Low-Latency MAC (LL-MAC) Protocol for a Multi-Hop Wireless Sensor Networks

In this paper, we present a new MAC protocol, called Low-Latency MAC (LL-MAC) protocol for muti-hop Wireless Sensor Networks. The LL-MAC is designed for the object tracking applications such as animal invasion, flight detection and wild animal detection. In these applications, the object appearance event does not occur frequently. But when an event occurs, many measured data by sensor nodes should be sent to a sink node as soon as possible. LL-MAC uses duty cycling contention-based MAC protocol. The operational cycle is divided into four periods: Sync, carrier sensing, Data, and Sleep. The Sleep period will be increased to send more packets by sender node when a target object appearance occurs. And a status bit in PION packet is used to indicate target appearance by the sender node. If this status bit is set to 1, all nodes know an object appearance and adjust their Sleep period to two times longer. After sending data packets, the sender node goes into sleep mode and wake ups again in two times slot times to send more data. Results showed that our LL-MAC protocol outperformed other protocols in terms of data packet delivery delay.