Internet-of-Things (IoT) networks are expected to support the wireless connection of massive energy limited IoT nodes. The emerging wireless powered backscatter communications (WPBC) enable IoT nodes to harvest energy from the incident radio frequency signals transmitted by a power beacon (PB) to support their circuit operation, but the energy consumption of the PB (a potentially high cost borne by the network operator) has not been sufficiently studied for WPBC. In this paper, we aim to minimize the energy consumption of the PB while satisfying the throughput requirement per IoT node by jointly optimizing the time division multiple access (TDMA) time slot duration and backscatter reflection coefficient of each IoT node and the PB transmit power per time slot. As the formulated joint optimization problem is non-convex, we transform it into a convex problem by using auxiliary variables, then employ the Lagrange dual method to obtain the optimal solutions. To reduce the implementation complexity required for adjusting the PB's transmit power every time slot, we keep the PB transmit power constant in each time block and solve the corresponding PB energy consumption minimization problem by using auxiliary variables, the block coordinated decent method and the successive convex approximation technique. Based on the above solutions, two iterative algorithms are proposed for the dynamic PB transmit power scheme and the static PB transmit power scheme. The simulation results show that the dynamic PB transmit power scheme and the static PB transmit power scheme both achieve a lower PB energy consumption than the benchmark schemes, and the former achieves the lowest PB energy consumption.

翻译：物联网（IoT）网络需支持海量能量受限型IoT节点的无线连接。新兴的无线供电反向散射通信（WPBC）技术使IoT节点能够从能量信标（PB）发射的入射射频信号中获取能量以维持电路运行，但PB的能耗（网络运营商需承担的高昂潜在成本）在WPBC领域尚未得到充分研究。本文旨在通过联合优化各IoT节点的时分多址（TDMA）时隙长度、反向散射反射系数及PB每时隙发射功率，在满足每IoT节点吞吐量需求的同时最小化PB能耗。由于所构建的联合优化问题为非凸问题，我们通过引入辅助变量将其转化为凸问题，进而采用拉格朗日对偶方法获取最优解。为降低每时隙调节PB发射功率所需的实现复杂度，我们保持每时间块内PB发射功率恒定，并利用辅助变量、块坐标下降法与逐次凸逼近技术求解相应的PB能耗最小化问题。基于上述求解方案，针对动态PB发射功率方案与静态PB发射功率方案分别提出两种迭代算法。仿真结果表明，动态与静态PB发射功率方案相比基准方案均能实现更低的PB能耗，其中动态方案可实现最低的PB能耗。