HAS-MAC: A Hybrid Asynchronous and Synchronous Communication System for Energy-Harvesting Wireless Sensor Networks

In Energy-Harvesting Wireless Sensor Networks (EH-WSNs), sensors have to continuously adapt their duty cycle to regulate energy consumption according to available energy. Therefore, it is unpractical to preserve an invariable working-schedule for a sensor and relay on a fixed routing path for a long time. For achieving packets forwarding effectively with low transmission latency, asynchronous and synchronous Medium Access Control (MAC) protocols are adopted widely regulating energy consumption in EH-WSNs. Since they bear a clear set of advantages and disadvantages, we propose a communication scheme that hybridizes asynchronous and synchronous MAC protocols for reducing average End-to-End delay in EH-WSNs, where a sensor will switch between the asynchronous and synchronous systems according to its energy supplement and practical scenario for adapting to its duty cycle. Our algorithm is suitable for not only low traffic load, but also high/periodic traffic situation. Especially, when working-schedules of sensors are adjusted dynamically depending on the energy environment, our algorithm provides better performance in EH-WSNs. Through extensive simulation and experiments, we demonstrate that our algorithm is efficient in reducing data transmission latency in EH-WSNs.