MIMO Broadcasting for Simultaneous Wireless Information and Power Transfer

This paper studies the performance limits of multi-antenna wireless broadcasting systems for simultaneous information and power (energy) transfer. For the purpose of exposition, a three-node network is investigated, in which one receiver harvests energy and another receiver decodes information separately from the signals broadcast by a common transmitter. Two scenarios are examined, where the information and energy receivers are separated and see different channels from the transmitter, or co-located and see the same channel from the transmitter. For the case of separated receivers, we derive the optimal transmission strategies to achieve different tradeoffs for maximal information rate versus energy transfer, which are characterized by the boundary of a so-called rate-energy (R-E) region. For the case of co-located receivers, we show an outer bound for the achievable R-E region, due to the potential limitation that practical circuits for harvesting energy from radio signals are not yet able to decode the information. Under such constraint, we propose two practical receiver designs for the co-located receivers, namely, time switching and power splitting, and characterize their achievable R-E regions by comparing with the outer bound.