Hybrid NOMA/OMA with Buffer-Aided Relaying for Cooperative Uplink System

In this paper, we consider a cooperative uplink network consisting of two users, a half-duplex decode-and-forward (DF) relay and a base station (BS). In the relaying network, the two users transmit packets to the buffer-aided relay using non-orthogonal multiple access (NOMA) or orthogonal multiple access (OMA) technology. We proposed a hybrid NOMA/OMA based mode selection (MS) scheme, which adaptively switches between the NOMA and OMA transmission modes according to the instantaneous strength of wireless links and the buffer state. Then, the state transmission matrix probabilities of the corresponding Markov chain is analyzed, and the performance in terms of sum throughput, outage probability, average packet delay and diversity gain are evaluated with closed form expressions. Numerical results are provided to demonstrate that hybrid NOMA/OMA achieves significant performance gains compared to conventional NOMA and OMA in most scenarios.