Underwater Multirobot Cooperative Intervention MAC Protocol

Abstract

This work introduces a Medium Access Control (MAC) protocol designed to allow a group of underwater robots that share a wireless communication channel to effectively communicate with each other. The goal of the Underwater Multirobot Cooperative Intervention MAC (UMCI-MAC) protocol presented in this work is to minimize the end to end delay and the jitter. The access to the medium in UMCI-MAC follows a Time Division Multiple Access (TDMA) strategy which is arbitrated by a master, which also has the capability to prioritize the transmission of some nodes over the rest of the network. Two experiments have been carried out with a team of four Autonomous Underwater Vehicles (AUV) in order to compare this protocol with Aloha-CS and S-FAMA MAC protocols used in Underwater Wireless Sensor Networks (UWSN). In the first experiment, the communications and the AUVs have been simulated using UWSim-NET. The objective of this experiment was to evaluate all three protocols in terms of delay, jitter, efficiency, collisions and throughput depending on the size of the data packet and the rate of packet delivery in the application layer for each robot. The results of this experiment proved that UMCI-MAC successfully avoids packet collisions and outperforms the other two protocols in terms of delay, jitter and efficiency. The second experiment consisted of a Hardware In The Loop (HIL) teleoperation of a team of four robots. One of the AUVs was a real BlueROV in a water tank, while the remaining AUVs and the communications were simulated with UWSim-NET. It demonstrates the impact of the MAC protocols in underwater acoustic links. Of the three MAC protocols evaluated in this work, UMCI-MAC was the only one which succeeded in the proposed teleoperation experiment. Thus demonstrating its suitability as a communications protocol in underwater cooperative robotics.