Multi-antenna relay assisted NOMA network with multiple imperfect factors

Abstract

In this paper, a 5G downlink multi-antenna relay assisted non-orthogonal multiple access (NOMA) communication system is investigated. The relay can work in half-duplex (HD) or full-duplex (FD) mode with maximum-ratio-combining/transmission antenna selection (MRC/TAS) scheme, and the direct links between the source and destinations are also considered. The exact expressions for the outage probability are derived when considering the effects of hardware impairment (HDI), imperfect successive interference cancellation (ipSIC), channel estimation error(CEE), antenna number and loop-interference (LI) for FD mode. Then, based on the accurate outage probability, the approximate low bound and asymptotic results are derived. From the derived formulas, we find that the maximum diversity order of the considered system is min{(1−μ)N+1,M+1} when CEE does not appear, where μ is the LI cancellation grade, N and M are the receiving and transmitting antenna number equipped at the relay. Otherwise the diversity decreases to one or zero regardless of multi-antenna when CEE appears, but multiple antennas still improve system performance by promoting the array gain. The FD mode may outperform the HD mode with less LI which is decided by μ. Monte Carlo simulations are also done to validate the correctness of theoretical analysis.