sent from the MAC to the PHY and also in the SRS indication sent back from the PHY to the MAC. This way we can associate the measurement with the measurement request message.</p> </div> </section> </section> </section> <section class="ltx_section" id="S4"> <h2 class="ltx_title ltx_title_section"> <span class="ltx_tag ltx_tag_section">IV </span><span class="ltx_text ltx_font_smallcaps" id="S4.1.1">Validation of our Open-Source UL-TDoA positioning</span> </h2> <div class="ltx_para" id="S4.p1"> <p class="ltx_p" id="S4.p1.1">In this section, we validate our open-source UL-TDoA positioning implementation within the OpenAirInterface (OAI) framework. We conducted end-to-end protocol testing and message exchange validation using two different setups: the OAI-RF simulator-based <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib15" title="">15</a>]</cite> setup and the O-RAN-based Localization Testbed at EURECOM. The OAI-RF simulator allowed us to test the complete message flow and protocol interactions in a controlled environment, while the O-RAN-based Localization Testbed provided a real-world scenario to further validate the functionality and reliability of our UL-TDoA implementation. These setups ensure the robustness of our implementation and confirm its capability to support UL-TDoA positioning.</p> </div> <section class="ltx_subsection" id="S4.SS1"> <h3 class="ltx_title ltx_title_subsection"> <span class="ltx_tag ltx_tag_subsection"><span class="ltx_text" id="S4.SS1.5.1.1">IV-A</span> </span><span class="ltx_text ltx_font_italic" id="S4.SS1.6.2">OAI-rfsimulator based setup</span> </h3> <div class="ltx_para" id="S4.SS1.p1"> <p class="ltx_p" id="S4.SS1.p1.1">Our first validation approach uses a setup based on the OAI-RF simulator, a tool within the OpenAirInterface (OAI) framework designed to emulate RF environments. This virtualized environment allows for the testing of various network scenarios without physical hardware, enabling end-to-end protocol and message exchange validation. By replicating real-world RF conditions, the OAI-RF simulator supports the validation of 5G functionalities, such as UL-TDoA positioning, in a controlled and repeatable manner, making it a valuable asset for testing and refining implementations efficiently.</p> </div> <figure class="ltx_figure" id="S4.F6"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="256" id="S4.F6.g1" src="extracted/6285822/fig/rfim_positioning.jpg" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 6: </span>OAI-RF simulator-based setup</figcaption> </figure> <div class="ltx_para" id="S4.SS1.p2"> <p class="ltx_p" id="S4.SS1.p2.1">A detailed tutorial on building an OAI-RF simulator-based setup can be found here<cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib16" title="">16</a>]</cite>. The working branch for our implementation is named <span class="ltx_text ltx_font_italic" id="S4.SS1.p2.1.1">NRPPA_Procedures</span> <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib17" title="">17</a>]</cite>. In the following, we discuss the key aspects of our setup and provide relevant log details.</p> </div> <section class="ltx_subsubsection" id="S4.SS1.SSS1"> <h4 class="ltx_title ltx_title_subsubsection"> <span class="ltx_tag ltx_tag_subsubsection"><span class="ltx_text" id="S4.SS1.SSS1.5.1.1">IV-A</span>1 </span>Preparing the Setup</h4> <div class="ltx_para" id="S4.SS1.SSS1.p1"> <p class="ltx_p" id="S4.SS1.SSS1.p1.1">The first step is to deploy the 5G core. In our setup, we utilized a Docker-based deployment of the OAI 5G core. The Docker images for the 5G core network functions (NFs) are open source, publicly available, and can be pulled to the local server using the following commands.</p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p2"> <p class="ltx_p" id="S4.SS1.SSS1.p2.1"><span class="ltx_text ltx_font_typewriter" id="S4.SS1.SSS1.p2.1.1" style="font-size:70%;"><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p2.1.1.1" style="width:0.0pt;"></span><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p2.1.1.2" style="width:469.8pt;">#Pull OAI Core Network Functions</span></span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.2" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/ims:latest</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.3" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-amf:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.4" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-nrf:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.5" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-smf:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.6" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-udr:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.7" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-upf:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.8" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-udm:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.9" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-ausf:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.10" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/oai-lmf:develop</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p2.1.11" style="font-size:70%;width:469.8pt;">docker pull oaisoftwarealliance/trf-gen-cn5g:latest</span> The next step is to clone the OAI 5G RAN repository <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib17" title="">17</a>]</cite> and build the RFsimulator-based gNB and UE. Our work is part of the <span class="ltx_text ltx_font_italic" id="S4.SS1.SSS1.p2.1.12">NRPPA_Procedures</span> branch<span class="ltx_note ltx_role_footnote" id="footnote3"><sup class="ltx_note_mark">3</sup><span class="ltx_note_outer"><span class="ltx_note_content"><sup class="ltx_note_mark">3</sup><span class="ltx_tag ltx_tag_note">3</span>The main branch of the OAI 5G RAN repository is <span class="ltx_text ltx_font_italic" id="footnote3.1">develop</span>, and all new features are eventually merged into this branch. If the NRPPA_Procedures branch no longer exists, it indicates that the features have been merged into the <span class="ltx_text ltx_font_italic" id="footnote3.2">develop</span> branch of the OAI 5G RAN repository, and you should use the <span class="ltx_text ltx_font_italic" id="footnote3.3">develop</span> branch instead.</span></span></span>.</p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p3"> <p class="ltx_p" id="S4.SS1.SSS1.p3.1"><span class="ltx_text ltx_font_typewriter" id="S4.SS1.SSS1.p3.1.1" style="font-size:70%;"><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p3.1.1.1" style="width:0.0pt;"></span><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p3.1.1.2" style="width:469.8pt;"> git clone https://gitlab.eurecom.fr/oai/openairinterface5g.git</span></span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p3.1.2" style="font-size:70%;width:469.8pt;"> cd openairinterface5g/cmake_targets</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p3.1.3" style="font-size:70%;width:469.8pt;"> git checkout NRPPA_Procedures</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p3.1.4" style="font-size:70%;width:469.8pt;"> # install dependencies</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p3.1.5" style="font-size:70%;width:469.8pt;"> ./build_oai -I</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p3.1.6" style="font-size:70%;width:469.8pt;"> # compile gNB and nrUE</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p3.1.7" style="font-size:70%;width:469.8pt;"> ./build_oai --gNB --nrUE -w SIMU</span></p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p4"> <p class="ltx_p" id="S4.SS1.SSS1.p4.1">Once the NF images have been pulled and the RFsimulator-based gNB and UE have been successfully built, we are ready to deploy our RFsimulator-based setup using these components. Use the following commands to deploy the 5G core.