WSN system is a new type of information acquisition system composed of wireless sensor nodes, aggregation nodes, data processing centers and data browsing centers. The sensor node collects all kinds of information in the physical world, and then realizes the exchange and aggregation of information through special network protocols. After that, the information in the physical world is aggregated in the network database server through Internet, GPRS and GSM. In this way, the information of the physical world completely into the information world. The end information users can obtain the information anytime and anywhere through browsers, mobile phones and PDAs. Such a system could greatly expand people’s ability to perceive and understand the world.

1) WSN structure composition

WSN refers to a network of sensor nodes arranged in the physical environment organized by wireless communication. Sensor nodes are used to complete data collection, and send data to the network through the sensor network, and finally received by a specific application system.

The hierarchical structure of WSN is usually divided into physical layer, data link layer, network layer, transport layer and application layer.

(1) The physical layer defines the physical parameters of the communication between the base station (Sink) and the node (Node) in the WSN, such as which frequency band to use and which signal modulation and demodulation method to use.

(2) The data link layer defines the initialization of each node, completes its own network definition by sending and receiving messages such as Beacon, Request, and Associate, and defines the debugging strategy of the data link layer (MAC) frame. , to avoid communication conflicts between multiple sending and receiving nodes.

(3) The network layer is responsible for completing the collection of logical routing information, so that the sending and receiving network data packets can reach the target node through the optimal path according to different strategies.

(4) The transport layer provides the reliability of data packet transmission and provides the entry for the application layer.

(5) The application layer finally integrates the collected node information to meet the computing needs of different applications.

The typical hardware structure of WSN node mainly includes battery and power management circuit, sensor, signal conditioning circuit, AID converter, memory, microprocessor and radio frequency module. The node is powered by a battery, and once the power is exhausted, the node loses its ability to work. In order to save power to the greatest extent, in terms of hardware design, it is necessary to use low-power devices as much as possible. When there is no communication task, the power supply of the radio frequency part should be cut off: In terms of software design, each layer of communication protocols should focus on energy conservation, and when necessary Some other network performance metrics can be sacrificed for higher power efficiency.

2) WSN networking structure

WSN usually has two networking structures such as flat topology structure and logical hierarchical structure. In a flat topology, all network nodes are in the same and equal status, and there is no level and level difference, so it is also called a peer-to-peer structure: network nodes in a logical hierarchical structure are based on certain rules (such as geographic location, application requirements, etc.). etc.) are divided into clusters, each cluster consists of a cluster head and member nodes.

3) WSN node structure

In order to meet the requirements of various existing wireless and wired network technologies and protocols, the standard and non-standard signals output by various sensors are converted into signals required by the network, and corresponding node technologies and node products are produced. In the basic structure of the WSN node, it includes a sensing unit (consisting of sensors and A/D converters), a processing unit (including a processor, memory, embedded operating system, etc.), a wireless communication unit (consisting of wireless network, MAC and transceiver) and energy unit, etc. In addition, other functional units that can be selected include a positioning system, a mobile system, and a self-powered power supply system. In the nodes of WSN, in addition to the processing unit and the wireless communication unit, the most important thing is the energy unit, which determines the overall life cycle of the sensor. The requirements for the energy unit are small size, no pollution, low cost, and good discharge characteristics. and environmental adaptability. The characteristics of node technology and network technology are high technical content, complex standards, good existing foundation, and a relatively high possibility of achieving large enterprises, especially under the conditions of continuous expansion of the market.

In WSN, nodes can be deployed in a large number in or near the sensed object by means of aircraft distribution or manual arrangement. These nodes form a wireless network through self-organization, and cooperate to sense, collect and process network coverage in real time. For the information in the area, the data information in the area is transmitted to the remote control management center (the user management module in the Savant system) through the receiver and transmitter through the multi-hop network. In addition, the remote control management center can also control and operate the network nodes in real time.

Responsible editor: haq

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