Performance analysis of MIMO-based CR–NOMA communication systems

This paper has collectively exploited cognitive radio (CR), non-orthogonal multiple access (NOMA) and multiple-input-multiple-output (MIMO) communication systems in order to propose a spectral-and interference-efficient framework which is named as MIMO-based CR–NOMA communication system. The proposed framework is analysed for the uplink and downlink scenarios. Further, the closed-form expressions for throughput at each user due to the number of transmitting-and receiving-antennas are derived numerically for the downlink-and uplink-scenarios. In addition to this, the total/sum throughput for different frameworks such as CR–NOMA, CR–MIMO and MIMO-based CR–NOMA systems is derived for both the downlink and uplink scenarios. Moreover, in order to satisfy the interference constraints at the primary user due to cell-edge/far-user [cognitive user (CU)-4] transmission in the uplink scenario, a new metric known as interference efficiency is derived. Furthermore, the proposed frameworks are simulated for downlink and uplink scenarios and the relationship between throughput of cell-centred/near-user (CU-1) and CU-4 are presented. Moreover, the total throughput for different frameworks and interference efficiency is also illustrated with the simulation results. The simulation results reveal that the proposed MIMO-based CR–NOMA system outperforms the existing MIMO–NOMA, CR–NOMA and CR–OMA systems in terms of the CUs' individual throughput, total throughput and interference efficiency of the system.