</p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p5"> <p class="ltx_p" id="S4.SS1.SSS1.p5.1"><span class="ltx_text ltx_font_typewriter" id="S4.SS1.SSS1.p5.1.1" style="font-size:70%;"><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p5.1.1.1" style="width:0.0pt;"></span><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p5.1.1.2" style="width:469.8pt;">cd openairinterface5g/doc/tutorial_resources/oai-cn5g</span></span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p5.1.2" style="font-size:70%;width:469.8pt;">docker compose -f docker-compose.yaml up -d</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p5.1.3" style="font-size:70%;width:469.8pt;"># verify the deployment</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p5.1.4" style="font-size:70%;width:469.8pt;">docker ps -a</span></p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p6"> <p class="ltx_p" id="S4.SS1.SSS1.p6.1">Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F7" title="Figure 7 ‣ IV-A1 Preparing the Setup ‣ IV-A OAI-rfsimulator based setup ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">7</span></a> shows the logs from a successful 5G core deployment.</p> </div> <figure class="ltx_figure" id="S4.F7"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="85" id="S4.F7.g1" src="extracted/6285822/fig/dockerps-a.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 7: </span>5G core deployment logs</figcaption> </figure> <div class="ltx_para" id="S4.SS1.SSS1.p7"> <p class="ltx_p" id="S4.SS1.SSS1.p7.1">The logs of the AMF can be checked using the following command.</p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p8"> <p class="ltx_p" id="S4.SS1.SSS1.p8.1"><span class="ltx_text ltx_font_typewriter" id="S4.SS1.SSS1.p8.1.1" style="font-size:70%;"><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p8.1.1.1" style="width:0.0pt;"></span><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p8.1.1.2" style="width:469.8pt;"> docker logs oai-amf -f</span></span></p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p9"> <p class="ltx_p" id="S4.SS1.SSS1.p9.1">Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F8" title="Figure 8 ‣ IV-A1 Preparing the Setup ‣ IV-A OAI-rfsimulator based setup ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">8</span></a> shows the AMF logs prior to starting the gNB and UE.</p> </div> <figure class="ltx_figure" id="S4.F8"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="196" id="S4.F8.g1" src="extracted/6285822/fig/amflog.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 8: </span>AMF logs before running gNB and UE </figcaption> </figure> <div class="ltx_para" id="S4.SS1.SSS1.p10"> <p class="ltx_p" id="S4.SS1.SSS1.p10.1">Next, we start the gNB and UE using the following commands</p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p11"> <p class="ltx_p" id="S4.SS1.SSS1.p11.1"><span class="ltx_text ltx_font_typewriter" id="S4.SS1.SSS1.p11.1.1" style="font-size:70%;"><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p11.1.1.1" style="width:0.0pt;"></span><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p11.1.1.2" style="width:469.8pt;">#open a terminal to run the gNB</span></span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p11.1.2" style="font-size:70%;width:469.8pt;">cd openairinterface5g/cmake_targets/ran_build/build</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p11.1.3" style="font-size:70%;width:469.8pt;">sudo RFSIMULATOR=server ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-NR-5GC/CONF/ gnb.sa.band78.fr1.106PRB.usrpb210.conf --gNBs.[0].min_rxtxtime 6 --rfsim --sa</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p11.1.4" style="font-size:70%;width:469.8pt;">#open another terminal to run the UE</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p11.1.5" style="font-size:70%;width:469.8pt;">cd openairinterface5g/cmake_targets/ran_build/build</span><span class="ltx_text ltx_font_typewriter ltx_inline-block" id="S4.SS1.SSS1.p11.1.6" style="font-size:70%;width:469.8pt;">sudo RFSIMULATOR=127.0.0.1 ./nr-uesoftmodem -r 106 --numerology 1 --band 78 -C 3619200000 --sa --uicc0.imsi 001010000000001 --rfsim</span></p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p12"> <p class="ltx_p" id="S4.SS1.SSS1.p12.1">Figures <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F9" title="Figure 9 ‣ IV-A1 Preparing the Setup ‣ IV-A OAI-rfsimulator based setup ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">9</span></a>–<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F11" title="Figure 11 ‣ IV-A1 Preparing the Setup ‣ IV-A OAI-rfsimulator based setup ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">11</span></a> show example logs of the gNB, UE, and AMF when the UE is in the connected state.</p> </div> <figure class="ltx_figure" id="S4.F9"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="245" id="S4.F9.g1" src="extracted/6285822/fig/gNBconnected.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 9: </span>Example logs of gNB in the UE connected state.</figcaption> </figure> <figure class="ltx_figure" id="S4.F10"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="416" id="S4.F10.g1" src="extracted/6285822/fig/UEconnected.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 10: </span>Example logs of UE in the connected state.</figcaption> </figure> <figure class="ltx_figure" id="S4.F11"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="177" id="S4.F11.g1" src="extracted/6285822/fig/amfconnectlog.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 11: </span>Example logs of AMF in the UE connected state. </figcaption> </figure> <div class="ltx_para" id="S4.SS1.SSS1.p13"> <p class="ltx_p" id="S4.SS1.SSS1.p13.1">Now we are ready to start the positioning procedure for the UE. To initiate the positioning process for a specific UE, we send an HTTP POST request to the determine-location API of the LMF. The request contains a data structure of type InputData <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib10" title="">10</a>, Section 6.1.6.2.2]</cite>, which includes the IMSI value of the UE. We can initiate the positioning request using the following command, where the IP address of the LMF is <math alttext="192.168.70.141" class="ltx_Math" display="inline" id="S4.SS1.SSS1.p13.1.m1.1"><semantics id="S4.SS1.SSS1.p13.1.m1.1a"><mn id="S4.SS1.SSS1.p13.1.m1.1.1" xref="S4.SS1.SSS1.p13.1.m1.1.1.cmml">192.168.70.141</mn><annotation-xml encoding="MathML-Content" id="S4.SS1.SSS1.p13.1.m1.1b"><cn id="S4.SS1.SSS1.p13.1.m1.1.1.cmml" type="float" xref="S4.SS1.SSS1.p13.1.m1.1.1">192.168.70.141</cn></annotation-xml><annotation encoding="application/x-tex" id="S4.SS1.SSS1.p13.1.m1.1c">192.168.70.141</annotation><annotation encoding="application/x-llamapun" id="S4.SS1.SSS1.p13.1.m1.1d">192.168.70.141</annotation></semantics></math>.