Round Trip Time Estimation Utilizing Cyclic Shift of Uplink Reference Signal

TL;DR

This paper introduces a novel method to accurately estimate round trip time in 5G NR by leveraging cyclic shifts of a new uplink reference signal, reducing overhead and latency.

Contribution

It proposes a Zadoff-Chu based wideband uplink reference signal and a cyclic shift technique to directly estimate absolute uplink channel impulse response and RTT.

Findings

Experimental validation on real-world testbed confirms effectiveness.

Significant reduction in overhead and latency compared to existing methods.

Method enables more precise timing synchronization in 5G NR.

Abstract

In the context of fifth-generation new radio (5G NR) technology, it is not possible to directly obtain an absolute uplink (UL) channel impulse response (CIR) at the base station (gNB) from a user equipment (UE). The UL CIR obtained through the sounding reference signal (SRS) is always time-shifted by the timing advance (TA) applied at the UE. The TA is crucial for maintaining UL synchronization, and transmitting SRS without applying the TA will result in interference. In this work, we propose a new method to obtain absolute UL CIR from a UE and then use it to estimate the round trip time (RTT) at the gNB. This method requires enhancing the current 5G protocol stack with a new Zadoff-Chu (ZC) based wideband uplink reference signal (URS). Capitalizing on the cyclic shift property of the URS sequence, we can obtain the RTT with a significant reduction in overhead and latency compared to existing schemes. The proposed method is experimentally validated using a real-world testbed based on OpenAirInterface (OAI).