[Paper Review] 5G NR Positioning Enhancements in 3GPP Release-18

Hyun-Su Cha, Gilsoo Lee+4 more|arXiv (Cornell University)|Jan 31, 2024

Wireless Communication Networks Research4 citations

TL;DR

This paper presents 3GPP Release-18's major advancements in 5G NR positioning, introducing carrier phase-based centimeter-level accuracy for 5G-Advanced networks, bandwidth aggregation for enhanced timing measurements, RedCap UE support via frequency hopping, low-power high-accuracy positioning (LPHAP), and sidelink-based positioning. These enhancements enable ultra-precise, GNSS-independent location services for industrial IoT, smart cities, and V2X applications.

ABSTRACT

New radio (NR) positioning in the Third Generation Partnership Project (3GPP) Release 18 (Rel-18) enables 5G-advanced networks to achieve ultra-high accuracy positioning without dependence on global navigation satellite systems (GNSS) with key enablers such as the carrier phase positioning technique, standardized for the first time in a cellular communications standard and setting a new baseline for future generations. In addition, Rel-18 NR supports positioning functionalities for reduced capability (RedCap) user equipment and bandwidth aggregation for positioning measurements. Moreover, the low power solutions are designed for low power high accuracy positioning use cases. Lastly, sidelink-based positioning is introduced in Rel-18. This article constitutes a comprehensive treatment of the Rel-18 NR positioning enhancements crucial for the development of next-generation networks.

Motivation & Objective

• Enable centimeter-level positioning accuracy in 5G-Advanced networks without reliance on GNSS.
• Address the limitations of reduced-capability (RedCap) user equipment (UE) in positioning by introducing frequency hopping for improved measurement accuracy despite bandwidth constraints.
• Support low-power, high-accuracy positioning for massive IIoT use cases with extended eDRX and multi-cell SRS support.
• Introduce sidelink (SL) positioning to extend positioning coverage to out-of-coverage UEs and enhance accuracy through hybrid positioning with cellular links.
• Standardize new positioning techniques—including carrier phase, SL-TDOA, SL-RTT, and SL-AoA—within 3GPP to enable future-proof, high-precision location services.

Proposed method

• Implement carrier phase positioning using downlink reference signal (RS) phase measurements to estimate distance via $ d = \lambda N + \phi_{DL} $, enabling cm-level accuracy under favorable propagation conditions.
• Introduce bandwidth aggregation for positioning by combining multiple intra-band contiguous component carriers (CCs) to increase effective bandwidth beyond individual CC limits, improving timing measurement resolution.
• Enable RedCap UE positioning through SRS frequency hopping, allowing the UE to hop across sub-bands to maintain measurement accuracy despite 20 MHz (FR1) or 100 MHz (FR2) bandwidth constraints.
• Introduce extended discontinuous reception (eDRX) and multi-cell SRS support to reduce power consumption and extend battery life for LPHAP use cases.
• Define sidelink positioning via SL PRS and SL positioning protocol (SLPP) to exchange measurements and synchronization information, supporting TDOA, RTT, and AoA techniques over D2D links.
• Introduce antenna reference point (ARP) concept to support ARP-specific measurement reporting from multiple antenna panels, improving location estimation accuracy in vehicular and multi-antenna scenarios.

Experimental results

Research questions

• RQ1 How can 5G NR achieve centimeter-level positioning accuracy in 5G-Advanced networks without GNSS?
• RQ2 What techniques can overcome the bandwidth limitations of RedCap UEs to maintain high-accuracy positioning?
• RQ3 How can low-power, high-accuracy positioning be achieved for massive IIoT deployments with long battery life?
• RQ4 What are the key mechanisms to enable reliable and efficient sidelink-based positioning for V2X and out-of-coverage scenarios?
• RQ5 How can measurement reporting and synchronization be managed across multiple antenna panels and diverse synchronization sources in sidelink positioning?

Key findings

• Carrier phase positioning is standardized for the first time in a cellular standard, enabling cm-level positioning accuracy under favorable radio conditions.
• Bandwidth aggregation for positioning allows effective bandwidth extension beyond individual component carrier limits, improving timing measurement resolution and accuracy.
• Frequency hopping enables RedCap UEs to achieve satisfactory positioning accuracy despite 20 MHz (FR1) or 100 MHz (FR2) bandwidth limitations.
• Extended eDRX and multi-cell SRS support enable battery life of up to one year for LPHAP use cases, meeting industrial requirements.
• Sidelink positioning is introduced with SL-TDOA, SL-RTT, and SL-AoA techniques, supporting hybrid positioning and out-of-coverage operation.
• ARP-specific measurement reporting ensures accurate location estimation by associating measurements with specific antenna panels, mitigating errors from spatial separation.