</p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p14"> <p class="ltx_p" id="S4.SS1.SSS1.p14.1"><span class="ltx_text ltx_font_typewriter" id="S4.SS1.SSS1.p14.1.1" style="font-size:70%;"><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p14.1.1.1" style="width:0.0pt;"></span><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p14.1.1.2" style="width:469.8pt;"> curl --http2-prior-knowledge -H "Content-Type: application/json" -d "@InputData.json" -X POST http://192.168.70.141:8080/nlmf-loc/v1/determine-location</span></span></p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p15"> <p class="ltx_p" id="S4.SS1.SSS1.p15.1">Figures <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F12" title="Figure 12 ‣ IV-A1 Preparing the Setup ‣ IV-A OAI-rfsimulator based setup ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">12</span></a>–<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F14" title="Figure 14 ‣ IV-A1 Preparing the Setup ‣ IV-A OAI-rfsimulator based setup ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">14</span></a> show example logs of the gNB and LMF after initiating the positioning request. The LMF logs can be checked using the following command.</p> </div> <div class="ltx_para" id="S4.SS1.SSS1.p16"> <p class="ltx_p" id="S4.SS1.SSS1.p16.1"><span class="ltx_text ltx_font_typewriter" id="S4.SS1.SSS1.p16.1.1" style="font-size:70%;"><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p16.1.1.1" style="width:0.0pt;"></span><span class="ltx_text ltx_inline-block" id="S4.SS1.SSS1.p16.1.1.2" style="width:469.8pt;"> docker logs oai-lmf -f</span></span></p> </div> <figure class="ltx_figure" id="S4.F12"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="383" id="S4.F12.g1" src="extracted/6285822/fig/gNBTRP.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 12: </span>Example logs when gNB received TRP information request </figcaption> </figure> <figure class="ltx_figure" id="S4.F13"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="69" id="S4.F13.g1" src="extracted/6285822/fig/lmfTRP.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 13: </span>Example logs when LMF received TRP information response </figcaption> </figure> <figure class="ltx_figure" id="S4.F14"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="177" id="S4.F14.g1" src="extracted/6285822/fig/lmfToA.png" width="598"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 14: </span>Example logs when LMF received ToA information</figcaption> </figure> </section> </section> <section class="ltx_subsection" id="S4.SS2"> <h3 class="ltx_title ltx_title_subsection"> <span class="ltx_tag ltx_tag_subsection"><span class="ltx_text" id="S4.SS2.5.1.1">IV-B</span> </span><span class="ltx_text ltx_font_italic" id="S4.SS2.6.2">O-RAN based Localization Testbed at EURECOM</span> </h3> <div class="ltx_para" id="S4.SS2.p1"> <p class="ltx_p" id="S4.SS2.p1.1">The localization testbed is part of the larger Open5G testbed deployed at EURECOM. The overall testbed consists of computing and switching infrastructure interconnected through high-speed fiber links with various radios (either software defined radios like the USRP or commercial O-RAN radio units) allowing for virtualized deployment of 5G networks. A critical component of the EURECOM 5G testbed is its integration with OpenAirInterface, which provides all the virtualized network functions to run the 5G network.</p> </div> <section class="ltx_subsubsection" id="S4.SS2.SSS1"> <h4 class="ltx_title ltx_title_subsubsection"> <span class="ltx_tag ltx_tag_subsubsection"><span class="ltx_text" id="S4.SS2.SSS1.5.1.1">IV-B</span>1 </span>Deployment</h4> <div class="ltx_para" id="S4.SS2.SSS1.p1"> <p class="ltx_p" id="S4.SS2.SSS1.p1.1">In order to evaluate the localization features described above, we have deployed 3 additional O-RUs from Firecell outdoors (see Table <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.T1" title="TABLE I ‣ IV-B1 Deployment ‣ IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">I</span></a> for details). An aerial photo of the EURECOM building is shown in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F15" title="Figure 15 ‣ IV-B1 Deployment ‣ IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">15</span></a>. The building has two symmetric wings and two different levels following the slope of the hill it is built on. The top level roof features two antenna sites, one on each wing, which are part of the greater EURECOM 5G testbed. Each site has multiple fibre connections that run directly into EURECOM’s server room which hosts the computing and switching infrastructure. We have deployed a Firecell RU on each of these sites and each RU drives 2 external antennas, which have been mounted on the railings of the roof and are connected to the RU through a 10m low loss cable (the cable introduces an attenuation of 7 dB, which has been included in the link budget). These antennas overlook the lower roof of the Eurecom building, which is three floors below. The northeast wing of the lower roof is accessible to people and is used as an experimentation area. The southwest wing of the lower roof is off-limits for people and features a third RU whose antennas are deployed on small tripods spaced 10m apart and at a height of 2m. Our deployment can be seen in Figures <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F15" title="Figure 15 ‣ IV-B1 Deployment ‣ IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">15</span></a> and <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F17" title="Figure 17 ‣ IV-B3 Ground truth measurements ‣ IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">17</span></a>.</p> </div> <figure class="ltx_table" id="S4.T1"> <figcaption class="ltx_caption"><span class="ltx_tag ltx_tag_table">TABLE I: </span>Parameters of the Firecell O-RU</figcaption> <table class="ltx_tabular ltx_centering ltx_align_middle" id="S4.T1.1.1"> <tr class="ltx_tr" id="S4.T1.1.1.2"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" colspan="2" id="S4.T1.1.1.2.1"><span class="ltx_text ltx_font_bold" id="S4.T1.1.1.2.1.1">NR Radio Specification</span></td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.3"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r ltx_border_t" id="S4.T1.1.1.3.1">Band</td> <td class="ltx_td ltx_align_left ltx_border_r ltx_border_t" id="S4.T1.1.1.3.2">n77</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.4"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.4.1">Occupied Bandwidth(max)</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.4.2">100MHz</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.5"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.5.1">Duplex Mode</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.5.2">TDD</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.6"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.6.1">Sub Carrier