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1、-Zigbee Wireless Sensor Network in Environmental Monitoring ApplicationsI.ZIGBEE TECHNOLOGY 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
2、 reliable, highly secure wireless networking protocol targeted towards automation and remote control applications. Its depicts two key performance characteristics wireless radio range and data transmission rate of the wireless spectrum. Comparing to other wireless networking protocols such as Blueto
3、oth, 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、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.Fig.1 Framework The IEEE 802.15.4 has two PHY layers that operat
5、e 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.B. Zigbees Topology T
6、he 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, dire
7、ctly 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 th
8、e network using a hierarchical routing strategy. Mesh networks allow full peer-to-peer communication.Fig.2 Mesh topologies 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 netw
9、ork, 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 joi
10、n or leave it. Moreover, it can provide binding and address-table services, and save messages until they can be delivered.Fig.3 Zigbee network modelII.THE GREENHOUSE ENVIRONMENTAL MONITORINGSYSTEM DESIGN Traditional agriculture only use machinery and equipment which isolating and no communicating ab
11、ility. And farmers have to monitor crops growth by themselves. Even if some people use electrical devices, but most of them were restricted to simple communication between control computer and end devices like sensors instead of wire connection, which couldnt be strictly defined as wireless sensor n
12、etwork. Therefore, by through using sensor networks and, agriculture could become more automation, more networking and smarter. In this project, we should deploy five kinds of sensors in the greenhouse basement. By through these deployed sensors, the parameters such as temperature in the greenhouse,
13、 soil temperature, dew point, humidity and light intensity can be detected real time. It is key to collect different parameters from all kinds of sensors. And in the greenhouse, monitoring the vegetables growing conditions is the top issue. Therefore, longer battery life and lower data rate and less
14、 complexity are very important. From the introduction about above, we know that meet the requirements for reliability, security, low costs and low power.A. System Overview The overview of Greenhouse environmental monitoring system, which is made up by one sink node (coordinator), many sensor nodes,
15、workstation and database. Mote node and sensor node together composed of each collecting node. When sensors collect parameters real time, such as temperature in the greenhouse, soil temperature, dew point, humidity and light intensity, these data will be offered to A/D converter, then by through qua
16、ntizing and encoding become the digital signal that is able to transmit by wireless sensor communicating node. Each wireless sensor communicating node has ability of transmitting, receiving function. In this WSN, sensor nodes deployed in the greenhouse, which can collect real time data and transmit
17、data to sink node (Coordinator) by the way of multi-hop. Sink node complete the task of data analysis and data storage. Meanwhile, sink node is connected with GPRS/CDMA can provide remote control and data download service. In the monitoring and controlling room, by running greenhouse management soft
