Transmit beamforming for simultaneous wireless information and power transfer

Recently, simultaneous wireless information and power transfer (SWIPT) has attracted significant research attention. By exploiting an efficient use of radio frequency (RF) signals for both wireless information transfer (WIT) and wireless power transfer (WPT) at the same time, SWIPT is a promising technology to provide cost-effective information and energy access to wireless devices in various applications in future. To improve the efficiency of SWIPT, transmit beamforming has been recognized as a key technique, where multiple antennas are used at the transmitter to adaptively form transmit beams toward multiple information and energy user receivers to effectively compensate the path loss as well as mitigate the inter-user interference. However, it is a challenging task to optimally design the beamforming in SWIPT due to the new rate-energy trade-off between information and energy receivers, their practical designs, as well as the potential security risk that energy receivers may eavesdrop the signals for information receivers. This chapter provides an overview on recent advances in transmit beamforming design for SWIPT by tackling the above challenges. In particular, we focus on transmit beamforming optimization problems in a multiuser multiple-input single-output (MISO) broadcast channel setup, under different types of practical receiver structures (e.g., time-switching and power-splitting receivers). Extensions to other setups and practical considerations are also discussed.