Multiuser Bandwidth Minimization with Individual Rate Requirements for Non-Orthogonal Multiple Access

Non-Orthogonal Multiple Access (NOMA) for a multi-user single- input single-output (SISO) setup is studied in the power and the frequency domains simultaneously. The problem of sum-bandwidth minimization under perfect channel state information is solved for various combinations of rate requirements and user pairings. In this process, an iterative Tabu-search based algorithm is applied to avoid an exhaustive search over all possible user pairing combinations. It is assumed that each constituent user of the pair has a required quality of service and a flat power spectrum. Further, for each user pair, the NOMA operating region is defined by dividing the allocated bandwidth into two non-overlapping Orthogonal Multiple Access (OMA) sub-bands and an overlapping NOMA sub-band. Such an assumption achieves a greater capacity region when compared to the conventional power domain only NOMA. Also for most of the rate requirements, only one of the OMA sub-bands is active in addition to the NOMA sub-band. This simplifies the NOMA user rate expressions and power allocation process. To verify the performance gain, NOMA is compared to an OMA technique.