Residual Time Based Energy Harvesting for Framed Slotted ALOHA Based Wireless Powered IoT Networks

This paper considers a wireless power transfer for framed slotted ALOHA in wireless powered Internet of Things (IoT) networks. Compared to devices in conventional networks, IoT devices might produce smaller packets which size might be hundreds of bits. That is, it is possible that packet size is smaller than a time slot. Given a constant slot time, as a packet is sent in a time slot, it is possible to leave residual time not being used. Thus, this paper proposes a residual time based energy harvesting scheme. In the proposed scheme, a base station utilizes the residual time in a time slot to send an RF charging signal, besides using entirely idle slots. Using the proposed scheme, devices can harvest more energy and then increase transmission rates. An analysis is developed to study the performances of the proposed residual time based energy harvesting scheme. Compared with a prior system where a base station sends RF charging signals merely in entirely idle time slots, numerical results show that the residual time based energy harvesting scheme produces a significantly higher mean transmission rate.