Multi-Antenna Constant Envelope Wireless Power Transfer

In this paper, we study wireless power transfer in a multiuser multiple-input single-output (MISO) system, where a base station equipped with N antennas wirelessly transfers power to distributed single-antenna users. To reduce the implementation cost, we propose a constant-envelope analog beamforming scheme to simultaneously transfer power to multiple users which requires only a single radio frequency (RF) chain at the multi-antenna transmitter. We show that the proposed constant-envelope beamforming design only incurs about 1 dB power loss under homogeneous and independent Rayleigh fading, as compared with the optimal variable-envelope digital beamforming design that however requires N RF chains, one for each transmit antenna.