Strategies for Mitigating the Sensor Network Hot Spot Problem

In multi-hop wireless sensor networks that are characterized by many-to-one (convergecast) traffic patterns, problems related to energy imbalance among sensors often appear. When the transmission range is fixed for nodes throughout the network, the amount of traffic that sensors are required to forward increases dramatically as the distance to the data sink becomes smaller. Thus, sensors closest to the data sink tend to die early, leaving areas of the network completely unmonitored and causing network partitions. Alternatively, if all sensors transmit directly to the data sink, the furthest nodes from the data sink will die much more quickly than those close to the sink. Network lifetime can be improved to a limited extent by the use of a more intelligent transmission power control policy that balances the energy used in each node by requiring nodes further from the data sink to transmit over longer distances (although not directly to the data sink). However, transmission power control alone is not enough to solve the hot spot problem. Rather, policies such as data sink movement or data aggregation are necessary for the network to operate in an energy efficient manner. Since the movement of the data sink and the deployment of an aggregator node may be significantly more expensive than the deployment of an ordinary microsensor node, there is a cost tradeoff involved in both of these approaches. This paper provides an analysis of each of these policies for mitigating the sensor network hot spot problem, considering energy efficiency as well as cost efficiency.