Optimal SWIPT Beamforming for MISO Interfering Broadcast Channels with Multi - Type Receivers

Recently, transmit beamforming for simultaneous wireless information and power transfer (SWIPT) has received considerable attention. Extensive studies have been done on MISO/MIMO SWIPT beamforming for broadcast channels (BCs) and interfering broadcast channels (IBCs). However, for IBCs the optimal SWIPT beamforming solution is in general not available. In this work, we consider SWIPT beamforming for multiuser MISO IBCs with multi-type receives, including pure information receivers (IRs), pure energy receivers (ERs) and simultaneous information and energy receivers. A power minimization problem with SINR and power transfer constraints on the receivers is considered. This problem is shown to be NP-hard in general. In order to get an efficient SWIPT beamforming solution, the energy-signal-aided SWIPT beamforming scheme is employed at the transmission. We show that with the help of the energy signals, the resultant beamforming problem is no longer NP-hard, and can be optimally solved by semidefinite relaxation (SDR). The key to this is to apply a recently developed low-rank solution result on a class of semidefinite programs (SDPs) to pin down the SDR tightness. Simulation results also demonstrate the efficacy of the energy signals in reducing the transmit power.