Algorithm for equalization of cluster lifetimes in a multi-level Beacon enabled 802.15.4 sensor network

We consider the problem of maintaining the prescribed event sensing reliability while maximizing cluster and network lifetime in a multi-cluster 802.15.4 sensor network. Clusters are connected through bridges which also act as cluster coordinators; both ordinary nodes and bridges resolve contention using the CSMA-CA algorithm. Cluster lifetime is maximized through the use of redundant sensors which are periodically sent to sleep using a simple distributed activity management algorithm. Network lifetime is maximized by equalizing energy consumption per backoff period in all clusters through the adjustment of the number of nodes. We model this problem analytically using the datasheet for tmote_sky ultra low power IEEE 802.15.4 compliant wireless sensor module [tmote sky lowpower wireless sensor module, Moteiv Corporation, San Francisco, CA, www.moteiv.com, tmote datasheet 802.15.4, 2006] and derive the probability distribution of the network lifetime. We also derive the expression for node count that compensates for the increased load due to contention caused by the bridge. Numerical results show that this technique easily equalizes cluster lifetimes.