A reliable peer-to-peer protocol for multi-robot operating in mobile ad-hoc wireless networks

Abstract

Cooperative behaviour in multi-robot systems are based on distributed negotiation mechanisms. A set of autonomous robots playing soccer may cooperate in deciding a suitable game strategy or role playing. Degradation in broadcast and multicast services are widely observed due to the lack of reliable broadcast in current IEEE 802.11. A reliable, Peer-To-Peer (P2P), fast auction-based broadcast is proposed for a team of robots playing soccer interconnected using an adhoc wireless mobile network. Auction broadcast includes a sequence order to determine the reply order of all nodes. This helps minimizing the potential of Medium Access Control (MAC) conflicts. Repeated back-off are not desired especially at low load. Uncoordinated negotiation lead to multiple outstanding auctions originated by distinct nodes. In this case, the sequence order becomes useless as auction times are interleaved. An adaptive MAC is proposed to dynamically adjust the reply. Protocols are implemented as symmetric multi-threaded software on an experimental Wireless Local Area Network (WLAN) embedded system. Evaluation reports the distribution of auction completion times for peer-to-peer operations for both static and mobile nodes. Protocol trade-offs with respect to auction response time, symmetry and fairness, and power consumption are discussed. Proposed protocols are embedded as a library for multi-robot Cooperative Behaviours (CBs). Evaluation shows the proposed protocol preferences versus the behavioural primitives with specific communication patterns.