Admission control issues in 802.15.4 sensor clusters

Wireless sensor networks are expected to provide reliable event sensing at the network sink for the longest possible time. These requirements are somewhat conflicting, esp. in the case of networks that use medium access protocols based on the ubiquitous CSMA-CA mechanism, where collisions may substantially affect transmission efficiency and thus impair network lifetime. This is the case with beacon enabled IEEE 802.15.4 network clusters [2], despite the fact that the low rate WPAN (LR-WPAN) standard is considered as an important enabling technology for widespread, standardized deployment of sensor networks [1]. In 802.15.4 clusters, energy is wasted in packet collisions and active measures must be taken to counter this effect. A general solution to the above problem may be found in the mechanism of admission control [12], in which a central authority—most likely, a network coordinator or cluster head—admits or rejects requests by individual nodes to join the network or cluster. Most common form of admission control is a contention-based mechanism which strives to maintain high utilization in the network under consideration, whilst simultaneously minimizing contention. This goal