Zigbee Wireless Sensor Network in Environmental Monitoring Applications Constructing an intelligent traffic monitoring system firstly depends on automatic identification for vehicles. At present, automatic identification technology based on image and vehicle license plate is going to fall in the trap due to its low recognition rate and affection by adverse weather. Thus it is necessary to apply new technologies to solve this problem, and technologies based on Internet of Things provide a new approach for it. In this paper, we explored this issue and proposed a feasible scheme. At first, we took global unique EPC code as identity identification of vehicles in stead of vehicle license plate and utilized RFID reader to read EPC code by RF electromagnetic wave, which completely solved the problem of no all-weather operations. Secondly, we obtained positioning information of vehicles by using GPS technology. Thirdly, because GPRS provides high-speed wireless IP services for mobile users, fully supports the TCP/IP, we took wireless GPRS scheme to transmit data of mobile objects. The realization of automatic detection and transmission of data provided a fundamental guarantee for constructing an intelligent traffic monitoring system. And then, we designed and discussed in turn its network architecture, data flow analysis, hardware logic structure, software flow, as well as its intelligent decision-making module. Research and design show that it is feasible and inexpensive to construct an intelligent traffic monitoring system based on Internet of Things, and the intelligent traffic monitoring system based on Internet of Things has a number of advantages such low cost, high reliability, never affected by adverse weather, all weather operations etc. Therefore, it will have a broad applying perspective.33858

Zigbee is a wireless standard based on IEEE802.15.4 that was developed to address the unique needs of most wireless sensing and control applications.  Technology is low cost, low power, a low data rate, highly reliable, highly secure wireless networking protocol targeted towards automation and remote control applications. It’s depicts two key performance characteristics – wireless radio range and data transmission rate of the wireless spectrum. Comparing to other wireless networking protocols such as Bluetooth, Wi-Fi, UWB and so on, shows excellent transmission ability in lower transmission rate and highly capacity of network.
A.  Zigbee Framework
  Framework is made up of a set of blocks called layers. Each layer performs a specific set of services for the layer above. As shown in Fig.1. The IEEE 802.15.4 standard defines the two lower layers: the physical (PHY) layer and the medium access control (MAC) layer. The Alliance builds on this foundation by providing the network and security layer and the framework for the application layer.
The IEEE 802.15.4 has two PHY layers that operate in two separate frequency ranges: 868/915 MHz and 2.4GHz. Moreover, MAC sub-layer controls access to the radio channel using a CSMA-CA mechanism. Its responsibilities may also include transmitting beacon frames, synchronization, and providing a reliable transmission mechanism.
The network layer supports star, tree, and mesh topologies, as shown in Fig.2. In a star topology, the network is controlled by one single device called coordinator. The coordinator is responsible for initiating and maintaining the devices on the network. All other devices, known as end devices, directly communicate with the coordinator. In mesh and tree topologies, the coordinator is responsible for starting the network and for choosing certain key network parameters, but the network may be extended through the use of routers. In tree networks, routers move data and control messages through the network using a hierarchical routing strategy. Mesh networks allow full peer-to-peer communication.
Fig.3 is a network model, it shows that supports both single-hop star topology constructed with one coordinator in the center and the end devices, and mesh topology. In the network, the intelligent nodes are composed by Full Function Device (FFD) and Reduced Function Device (RFD). Only the FFN defines the full functionality and can become a network coordinator. Coordinator manages the network, it is to say that coordinator can start a network and allow other devices to join or leave it. Moreover, it can provide binding and address-table services, and save messages until they can be delivered. ZigBee无线传感器网络英文文献和中文翻译:http://www.youerw.com/fanyi/lunwen_31155.html