As Internet of Things (IoT) devices proliferate, sustainable methods for powering them are becoming indispensable. The wireless provision of power enables battery-free operation and is crucial for complying with weight and size restrictions. For the energy harvesting components of these devices to be small, a high operating frequency is necessary. In conjunction with an electrically large antenna, the receivers may be located in the radiating near-field (Fresnel) region, e.g., in indoor scenarios. In this paper, we propose a wireless power transfer system to ensure a reliable supply of power to an arbitrary number of mobile, low-power, and single-antenna receivers, which are located in a three-dimensional cuboid room. To this end, we formulate a max-min optimisation problem to determine the optimal allocation of transmit power among an infinite number of radiating elements of the system's transmit antenna array. Thereby, the optimal deployment, i.e, the set of transmit antenna positions that are allocated non-zero transmit power according to the optimal allocation, is obtained implicitly. Generally, the set of transmit antenna positions corresponding to the optimal deployment has Lebesgue measure zero and the closure of the set has empty interior. Moreover, for a one-dimensional transmit antenna array, the set of transmit antenna positions is proven to be finite. The proposed optimal solution is validated through simulation. Simulation results indicate that the optimal deployment requires a finite number of transmit antennas and depends on the geometry of the environment and the dimensionality of the transmit antenna array. The robustness of the solution, which is obtained under a line-of-sight (LoS) assumption between the transmitter and receiver, is assessed in an isotropic scattering environment containing a strong LoS component.

翻译：随着物联网（IoT）设备激增，为其供电的可持续方法变得不可或缺。无线供能技术可实现无电池工作，且对于满足设备重量与尺寸限制至关重要。为使这些设备的能量收集组件小型化，需采用高工作频率。结合电大尺寸天线，接收器可能位于辐射近场（菲涅尔）区域，例如室内场景。本文提出一种无线能量传输系统，以确保为三维长方体房间内任意数量的移动、低功耗、单天线接收器提供可靠供能。为此，我们构建了一个最大-最小优化问题，以确定系统发射天线阵列中无穷多个辐射单元的最优发射功率分配。由此，可隐式获得最优部署方案，即根据最优分配被分配非零发射功率的发射天线位置集合。一般而言，最优部署对应的发射天线位置集合的勒贝格测度为零，且该集合的闭包内部为空。此外，对于一维发射天线阵列，可证明发射天线位置集合是有限的。通过仿真验证了所提最优方案的有效性。仿真结果表明，最优部署需要有限数量的发射天线，且其取决于环境几何结构与发射天线阵列的维度。在包含强视距（LoS）分量的各向同性散射环境中，评估了基于发射器与接收器间视距假设所得方案解的鲁棒性。