This paper studies an intelligent reflecting surface (IRS) aided wireless powered sensor network (WPSN). Specifically, a power station (PS) provides wireless energy to multiple internet of thing (IoT) devices which supports them to deliver their own messages to an access point (AP). Moreover, we deploy an IRS to enhance the performance of the WPSN by intelligently adjusting the phase shift of each reflecting element. To evaluate the performance of the IRS assisted WPSN, we maximize its sum throughput to jointly optimize the phase shift matrices and the transmission time allocations. Due to the non-convexity of the formulated optimization problem, we first derive the optimal phase shifts of the wireless information transfer (WIT) in closed-form. Consequently, a semi-definite programming (SDP) relaxed approach is considered to jointly design the phase shift matrix of the wireless energy transfer (WET) and the transmission time allocations. In addition, we propose a low complexity scheme to gain insights and reduce the computational complexity incurred by the SDP relaxed scheme. Specifically, the optimal solutions of the phase shifts and the transmission time allocation are derived in closed-form by the Majorization-Minimization (MM) algorithm, the Lagrange dual method and the Karush-Kuhn-Tucker (KKT) conditions. Finally, numerical results are presented to validate the proposed schemes and confirm the beneficial role of the IRS in comparison to the benchmark schemes, where the proposed IRS assisted scheme achieves almost 100% higher sum throughput, in comparison to the counterpart without IRS.

中文翻译：

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用于物联网的智能反射表面辅助无线供电传感器网络

本文研究了一种智能反射面（IRS）辅助无线供电传感器网络（WPSN）。具体来说，发电站 (PS) 为多个物联网 (IoT) 设备提供无线能量，支持它们将自己的消息传送到接入点 (AP)。此外，我们部署了 IRS，通过智能调整每个反射元件的相移来增强 WPSN 的性能。为了评估 IRS 辅助 WPSN 的性能，我们最大化其总吞吐量以联合优化相移矩阵和传输时间分配。由于公式化优化问题的非凸性，我们首先推导出封闭形式的无线信息传输 (WIT) 的最佳相移。最后，考虑采用半定规划（SDP）松弛方法来联合设计无线能量传输（WET）的相移矩阵和传输时间分配。此外，我们提出了一种低复杂度的方案，以获取洞察力并降低 SDP 松弛方案引起的计算复杂度。具体而言，相移和传输时间分配的最优解是通过主最小化(MM)算法、拉格朗日对偶法和卡鲁什-库恩-塔克(KKT)条件以封闭形式导出的。最后，给出了数值结果以验证所提出的方案并确认 IRS 与基准方案相比的有益作用，与没有 IRS 的对应方案相比，所提出的 IRS 辅助方案实现了几乎 100% 的总吞吐量。