Hybrid SIC with Residual Error Factor in Wireless Powered Communications

A wireless powered communication network (WPCN) has a periodic time frame divided into two stages; the first one is devoted to power transfer to mobile users while uplink data transmission takes place in the second stage. This paper studies impact of a new method for pairing users in non-orthogonal multiple access (NOMA), called Hybrid SIC (HSIC), on the performance of a NOMA-based WPCN system when imperfect successive interference cancellation (SIC) is assumed. Two well-known variants of SIC, channel state information (CSI)-based and quality of service (QoS)-based SIC schemes, are often considered separately during user pairing. With HSIC, the best of those two variants can be achieved by a proper switching between them. In this paper, we firstly adapt the HSIC scheme to the WPCN scenario where there is a delay sensitive user requesting a low data rate, called primary user, and other users that are delay tolerant and request a higher data rate, called secondary users. Using NOMA, one of the secondary users is admitted to share the same resources block with the primary user. Then, we formulate an optimization problem for solving the admitted user's data rate maximization subject to QoS guarantee for the primary user assuming imperfect SIC. Moreover, we propose a method to solve this problem that can be seen as a generalization of the original HSIC method. Simulation results show that the proposed solution is capable of protecting primary user QoS while maximizing admitted user's data rate in different scenarios with perfect and imperfect SIC.