On the Performance of Uplink Power-Domain NOMA with Imperfect CSI and SIC in 6G Networks

Sixth generation (6G) networks must adopt spectral-efficient communication techniques to ensure massive connectivity for coexisting humans and machines. However, the impact of various practical issues must be analyzed and addressed, including imperfect channel state information (CSI), stemming by the channel estimation error (CEE) and feedback delay (F-D) with time-variant channels. This paper focuses on these issues in the context of uplink networks, relying on power-domain non-orthogonal multiple access (NOMA). Moreover, the degrading effect of imperfect successive interference cancellation (SIC), when randomly deployed multiple mobile terminals communicate with a single base station (BS) is considered. The system performance is measured by means of outage probability, error probability, ergodic rate, throughput, energy efficiency, and spectral efficiency. Analytical, asymptotic, and computer simulation results demonstrate that CEE causes system coding gain losses for low signal-to-noise ratio (SNR) while the disruptive effects of CEE become negligible in the high SNR. Results also show that F-D does not degrade the system performance in the low SNR but it causes system coding gain losses for high SNR. Also, imperfect SIC does not have any detrimental effect on the system performance for low SNR but results in reduced coding gain for high SNR. The theoretical and simulation findings of this study quantify the detrimental effect of practical limitations in NOMA-based uplink networks with coexisting users and devices, facilitating the adoption of optimized parameters to improve network performance.