18、ware, the sink node can periodically receives the data from the wireless sensor nodes and displays them on monitors.B. Node Hardware Design Sensor nodes are the basic units of WSN. The hardware platform is made up sensor nodes closely related to the specific application requirements. Therefore, the
19、most important work is the nodes design which can perfect implement the function of detecting and transmission as a WSN node, and perform its technology characteristics. Fig.4 shows the universal structure of the WSN nodes. Power module provides the necessary energy for the sensor nodes. Data collec
20、tion module is used to receive and convert signals of sensors. Data processing and control modules functions are node device control, task scheduling, and energy computing and so on. Communication module is used to send data between nodes and frequency chosen and so on.Fig.4 Universal structure of t
21、he wsn nodes In the data transfer unit, the module is embedded to match the MAC layer and the NET layer of the protocol. We choose CC2430 as the protocol chips, which integrated the CPU, RF transceiver, net protocol and the RAM together. CC2430 uses an 8 bit MCU (8051), and has 128KB programmable fl
22、ash memory and 8KB RAM. It also includes A/D converter, some Timers, AES128 Coprocessor, Watchdog Timer, 32K crystal Sleep mode Timer, Power on Reset, Brown out Detection and 21 I/Os. Based on the chips, many modules for the protocol are provided. And the transfer unit could be easily designed based
23、 on the modules. As an example of a sensor end device integrated temperature, humidity and light, the design is shown in Fig. 5. Fig.5 The hardware design of a sensor node The SHT11 is a single chip relative humidity and temperature multi sensor module comprising a calibrated digital output. It can
24、test the soil temperature and humidity. The DS18B20 is a digital temperature sensor, which has 3 pins and data pin can link MSP430 directly. It can detect temperature in greenhouse. The TCS320 is a digital light sensor. SHT11, DS18B20 and TCS320 are both digital sensors with small size and low power
25、 consumption. Other sensor nodes can be obtained by changing the sensors. The sensor nodes are powered from onboard batteries and the coordinator also allows to be powered from an external power supply determined by a jumper.C. Node Software Design The application system consists of a coordinator an
26、d several end devices. The general structure of the code in each is the same, with an initialization followed by a main loop. The software flow of coordinator, upon the coordinator being started, the first action of the application is the initialization of the hardware, liquid crystal, stack and app
27、lication variables and opening the interrupt. Then a network will be formatted. If this net has been formatted successfully, some network information, such as physical address, net ID, channel number will be shown on the LCD. Then program will step into application layer and monitor signal. If there
28、 is end device or router want to join in this net, LCD will shown this information, and show the physical address of applying node, and the coordinator will allocate a net address to this node. If the node has been joined in this network, the data transmitted by this node will be received by coordin
29、ator and shown in the LCD. The software flow of a sensor node, as each sensor node is switched on, it scans all channels and, after seeing any beacons, checks that the coordinator is the one that it is looking for. It then performs a synchronization and association. Once association is complete, the
