Wireless Power Transfer in mmWave Massive MIMO Systems With/Without Rain Attenuation

This paper studies the performance of wireless power transfer (WPT) in millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems operating in rainy or non-rainy conditions. Accounting for rainfall effects, path loss, and small-scale fading, a comprehensive channel model suitable for modeling the energy propagation in mmWave massive MIMO systems is first developed. Based on this model, a framework for the channel estimation necessary at the hybrid data-and-energy access point (HAP) is provided, and various analytical results on the estimated channel matrix are obtained. Then, using the law of energy conservation, the downlink energy transferred by the HAP and harvested by the user equipments (UEs) is analyzed, and investigated in several important scenarios. The results reveal that the asymptotic harvested energy increases linearly with the number of HAP antennas and the number of UEs, whereas it decreases exponentially with the rain parameters which monotonically increase with the operating frequency. It is also demonstrated that severe rain attenuation can even make the WPT impossible. Afterwards, the scenario where UEs are randomly distributed is investigated, and important insights are gained. In particular, for a WPT system with coverage radius $R_{\mathrm {n}}$ and exclusion radius $R_{\mathrm {e}}$ , the average asymptotic harvested energy significantly increases with decreasing $R_{\mathrm {e}}$ and $R_{\mathrm {n}}$ , which confirms that small-cells configurations will be viable solutions for enhancing WPT performances in mmWave massive MIMO networks.