Low Complexity Based QR-LRL OSIC Detector for Downlink NOMA-MIMO Systems

Power domain NOMA SISO system achieve more capacity compared to OMA system for a given power. To enhance the overall system capacity, NOMA-MIMO based downlink system with superposition coding (SC) coding is considered in this work. With the incorporation of MIMO, the detector subject to interuser as well as interantenna interference. Conventionally, after receiving the signal from the base station (BS), each user eliminates the interantenna interference using zero-forcing (ZF) based linear detector. This paper proposes low-complexity based QR-LRL detector to overcome jointly the interuser interference and interantenna interference. The performance of the proposed detector under BER and capacity metrics compared with ZFSIC and ML detectors. Simulation results show that the proposed receiver guarantees near ML performance with lower complexity for NOMA-MIMO downlink systems. It presents the sumrate improvement for various MIMO configurations with different modulation orders. It also provides optimal power allocation factor $(\alpha)$ to experience the same BER at both the near user (NU) and the far user (FU) using ZF and QR-LRL detector.