Research Of IEEE802.15.4Wireless Sensor Network And Its Apply In Environmental Monitoring

IEEE Std802.15.4protocol is developed for the LR-WPAN (Low-Rate Wireless Personal Area Network) by the IEEE Standardization Committee, it is a communication standard which focuses on low transmission rate, low power consumption, low cost, low degree of complexity, the protocol specifies the PHY(physical layer) and MAC(media access control layer), which aims to provide a unified standard for low-speed interconnection between different devices in the area of personal, family, or specify areas. As a low-cost, simple structure wireless communication network, LR-WPAN makes the use in the application environment of the low throughput and low power wireless transmission becomes possible. Compared with the WLAN, LR-WPAN needs considerably less infrastructure. With the rapid development of wireless communication technology and sensor technology, makes the WSN(Wireless Sensor Networks) has become a research hotspot, which fusion of sensor technology, communication technology and embedded computing technology. Because WSN and LR-WPAN network has many similarities, so IEEE802.15.4protocol is regarded as the communication standard for WSN by many research institutions. Nowadays, WSN has broad application prospects in environmental monitoring, military reconnaissance, medical monitoring, home security and so on.This paper analyzes the protocol of the IEEE802.15.4standard at first, mainly studies its protocol stack architecture, the functions and characteristics of physical layer and MAC layer, and analyzed the superframe structure, CSMA/CA algorithm, GTS mechanism. On this basis, establishes a simulation model of IEEE802.15.4by using the network simulation software OPNET. Based on the established network simulation model, node simulation model and process simulation model of the star network, evaluated the performance of the IEEE802.15.4protocol. According to the problems of energy consumption and time latency in the IEEE802.15.4network, analyzed the duty-cycle under the beacon-enabled mode in star network. According to the simulation and analysis of the two key parameters:SO and BO, which influence the duty-cycle. Concluded the range of parameter configuration to balance the energy consumption and latency, and these analyses can be good references for the set of network parameters. After the simulation and analysis of the IEEE802.15.4protocol, this paper developed and implemented an environmental monitoring system based on the IRIS node hardware platform and TinyOS embedded operating system, IRIS node based on the RF chip AT86RF230. Firstly, this paper analyzes the component, communication model and scheduling strategy of TinyOS, according to the characteristics of SHT71and principles of multi-hop networking in wireless sensor network, designed environmental parameter acquisition program and networking program using nesC language, implemented the collection of temperature and humidity and multi-hop networking functions. Through middleware XServe, it realizes the function of parsing the XML data flow to the temperature and humidity and displaying them by Cygwin. Experimental results of the environmental monitoring system show that the system can realize the functions of environmental parameter gathering and multi-hop wireless transmission.