Unpredictable nature of fading channels and difficulty in tracking channel state information pose major challenge in wireless energy harvesting communication system design. In this work, we address relay selection problem for wireless powered communication networks, where the relays harvest energy from the source radio frequency signals. A single source–destination pair is considered without a direct link. The connecting relay nodes are equipped with storage batteries of infinite size. We assume that the channel state information (CSI) on the source–relay link is available at the relay nodes. Depending on the availability of the CSI on the relay–destination link at the relay node, we propose two relay selection schemes and evaluate their outage probability. Availability of the CSI at the relay node on the relay–destination link considerably improves the performance due to additional flexibility in the relay selection mechanism. Due to absence of CSI throughout the network at the time of transmission path selection, the analysis of the problem is not tractable. Therefore, we relax our assumptions on availability of CSI and closed-form expressions of the outage probability as a function of the amount of the available harvested energy are derived for both CSI availability cases. Finally, we numerically quantify the performance for the proposed schemes and compare the outage probability for fixed and equal number of wireless powered forwarding relays.

衰落信道的不可预测性和跟踪信道状态信息的困难对无线能量收集通信系统设计提出了重大挑战。在这项工作中，我们解决了无线通信网络的中继选择问题，其中中继从源射频信号中收集能量。单个源－目标对被认为没有直接链接。连接的中继节点装有无限大小的蓄电池。我们假设源－中继链路上的信道状态信息（CSI）在中继节点上可用。根据中继节点上中继目标链路上CSI的可用性，我们提出两种中继选择方案并评估其中断概率。由于中继选择机制的额外灵活性，CSI在中继目标链路上的中继节点上的可用性大大提高了性能。由于在选择传输路径时整个网络中没有CSI，因此对该问题进行分析是不容易的。因此，我们放宽了对CSI可用性的假设，并针对这两种CSI可用性案例推导了中断概率作为可用收获能量的函数的闭式概率表达式。最后，我们在数值上量化了所提出方案的性能，并比较了固定数量和相等数量的无线转发中继的中断概率。由于在选择传输路径时整个网络中没有CSI，因此对该问题进行分析是不容易的。因此，我们放宽了对CSI可用性的假设，并针对这两种CSI可用性案例推导了中断概率作为可用收获能量的函数的闭式概率表达式。最后，我们在数值上量化了所提出方案的性能，并比较了固定数量和相等数量的无线转发中继的中断概率。由于在选择传输路径时整个网络中没有CSI，因此对该问题进行分析是不容易的。因此，我们放宽了对CSI可用性的假设，并针对这两种CSI可用性案例推导了中断概率作为可用收获能量的函数的闭式概率表达式。最后，我们在数值上量化了所提出方案的性能，并比较了固定数量和相等数量的无线转发中继的中断概率。