A Tradeoff between Information and Power Transfers Using a Large-Scale Array of Dense Distributed Antennas

The paper presents a new indoor system where a large-scale array of dense distributed antennas, called a ubiquitous array (UA), is deployed for simultaneous wireless information-and- power transfer (SWIPT) to passive mobile devices. Thereby, the UA not only provides energy-efficient wireless access to mobiles but also eliminate their need for battery recharging via cables. For tractability, a single-user system is considered where the UA is modeled as a continuous spherical array and a K-antenna receiver is located at the UA center. Free-space channels are assumed. Then using the theories of EM-wave propagation and spherical harmonics, a fundamental tradeoff between the information transfer (IT) and power transfer (PT) is discovered and described as follows. As the separation distances between receive antennas uniformly decrease, the PT efficiency, namely the ratio between the transmit and receive powers, is increased by K times but the spatial multiplexing gain for IT reduces from K to one. In addition, with receive antennas fixed, the PT efficiency is shown to be independent with the propagation distance (or equivalently the UA radius), suppressing path loss that is the bottleneck for efficient microwave power transfer.