Enhanced Channel Feedback Schemes for Downlink NOMA Combined with Closed-Loop SU-MIMO

Abstract

As a promising downlink multiple access scheme for further cellular enhancements toward 5G, non- orthogonal multiple access (NOMA) improves both cell average and cell-edge user throughput compared to orthogonal multiple access (OMA). Our previous work showed that NOMA can improve system performance compared with OMA even when combined with multiple- input multiple-output (MIMO). However, for NOMA with MIMO, the inter-user interference becomes a dominant part of the signal-to-interference-and-noise ratio (SINR). Thus, the conventional channel information feedback scheme, which is based on channel quality indicator (CQI) feedback for OMA, is insufficient for base station (BS) to perform accurate modulation and coding scheme (MCS) selection for NOMA users. In this paper, we propose two enhanced channel feedback schemes to improve performance of channel feedback for NOMA systems. One is based on outer loop link adaptation (OLLA), which controls the feedback update by a predefined time window to improve the accuracy. No extra feedback signaling is needed in the scheme. The other one improves the original channel feedback by an extra quantized increment feedback from user equipment (UE) to BS, which benefits BS with more information for MCS selection. The performance improvements of NOMA with closed- loop (CL) single-user (SU) MIMO are investigated by system-level simulations with practical assumptions. Simulation results show that the performance gains of NOMA for both cell average and cell-edge user throughputs improve with the proposed channel feedback schemes.