Energy Beamforming With One-Bit Feedback

Abstract

Wireless energy transfer (WET) has attracted significant attention recently\nfor providing energy supplies wirelessly to electrical devices without the need\nof wires or cables. Among different types of WET techniques, the radio\nfrequency (RF) signal enabled far-field WET is most practically appealing to\npower energy constrained wireless networks in a broadcast manner. To overcome\nthe significant path loss over wireless channels, multi-antenna or\nmultiple-input multiple-output (MIMO) techniques have been proposed to enhance\nthe transmission efficiency and distance for RF-based WET. However, in order to\nreap the large energy beamforming gain in MIMO WET, acquiring the channel state\ninformation (CSI) at the energy transmitter (ET) is an essential task. This\ntask is particularly challenging for WET systems, since existing channel\ntraining and feedback methods used for communication receivers may not be\nimplementable at the energy receiver (ER) due to its hardware limitation. To\ntackle this problem, in this paper we consider a multiuser MIMO system for WET,\nwhere a multiple-antenna ET broadcasts wireless energy to a group of\nmultiple-antenna ERs concurrently via transmit energy beamforming. By taking\ninto account the practical energy harvesting circuits at the ER, we propose a\nnew channel learning method that requires only one feedback bit from each ER to\nthe ET per feedback interval. The feedback bit indicates the increase or\ndecrease of the harvested energy by each ER between the present and previous\nintervals, which can be measured without changing the existing hardware at the\nER. Based on such feedback information, the ET adjusts transmit beamforming in\ndifferent training intervals and at the same time obtains improved estimates of\nthe MIMO channels to ERs by applying a new approach termed analytic center\ncutting plane method (ACCPM).\n