Non-orthogonal multiple access with cooperative truncated ARQ and relay selection

Abstract

In this paper, we propose a cooperative truncated automatic repeat-request (T-ARQ)-based non-orthogonal multiple access schemes with relay selection. There are two phases in our proposed scheme. In the broadcast phase, an access point superimposes the signals of near-user U1 and far-user U2 and then broadcasts the composite signal to both users and all the relays. All the terminals will try to decode the signal of U2 by treating the signal of U1 as interference. After that, U1 and relays will further decode the signal of U1 by canceling the signal of U2. The relays that can correctly decode the signals of U2 and U1 are classified into two decoding sets. In the cooperative T-ARQ phase, the relay from the decoding set with the best channel quality toward U2 or U1 is selected to retransmit the signal if necessary. Considering the various decoding statuses of U1, U2, and relays, we analyze the system throughput and reveal the impacts of key parameters, such as power allocation factor, transmit power, and target rate. The numerical results show that our proposed scheme can achieve much higher throughput than the T-ARQ-based time-division multiple access schemes.