A near-field simultaneous wireless information and power transfer (SWIPT) network is investigated, where the hybrid beamforming architecture is employed at the base station (BS) for information transmission while charging energy harvesting users. A transmit power minimization problem is formulated by jointly optimizing of the analog beamformer, the baseband digital information/energy beamformers, and the number of dedicated energy beams. To tackle the uncertain number of dedicated energy beams, a semidefinite relaxation based rank-one solution construction method is proposed to obtain the optimal baseband digital beamformers under the fixed analog precoder. Based on the structure of the optimal baseband digital beamformers, it is proved that no dedicated energy beam is required in near-field SWIPT. To further exploit this insight, a penalty-based two-layer (PTL) algorithm is proposed to optimize the analog beamformer and baseband digital information beamformers. By employing the block coordinate descent method, the optimal analog beamformer and baseband digital information beamformers are obtained in the closed-form expressions. Moreover, to reduce the high computational complexity caused by the large number of antennas, a low-complexity two-stage algorithm is proposed. Numerical results illustrate that: 1) the proposed PTL algorithm can achieve the near-optimal performance; and 2) in contract to the far-field SWIPT, single near-field beamformer can focus the energy on multiple locations.

翻译：本文研究了一种近场同时无线信息与功率传输（SWIPT）网络，其中基站（BS）采用混合波束成形架构，在传输信息的同时为能量收集用户充电。通过联合优化模拟波束成形器、基带数字信息/能量波束成形器以及专用能量波束的数量，构建了一个发射功率最小化问题。为应对专用能量波束数量的不确定性，提出了一种基于半定松弛的秩一解构造方法，在固定模拟预编码器下获取最优基带数字波束成形器。基于最优基带数字波束成形器的结构，证明了近场SWIPT无需专用能量波束。基于这一发现，提出了一种基于惩罚的双层（PTL）算法来优化模拟波束成形器和基带数字信息波束成形器。通过采用块坐标下降法，以闭式表达式获得了最优模拟波束成形器和基带数字信息波束成形器。此外，为降低大规模天线带来的高计算复杂度，提出了一种低复杂度的两阶段算法。数值结果表明：1）所提出的PTL算法能够实现近似最优性能；2）与远场SWIPT相比，单个近场波束成形器可将能量聚焦于多个位置。