A Hybrid Uplink Multiple Access Method Based on NOMA and SDMA

We introduce a hybrid uplink multiple access method with a multi-antenna base station (BS) and two naive single-antenna users. Both users with no channel state information (CSI) have low computational power and simultaneously transmit their information to the receiver on the same frequency band. The CSI is assumed to be available only at the receive side. Both perfect and imperfect CSI scenarios are inspected. The decoding process at the BS relies on an adaptive combination of two eminent multiple access techniques, namely power-domain non-orthogonal multiple access and space-division multiple access. In order to reap the advantages of both approaches, the hybrid algorithm attentively switches between two multiple access methods depending on the transmit power and channels of the users. It is shown that a considerable reduction in the transmit power of the users can be attained in terms of sum rate and outage probability criteria, which are suitable performance metrics when the transmitters are not provided with any form of CSI. In addition, the investigated techniques are statistically analyzed by deriving novel and original analytical expressions for all the considered schemes.