Scheduling of relay nodes in a heterogeneous wireless sensor network

Abstract

Wireless sensor network is composed of large number of sensor nodes with limited battery power which cannot support long range communication. Sensor nodes' battery cannot be replaced due to adverse environment which causes connectivity failure in sensor network. Besides, sensors have short communication ranges and relay nodes are usually more powerful than sensor nodes. Relay nodes have longer communication range than sensor nodes. Therefore, to assist sensor nodes if relay nodes are added, communication will be more reliable. Usually relay nodes communicate with sensor nodes, or other relay nodes, or the base stations. It is desirable to place the minimum number of relay nodes in sensor network and keep the minimum number of relay nodes working to save network energy consumption. Most of the existing work on placing relay nodes in wireless sensor networks assume homogeneous network where sensor nodes and relay nodes have identical characteristics which is not realistic. This thesis work addresses the problem to find the optimal load balancing strategy where the minimum number of relay nodes be working to provide network connectivity considering heterogeneous properties of the network nodes. We study heterogeneous property of relay nodes and show that, existing algorithms do not support heterogeneous environment. Then, we give models, considering heterogeneous properties where we schedule wake up and sleep times for relay nodes to optimize the connectivity with the goal of saving network energy expenditure. We give two different guaranteed optimal models which keep the minimum number of relay nodes awake resulting to the optimal load balancing.