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Mr Chairman

时间:2012-04-19


Mr Chairman,representatives: I am very glad to have the opportunity to report my research on such an occasion.What I am going to talk about is a WSN-based greenhouse environment monitoring system.I will give this talk in three parts.the first part deals with design background.the second part concerns WSN technology.and then the last part is related to system design.now let us focus on the first part.

People usually use greenhouse for cultivation in low temperature seasons.traditional GEMS adopts wire-connection to realize the communication between sensors and data acquisition ,which has caused complicated on-site deployment , wiring,poor mobility of devices,and high cost wireless sensor networks comprise of spatially distributed autonomous devices which collect datas using a wireless medium.compared to their wired counterparts,WSNs exhibit several unique properities such as large scale of deployment,mobility of nodes, temporary installations, dynamic network topologies.

Zigbee is a wireless standard based on IEEE802.15.4.it is low cost,low power,highly reliable,highly secure . Fig.2 depicts two key performance characteristics – wireless radio range and data transmission rate of the wireless spectrum. Comparing to other wireless networking protocols ,ZigBee shows excellent transmission ability in lower transmission rate and highly capacity of network. .ZigBee meet the requirements for reliability,security,low costs and low power-consumption in the GEMS.

ZigBee framework is made up of a set of blocks called layers. As shown in Fig.3. The IEEE 802.15.4 standard defines the two lower layers: the physical (PHY) layer and the medium access control (MAC) layer. The ZigBee Alliance builds on this foundation by providing the network and security layer and the framework for the application layer .

Fig.5 is a ZigBee network model, it supports both single-hop star topology and mesh topology. Coordinator manages the network, it can provide binding and address-table services, and save messages until they can be delivered.

In this project ,we deploy five kinds of sensors in the greenhouse basement .through these deployed sensors, temperature,soil temperature,dew point,humidity and light intensity can be detected real time.figure is the overview of GEMS.when sensor nodes collect parameters real time,coordinator completes the task of data analysis and storage,menawhlie ,it is connected with GPRS/CDMA.In the monitoring center,by running greenhouse management software,coordinator can periodically receive data from the wireless sensor nodes and display them on monitors.

Figure shows the universal structure of 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.communication module is used to tranmit data between nodes.

In the data transfer unit,the ZigBee module is embeded to match the MAC layer and the NET layer.we choose CC2430 as the ZigBee protocol chips,which ingegrated the CPU,RF transceiver,net protocol and the RAM together.The SHT11 can test the soil temperature and humidity.the DS18B20 is a digital temperature sensor,which has 3 pins and data pin .the TCS320 is a digital light sensor.these sensor nodes are powered by onboard batteries The figure show the software flow of coordinator.once started,the first action is the initialization of the hardware,satck and application variables.then a network will be formatted.and then physical address ,net ID,channel number will be showen on the LCD.then program will step into application layer and monitor ZigBee signal.if there is end device or router want to join in this net, LCD will show this information,the coordinator will allocate a net address.and the data transmitted by this node will be received by coordinator and shown in the LCD Figure show 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 it is looking 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 colletc data noce again and sent to coordinator.

Currently,we have carried out experimental deployment of GEMS in the intelligent greenhouse.as shown in figure,at different times.there is distinct difference for light intensity and soil temperature monitored respectively for the nodes deployed at different locations. GEMS has the advantages of low cost,low power and easy maintenance. It can collect important environment factors which influence plants’growth.it also realizes the wide area transmission of the information.there is still room for improving the system functionality and increasing the practicality of the system.the future work includes the following firsr,According to the actual application requirement, we will monitor other environment factors which influence crop's growth, thus realizing a more systematic and comprehensive monitoring of the greenhouse environment. 2. Carry out reliability analysis and accelerated fatigue testing on GEMS. By establishing reliability model, we can realize the system fault pre-warning and predict the residual life. That is all, thank you ,ladies and gentleman.


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