This paper presents the combination of energy harvesting (EH) at the wireless sensor and cooperative communications for low-power wide-area (LPWA) systems. Firstly, the Internet of Things sensor harvests the energy from the power beacon with multiple transmit antennas via radio frequency signals and then uses the harvested energy to transmit signals to multiple gateways with multiple receive antennas. Then, the cooperative communications is applied at the server based on the gateway outputs. By mathematical analysis, we derive the exact closed-form expressions of outage probabilities (OPs), throughput, and symbol error probabilities (SEPs) of the EH-LPWA system over Nakagami-$m$ fading channel in the cases without and with cooperative communications. Our expressions can be considered as the first results applying EH for LPWA systems with mathematical analysis. Then, we obtain the optimal value of the time switching ratio that minimizes the OPs and SEPs and maximizes the throughput of the considered EH-LPWA system. Numerical results have clarified that, the distances, path loss exponent, and data transmission rate have a strong impact on the OPs, throughput, and SEPs. Particularly, using a half of transmission blocks for EH can maximize the system performance. Moreover, when the number of transmit antennas at power beacon is equal to the number of receive antennas at gateways, the system performance can be improved significantly. Finally, the accuracy of the obtained expressions is demonstrated via Monte-Carlo simulations.

本文介绍了无线传感器的能量收集 (EH) 与低功耗广域 (LPWA) 系统的协作通信的组合。首先，物联网传感器通过射频信号从具有多个发射天线的功率信标中收集能量，然后利用收集到的能量将信号传输到具有多个接收天线的多个网关。然后，基于网关输出在服务器上应用协作通信。通过数学分析，我们推导出 EH-LPWA 系统在 Nakagami 上的中断概率 (OP)、吞吐量和符号错误概率 (SEP) 的精确闭式表达式$米$在没有和有合作通信的情况下衰落信道。我们的表达式可以被认为是通过数学分析将 EH 应用于 LPWA 系统的第一个结果。然后，我们获得了最小化 OP 和 SEP 并使所考虑的 EH-LPWA 系统的吞吐量最大化的时间切换比的最佳值。数值结果表明，距离、路径损耗指数和数据传输速率对 OP、吞吐量和 SEP 有很大影响。特别是，将一半的传输块用于 EH 可以最大限度地提高系统性能。此外，当功率信标处的发射天线数与网关处的接收天线数相等时，可以显着提高系统性能。最后，通过蒙特卡罗模拟证明了所获得表达式的准确性。