Adaptive Channel Access Mechanism for Zigbee (IEEE 802.15.4)

The IEEE 802.15.4 (also known as Zigbee) is a new wireless personal area network (PAN) standard designed for wireless monitoring and control applications. The Zigbee standard is based on CSMA-CA for contention based medium access. In this paper a study of the Adaptive backoff exponent (BE) management of CSMA-CA for 802.15.4 is presented. The BEs determine the number of backoff slots that the device shall wait before accessing the channel. The power consumption requirements make CSMA-CA use fewer BEs which increase the probability of devices choosing identical BEs and as a result, wait for the same number of backoff slots in some cases. This often leads to degradation of system performance at congestion scenarios, due to higher number of collisions. This paper addresses the problem by proposing an adaptive mechanism to the current implementation of the backoff exponent management, based on a decision criterion. As a result of the implementation, potential packet collisions are reduced. The results of NS-2 simulations are presented, indicating an overall improvement in network performance