An Enhanced Relay Selection Scheme for NOMA-based Cooperative Opportunistic Multicast Scheme

Non-orthogonal multiple access (NOMA) based cooperative opportunistic multicast scheme uses the efficient relay selection range (ERSR) with a fixed radius to select user relay (UR). This results in UR redundancy, especially in the cell centre with high density of candidate UR. Coverage efficiency, defined as the ratio of the number of successful users to that of URs, is low. Aiming at this problem, a range division user relay selection scheme (termed as RDUR) is proposed in this paper. Firstly, it divides the circular coverage range of base station into several continuous annular areas (AAs). Secondly, different AAs are allocated different ERSRs (i.e., the radius of ERSR is different), which decides the width of AA. Lastly, the ERSR set that optimizes system coverage efficiency is used to perform UR selection. From simulation results, through RDUR, coverage efficiency increases by at least 28%, even though capacity efficiency decreases by 6%.