Spacing</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.6.2">30KHz</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.7"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.7.1">MIMO</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.7.2">4T4R</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.8"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.8.1">RF Output Power per port</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.8.2">250mWatt/ 24dBm</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.9"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.9.1">Antennas</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.9.2">Internal/External</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.10"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" colspan="2" id="S4.T1.1.1.10.1"><span class="ltx_text ltx_font_bold" id="S4.T1.1.1.10.1.1">Connectivity Specification</span></td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.11"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r ltx_border_t" id="S4.T1.1.1.11.1">Physical</td> <td class="ltx_td ltx_align_left ltx_border_r ltx_border_t" id="S4.T1.1.1.11.2"> <span class="ltx_text" id="S4.T1.1.1.11.2.1"></span><span class="ltx_text" id="S4.T1.1.1.11.2.2"> <span class="ltx_tabular ltx_align_middle" id="S4.T1.1.1.11.2.2.1"> <span class="ltx_tr" id="S4.T1.1.1.11.2.2.1.1"> <span class="ltx_td ltx_nopad_r ltx_align_left" id="S4.T1.1.1.11.2.2.1.1.1">10G Base-T over SFP</span></span> <span class="ltx_tr" id="S4.T1.1.1.11.2.2.1.2"> <span class="ltx_td ltx_nopad_r ltx_align_left" id="S4.T1.1.1.11.2.2.1.2.1">1G Base-T over Ethernet</span></span> </span></span><span class="ltx_text" id="S4.T1.1.1.11.2.3"></span></td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.12"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.12.1">Interface Protocol</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.12.2">ORAN Split 7-2 CAT-A</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.13"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.13.1">Time and Synchronization</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.13.2">IEEE 1588v2, ITU T G.8275.1</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.14"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" colspan="2" id="S4.T1.1.1.14.1"><span class="ltx_text ltx_font_bold" id="S4.T1.1.1.14.1.1">Environmental Specification</span></td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.15"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r ltx_border_t" id="S4.T1.1.1.15.1">Powering</td> <td class="ltx_td ltx_align_left ltx_border_r ltx_border_t" id="S4.T1.1.1.15.2">PoE ++ Type 3 IEEE802.3bt</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.16"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.16.1">Dimension (mm)</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.16.2">250mm x 213.5mm x 92.1</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.1"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.1.2">Weight</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.1.1"> <math alttext="<" class="ltx_Math" display="inline" id="S4.T1.1.1.1.1.m1.1"><semantics id="S4.T1.1.1.1.1.m1.1a"><mo id="S4.T1.1.1.1.1.m1.1.1" xref="S4.T1.1.1.1.1.m1.1.1.cmml"><</mo><annotation-xml encoding="MathML-Content" id="S4.T1.1.1.1.1.m1.1b"><lt id="S4.T1.1.1.1.1.m1.1.1.cmml" xref="S4.T1.1.1.1.1.m1.1.1"></lt></annotation-xml><annotation encoding="application/x-tex" id="S4.T1.1.1.1.1.m1.1c"><</annotation><annotation encoding="application/x-llamapun" id="S4.T1.1.1.1.1.m1.1d"><</annotation></semantics></math>4Kg</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.17"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.17.1">Operating Temperature</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.17.2">-5 to 40C / -40 to 55C</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.18"> <td class="ltx_td ltx_align_left ltx_border_l ltx_border_r" id="S4.T1.1.1.18.1">Environmental</td> <td class="ltx_td ltx_align_left ltx_border_r" id="S4.T1.1.1.18.2">IP31/ IP65</td> </tr> <tr class="ltx_tr" id="S4.T1.1.1.19"> <td class="ltx_td ltx_align_left ltx_border_b ltx_border_l ltx_border_r" id="S4.T1.1.1.19.1">Mounting Style</td> <td class="ltx_td ltx_align_left ltx_border_b ltx_border_r" id="S4.T1.1.1.19.2">Wall/ Pole / Ceiling</td> </tr> </table> </figure> <figure class="ltx_figure" id="S4.F15"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="213" id="S4.F15.1.g1" src="x2.png" width="373"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 15: </span>Deployment of the localization testbed at EURECOM.</figcaption> </figure> </section> <section class="ltx_subsubsection" id="S4.SS2.SSS2"> <h4 class="ltx_title ltx_title_subsubsection"> <span class="ltx_tag ltx_tag_subsubsection"><span class="ltx_text" id="S4.SS2.SSS2.5.1.1">IV-B</span>2 </span>Logical Architecture</h4> <div class="ltx_para" id="S4.SS2.SSS2.p1"> <p class="ltx_p" id="S4.SS2.SSS2.p1.1">The logical architecture of the localization testbed is depicted in Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F16" title="Figure 16 ‣ IV-B2 Logical Architecture ‣ IV-B O-RAN based Localization Testbed at EURECOM ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">16</span></a>. It follows a basic O-RAN architecture with sync option LLS-C3, i.e., the synchronization is managed by a Primary Reference Time Clock (PRTC) and a Telecom Grandmaster (T-GM) that are situated within the fronthaul network. The timing signals are distributed from the PRTC/T-GM to the O-RU and the O-DU via the fronthaul network (in our case a Cisco 93180-YC-FX3).</p> </div> <div class="ltx_para" id="S4.SS2.SSS2.p2"> <p class="ltx_p" id="S4.SS2.SSS2.p2.1">The CU and DU run on a server ”colibri” with a Intel(R) Xeon(R) Gold 6354 CPU @ 3.00GHz CPUs with 18 cores each. For the fronthaul network it uses an Intel X710 4x10Gbps NIC. Two of the four ports are used to connect to the backhaul network (via a CISCO C9364C-GX switch) and the two other ports are connected to the fronthaul network. The core network runs on the server ”alambix” in a docker environment.</p> </div> <figure class="ltx_figure" id="S4.F16"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="124" id="S4.F16.1.g1" src="extracted/6285822/fig/testbed_logicalblue.png" width="269"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 16: </span>Logical architecture of the localization testbed.