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.
