外文资料
The Greenhou Environment Monitoring System Bad on Wireless Sensor Network
Technology
Ⅰ. INTRODUCTION
Wireless nsor network(WSN) integrates the nsor network techonology, information processing technology and network communication technology with the feature of small size, low cost and easy maintenance, which has a wide application in the area of environment data collection,curity monitoring and target tracking. It compris a great many wireless nsor nodes deployed in the monitoring region, and through wireless communication a multi-hop lf-organizing network system is formed. Its role is to coordinate the perception , acquisition and process of the information of its perceptual objects within the area covered by the network, and returned data to the obrver. At prent, large amount of widely-distributed electronic detection devices and implementing f
acilities are greatly ud in greenhou production , resulting in intertwining cables in the greenhou production . Furthermore , the corresponding location of the installations and facilities should be adjusted when the crops experience evolution successions, and sometimes the cables connecting various devices and facilities should also need to be rearranged, which not only caus the increa of the investment costs of the greenhou and the difficulties of maintenance, but also may affect plant growth. To realize scientifically and rationally automatic detection of the parameters of the greenhou environment, this study introduced a new low-cost and short-range wireless network transmission technology into the Greenhou Monitoring System, and created a greenhou wireless nsor network monitoring system. The monitoring system consists of monitoring and control center , network coordinator and a number of terminal nodes. It could realize speedy and accurate test of greenhou parameters. It has a great uful value in improving the maintainability and space utilization.
Ⅱ. ZIGBEE TEACHNOLOGY
ZiBee is a new wireless communication technology with short distance, low complexity, low energy consumption, show data rate and low lost, and it is bad on IEEE 802. 15.4 standard with the capacity of coordinating mutual communication among thousands of tiny nsors.Through the radio waves, the nsors can transmit the data from one nsor to another with small energy cost and high efficiency. Compared with various existing wireless communication technology, ZigBee technology has the lowest energy consumption and cost. Becau of the slow data rate and the small range of communication, ZigBee technology also make it the best choice for wireless nsor networks. Therefore, it has the practical significance when applied in the crop environmental monitoring system.
跆拳道品势ZigBee has the following features:
ZigBee us a variety of power-saving modes to guarantee that it could be ud for at least six months to two years powered by two AA batteries.
ZigBee us the avoidance collision mechanism in CSMA/CA and pre-t a prior particul纯净近义词
ar time slot for a fixed bandwidth communications rvice in order to avoid competition and conflict when nding data. MAC layer adopts a fully confirmed data transport mechanism, and each packet nt by the receiver must wait for confirmation.
ZigBee has lf-organizing features that one node can n other ones without any human interventions, and connect with each other automatically to create a completed network.
赞美父亲的优美句子It also obtains lf-recovery function that the network can repair itlf when a node is added or deleted, the position of a node is changed, or a breakdown occurred. It also can adjust the topology structure to ensure that the whole system can work normally without any human interventions.
ZigBee protocol is patent-free that the equipment cost is reduced effectively. ZigBee’s working frequency is flexible, namely 2.4GHz licen-free frequency, which means unlimited communication without using fees.
竹子的用途
One ZigBee network can accommodate up to 254 rvo devices and a master device, while more than 200 ZigBee network could exist in one region.
磁盘重新分区
ZigBee supports data integrity and authentication functions, and the encryption algorithm adopts AES-128 function.All applications could determine their own curity properties flexibly.
Ⅲ. THE BUELDING PRINCIPLE OF WIRELESS NETWORK
ZigBee has 3 topology structure which are Star, Cluster tree,and Mesh and 2 physical equipments which are FFD and RFD. FFD is always ud as coordinator of network, lector of router and terminal device for ZigBee in the 3 topology structures. RFD is ud in the terminal device only. The network coordinator’s work is to initialize and update the topology of the network, transmit the network symbol, manage network nodes, store the nodes’ information, provide the associated routing information between nodes and store the data of nodes, etc.In order to nd, receive the routing data, the router should join in the ZigBee network. And then it can allow other router and terminal devices
to connect. The router can nd and receive the data when it joins in to the whole network however the router cannot access other devices join in. Furthermore, the data just only can be nt and received by the master-node not through the router.
ZigBee network is also named ZigBeePAN.When the coordinator is ud for the first time,ZigBee can carry out energy scanning in multiple channels, and after that, it will scan the remaining channels.At the time the coordinator will nd a broadcast that is one-hop symbol request. Any other coordinators and routers nearby will nd the symbol frame to the former coordinator to respond to the symbol request. Beacon frame contains information including the PAN, the PAN identifier, and whether the equipment is allowed to join in the network or not.
