1、Zigbee Wireless Sensor And Its Applications in Environmental Monitoring1.1 Standars Wireless sensor standards have been developed with the key design requirement for low power consumption. The standard defines the functions and protocols necessary for sensor nodes to interface with a variety of netw
2、orks.Someof these standardincludeIEEE802.15.4,ZigBee,WirelessHART,ISA100.11,IETF6LoW-PAN,IEEE802.15.3,Wibree.The follow-ing paragraphs describes these standards in more detail. IEEE802.15.4:IEEE802.15.437 is the proposed stan-dard for low rate wireless personal area networks (LR-WPANs).IEEE802.15.4
3、focuses on low cost of deployment,low complexity, and low power consumption.IEEE802.15.4 is designed for wireless sensor applications that require short range communication to maximize battery life. The standard allows the formation of the star and peer-to-peer topology for communication between net
4、-work devices.Devices in the star topology communicate with a central controller while in the peer-to-peer topol-ogy ad hoc and self-configuring networks can be formed.IEEE802.15.4devices are designed to support the physical and data-link layer protocols.The physical layer supports 868/915 MHz low b
5、ands and 2.4 GHz high bands. The MAC layer controls access to the radio channel using the CSMA-CA mechanism.The MAC layer is also responsible for validating frames, frame delivery, network interface, network synchronization, device association, and secure services.Wireless sensor applications using
6、IEEE802.15.4 include residential, industrial, and environment monitor-ing, control and automation. ZigBee 38,39 defines the higher layer communication protocols built on the IEEE 802.15.4 standards for LR-PANs. ZigBee is a simple, low cost, and low power wireless com- munication technology used in e
7、mbedded applications.ZigBee devices can form mesh networks connecting hun- dreds to thousands of devices together. ZigBee devices use very little power and can operate on a cell battery for many years. There are three types of ZigBee devices:Zig-Bee coordinator,ZigBee router, and ZigBee end device.Z
8、ig-Bee coordinator initiates network formation,stores information, and can bridge networks together. ZigBee routers link groups of devices together and provide mul-ti-hop communication across devices. ZigBee end devic consists of the sensors, actuators, and controllers that col-lects data and commun
9、icates only with the router or the coordinator. The ZigBee standard was publicly available as of June 2005. WirelessHART:The WirelessHART40,41 standard pro-vides a wireless network communication protocol for pro-cess measurement and control applications.The standard is based on IEEE802.15.4 for low
10、power 2.4 GHz operation. WirelessHART is compatible with all existing devices, tools, and systems. WirelessHART is reliable, secure, and energy efficient. It supports mesh networking,channel hopping, and time-synchronized messaging.Network com-munication is secure with encryption,verification,authen
11、-tication,and key management.Power management options enable the wireless devices to be more energy effi-cient.WirelessHART is designed to support mesh, star, and combined network topologies. A WirelessHART network consists of wireless field devices,gateways, process auto- mation controller, host ap
12、plications,and network man-ager.Wireless field devices are connected to process or plant equipment.Gateways enable the communication be-tween the wireless field devices and the host applications. The process automation controller serves as a single con-troller for continuous process.The network mana
13、ger con-figures the network and schedule communication between devices. It also manages the routing and network traffic. The network manager can be integrated into the gateway, host application, or process automation control-ler. WirelessHART standards were released to the industry in September 2007
14、 and will soon be available in commer- cial products. ISA100.11a: ISA100.11a 42 standard is designed for low data rate wireless monitoring and process automation applications. It defines the specifications for the OSI layer, security, and system management.The standard focuses on low energy consumpt
15、ion,scalability, infrastructure,robustness, and interoperability with other wireless de-vices. ISA100.11a networks use only 2.4 GHz radio and channel hopping to increase reliability and minimize inter-ference.It offers both meshing and star network topolo-gies. ISA100.11a also provides simple, exibl
16、e, and scaleable security functionality. 6LoWPAN: IPv6-based Low power Wireless Personal Area Networks 43-45 enables IPv6 packets communica-tion over an IEEE802.15.4 based network.Low power device can communicate directly with IP devices using IP-based protocols. Using 6LoWPAN,low power devices have
17、 all the benefits of IP communication and management.6LoWPAN standard provides an adaptation layer, new packet format, and address management. Because IPv6 packet sizes are much larger than the frame size of IEEE 802.15.4, an adaptation layer is used. The adaptation layer carries out the functionali
18、ty for header compression. With header compression, smaller packets are created to fit into an IEEE 802.15.4 frame size. Address management mecha- nism handles the forming of device addresses for commu-nication. 6LoWPAN is designed for applications with low data rate devices that requires Internet c
19、ommunication. IEEE802.15.3:IEEE802.15.346 is a physical and MAC layer standard for high data rateWPAN. It is designed to support real-time multi-media streaming of video and mu-sic.IEEE802.15.3 operates on a 2.4 GHz radio and has data rates starting from 11 Mbps to 55 Mbps.The standard uses time div
20、ision multiple access (TDMA) to ensure quality of service. It supports both synchronous and asynchronous data transfer and addresses power consumption, data rate scalability, and frequency performance. The standard is used in devices such as wireless speakers, portable video electronics, and wireles
