Payload-Adaptive Hybrid MAC Protocol for Sustainable Internet of Things Networks: Protocol Design and Adaptive Adjustment Mechanisms

Wireless energy transfer (WET) technology enables Internet of Things (IoT) networks to have longer lifetime without the need of frequent battery replacements. This article proposes a payload-adaptive hybrid MAC (PAH-MAC) protocol by considering both contention and time-slot allocation among sensors for large-scale data collection scenarios within WET-enhanced IoT networks. The PAH-MAC protocol employs different access strategies based on the payload size of data packets. Furthermore, leveraging synchronization mechanisms, the coordinator periodically dispatches energy packets to replenish the battery of all sensors. The stationary performance of PAH-MAC protocol is analyzed by invoking Markov chains. Considering the traffic variations caused by changes in the number of sensors in the network, a slot adaptive adjustment algorithm is proposed to maximize the throughput and energy performance. Therefore, the coordinator adaptively adjusts the duration of the contention period and the energy transmission period within the next superframe according to access conditions observed in current superframe. Another transmission power adjustment algorithm is proposed for sensors to improve their energy efficiency. According to our simulation, our proposed protocol consumes less energy in low-traffic scenarios than the classic carrier-sense multiple access/CA and another baseline protocol. Furthermore, in high-traffic scenarios, our proposed protocol achieves higher throughput, lower latency, and lower energy consumption than its counterpart.