Non-orthogonal Multiple Access in Wireless Powered Communication Networks

Abstract

In a WPCN, the distances between the users and the power beacon (PB) or the information receiver (IR) are different, which results in unfair transmission rates among different users. NOMA, the basic principle of which is that the users can achieve multiple access by exploiting the power domain multiplexing, is applied in the WPCN to improve user fairness. However, the successive interference cancellation (SIC) constraints, the prerequisite of applying NOMA successfully, are not considered in most existing literatures. In this chapter, the effect of SIC constraints on the throughput of the WPCN with NOMA is investigated, where the users harvest energy from RF signals radiated by the PB, and then use the harvested energy to simultaneously transmit information to the IR. First, the throughput maximization problem is formulated to find the optimal time and energy allocation scheme. Then, to derive the closed-form solution, the optimization problem is further divided into two sub-problems by exploiting the optimal structure of constraints. Finally, simulations on the effect of SIC constraints show the importance of the distinctness among users’ channel power gains for the WPCN with NOMA.