21、s connectivity for gaming, cordless phones, printers, and televisions. Wibree: Wibree 47 is a wireless communication tech-nology designed for low power consumption, short-range communication, and low cost devices. Wibree allows the communication between small battery-powered devices and Bluetooth de
22、vices.Small battery powered devices in-clude watches, wireless keyboard, and sports sensors which connect to host devices such as personal computer or cellular phones. Wibree operates on 2.4 GHz and has a data rate of 1 Mbps. The linking distance between the de-vices is 5-10 m.Wibree is designed to
23、work with Blue-tooth. Bluetooth with Wibree makes the devices smaller and more energy-efficient. Bluetooth-Wibree utilizes the existing Bluetooth RF and enables ultra-low power con-sumption. Wibree was released publicly in October 2006. 1.2 The greenhouse environmental monitoring system design Tradi
24、tional agriculture only use machinery and equipment which isolating and no communicating ability. 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
25、 sensors instead of wire connection, which couldnt be strictly defined as wireless sensor network. 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 basemen
26、t. By through these deployed sensors, the parameters such as temperature in the greenhouse, 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 growi
27、ng conditions is the top issue. Therefore, longer battery life and lower data rate and less 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 environmen
28、tal monitoring system, which is made up by one sink node (coordinator), many sensor nodes, 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, hum
29、idity and light intensity, these data will be offered to A/D converter, then by through quantizing 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 W
30、SN, sensor nodes deployed in the greenhouse, which can collect real time data and transmit 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 down
31、load service. In the monitoring and controlling room, by running greenhouse management software, 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 mad
32、e up sensor nodes closely related to the specific application requirements. Therefore, the 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
33、the WSN nodes. Power module provides the necessary energy for the sensor nodes. Data collection 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 us
34、ed to send data between nodes and frequency chosen and so on.Fig.4 Universal structure of the 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 pr
35、otocol and the RAM together. CC2430 uses an 8 bit MCU (8051), and has 128KB programmable flash 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
36、modules for the protocol are provided. And the transfer unit could be easily designed based 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 h
37、umidity and temperature multi sensor module comprising a calibrated digital output. It can 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 lig
38、ht sensor. SHT11, DS18B20 and TCS320 are both digital sensors with small size and low power 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 determi
39、ned by a jumper.C. Node Software Design The application system consists of a coordinator and 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 act
40、ion of the application is the initialization of the hardware, liquid crystal, stack and application 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 s
41、hown on the LCD. Then program will step into application layer and monitor signal. If there 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
42、 been joined in this network, the data transmitted by this node will be received by coordinator 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
43、 for. It then performs a synchronization and association. Once association is complete, the 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 on
44、ce again and send to coordinator until sending successfully.D. Greenhouse Monitoring Software 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: s
45、etting controlling conditions, setting Timer, setting relevant parameters and showing current status. By setting some parameters, it can perform the functions of communicating with port, data collection and data viewing.1.3 Overview of key issuesCurrent state-of-the-art sensor technology provides a
46、solution to design and develop many types of wireless sen-sor applications. A summary of existing sensor technolo-gies is provided in Appendix A. Available sensors in the market include generic (multi-purpose) nodes and gate- way (bridge) nodes. A generic (multi-purpose) sensor nodes task is to take
47、 measurements from the monitored environment. It may be equipped with a variety of devices which can measure various physical attributes such as light, temperature, humidity, barometric pressure, veloc-ity, acceleration, acoustics, magnetic field, etc.Gateway (bridge) nodes gather data from generic
48、sensors and relay them to the base station. Gateway nodes have higher pro-cessing capability,battery power, and transmission (radio) range. A combination of generic and gateway nodes is typ-ically deployed to form a WSN. To enable wireless sensor applications using sensor tech-nologies, the range of
49、 tasks can be broadly classified into three groups as shown in Fig. 1. The first group is the system. Eachsensor nodeis an individual system.In order to support different application software on a sensor system, develop-ment of new platforms, operating systems, and storage schemes are needed. The second group is communication protocols, which enable communication between the appli-cation and sensors. They also enable communication be-tween the sensor node
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