Spatiotemporal Medium Access Control for Wireless Powered IoT Networks

We study a wireless powered Internet-of-Things (IoT) network, which consists of spatially distributed energy harvesting (EH) nodes and a hybrid access point (HAP). The energy requirements of exponentially increasing IoT nodes could be fulfilled using the wireless EH. However, the spatiotemporal diversity may affect the performance of wireless EH networks due to the arbitrary information transmissions and varying amount of harvesting energy. In this article, we propose a new access control mechanism based on frame-slotted ALOHA considering the spatiotemporal diversity of nodes for distributed wireless powered IoT networks. In the proposed scheme, the nodes efficiently utilize the available time and power resources to enhance the achievable network throughput. The varying amount of harvested energy due to the harvesting duration and random distance from the power beacon (PB) affects the network performance. The contending nodes for a shared channel, randomly choose slots in a slotted frame, harvest energy, and transmit information using the harvested energy. We analyze the transmission probability of nodes affected by fading channel gains and formulate an optimization problem to find the optimal frame size for the contending number of nodes to maximize the achievable network throughput. The proposed scheme enhances the achievable throughput up to 12.5% and energy efficiency up to 20% over the conventional scheme.