Non-orthogonal Multiple Access for Uplink Cooperative Amplify-and-Forward Relay Networks

In this paper, the cooperative amplify-and-forward relay (CAFR) network is combined with power-division non-orthogonal multiple access (NOMA) and adopted to serve two uplink user terminals (UTs), including weak UT and frequency-division-duplex strong UT, which operate under the device-to-device communication mechanism. Specifically, strong UT receives the message from weak UT and transmits the amplified-and-forwarded message signal from weak UT and its own message by power-division NOMA to base station (BS). User fairness is taken into account in optimizing the power allocation for NOMA. Compared with traditional orthogonal multiple access network, the NOMA-assisted CAFR network can increase the system throughput remarkably and provide high user fairness when the uplink two-user network exhibits one weak UT-to-BS link but sufficiently strong UT-to-UT link and the other strong UT-to-BS link.