Novel Round Trip Time Estimation in 5G NR

TL;DR

The paper tackles RTT-based positioning in 5G NR by removing the need for centralized timing references. It introduces signaling enhancements via a new DCI Format X_Y to trigger multiple UL SRS measurements and leverages a TA-based coarse RTT refined with a matched-filter over coherent SRS channel estimates, all without requiring continuous DL PRS resources. key contributions include the LS-based SRS channel estimation, a practical matched-filter RTT estimator, and a signaling scheme that supports both NR_RRC_INACTIVE and NR_RRC_CONNECTED states while mitigating clock drift. Real-world OpenAirInterface experiments demonstrate meter-level range accuracy at 40 MHz bandwidth even in low-SNR, highlighting the method’s potential for NR-based positioning in indoor or GPS-denied environments.

Abstract

The fifth generation new radio (5G NR) technology is expected to fulfill reliable and accurate positioning requirements of industry use cases, such as autonomous robots, connected vehicles, and future factories. Starting from Third Generation Partnership Project (3GPP) Release-16, several enhanced positioning solutions are featured in the 5G standards, including the multi-cell round trip time (multi-RTT) method. This work presents a novel framework to estimate the round-trip time (RTT) between a user equipment (UE) and a base station (gNB) in 5G NR. Unlike the existing scheme in the standards, RTT can be estimated without the need to send timing measurements from both the gNB and UE to a central node. The proposed method relies on obtaining multiple coherent uplink wide-band channel measurements at the gNB by circumventing the timing advance control loops and the clock drift. The performance is evaluated through experiments leveraging a real world 5G testbed based on OpenAirInterface (OAI). Under a moderate system bandwidth of 40MHz, the experimental results show meter level range accuracy even in low signal-to-noise ratio (SNR) conditions.

Figures (8)

• Figure 1: 5G synchronization.
• Figure 2: UE UL timing correction with TA commands.
• Figure 3: Proposed signaling mechanism for RTT estimation.
• Figure 4: Effect of clock drift on RTT in commercial UE.
• Figure 5: Experimental setup in the anechoic chamber.