</figcaption> </figure> </section> <section class="ltx_subsubsection" id="S4.SS2.SSS3"> <h4 class="ltx_title ltx_title_subsubsection"> <span class="ltx_tag ltx_tag_subsubsection"><span class="ltx_text" id="S4.SS2.SSS3.5.1.1">IV-B</span>3 </span>Ground truth measurements</h4> <div class="ltx_para" id="S4.SS2.SSS3.p1"> <p class="ltx_p" id="S4.SS2.SSS3.p1.4">In this work, 16 ground truth positions (A-P) on the Eurecom experimentation area were selected in a relative Cartesian coordinate system. The distances from each point to all antennas of the testbed were measured using a BOSCH GLM-150-C laser distance meter, suited for outdoor applications and long-distance measurements with a range of 0.08 to 150.00 meters. The laser was mounted on a tripod at a height of 1.3 meters, approximating the typical height when a person holds a UE. The first antenna, located on RU3 at the corner of the building, served as the reference point with coordinates (x=0, y=0, z=2.2). The positions of the other antennas were measured relative to this reference. The recorded distances were then used in nonlinear Euclidean distance equations to calculate the relative Cartesian coordinates for each ground truth point. For all the points <math alttext="P_{i}" class="ltx_Math" display="inline" id="S4.SS2.SSS3.p1.1.m1.1"><semantics id="S4.SS2.SSS3.p1.1.m1.1a"><msub id="S4.SS2.SSS3.p1.1.m1.1.1" xref="S4.SS2.SSS3.p1.1.m1.1.1.cmml"><mi id="S4.SS2.SSS3.p1.1.m1.1.1.2" xref="S4.SS2.SSS3.p1.1.m1.1.1.2.cmml">P</mi><mi id="S4.SS2.SSS3.p1.1.m1.1.1.3" xref="S4.SS2.SSS3.p1.1.m1.1.1.3.cmml">i</mi></msub><annotation-xml encoding="MathML-Content" id="S4.SS2.SSS3.p1.1.m1.1b"><apply id="S4.SS2.SSS3.p1.1.m1.1.1.cmml" xref="S4.SS2.SSS3.p1.1.m1.1.1"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p1.1.m1.1.1.1.cmml" xref="S4.SS2.SSS3.p1.1.m1.1.1">subscript</csymbol><ci id="S4.SS2.SSS3.p1.1.m1.1.1.2.cmml" xref="S4.SS2.SSS3.p1.1.m1.1.1.2">𝑃</ci><ci id="S4.SS2.SSS3.p1.1.m1.1.1.3.cmml" xref="S4.SS2.SSS3.p1.1.m1.1.1.3">𝑖</ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S4.SS2.SSS3.p1.1.m1.1c">P_{i}</annotation><annotation encoding="application/x-llamapun" id="S4.SS2.SSS3.p1.1.m1.1d">italic_P start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT</annotation></semantics></math> with unknown position and antennas <math alttext="A_{j}" class="ltx_Math" display="inline" id="S4.SS2.SSS3.p1.2.m2.1"><semantics id="S4.SS2.SSS3.p1.2.m2.1a"><msub id="S4.SS2.SSS3.p1.2.m2.1.1" xref="S4.SS2.SSS3.p1.2.m2.1.1.cmml"><mi id="S4.SS2.SSS3.p1.2.m2.1.1.2" xref="S4.SS2.SSS3.p1.2.m2.1.1.2.cmml">A</mi><mi id="S4.SS2.SSS3.p1.2.m2.1.1.3" xref="S4.SS2.SSS3.p1.2.m2.1.1.3.cmml">j</mi></msub><annotation-xml encoding="MathML-Content" id="S4.SS2.SSS3.p1.2.m2.1b"><apply id="S4.SS2.SSS3.p1.2.m2.1.1.cmml" xref="S4.SS2.SSS3.p1.2.m2.1.1"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p1.2.m2.1.1.1.cmml" xref="S4.SS2.SSS3.p1.2.m2.1.1">subscript</csymbol><ci id="S4.SS2.SSS3.p1.2.m2.1.1.2.cmml" xref="S4.SS2.SSS3.p1.2.m2.1.1.2">𝐴</ci><ci id="S4.SS2.SSS3.p1.2.m2.1.1.3.cmml" xref="S4.SS2.SSS3.p1.2.m2.1.1.3">𝑗</ci></apply></annotation-xml><annotation encoding="application/x-tex" id="S4.SS2.SSS3.p1.2.m2.1c">A_{j}</annotation><annotation encoding="application/x-llamapun" id="S4.SS2.SSS3.p1.2.m2.1d">italic_A start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT</annotation></semantics></math> with known and fixed position the following distance <math alttext="d_{i,j}" class="ltx_Math" display="inline" id="S4.SS2.SSS3.p1.3.m3.2"><semantics id="S4.SS2.SSS3.p1.3.m3.2a"><msub id="S4.SS2.SSS3.p1.3.m3.2.3" xref="S4.SS2.SSS3.p1.3.m3.2.3.cmml"><mi id="S4.SS2.SSS3.p1.3.m3.2.3.2" xref="S4.SS2.SSS3.p1.3.m3.2.3.2.cmml">d</mi><mrow id="S4.SS2.SSS3.p1.3.m3.2.2.2.4" xref="S4.SS2.SSS3.p1.3.m3.2.2.2.3.cmml"><mi id="S4.SS2.SSS3.p1.3.m3.1.1.1.1" xref="S4.SS2.SSS3.p1.3.m3.1.1.1.1.cmml">i</mi><mo id="S4.SS2.SSS3.p1.3.m3.2.2.2.4.1" xref="S4.SS2.SSS3.p1.3.m3.2.2.2.3.cmml">,</mo><mi id="S4.SS2.SSS3.p1.3.m3.2.2.2.2" xref="S4.SS2.SSS3.p1.3.m3.2.2.2.2.cmml">j</mi></mrow></msub><annotation-xml encoding="MathML-Content" id="S4.SS2.SSS3.p1.3.m3.2b"><apply id="S4.SS2.SSS3.p1.3.m3.2.3.cmml" xref="S4.SS2.SSS3.p1.3.m3.2.3"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p1.3.m3.2.3.1.cmml" xref="S4.SS2.SSS3.p1.3.m3.2.3">subscript</csymbol><ci id="S4.SS2.SSS3.p1.3.m3.2.3.2.cmml" xref="S4.SS2.SSS3.p1.3.m3.2.3.2">𝑑</ci><list id="S4.SS2.SSS3.p1.3.m3.2.2.2.3.cmml" xref="S4.SS2.SSS3.p1.3.m3.2.2.2.4"><ci id="S4.SS2.SSS3.p1.3.m3.1.1.1.1.cmml" xref="S4.SS2.SSS3.p1.3.m3.1.1.1.1">𝑖</ci><ci id="S4.SS2.SSS3.p1.3.m3.2.2.2.2.cmml" xref="S4.SS2.SSS3.p1.3.m3.2.2.2.2">𝑗</ci></list></apply></annotation-xml><annotation encoding="application/x-tex" id="S4.SS2.SSS3.p1.3.m3.2c">d_{i,j}</annotation><annotation encoding="application/x-llamapun" id="S4.SS2.SSS3.p1.3.m3.2d">italic_d start_POSTSUBSCRIPT italic_i , italic_j end_POSTSUBSCRIPT</annotation></semantics></math> system of equations has to be solved to find <math alttext="P_{i}=\{x_{i},y_{i}\}" class="ltx_Math" display="inline" id="S4.SS2.SSS3.p1.4.m4.2"><semantics id="S4.SS2.SSS3.p1.4.m4.2a"><mrow id="S4.SS2.SSS3.p1.4.m4.2.2" xref="S4.SS2.SSS3.p1.4.m4.2.2.cmml"><msub id="S4.SS2.SSS3.p1.4.m4.2.2.4" xref="S4.SS2.SSS3.p1.4.m4.2.2.4.cmml"><mi id="S4.SS2.SSS3.p1.4.m4.2.2.4.2" xref="S4.SS2.SSS3.p1.4.m4.2.2.4.2.cmml">P</mi><mi id="S4.SS2.SSS3.p1.4.m4.2.2.4.3" xref="S4.SS2.SSS3.p1.4.m4.2.2.4.3.cmml">i</mi></msub><mo id="S4.SS2.SSS3.p1.4.m4.2.2.3" xref="S4.SS2.SSS3.p1.4.m4.2.2.3.cmml">=</mo><mrow id="S4.SS2.SSS3.p1.4.m4.2.2.2.2" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.3.cmml"><mo id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.3" stretchy="false" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.3.cmml">{</mo><msub id="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1" xref="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.cmml"><mi id="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.2" xref="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.2.cmml">x</mi><mi id="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.3" xref="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.3.cmml">i</mi></msub><mo id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.4" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.3.cmml">,</mo><msub id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.cmml"><mi id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.2" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.2.cmml">y</mi><mi id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.3" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.3.cmml">i</mi></msub><mo id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.5" stretchy="false" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.3.cmml">}</mo></mrow></mrow><annotation-xml encoding="MathML-Content" id="S4.SS2.SSS3.p1.4.m4.2b"><apply id="S4.SS2.SSS3.p1.4.m4.2.2.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2"><eq id="S4.SS2.SSS3.p1.4.m4.2.2.3.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.3"></eq><apply id="S4.SS2.SSS3.p1.4.m4.2.2.4.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.4"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p1.4.m4.2.2.4.1.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.4">subscript</csymbol><ci id="S4.SS2.SSS3.p1.4.m4.2.2.4.2.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.4.2">𝑃</ci><ci id="S4.SS2.SSS3.p1.4.m4.2.2.4.3.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.4.3">𝑖</ci></apply><set id="S4.SS2.SSS3.p1.4.m4.2.2.2.3.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2"><apply id="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.cmml" xref="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.1.cmml" xref="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1">subscript</csymbol><ci id="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.2.cmml" xref="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.2">𝑥</ci><ci id="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.3.cmml" xref="S4.SS2.SSS3.p1.4.m4.1.1.1.1.1.3">𝑖</ci></apply><apply id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.1.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2">subscript</csymbol><ci id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.2.