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.Â

A document by Volkan Ozduran . Click on the document to view its contents.

In this study, we focus on an MCN where the direct links towards a shore BS are not available, due to excessive fading conditions. For this case, we use a UAV swarm to provide improved wireless connectivity, adopting non-orthogonal multiple access (NOMA) for high resource efficiency. In downlink communication, UAVs take into consideration the desired service rate and the channel quality of their links towards the maritime nodes. In the uplink, UAVs employ dynamic decoding ordering to enhance the performance of successive interference cancellation, avoiding fixed ordering of the maritime nodesâ\euro™ signals. Moreover, to ensure highly flexible UAV selection, UAVs have buffers to store data. Performance comparisons show that the UAV swarm-aided MCN enjoys increased average sum-rate by relying on multi-criteria-based interference cancellation and buffer-aided UAVs, over other benchmark schemes in the downlink and uplink.