A medium access control protocol that supports a seamless handover in wireless sensor networks

This paper introduces a mobility-aware medium access control protocol for multi-hop wireless sensor networks (MA-MAC). The protocol evaluates the RSSI values of acknowledgement packets and determines whether a gradual deterioration in the RSSI values eventually leads to a disconnection. If it does, it initiates a handover by switching transmission from a unicast to a broadcast mode and by embedding neighbour discovery requests in the broadcast data packets. While the mobile node continues transmitting data packets via the existing link, the neighbour discovery requests enable it to discover new nodes that can serve as intermediate nodes. Once an intermediate node is found, the mobile node establishes a link with it and switches transmission back to unicast. Conceptually, MA-MAC's handover feature can be implemented by extending any of the existing transmitter initiated, energy-efficient protocols such as XMAC or BMAC. Our present implementation is based on the XMAC protocol. The paper reports how the protocol performs as the speed of mobility, handover threshold, and sending interval vary.