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This paper studies a multiuser multiple-input single-output (MISO) broadcast system for simultaneous wireless information and power transfer (SWIPT), where a multi-antenna access point (AP) sends information and energy simultaneously via beamforming to multiple single-antenna receivers. We maximize the weighted sum-power transferred to energy harvesting (EH) receivers subject to a set of minimum signal-to-interference-and-noise ratio (SINR) constraints at information decoding (ID) receivers. In particular, we consider two types of ID receivers, namely Type I and Type II receivers, without and with the capability of cancelling the interference from energy signals, respectively. For each type of ID receivers, we formulate the joint information and energy transmit beamforming problem as a non-convex quadratically constrained quadratic program (QC-QP), for which the globally optimal solution is obtained by applying the technique of semidefinite relaxation (SDR). It is shown that for Type I ID receivers, dedicated energy beamforming is not needed to achieve the optimal solution, while for Type II ID receivers, employing no more than one energy beam is optimal.
Xu et al. (Wed,) studied this question.