Performance Analysis of Energy Efficient Cooperative SWIPT NOMA-Assisted Cognitive Satellite-Terrestrial Networks

This study explores an energy-efficient cooperative simultaneous wireless information and power transfer (SWIPT) non-orthogonal multiple access (NOMA)-assisted cognitive satellite-terrestrial network (CSTN), enhancing system performance. The network comprises a primary satellite source, its destination, and a secondary terrestrial source-destination pair. The primary satellite source employs NOMA to serve users, while the secondary source assists primary communication through cooperative relaying. This shared relay harvests energy through a nonlinear energy harvesting model and utilizes a time-switching protocol for information decoding and energy harvesting. The secondary source transmits a superposed signal of primary and secondary messages to their destinations using NOMA protocol. To further enhance the system performance, maximal ratio combining (MRC), selection combining (SC), and time-switching schemes are employed to process the received signal at the primary user. Considering Shadowed-Rician satellite channels and Rayleigh-distributed terrestrial channels, analytical expressions for outage probability (OP), system outage probability (SOP), throughput, and energy efficiency (EE) are evaluated for both users with perfect and imperfect successive interference cancellation (SIC) by using the stochastic geometry method, and are validated by means of MATLAB-based simulations. In addition, the performances of primary and secondary users are further improved by using an optimal power distribution scheme which is implemented at the shared relay.