Energy-efficient Communication Protocol for Wireless Sensor Networks
Nodes in wireless sensor networks usually rely on battery energy. In applications with high number of sensor nodes and huge area of monitored environment replacing battery becomes an arduous task. Sometimes it is even impossible, if the exact location of the sensor node is unknown. This motivates researchers to work on energy saving mechanisms in order to increase lifetime of network and application. Apparently, a sensor node consumes the most of its energy in active mode. State-of-the-art micro-controllers offer several operational modes. This allows nodes to run in sleep mode where energy consumption can be a couple of hundred times less. Besides this, communication is the main energy consumer. This led us to proposes an energy-efficient medium access control (MAC) protocol for wireless sensor networks, called Energy Saving Token Ring Protocol (ESTR). ESTR bases on the well-known token ring protocol which is a fair and offers high-performance. The sensor nodes are connected to each other forming a ring where only the node that holds the token is active and able to communicate. ESTR uses this feature to introduce sleep periods for inactive sensor nodes that do not want to send or receive any messages. Since, token holding times are fixed for the network, sensors can calculate active and sleep times each period. This leads to much better energy results and increases lifetime of overall network. Additionally, ESTR minimizes energy that is wasted through idle-listening and overhearing. Furthermore, the proposed protocol supports multiple interconnected rings. This keeps network complexity low and allows to form smaller rings based on geographic location of nodes. By interconnection of several rings, connectivity throughout the network is ensured. ESTR offers a flexible mechanism to control throughput and energy consumption by setting maximum ring size. Furthermore, the token that is exchanged between neighboring nodes includes energy information of preceding node. The current node adopts its sleep time for the next period to balance overall energy of ring. This clearly increases lifetime of network.
ESTR is evaluated using network simulator NS-2 and achieves the best energy results compared to other MAC protocols.
Keywords: Wireless sensor network, MAC protocol, energy-saving, energy efficient, token ring, self-optimization