Resource Allocation for Sounding Reference Signal in 5G Massive MIMO Under Channel Aging

This paper investigates the impact of resource allocation for sounding reference signal (SRS) on downlink (DL) beamforming (BF) in 5G new radio (NR) sub-6 GHz massive multiple-input multiple-output (MIMO) system, under the effects of channel aging. SRS-based dynamic BF offers the best-in-class spatial multiplexing gain and beam control in multiuser MIMO systems. However, its dependency on the accuracy of instantaneous channel information available at the base station makes the method vulnerable to channel aging, which can be significantly controlled by varying the SRS resource allocation. In this work, we introduce a novel full-band channel sounding technique in a single time-slot by frequency-hopping over multiple symbols in the same slot. The proposed method enables uplink power saving for a user, and thus can be adopted by cell-edge users as well. We investigate our novel technique for SRS resource allocation by comparing it with 5G NR’s SRS allocation schemes, as well as with synchronization signal block (SSB)-based static BF. Specifically, we demonstrate the DL BF throughput and outer-loop link adaptation offset with 5G NR system-level simulations using the 3GPP urban micro channel model and reveal practical insights into static and dynamic BF methods under the deleterious impacts of channel aging.