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1、A wireless solution for greenhouse monitoring andA wireless solution for greenhouse monitoring andcontrol systembased on ZigBee technologycontrol systembased on ZigBee technologyZHANG Qian， YANG Xiang-long， ZHOU Yiming,WANG Li-ren, GUO XishanAbstractAbstract：With the rapid development of wireless te
2、chnologies，it is possiblefor Chinese greenhouses to be equipped with wireless sensor networks due totheir lowcost, simplicity and mobility。 In the current study, we compared theadvantages of ZigBee with other two similar wireless networking protocols，Wi-Fi and Bluetooth， and proposed a wireless solu
3、tion for greenhousemonitoring and control system based on ZigBee technology. As an explorativeapplication of ZigBee technology in Chinese greenhouse, it may promoteChinese protected agriculture.KeyKey words:words: Greenhouse, Monitoring and control ，Wireless, ZigBee,IEEE802。15.4, JN5121INTRODUCTIONI
4、NTRODUCTIONWireless technologies have been rapidly developed during recent years。Starting from military and industrial controls, it is now being widely applied inenvironmental monitoring and agriculture. Its advantages include the liability，simplicity, and low cost in both installation and maintenan
5、ce 。 In greenhousecontrol applications, Serodio et al.（1998; 2001) developed and tested asimilarly distributed data acquisition and control system for managing a set ofgreenhouses. Inside each greenhouse， a WLAN network with a radiofrequency of 433。92 MHz was used to link a sensor network to a local
6、controller. Morais et al。(1996） implemented a wireless data acquisitionnetwork to collect outdoor and indoor climate data of greenhouses in Portugal.Mizunuma et al。 （2003） deployed a WLAN in a farm field and greenhouse tomonitor plant growth and implemented remote control for the productionsystem. M
7、ancuso and Bustaffa （2006) worked at a short-term deployment ofa wireless sensors network in a tomato greenhouse in the south of Italy.In China， Liu and Ying (2003） reported a greenhouse monitoring andcontrolsystemusing theBluetoothtechnology.Thesystemcollectedenvironmental data from a sensor networ
8、k in a greenhouse and transmittedthem to a central control system。 Qiao et al。 （2005） introduced systematicframes of wirelesssensor networks and expatiated their agricultural applications such asmonitoring greenhouse, irrigation, precision farming and so on. Luo et al。(2006) designed wireless sensor
9、s for greenhouse monitoring 。 The wirelesscommunication was based on nRF401 wireless module， working at 433 MHzISM frequency. Wu et al。（2006） reported the design and implementation ofGreenhouse Wireless Data Acquisition System based on CC2420, as alow-cost transceiver designed specifically for low-p
10、ower, lowvoltage RFapplications at the 2。4 GHz unlicensed ISM band。 Li et al.（2007) reviewedcable and wireless communications used in agriculture ， and compared theiradvanadvantages and disadvantagesWireless sensor technology， however， is still at its early developmentphase in China， and its applica
11、tions in Chinese greenhouses remain few. Inthe current study, we compare the advantages of ZigBee with two similarwireless communications, Wi-Fi and Bluetooth, and propose a wirelesssolution forgreenhouse monitoring and control system based on ZigBee technologyCOMPARISON OF ZIGBEE, WI-FICOMPARISON O
12、F ZIGBEE, WI-FI， AND BLUETOOTHAND BLUETOOTHPROTOCOLSPROTOCOLSWi-Fi, Bluetooth and ZigBee work at similar RF frequencies， and theirapplications sometimes overlap （Seager, 2006）. In the current study, wechose the following five main factors of greenhouse networks to compare:cost， data rate, number of
13、nodes， current consumption and battery life（1) Cost。ZigBee chip is US 1 or less, the lowest；Wi-Fi and Bluetoothchips are 4 and 3， respectively. The overall system cost can besignificantly reduced by the employment of ZigBee chip。（2） Data rate. ZigBee is 250 kbps, while WiFi and Bluetooth are 54Mbps
14、and 12 Mbps， respectively。 Despite the lowest data rate， ZigBee issufficient for a greenhouse. Generally, data traffic in a greenhouse islowusually small messages such as the change of temperature or acommand from the controller to an actuator。 And also, low data rate helps toprolong the battery lif
15、e。（3) Number of nodes. The capacity of network is determined by thenumber of nodes, and ZigBee has up to 254 nodes， the largest among thethree. It meets the application demand of more and more sensors andactuators in a greenhouse.（4） Current consumption。 ZigBee has the lowest current consumption,30
16、mA， while Wi-Fi, 350 mA, and Bluetooth， 65170 mA。 It also greatlyhelps toprolong the battery life.(5） Battery life。 ZigBee chip has the longest battery life, a few months oreven years。As a whole， ZigBee technology offers long battery life, small size， highreliability, automatic or semi-automatic ins
17、tallation， and, particularly, a lowsystem cost. Therefore, it is a better choice for greenhouse monitoring andcontrol than other wireless protocolsOUR WIRELESS SOLUTION FOR GREENHOUSEOUR WIRELESS SOLUTION FOR GREENHOUSEOverview of the solutionOverview of the solutionAs shown in Fig.1， wireless senso
18、rs， such as temperature sensor，humidity sensor， light sensor and so on (integrated with PIC 16F877 andZigBee module)， collect the environmental information and transmit it tohand-held controller (HHC） （integrated with ARM MCU and ZigBee module） .In HHC， thedata is stored and displayed on the LCD。 Af
19、ter the data being dealt throughcontrol algorithm, the HHC sends control commands to the actuators (alsointegrated with PIC 16F877 and ZigBee module)。 The actuators accomplishthe actual control task. All the wireless nodes are based on ZigBee module.We designed the nodes based on JN5121 module produ
20、ced by JennicCompany （Jennic Ltd。， 2006a）.The JN5121 is the first in a series oflowpower，low-cost IEEE802.15.4 compliant wireless microcontrollers， combining anonchip 32bit RISC (Reduced Instruction Set Computing) core, a fullycompliant 2。 4 GHz IEEE802。 15。 4 transceiver，64 kB ROM and 96 kB RAM。The
21、 high level of integration helps to reduce the overall system cost。 TheJN5121 connects upper controller and sensors/actuators through SPI (SerialPeripheral Interface) or parallelNetwork establishmentSinem Coleri Ergen （2004） summarized three types of topologies ofZigBee: star topology, peer-topeer t
22、opology and cluster tree topology. In thestar topology，the communication is established between devices and a singlecentral controller, called the PAN (Personal Area Network) coordinator. ThePAN coordinator may be mains powered， while the devices are most likelybattery-powered。 Each star network cho
23、oses a PAN identifier, which is notcurrently used by any other network within the radio sphere of influence。Thisallows each star network to operate independently.In our project， we established the network according to the star topology。As shown in Fig.2, once the HHC (FFD，Full Function Device）is act
24、ivated forthe first time， it establishes its own network and becomes the PANcoordinator. Then it initializes the hardware, stack and application variables，choosing an unused PAN identifier of zero， and broadcasting beacon framesto sensors and actuators (RFD， Reduced Function Device)。 Sensors andactu
25、ators receiving a beacon frame may request to join the network。 TheHHC will add them as a child device in its neighbor list and return a response.The sensors and actuators will add the HHC as its parent in their neighbor listand return an acknowledgement。 The HHC monitors all network nodes inrealtime, maintaining the network information database PIB
