Reference Signal Enhancement in 5G for Extended Coverage in Multi-User Scenarios

Standardization of New Radio (NR) in the third generation partnership project (3GPP) introduced staggered reference signal transmission for positioning. Staggering facilitates unambiguously reaching base stations at larger distances in power-limited scenarios in the uplink. When linear phase is applied to a base sequence in the frequency domain, this translates to the time shifted version of the corresponding sequence in the time domain. This property enables an efficient assignment of resources to multiple user equipments (UEs) or antenna ports. In this paper, we address the issue of interference arising from multiplexing UEs or antenna ports using cyclic shift in scenarios where reference signals are transmitted using a staggered pattern. An evaluation of the effects shows that non-linear phase and limited range of the search window based on the Rel. 16 sounding reference signal (SRS) design causes false detection and erroneous Time of Arrival (ToA) estimates, which impairs the positioning accuracy. A solution is proposed by applying phase correction and range extension to existing base sequences, thereby ensuring backward compatibility of existing network elements. We show that the proposed approach provides more reliable ToA estimates. System level simulations demonstrate that the proposed solution mitigates these effects compared to the state-of-the-art mechanism.