Analysis of Network Architectures for Zigbee Sensor Clusters P. M. Ameer, Anurag Kumar, D. Manjunath, ECE Department, Indian Institute of Science, Bangalore, India Ramakrishna Boyina Honeywell Technology Solutions Pvt. Ltd., Bangalore, India Abstract We provide a comparative performance analysis of network architectures for beacon enabled Zigbee sensor clusters using the CSMA/CA MAC defined in the IEEE 802.15.4 standard, and organised as (i) a star topology, and (ii) a two-hop topology. We provide analytical models for obtaining performance measures such as mean network delay, and mean node lifetime. We find that the star topology is substantially superior both in delay performance and lifetime performance than the two-hop topology. Keywords: wireless sensor network lifetime, sensor network performance, fixed point analysis 1 Introduction The IEEE 802.15.4 standard has evolved to realize the Physical (PHY) and Multiple Access Control (MAC) layers of such LR-WPANS [1]. The ZigBee alliance has developed the network and upper layers [2]. Our objective is to analyse the performance of such LR-WPANS for industrial monitoring and con- trol applications. Such applications aim to replace existing wired sensor networks (e.g., Fieldbus net- works) with wireless ad hoc sensor networks. The end to end applications, however, will initially re- main unchanged. Hence the concern is whether the wireless network will be able to carry the measure- ment and alarm traffic with the same level of per- formance as the wired network. In this paper, we provide the results of our analysis of tree topology sensor networks, based on the IEEE 802.15.4 stan- dard, in which packets flow only from the sensors to the head of the hub of the tree (i.e., the PAN coordinator). B D C A Figure 1: A cluster of Zigbee devices organised as a one-hop topology (left) and the same layout of devices operating as a two-hop topology (right). In Figure 1, we depict a number of Zigbee nodes organised as a one or two level tree rooted at the PAN (Personal Area Network) coordinator. The one level tree can also be called a star topology, for which an analytical model is developed in [3]. In the two level tree, from any sensor node to the PAN co- ordinator there are at most two hops. Hence we call this a two hop network. The star topology is operated by the PAN coordinator sending a peri- odic beacon, and all the nodes synchronising to the timing created by the beacon. We call this a Single Beacon Single Hop (SBSH) network. In the two- hop topology also there is only one beacon, which is sent by the PAN coordinator. All nodes syn- chronise to this beacon, and all intermediate nodes (transit nodes) are in the receive mode at all times. We call this the Single Beacon Multi-Hop (SBMH) network. The objective of the network is to transport mea- surement packets from the sensor nodes to the PAN coordinator at the centre of the network. In the case of the star topology, evidently only one trans- mission can take place at a time, since there is only one receiver. On the other hand in the case of the multihop topology it is possible, in general, to have multiple transmissions going on at different places in the network at the same time, i.e., spatial reuse is possible. However, we have found that for these low range CSMA based networks; spatial reuse, while possible is unlikely. Hence we do not consider spa- tial reuse in our model. For SBSH and SBMH archi- tectures we need to study the following questions. 1. What is the throughput and delay performance of the architectures? 2. What is the energy con- sumption? How long will the device batteries last? We begin by reviewing our analytical model for a star topology network [3]. Then we build on this model to develop an analysis for a two hop network. In [4] Zheng And Lee have provided a simulation study of IEEE 802.15.4. In [5] the authors provide a lifetime analysis of a star topology Zigbee network for a body area network application. In [6] the au- thors consider a beacon enabled star topology net- work with bidirectional traffic. Each node is mod- 1