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.2">𝑦</ci><ci id="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.3.cmml" xref="S4.SS2.SSS3.p1.4.m4.2.2.2.2.2.3">𝑖</ci></apply></set></apply></annotation-xml><annotation encoding="application/x-tex" id="S4.SS2.SSS3.p1.4.m4.2c">P_{i}=\{x_{i},y_{i}\}</annotation><annotation encoding="application/x-llamapun" id="S4.SS2.SSS3.p1.4.m4.2d">italic_P start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT = { italic_x start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT , italic_y start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT }</annotation></semantics></math></p> </div> <div class="ltx_para" id="S4.SS2.SSS3.p2"> <table class="ltx_equation ltx_eqn_table" id="S4.E7"> <tbody><tr class="ltx_equation ltx_eqn_row ltx_align_baseline"> <td class="ltx_eqn_cell ltx_eqn_center_padleft"></td> <td class="ltx_eqn_cell ltx_align_center"><math alttext="d_{ij}=\sqrt{(x_{i}-x_{j})^{2}+(y_{i}-y_{j})^{2}+(z_{i}-z_{j})^{2}}" class="ltx_Math" display="block" id="S4.E7.m1.3"><semantics id="S4.E7.m1.3a"><mrow id="S4.E7.m1.3.4" xref="S4.E7.m1.3.4.cmml"><msub id="S4.E7.m1.3.4.2" xref="S4.E7.m1.3.4.2.cmml"><mi id="S4.E7.m1.3.4.2.2" xref="S4.E7.m1.3.4.2.2.cmml">d</mi><mrow id="S4.E7.m1.3.4.2.3" xref="S4.E7.m1.3.4.2.3.cmml"><mi id="S4.E7.m1.3.4.2.3.2" xref="S4.E7.m1.3.4.2.3.2.cmml">i</mi><mo id="S4.E7.m1.3.4.2.3.1" 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italic_x start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT - italic_x start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT ) start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT + ( italic_y start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT - italic_y start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT ) start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT + ( italic_z start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT - italic_z start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT ) start_POSTSUPERSCRIPT 2 end_POSTSUPERSCRIPT end_ARG - italic_d start_POSTSUBSCRIPT italic_i , italic_j end_POSTSUBSCRIPT = 0</annotation></semantics></math></td> <td class="ltx_eqn_cell ltx_eqn_center_padright"></td> <td class="ltx_eqn_cell ltx_eqn_eqno ltx_align_middle ltx_align_right" rowspan="1"><span class="ltx_tag ltx_tag_equation ltx_align_right">(8)</span></td> </tr></tbody> </table> </div> <div class="ltx_para" id="S4.SS2.SSS3.p3"> <p class="ltx_p" id="S4.SS2.SSS3.p3.3">In MATLAB <span class="ltx_text ltx_font_typewriter" id="S4.SS2.SSS3.p3.3.1">fsolve</span> is a numerical solver used to find the roots of systems of nonlinear equations <math alttext="f_{i}(x_{i},y_{i})" class="ltx_Math" display="inline" id="S4.SS2.SSS3.p3.1.m1.2"><semantics id="S4.SS2.SSS3.p3.1.m1.2a"><mrow id="S4.SS2.SSS3.p3.1.m1.2.2" xref="S4.SS2.SSS3.p3.1.m1.2.2.cmml"><msub id="S4.SS2.SSS3.p3.1.m1.2.2.4" xref="S4.SS2.SSS3.p3.1.m1.2.2.4.cmml"><mi id="S4.SS2.SSS3.p3.1.m1.2.2.4.2" xref="S4.SS2.SSS3.p3.1.m1.2.2.4.2.cmml">f</mi><mi id="S4.SS2.SSS3.p3.1.m1.2.2.4.3" xref="S4.SS2.SSS3.p3.1.m1.2.2.4.3.cmml">i</mi></msub><mo id="S4.SS2.SSS3.p3.1.m1.2.2.3" xref="S4.SS2.SSS3.p3.1.m1.2.2.3.cmml">⁢</mo><mrow id="S4.SS2.SSS3.p3.1.m1.2.2.2.2" xref="S4.SS2.SSS3.p3.1.m1.2.2.2.3.cmml"><mo id="S4.SS2.SSS3.p3.1.m1.2.2.2.2.3" stretchy="false" xref="S4.SS2.SSS3.p3.1.m1.2.2.2.3.cmml">(</mo><msub id="S4.SS2.SSS3.p3.1.m1.1.1.1.1.1" xref="S4.SS2.SSS3.p3.1.m1.1.1.1.1.1.cmml"><mi id="S4.SS2.SSS3.p3.1.m1.1.1.1.1.1.2" 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xref="S4.SS2.SSS3.p3.1.m1.2.2.2.2.2.2">𝑦</ci><ci id="S4.SS2.SSS3.p3.1.m1.2.2.2.2.2.3.cmml" xref="S4.SS2.SSS3.p3.1.m1.2.2.2.2.2.3">𝑖</ci></apply></interval></apply></annotation-xml><annotation encoding="application/x-tex" id="S4.SS2.SSS3.p3.1.m1.2c">f_{i}(x_{i},y_{i})</annotation><annotation encoding="application/x-llamapun" id="S4.SS2.SSS3.p3.1.m1.2d">italic_f start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT ( italic_x start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT , italic_y start_POSTSUBSCRIPT italic_i end_POSTSUBSCRIPT )</annotation></semantics></math>. When solving for the coordinates of un unknown point based on known distances to a set of antennas, <span class="ltx_text ltx_font_typewriter" id="S4.SS2.SSS3.p3.3.2">fsolve</span> adjusts the values of <math alttext="(x_{j},y_{j})" class="ltx_Math" display="inline" id="S4.SS2.SSS3.p3.2.m2.2"><semantics id="S4.SS2.SSS3.p3.2.m2.2a"><mrow id="S4.SS2.SSS3.p3.2.m2.2.2.2" xref="S4.SS2.SSS3.p3.2.m2.2.2.3.cmml"><mo id="S4.SS2.SSS3.p3.2.m2.2.2.2.3" stretchy="false" xref="S4.SS2.SSS3.p3.2.m2.2.2.3.cmml">(</mo><msub id="S4.SS2.SSS3.p3.2.m2.1.1.1.1" xref="S4.SS2.SSS3.p3.2.m2.1.1.1.1.cmml"><mi id="S4.SS2.SSS3.p3.2.m2.1.1.1.1.2" xref="S4.SS2.SSS3.p3.2.m2.1.1.1.1.2.cmml">x</mi><mi id="S4.SS2.SSS3.p3.2.m2.1.1.1.1.3" xref="S4.SS2.SSS3.p3.2.m2.1.1.1.1.3.cmml">j</mi></msub><mo id="S4.SS2.SSS3.p3.2.m2.2.2.2.4" xref="S4.SS2.SSS3.p3.2.m2.2.2.3.cmml">,</mo><msub id="S4.SS2.SSS3.p3.2.m2.2.2.2.2" xref="S4.SS2.SSS3.p3.2.m2.2.2.2.2.cmml"><mi id="S4.SS2.SSS3.p3.2.m2.2.2.2.2.2" xref="S4.SS2.SSS3.p3.2.m2.2.2.2.2.2.cmml">y</mi><mi id="S4.SS2.SSS3.p3.2.m2.2.2.2.2.3" xref="S4.SS2.SSS3.p3.2.m2.2.2.2.2.3.cmml">j</mi></msub><mo id="S4.SS2.SSS3.p3.2.m2.2.2.2.5" stretchy="false" xref="S4.SS2.SSS3.p3.2.m2.2.2.3.cmml">)</mo></mrow><annotation-xml encoding="MathML-Content" id="S4.SS2.SSS3.p3.2.m2.2b"><interval closure="open" id="S4.SS2.SSS3.p3.2.m2.2.2.3.cmml" xref="S4.SS2.SSS3.p3.2.m2.2.2.2"><apply id="S4.SS2.SSS3.p3.2.m2.1.1.1.1.cmml" xref="S4.SS2.SSS3.p3.2.m2.1.1.1.1"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p3.2.m2.1.1.1.1.1.cmml" xref="S4.SS2.SSS3.p3.2.m2.1.1.1.1">subscript</csymbol><ci id="S4.SS2.SSS3.p3.2.m2.1.1.1.1.2.cmml" xref="S4.SS2.SSS3.p3.2.m2.1.1.1.1.2">𝑥</ci><ci id="S4.SS2.SSS3.p3.2.m2.1.1.1.1.3.cmml" xref="S4.SS2.SSS3.p3.2.m2.1.1.1.1.3">𝑗</ci></apply><apply id="S4.SS2.SSS3.p3.2.m2.2.2.2.2.cmml" xref="S4.SS2.SSS3.p3.2.m2.2.2.2.2"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p3.2.m2.2.2.2.2.1.cmml" xref="S4.SS2.SSS3.p3.2.m2.2.2.2.2">subscript</csymbol><ci id="S4.SS2.SSS3.p3.2.m2.2.2.2.2.2.cmml" xref="S4.SS2.SSS3.p3.2.m2.2.2.2.2.2">𝑦</ci><ci id="S4.SS2.SSS3.p3.2.m2.2.2.2.2.3.cmml" xref="S4.SS2.SSS3.p3.2.m2.2.2.2.2.3">𝑗</ci></apply></interval></annotation-xml><annotation encoding="application/x-tex" id="S4.SS2.SSS3.p3.2.m2.2c">(x_{j},y_{j})</annotation><annotation encoding="application/x-llamapun" id="S4.SS2.SSS3.p3.2.m2.2d">( italic_x start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT , italic_y start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT )</annotation></semantics></math> iteratively. It minimizes the difference between the calculated distances (from the guessed coordinates to the known antenna positions) and the given distances. By doing this, <span class="ltx_text ltx_font_typewriter" id="S4.SS2.SSS3.p3.3.3">fsolve</span> finds the point <math alttext="(x_{j},y_{j})" class="ltx_Math" display="inline" id="S4.SS2.SSS3.p3.3.m3.2"><semantics id="S4.SS2.SSS3.p3.3.m3.2a"><mrow id="S4.SS2.SSS3.p3.3.m3.2.2.2" xref="S4.SS2.SSS3.p3.3.m3.2.2.3.cmml"><mo id="S4.SS2.SSS3.p3.3.m3.2.2.2.3" stretchy="false" xref="S4.SS2.SSS3.p3.3.m3.2.2.3.cmml">(</mo><msub