MIMO with Energy Recycling.

In this paper, multiple-input-single-output (MISO) point-to-point communication system is considered, in which a multiple-input-multiple-output (MIMO) energy recycling (ER) transmitter is designed such that, each antenna can transmit information (multi-input) or recycle energy (multi-output) at any given point in time. The rate by such an ER-MISO communication system under an average transmission power constraint is shown to be achievable. Moreover, the optimal power allocation and the dynamic antenna selection policies that achieve the maximum communication rate are derived. The optimal dynamic antenna selection policy carefully switches the mode of the antennas between active-antennas (transmitting) and ER-antennas, where most of the harvested energy occurs from the neighboring antennas' transmissions, i.e., recycling. In addition, it is shown that, with ER, the achievable rate exceeds the capacity of the classical non-recycling counterpart. Since the complexity of the optimal dynamic antenna selection is exponential with the number of antennas, a linearithmic algorithm that has a minimal degradation in the achievable rate is proposed. Numerical results show that notable gain can be obtained by enabling ER. To address the major questions on the capability of ER and the impact of antenna coupling, hardware setup and experimental results for a four-antenna ER-transmitter are developed, based on a uniform linear array (ULA). As a result, hardware measurements indicate that the loss in the rate due to antenna coupling can be eliminated with sufficient antenna spacing and therefore, ER can achieve a significant gain.