Energy efficient medium access control with single sleep schedule for wireless sensor networks

S-MAC is a robust medium access control protocol for wireless sensor networks which is designed to be energy efficient. S-MAC nodes reduce energy expenditure by periodically turning off their receivers (sleeping) in a coordinated manner. Nodes form virtual clusters based on common sleep schedules. However, some nodes in S-MAC may have to wake up more often than the other nodes. This paper demonstrates in some wireless sensor networks using S-MAC, a significant proportion of the nodes may have to stay awake much longer than envisaged. The paper then proposes a modification of the protocol to eliminate the need for some nodes to stay awake longer than the other nodes. The modified version improves the energy efficiency and increases the life span of a wireless sensor network.