NOMA Transmission Systems: Overview of SIC Design and New Findings

Non-Orthogonal Multiple Access (NOMA) has been recently proposed as a good alternative to meet 5G and beyond requirements in terms of high spectral efficiency, massive connectivity, and low latency. It has been demonstrated that the use of NOMA in downlink has superior performance in terms of throughput, whereas the use in uplink outperforms OMA techniques in terms of fairness. A distinctive feature of NOMA is the presence of excessive multiple-access interference due to the case of usage of power domain to multiplex signals, thus the functional implementation of NOMA implies Successive Interference Cancelation (SIC) to combat this interference. Therefore, SIC design becomes the main point in the effectiveness of NOMA systems. On the other hand, hybrid schemes, NOMA/OMA, have been recently proposed to reduce the drawbacks of pure NOMA systems. However, in these schemes, it becomes necessary to distinguish NOMA and OMA users. Cognitive Radio techniques turn to be a good option to effectively separate NOMA/OMA users as well as to distinguish NOMA users. In this chapter, a brief overview of NOMA techniques related to Cognitive Radio technology (CR-NOMA) and SIC design reported in the literature is presented. Also, new findings about NOMA/OMA users’ recognition are described.