Ergodic Capacity of NOMA-Based Overlay Cognitive Integrated Satellite-UAV-Terrestrial Networks

Satellite communication has become a popular study topic owing to its inherent advantages of high capacity, large coverage, and no terrain restrictions. Also, it can be combined with terrestrial communication to overcome the shortcomings of current wireless communication, such as limited coverage and high destructibility. In recent years, the integrated satellite-unmanned aerial vehicle-terrestrial networks (IS-UAV-TNs) have aroused tremendous interests to effectively reduce the transmission latency and enhance quality-of-service with improved spectrum efficiency. However, the rapidly growing access demands and conventional spectrum allocation scheme lead to the shortage of spectrum resources. To tackle the mentioned challenge, the non-orthogonal multiple access (NOMA) scheme and cognitive radio technique are utilized in IS-UAV-TN, which can improve spectrum utilization. In our paper, the transmission capacity of an NOMA-enabled IS-UAV-TN under overlay mode is discussed, specifically, we derive the closed-form expressions of ergodic capacity for both primary and secondary networks. Besides, simulation results are provided to demonstrate the validity of the mathematical derivations and indicate the influences of critical system parameters on transmission performance. Furthermore, the orthogonal multiple access (OMA)-based scheme is compared with our NOMA-based scheme as a benchmark, which illustrates that our proposed scheme has better performance.