id="S4.SS2.SSS3.p3.3.m3.1.1.1.1" xref="S4.SS2.SSS3.p3.3.m3.1.1.1.1.cmml"><mi id="S4.SS2.SSS3.p3.3.m3.1.1.1.1.2" xref="S4.SS2.SSS3.p3.3.m3.1.1.1.1.2.cmml">x</mi><mi id="S4.SS2.SSS3.p3.3.m3.1.1.1.1.3" xref="S4.SS2.SSS3.p3.3.m3.1.1.1.1.3.cmml">j</mi></msub><mo id="S4.SS2.SSS3.p3.3.m3.2.2.2.4" xref="S4.SS2.SSS3.p3.3.m3.2.2.3.cmml">,</mo><msub id="S4.SS2.SSS3.p3.3.m3.2.2.2.2" xref="S4.SS2.SSS3.p3.3.m3.2.2.2.2.cmml"><mi id="S4.SS2.SSS3.p3.3.m3.2.2.2.2.2" xref="S4.SS2.SSS3.p3.3.m3.2.2.2.2.2.cmml">y</mi><mi id="S4.SS2.SSS3.p3.3.m3.2.2.2.2.3" xref="S4.SS2.SSS3.p3.3.m3.2.2.2.2.3.cmml">j</mi></msub><mo id="S4.SS2.SSS3.p3.3.m3.2.2.2.5" stretchy="false" xref="S4.SS2.SSS3.p3.3.m3.2.2.3.cmml">)</mo></mrow><annotation-xml encoding="MathML-Content" id="S4.SS2.SSS3.p3.3.m3.2b"><interval closure="open" id="S4.SS2.SSS3.p3.3.m3.2.2.3.cmml" xref="S4.SS2.SSS3.p3.3.m3.2.2.2"><apply id="S4.SS2.SSS3.p3.3.m3.1.1.1.1.cmml" xref="S4.SS2.SSS3.p3.3.m3.1.1.1.1"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p3.3.m3.1.1.1.1.1.cmml" xref="S4.SS2.SSS3.p3.3.m3.1.1.1.1">subscript</csymbol><ci id="S4.SS2.SSS3.p3.3.m3.1.1.1.1.2.cmml" xref="S4.SS2.SSS3.p3.3.m3.1.1.1.1.2">𝑥</ci><ci id="S4.SS2.SSS3.p3.3.m3.1.1.1.1.3.cmml" xref="S4.SS2.SSS3.p3.3.m3.1.1.1.1.3">𝑗</ci></apply><apply id="S4.SS2.SSS3.p3.3.m3.2.2.2.2.cmml" xref="S4.SS2.SSS3.p3.3.m3.2.2.2.2"><csymbol cd="ambiguous" id="S4.SS2.SSS3.p3.3.m3.2.2.2.2.1.cmml" xref="S4.SS2.SSS3.p3.3.m3.2.2.2.2">subscript</csymbol><ci id="S4.SS2.SSS3.p3.3.m3.2.2.2.2.2.cmml" xref="S4.SS2.SSS3.p3.3.m3.2.2.2.2.2">𝑦</ci><ci id="S4.SS2.SSS3.p3.3.m3.2.2.2.2.3.cmml" xref="S4.SS2.SSS3.p3.3.m3.2.2.2.2.3">𝑗</ci></apply></interval></annotation-xml><annotation encoding="application/x-tex" id="S4.SS2.SSS3.p3.3.m3.2c">(x_{j},y_{j})</annotation><annotation encoding="application/x-llamapun" id="S4.SS2.SSS3.p3.3.m3.2d">( italic_x start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT , italic_y start_POSTSUBSCRIPT italic_j end_POSTSUBSCRIPT )</annotation></semantics></math> that satisfies the system of equations, effectively solving for the unknown coordinates.</p> </div> <figure class="ltx_figure" id="S4.F17"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="130" id="S4.F17.1.g1" src="extracted/6285822/fig/trp2.png" width="299"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 17: </span>TRPs and ground truth positions</figcaption> </figure> </section> </section> <section class="ltx_subsection" id="S4.SS3"> <h3 class="ltx_title ltx_title_subsection"> <span class="ltx_tag ltx_tag_subsection"><span class="ltx_text" id="S4.SS3.5.1.1">IV-C</span> </span><span class="ltx_text ltx_font_italic" id="S4.SS3.6.2">Preprocessing and Position Estimation</span> </h3> <div class="ltx_para" id="S4.SS3.p1"> <p class="ltx_p" id="S4.SS3.p1.1">In a multi-RU positioning setup, precise RU synchronization is crucial for accurate TDoA measurements, as just a 1-nanosecond error can cause a 0.3-meter positioning inaccuracy. While in some setups this accuracy can be achieved, in our GEO5G testbed we have observed timing errors of up to 40ns. Using a common reference TRP across all RUs will therefore result in inaccurate TDoA measurements and degraded positioning estimates. </p> </div> <div class="ltx_para" id="S4.SS3.p2"> <p class="ltx_p" id="S4.SS3.p2.1">To mitigate this, a per-RU reference approach is adopted, where within each RU, one TRP is designated as the local reference for TDoA calculations, ensuring that all measurements within the RU remain internally consistent and unaffected by synchronization drifts in other RUs.</p> </div> <div class="ltx_para" id="S4.SS3.p3"> <p class="ltx_p" id="S4.SS3.p3.1">Next, to ensure robust TDoA estimation while mitigating synchronization errors, a two-stage filtering mechanism is employed. Firstly, by averaging over the <math alttext="N" class="ltx_Math" display="inline" id="S4.SS3.p3.1.m1.1"><semantics id="S4.SS3.p3.1.m1.1a"><mi id="S4.SS3.p3.1.m1.1.1" xref="S4.SS3.p3.1.m1.1.1.cmml">N</mi><annotation-xml encoding="MathML-Content" id="S4.SS3.p3.1.m1.1b"><ci id="S4.SS3.p3.1.m1.1.1.cmml" xref="S4.SS3.p3.1.m1.1.1">𝑁</ci></annotation-xml><annotation encoding="application/x-tex" id="S4.SS3.p3.1.m1.1c">N</annotation><annotation encoding="application/x-llamapun" id="S4.SS3.p3.1.m1.1d">italic_N</annotation></semantics></math> most recent TDoAs from each RU, we avoid small-scale fluctuations in the measurements. Secondly, for compensating larger spikes in the TDoAs, another filter is used that exploits the geographical information of the testing area. Knowing the minimum and maximum possible TDoA values based on known TRP positions, we define a filter that discards any invalid TDoA measurement and retains only those within a predefined bound, along with their corresponding TRP coordinates. This filtering approach effectively mitigates the impact of noisy measurements caused by multipath, Non-Line-of-Sight (NLoS) conditions, and hardware impairments. </p> </div> </section> <section class="ltx_subsection" id="S4.SS4"> <h3 class="ltx_title ltx_title_subsection"> <span class="ltx_tag ltx_tag_subsection"><span class="ltx_text" id="S4.SS4.5.1.1">IV-D</span> </span><span class="ltx_text ltx_font_italic" id="S4.SS4.6.2">Results</span> </h3> <div class="ltx_para" id="S4.SS4.p1"> <p class="ltx_p" id="S4.SS4.p1.1">This section validates the performance of our deployed 5G network by registering a UE and triggering the location determination API. The TRP coordinates and UL-RToA values from each TRP are used in a stochastic optimization method for position estimation from our previous work <cite class="ltx_cite ltx_citemacro_cite">[<a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#bib.bib18" title="">18</a>]</cite>. The positioning error was evaluated for two setups: a single RU (RU3) and a multi-RU (RU2 and RU3). The results show that multiple RUs improve accuracy by increasing TRP diversity in both the x and y axes. In the single RU setup, the TRPs are arranged linearly, causing higher uncertainty in the y-axis, which is reduced with the multi-RU setup. Points A, B, O, and P on the edge of the testing area show degraded accuracy due to NLoS, multipath and diffraction conditions to the buildings around them. Table <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.T2" title="TABLE II ‣ IV-D Results ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">II</span></a>, is summarizing the Mean Absolute Error (MAE) for both setups. Also, Figure <a class="ltx_ref" href="https://arxiv.org/html/2409.05217v3#S4.F18" title="Figure 18 ‣ IV-D Results ‣ IV Validation of our Open-Source UL-TDoA positioning ‣ From Concept to Reality: 5G Positioning with Open-Source Implementation of UL-TDoA in OpenAirInterface"><span class="ltx_text ltx_ref_tag">18</span></a> shows a mobile scenario where a person holds the UE and takes a trajectory covering all testing points in the multi-RU setup.