Non-orthogonal multiple access (NOMA) for cellular wireless communications
This thesis begins with an overview of the basic concept of NOMA by identifying the key working principle of NOMA systems and their respective power allocation requirements in both of downlink and uplink transmissions. Then, for cell-throughput maximization in both of downlink and uplink NOMA transmissions, the joint problem of user clustering and transmit power allocation is formulated as a mixed integer nonlinear program (MINLP). The formulated problem is solved in two steps: grouping users into disjoint cluster(s), and then optimizing power allocation at each cluster. After investigating NOMA for conventional downlink and uplink systems, the application of NOMA is investigated in downlink multiuser multiple-input multiple-output (MIMO) systems, by proposing a novel MIMO-NOMA model with linear beamforming technique. In this MIMO-NOMA system, users’ receive antennas are dynamically grouped into a number of disjoint clusters, and within each cluster a single beam is shared by all the receive antennas those adopt NOMA. The superiority of the proposed model is illustrated through extensive performance evaluations. Finally, the application of coordinated multi-point (CoMP) transmission technique is investigated in downlink multi-cell NOMA systems, considering distributed power allocation at each cell. In the proposed CoMP-NOMA model, CoMP transmission is used for users experiencing strong receive-signals from multiple cells while each cell independently adopts NOMA for resource allocation. The applicability and necessary conditions to use different CoMP schemes are identified under various network scenarios, and the corresponding throughput formulas are derived. The spectral efficiency gains of the proposed CoMP-NOMA model are also quantified.