L-CSMA: A MAC Protocol for Multihop Linear Wireless (Sensor) Networks

We consider a multi-hop wireless linear network, where multiple nodes are evenly spaced over a straight line. Two scenarios are addressed: a network where only one source generates traffic to be transmitted via multiple hops to the destination, and the case of linear sensor networks, where all nodes in the line generate data. A novel contention-based Medium Access Control (MAC) protocol, L-CSMA, specifically devised for linear topologies, is proposed. CSMA (Carrier Sensing Multiple Access) suffers from the well known hidden/exposed node problems: the scope of L-CSMA is to reduce their impact, while minimising the protocol overhead. L-CSMA assigns different levels of priority to nodes, depending on their positions in the line: nodes closer to destination have higher priority when accessing the channel. The priority is managed by assigning to nodes different durations of the carrier sensing phase. This mechanism speeds up the transmission of packets which are already in the path, making the transmission flow more efficient. Results show that L-CSMA outperforms existing contention-based MAC protocols. A mathematical model to derive the performance in terms of packet success probability and throughput is provided. The key idea of the model is the definition of the generic state at network-level, instead of node-level, and its representation through a set of bits indicating the status (activity or not) of the corresponding link. The model is validated through comparison with simulations.