Abstract: Considering the multi-user and non-orthogonal multiple access (NOMA) system, a multi-user and best relay NOMA system with full-duplex decode-and-forward was proposed. A best relay selection scheme was further proposed to maximize the achievable target user's information rate via max-min criterion. Then, the target user's outage probability was analyzed, and the closed-form expression was also given. The simulation results showed that, the advantage of the proposed best relay selection scheme was related with the number of users and the transmit power of the relay without regard to the optimal users' order. However, if the optimal users' order was taken into account, the best performance can be always be achieved by the proposed best relay selection scheme.

Key words: non-orthogonal multiple access, best relay, multi-user, outage probability