Opportunistic user selection schemes for energy harvesting-aware cooperative NOMA

As one of the promising technologies, non-orthogonal multiple access (NOMA) provides high system capacity, low latency, and massive connectivity. NOMA is expected to address several challenges in the fifth-generation (5G) and beyond wireless systems. In this paper, we consider the downlink Internet of Things (IoT) system with grouping user-relying NOMA techniques to improve the performance of the cell-edge user. In particular, we consider maximal harvested energy (MHE) scheme and best cooperative path (BCP) scheme to assist the cell-edge user. In MHE, the relay with highest harvested power is selected for cooperation, whereas the best cooperative path is selected in the BCP scheme. Then, we comprehensively investigate on the basic principles of energy harvesting, enabling relay selection scheme and evaluations of outage probability for these users. Meanwhile, we consider that the optimal performance can be achieved at several values related to power splitting factors of energy harvesting protocol and power allocation factors of NOMA scheme. Finally, yet importantly, we confirm the exactness of derived expressions through Monte-Carlo simulation.