Differential STBC NOMA: A new approach to downlink cooperative NOMA

Due to the ability of massive connectivity, large bandwidth, and low latency, the non-orthogonal multiple access (NOMA) is considered the best approach for the 5th generation and beyond. However, the system performance is declined when the number of users is increased as each user will experience a great number of successive interface cancelations (SIC) in the downlink. To improve system performance, the NOMA is combined with cooperative communication which gives more spectral efficiency and fairness as compared to non-cooperative NOMA. Furthermore, space-time block code (STBC)- cooperative NOMA-based users experienced less SIC as compared to conventional CNOMA. This paper evaluates the performance of differential STBC-CNOMA with keeping in mind the imperfect SIC, channel state information (CSI), and timing synchronization between distributed cooperating users. The simulations results show that differential STBC-CNOMA gives high performance in terms of outage probability and sum rate analysis as compared to simple STBC-NOMA and conventional CNOMA. Hence, the differential STBC-CNOMA seems to be a better and more effective solution to enhance system performance.