On optimizing power allocation and power splitting for MISO SWIPT systems with heterogeneous users

In this paper, we study the power allocation and power splitting problem for simultaneous wireless information and power transfer (SWIPT) in a multi-user MISO broadcast system, in which there are two types of single-antenna users: traditional users that only receive information and modern users that receive information and energy simultaneously from a multi-antenna base station via power splitting. We aim to maximize the minimum signal to interference plus noise ratio (SINR) of the users by jointly designing the power allocation at the transmitter and the power splitting strategy at the receivers under the maximum transmit power and the minimum energy harvesting constraints. In specific, we first apply the techniques of semidefinite relaxation (SDR) and zero-forcing (ZF) to solve the non-convex problems. Then we apply the zero forcing dirty paper coding (ZF-DPC) technique to eliminate the multi-user interference and derive the optimal solution in closed-form. Numerical results show that ZF-DPC provides higher achievable minimum SINR than SDR and ZF in most cases.