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Zigbee无线传感器网络英文文献只是分享.pdf
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Zigbee无线传感器网络英文文献只是分享.pdf
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Zigbee Wireless Sensor Network in Environmental Monitoring
Applications
I. ZIGBEE TECHNOLOGY
Zigbee is a wireless standard based on IEEE 802.15.4 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 reliable, highly secure wireless networking protocol
targeted towards automation and remote control applications. It’s depicts two key
performance characteristics – wireless radio range and data transmission rate of the wireless
spectrum. Comparing to other wireless networking protocols such as Bluetooth, 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 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 operate 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. Zigbee’s Topology
The 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
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is responsible for initiating and maintaining the devices on the network. All other devices,
known as end devices, directly 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 the 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
network, 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 join or leave it. Moreover, it can provide binding and
address-table services, and save messages until they can be delivered.
Fig.3 Zigbee network model
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II. THE GREENHOUSE ENVIRONMENTAL MONITORING
SYSTEM DESIGN
Traditional 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 sensors instead of wire
connection, which couldn’t 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 basement. 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 growing 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 environmental 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, humidity 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 WSN, 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 download 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.
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