Adaptive-opportunistic Aloha: A media access control protocol for unmanned aerial vehicle–wireless sensor network systems

Recognizing that data collection in a unmanned aerial vehicle–wireless sensor network system is significantly different from that in a conventional wireless sensor network system, we propose a media access control protocol called adaptive-opportunistic Aloha for unmanned aerial vehicle–wireless sensor network systems. Based on a cross-layered design, this proposed adaptive-opportunistic Aloha protocol takes several important factors into consideration, including distribution of sensors, energy consumption, and transmission efficiency. In order for unmanned aerial vehicle to uniformly collect data from the ground sensors that are distributed in a random fashion, adaptive-opportunistic Aloha adopts a priority-based mechanism for channel assignment and collision avoidance, and importantly, the priority could be adaptively changed according to locations and distribution of the sensors. To improve energy efficiency, the adaptive-opportunistic Aloha can effectively put the sensors into the sleep mode when they do not need to send data, and they will be woken up by a beacon signal from the unmanned aerial vehicle for data transmission. Unlike opportunistic Aloha protocol, a well-known unmanned aerial vehicle–wireless sensor network media access control protocol, the adaptive-opportunistic Aloha adds a handshake into every time interval of transmission to help enhance the throughput with an acceptable level of system bit error rate. Experiment results have shown that the proposed media access control protocol can improve the overall throughput of unmanned aerial vehicle–wireless sensor network systems by more than 30% over opportunistic Aloha.