Extremely large-scale array (XL-array) has emerged as a promising technology to enhance the spectrum efficiency and spatial resolution in future wireless networks by exploiting massive number of antennas for generating pencil-like beamforming. This also leads to a fundamental paradigm shift from conventional far-field communications towards the new near-field communications. In contrast to the existing works that mostly considered simultaneous wireless information and power transfer (SWIPT) in the far field, we consider in this paper a new and practical scenario, called mixed near- and far-field SWIPT, where energy harvesting (EH) and information decoding (ID) receivers are located in the near- and far-field regions of the XL-array base station (BS), respectively. Specifically, we formulate an optimization problem to maximize the weighted sum-power harvested at all EH receivers by jointly designing the BS beam scheduling and power allocation, under the constraints on the maximum sum-rate and BS transmit power. First, for the general case with multiple EH and ID receivers, we propose an efficient algorithm to obtain a suboptimal solution by utilizing the binary variable elimination and successive convex approximation methods. To obtain useful insights, we then study the joint design for special cases. In particular, we show that when there are multiple EH receivers and one ID receiver, in most cases, the optimal design is allocating a portion of power to the ID receiver for satisfying the rate constraint, while the remaining power is allocated to one EH receiver with the highest EH capability. This is in sharp contrast to the conventional far-field SWIPT case, for which all powers should be allocated to ID receivers. Numerical results show that our proposed joint design significantly outperforms other benchmark schemes without the optimization of beam scheduling and/or power allocation.

中文翻译：

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混合近场和远场通道中的 SWIPT：联合波束调度和功率分配


超大规模阵列（XL 阵列）已成为一项有前景的技术，通过利用大量天线生成铅笔状波束成形，来提高未来无线网络的频谱效率和空间分辨率。这也导致了从传统远场通信到新近场通信的根本范式转变。与主要考虑远场同步无线信息和电力传输（SWIPT）的现有工作相比，我们在本文中考虑了一种新的实用场景，称为混合近场和远场 SWIPT，其中能量收集（EH）和信息解码（ID）接收器分别位于XL阵列基站（BS）的近场和远场区域。具体来说，我们制定了一个优化问题，在最大总速率和基站发射功率的约束下，通过联合设计基站波束调度和功率分配，最大化所有 EH 接收器收获的加权总功率。首先，对于具有多个 EH 和 ID 接收器的一般情况，我们提出了一种有效的算法，利用二元变量消除和逐次凸逼近方法来获得次优解。为了获得有用的见解，我们然后研究特殊情况的联合设计。特别地，我们表明，当存在多个 EH 接收器和一个 ID 接收器时，在大多数情况下，最佳设计是将一部分功率分配给 ID 接收器以满足速率约束，而剩余功率分配给一个 EH 接收器具有最高的EH能力。这与传统的远场 SWIPT 情况形成鲜明对比，在传统的远场 SWIPT 情况下，所有功率都应分配给 ID 接收器。 数值结果表明，我们提出的联合设计在没有优化波束调度和/或功率分配的情况下显着优于其他基准方案。