Performance Evaluation Of A Beacon-enabled IEEE 802.15.4 Network With A Star Topology

IEEE 802.15.4 is a standard introduced for low-rate wireless personal area networks under the demand of low-date-rate applications, which provides features as low power consumption, low data rate, low complexity, short range, low cost, etc. It mainly fits the low-rate applications, and can be used for a wide variety of applications, such as home automation, industrial and agricultural controls, building automation, interactive toys, sensor networks, etc. Thus it enables the realization of ubiquitous networks.This paper first analyzes the development of wireless personal area networks, as well as the development, application areas and status of current researches on IEEE 802.15.4 protocol, and then studies the key techniques of the protocol, including protocol stack, frequency bands and modulation methods of physical layer, main function and protocol data unit format of physical and MAC layers, key parameters and flow chart of the CSMA/CA algorithm and the techniques of higher layers provided by ZigBee.On the basis of a thorough understanding of IEEE 802.15.4 protocol, the realization of IEEE 802.15.4 simulation system on the platform of the network simulation software OPNET is given. After the descriptions of the system structure and interfaces between modules, the process model, state machine and timer designs are given for the modules of each layer. Moreover, the message interactions of the main the procedures are shown which used in performance evaluation.The simulation scenario for home automation application is designed based on the simulation system. This paper evaluates the main performance parameters of a beacon-enabled IEEE 802.15.4 network in star topology, such as network throughput, average delay and network setup time, and analyzes the impacts of several factors towards those performance parameters, such as network load, packet length, number of nodes, duty cycle and startup time interval.The study shows that the saturation throughput of the network under beacon-enabled mode is about 65%, when the packet length is 100 bytes and the number of nodes is 10. The performance of IEEE 802.15.4 protocol is good, compared to the saturation throughput of IEEE 802.11a. The values of beacon order (BO) and superframe order (SO) have little influence on the network throughput and average delay when no inactive period exists, especially when they are in the range of 7 to 14. The network saturation throughput and average delay both decrease as the packet length decreases under the equivalent conditions. The key factor that influence the network saturation throughput and average delay is the packet length, and the number of nodes has little impact on them. Moreover, the impact of the number of nodes on the network setup time is within the acceptable range. That is to say the network scalability is fine. Through the analysis of the impact of the duty cycle and startup time interval on the network setup time, the suggested values of BO and SO are given to provide the guide for the configuration of system parameters under practical application.