Performance enhancement of user pairing and power allocation for downlink NOMA system: Fairness awareness

Among the different multiple access techniques, Non-Orthogonal Multiple Access (NOMA) is considered the most important topic these days due to the spectral efficiency that is needed to serve the increase in connected devices. For a downlink NOMA system, this research examines and studies User Pairing (UP) and Power Allocation (PA). To address the problem of Cell Mid Users (CMU) in conventional Near Far Paring (NFP), which occurs when there is a small channel gain difference between users pair, the power allocated to each user in the pair is so close that it causes a degradation in Successive Interference Cancelation (SIC) performance, an Enhanced Fair PA (EFPA) algorithm is proposed in this work to enhance the conventional NFP performance in terms of Cell Edge User (CEU) rate and system fairness. The simulation result shows that the proposed NFP EFPA is significantly better than the NFP Fixed PA and Uniform Channel Gain Difference (UCGD) schemes, where CEU rate is guaranteed and outperforms UCGD CEU in terms of ergodic capacity of about (18–22 bps/Hz) at (40 dBm) of transmit power and CMU capacity of about (20 bps/Hz) at (40 dBm) higher than the NFP fixed PA. Furthermore, the fairness index has significantly increased and can be approximately 25% more efficient than other schemes. The MATLAB programming language was used here to simulate the system.