30、 sensor node enters a regular loop of reading its sensors and putting out a frame containing the sensor data. If sending successfully, end device will step into idle state; by contrast, it will collect data once again and send to coordinator until sending successfully.D. Greenhouse Monitoring Softwa
31、re DesignWe use VB language to build an interface for the test and this greenhouse sensor network software can be installed and launched on any Windows-based operating system. It has 4 dialog box selections: setting controlling conditions, setting Timer, setting relevant parameters and showing curre
32、nt status. By setting some parameters, it can perform the functions of communicating with port, data collection and data viewing。Zigbee无线传感器网络在环境检测中的应用1. Zigbee技术Zigbee是一种基于IEEEE802.15.4的无线标准上被开发用来满足大多数无线传感器和控制应用的独特需求。Zigbee技术是低成本，低功耗，低数据速率，高可靠性，高度安全的无线网络协议实现自动化和远程控制应用的目标。它描述了两个关键的性能特点无线射频范围和无线频谱的数据
33、传输速率。相较于其他如蓝牙，Wi-Fi技术，超宽带等无线网络协议，Zigbee虽然传输速率慢但传输容量大的特点向我们展示了他出色的传输能力。A. 技术框架Zigbee的框架是有一组层组成的。上诉层中每一层都要执行一组特定的服务任务。如图所示。在IEEE802.15.4标准定义了两个较低层：物理层（PHY）和媒体接入控制（MAC）层。Zigbee联盟建立在网络层和安全层及应用层框架提供的基础上。 图1 技术框架 在IEEE802.15.4有两个phy层，它们在两个不同的频率范围操作:868/915兆赫和2.4GHz。此外，MAC子层控制访问无线电频道使用的CSMA-CA的机制。它的功能还可以包括
34、信标帧传输，同步，并开发一个可靠的传输机制。B.Zigbee技术的拓扑 Zigbee网络层支持星形，树形和网状拓扑结构，如图2所示。在星型拓扑结构中，网络是由一个叫做Zigbee协议器的单一设备控制的。Zigbee协议器负责发起和维护网络上面的设备。所有其他设备，称为终端设备，直接与Zigbee协议器连接。在网状和树状拓扑结构中，Zigbee协议器的作用是启动网络，并选择一些重要的网络参数，但是网络可以通过Zigbee路由器扩展。在树状网络中，路由器将通过使用分层路由策略移动数据和控制消息。网状网络允许完全对等的对等通信。图2 技术的拓扑 图3是一个Zigbee网络模型，它表明Zigbee支持
35、协议器中心的单挑星型拓扑结构和终端设备，以及网状拓扑构造。在Zigbee网络中，智能节电有全功能设备（FFD）和精简功能设备（RFD)组成。只有FFN定义了完整的Zigbee功能，并且可称为网络协议器。协议器管理网络，也就是说，协议器可以启动网络，并允许其他设备加入或离开它，此外，它还可以提供绑定和地址表服务，并保存，直到它们能传递信息。图3 Zigbee网络模型 2. 温室环境监测的系统设计 传统农业只使用孤立的和没有沟通能力的机器和设备。农民们必须自己亲自监控顾作物的生长。及时有些人用电气设备，但他们中的大多数只限于控制计算机和终端设备的简单通信，此终端设备像传感器而不是像线相连接的传感器
36、，严格意义上来说，不能被定义为无线传感器网络，因此，通过使用传感器网络和Zigbee，农业可能变得更加自动化，更加的网络化和智能化。 在这个项目中，我们要在温室的地下室部署5种传感器。通过这些部署的传感器，如温室的温度，土壤温度，露点，湿度和光照强度的参数可以实时监测。他的关键是从各种不同的传感器来收集不同的参数。而在温室，检测蔬菜的长势是首要问题。因此，延长电池的寿命，减少数据数率和降低复杂度是非常重要的。从上述关于Zigbee的介绍，我们知道Zigbee满足了可靠性，安全性，低成本，低功耗的要求。A、 系统概述温度环境监测系统是由一个接收器节点（协议器）。许多传感器节点，工作点和数据库采集
37、组成的。模特节点和传感器节点共同组成了每个收集节点。当传感器参数进行实时采集，如温室温度，土壤温度，露点，湿度，光照强度，这些数据将提供给A/D转换器，然后透过量化和编码称为数字信号，它能通过无线传感器通信节点传送。每一个无线传感器通信节点有传输和接收的能力。在这种传感器网络中，传感器节点部署在温室，它可以采集实时数据和通过多条方式传输数据到接收器节点（协议器）。接收器节点完成另外数据分析和存储的任务。同时，接收器节点与GPRS/CDMA连接可以提供远程控制和数据下载服务。在监控室通过运行温室管理软件，接收器节点可以定期收到来自无线传感器节点和在监视器上显示这些数据。B、节点的硬件设计在传感器
38、节点是无线传感器网络的基本单元。硬件平台是由密切相关的具体应用要求的传感区节点组成的。因此，最重要的工作是节点设计，可以完美执行无线传感器网络的传送和检测功能，并体现Zigbee的技术特点，图4显示了无线传感器网络节点的普遍结构。电源模块为传感器节点提供了必要的能量。数据采集模块被用来接收和转换传感器的信号。数据处理和控制模块的功能是节电设备控制，任务调度，能量计算等。通讯模块被用来在节点和频率选择之间传递数据等。图4 无线传感器网络节点的通用结构在数据传输单元，Zigbee模块是嵌入式的用来匹配Zigbee协议的MAC层和NET层。我们选择CC2430作为Zigbee一些的芯片。他把CPU，
39、射频收发器，网络协议和RAM集合在一起。CC2430运用一个8比特的微控制器（8051），并具有128K可编程内存和8KB的RAM。它还包括A/D转换，某些计时器，AE128协处理器，看门狗定时器，32K的晶体休眠模式定时器，上电复位，掉电检测和21个I/O操作系统。基于主芯片、为Zigbee协议提供许多模块。在哪些模块的基础上Zigbee传输单元可以很容易的被设计出来。 以一个集成温度，湿度和光照的传感器终端设备为例，设计如图5所示。图5 传感器节点的硬件设计 该SHT11是一种相对于湿度和温度的多传感器模块包括校准的数字输出的单芯片。它可以测试土壤的温度和湿度。DS18B20的数字温度传感
40、器，它有3个引脚，并且数据引脚可以直接连接MSP430.它可以检测到温室的温度。TC320是一种数字光传感器。DS18B20和TC320 SHT11，都是数字传感器，具有体积小，功耗低的特点。其它传感器节点可以通过改变传感器获得。传感器节点由供电板载电池供电，协调器还允许通过跳线由外部电源跳线供电。C、节点的软件设计应用系统有一个协调器和几个终端设备组成。每一个代码的一般结构是相同的，一个主循环后初始化。协调其软件流程，经协调器开始，应用程序的第一步是硬件，液晶，站和应用程序变量的初始化并且开放中断。然后，一个网络将被格式化。如果这个我那个罗已经被格式化成功，一些网络信息，如物理地址，网络ID
41、，通道号，将会显示在液晶显示屏上。然后，程序将进入应用层和监测Zigbee信号。如果有终端设备或者路由器想要加入这一网络，液晶显示屏将显示此信息，并显示了应用节点的物理地址，协议元江分配一个网络地址到该节点。如果节点已经加入了这个网络，数据由此节点传送，将由协调器接收，并且显示在液晶显示器上。一个传感器节点软件流程，当每个传感器节点被打开或者在遇到任何航标后一个正在被寻找的协调器被检测到时，他会扫描所有频道。然后执行同步和链接，一旦完成连接，传感器节点便会进入阅读传感器和输出包含节点数据框架的定期循环，如果发送成功，设备终端将进入空闲状态，相反，他会再次收集数据并且发送到协调器，直到发送成功。D、温室监控软件设计、我们用VB语言为测试来构建一个界面，这温室传感器网络的软件，可以安装任何基于Windows操作系统。它有4个对话框选择：设置控制条件，设置定时器了，设定相关参数，并显示当前的状态。通过设置一些参数，它可以执行和港口沟通的功能，数据收集和数据浏览。第 15 页-