</p> </div> <figure class="ltx_table" id="S4.T2"> <div class="ltx_inline-block ltx_align_center ltx_transformed_outer" id="S4.T2.1" style="width:216.8pt;height:86.3pt;vertical-align:-0.0pt;"><span class="ltx_transformed_inner" style="transform:translate(-95.0pt,37.8pt) scale(0.532920215143012,0.532920215143012) ;"> <table class="ltx_tabular ltx_align_middle" id="S4.T2.1.1"> <tr class="ltx_tr" id="S4.T2.1.1.1"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.1.1"><span class="ltx_text ltx_font_bold" id="S4.T2.1.1.1.1.1">Point</span></td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.1.2"><span class="ltx_text ltx_font_bold" id="S4.T2.1.1.1.2.1">1 RU MAE (m)</span></td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.1.3"><span class="ltx_text ltx_font_bold" id="S4.T2.1.1.1.3.1">2 RUs MAE (m)</span></td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.1.4"><span class="ltx_text ltx_font_bold" id="S4.T2.1.1.1.4.1">Point</span></td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.1.5"><span class="ltx_text ltx_font_bold" id="S4.T2.1.1.1.5.1">1 RU MAE (m)</span></td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.1.6"><span class="ltx_text ltx_font_bold" id="S4.T2.1.1.1.6.1">2 RUs MAE (m)</span></td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.2"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.2.1">A</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.2.2">4.77</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.2.3">1.88</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.2.4">I</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.2.5">3.02</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.2.6">0.60</td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.3"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.3.1">B</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.3.2">4.69</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.3.3">1.13</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.3.4">J</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.3.5">2.32</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.3.6">0.83</td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.4"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.4.1">C</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.4.2">0.81</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.4.3">0.82</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.4.4">K</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.4.5">3.38</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.4.6">0.82</td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.5"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.5.1">D</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.5.2">1.30</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.5.3">0.83</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.5.4">L</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.5.5">3.23</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.5.6">1.20</td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.6"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.6.1">E</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.6.2">2.37</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.6.3">0.95</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.6.4">M</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.6.5">3.34</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.6.6">0.64</td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.7"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.7.1">F</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.7.2">2.00</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.7.3">0.55</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.7.4">N</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.7.5">4.85</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.7.6">0.68</td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.8"> <td class="ltx_td ltx_align_center ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.8.1">G</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.8.2">2.27</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.8.3">0.92</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.8.4">O</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.8.5">5.41</td> <td class="ltx_td ltx_align_center ltx_border_r ltx_border_t" id="S4.T2.1.1.8.6">0.97</td> </tr> <tr class="ltx_tr" id="S4.T2.1.1.9"> <td class="ltx_td ltx_align_center ltx_border_b ltx_border_l ltx_border_r ltx_border_t" id="S4.T2.1.1.9.1">H</td> <td class="ltx_td ltx_align_center ltx_border_b ltx_border_r ltx_border_t" id="S4.T2.1.1.9.2">3.31</td> <td class="ltx_td ltx_align_center ltx_border_b ltx_border_r ltx_border_t" id="S4.T2.1.1.9.3">0.56</td> <td class="ltx_td ltx_align_center ltx_border_b ltx_border_r ltx_border_t" id="S4.T2.1.1.9.4">P</td> <td class="ltx_td ltx_align_center ltx_border_b ltx_border_r ltx_border_t" id="S4.T2.1.1.9.5">4.12</td> <td class="ltx_td ltx_align_center ltx_border_b ltx_border_r ltx_border_t" id="S4.T2.1.1.9.6">1.98</td> </tr> </table> </span></div> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_table">TABLE II: </span>MAE for single RU (RU3) and multi-RU (RU2+RU3) setups at points A-P</figcaption> </figure> <div class="ltx_para" id="S4.SS4.p2"> <p class="ltx_p" id="S4.SS4.p2.1">In future developments, a multi-gNB setup with additional RUs and increased TRPs is expected to enhance accuracy by enabling techniques such as multipath and NLoS mitigation.</p> </div> <figure class="ltx_figure" id="S4.F18"><img alt="Refer to caption" class="ltx_graphics ltx_centering ltx_img_landscape" height="131" id="S4.F18.1.g1" src="extracted/6285822/fig/est_pos_traj3.png" width="299"/> <figcaption class="ltx_caption ltx_centering"><span class="ltx_tag ltx_tag_figure">Figure 18: </span>UE tracking in a mobile scenario</figcaption> </figure> </section> </section> <section class="ltx_section" id="S5"> <h2 class="ltx_title ltx_title_section"> <span class="ltx_tag ltx_tag_section">V </span><span class="ltx_text ltx_font_smallcaps" id="S5.1.1">Conclusions</span> </h2> <div class="ltx_para" id="S5.p1"> <p class="ltx_p" id="S5.p1.1">This paper provided the first open-source implementation of the 3GPP UL-TDoA positioning method within the OAI framework, successfully integrating UL-TDoA into both the RAN and CN components. By adhering to 3GPP standards, this implementation enabled precise and real-time positioning of UE in 5G networks, offering a flexible alternative to proprietary solutions. The approach was validated through both simulation and real-world testing, demonstrating its reliability and accuracy. This work not only enhanced the capabilities of OAI for 5G positioning but also contributed to the broader research community by providing a valuable tool for further innovation and collaboration in the field of cellular network positioning technologies.</p> </div> </section> <section class="ltx_bibliography" id="bib"> <h2 class="ltx_title ltx_title_bibliography">References</h2> <ul class="ltx_biblist"> <li class="ltx_bibitem" id="bib.bib1"> <span class="ltx_tag ltx_tag_bibitem">[1]</span> <span class="ltx_bibblock"> 3GPP, “NG Radio Access Network (NG-RAN); Stage 2 functional specification of User Equipment (UE) positioning in NG-RAN,” 3GPP, Technical Specification 3GPP TS 38.305, 2020. </span> </li> <li class="ltx_bibitem" id="bib.bib2"> <span class="ltx_tag ltx_tag_bibitem">[2]</span> <span class="ltx_bibblock"> F. Kaltenberger, A. P. Silva, A. Gosain, L. Wang, and T.-T. 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