Load Migrating for the Hot Spots in Wireless Sensor Networks Using CTP

To suit the needs of data collection, routing protocols in WSN are normally required to form a collection tree where data flows from the source nodes to the sink nodes. These protocols, such as CTP and Multihop LQI, generally target at reducing the packet delivery cost without considering load balancing issues. We argue that load balancing is crucial for WSNs because load imbalance may cause certain nodes, which we call hot spots, to run out of energy faster than expected. The load imbalance may lead to holes and prominently degrade the performance of the network. In this paper, we propose BCTP (Balanced Collection Tree Protocol), which enhances CTP by enabling the network to migrate the load of the node under heavy traffic. BCTP uses the average transmission rate as the metric to measure a node´s long term traffic load. Once a node is found heavily loaded, BCTP adopts a stochastic routing strategy to balance the load. BCTP is evaluated by test bed experiments with 9 Telosb motes. Experiment result shows that BCTP can reduce the load of the hot spot by up to 61.9% in a densely deployed network.