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ZigBee is a recent wireless standard based on IEEE 802.15.4 for Personal Area Networks. Its use in Wireless Sensor Networks arouses many interests. In this paper, a performance analysis and an improvement of ZigBee routing protocol are carried out. ZigBee routing protocol uses a modified AODV by default and Hierarchical Tree Routing as last resort. Firstly, these two algorithms are compared in terms of delay performance and energy consumption. The results showed that Hierarchical Tree Routing provides shorter average end to end delay but performs poorly in terms of energy consumption. So for supporting real time communication, it is desirable to freely choose one or another according to the type of traffic (realtime and non real-time). Secondly, Hierarchical Tree Routing algorithm is slightly modified to provide shorter delays than the original one.

Abstract-IEEE 802.15.4 standard specifies a beacon-enabled mode which provides a synchronization environment using beacon transmissions. However, this mode is designed for single hop networks and its use in multi-hop networks is not straightforward. The main challenges of using beacon-enabled mode in multi-hop networks are how to efficiently schedule beacon transmissions to avoid direct and indirect beacon collisions and how to make a schedule tolerant to the clock drifts due to the low cost components. In this paper, we present TBoPS, a novel technique for scheduling beacons in the cluster tree topology. TBoPS uses a dedicated period called beacon only period (BOP) to schedule beacons at the beginning of IEEE 802.15.4 superframe. The advantages of TBoPS is that every beacon-enabled node selects a beacon schedule distributively during association. We analysed the robustness of TBoPS to clock drifts. We also show through simulations that all nodes in the network are synchronized and follow the same superframe structure.