The pace of technological development is getting faster and faster, and human beings are already in the information age. As the most important and basic technology for information acquisition, sensor technology has also been greatly developed. Sensor information acquisition technology has gradually evolved from the past singularity to integration, miniaturization and networking, and will bring an information revolution. Wireless sensor networks (WSN, wirelesssensornetworks) with sensory capabilities, computing capabilities, and communication capabilities integrate sensor technology, embedded computing technology, distributed information processing technology, and communication technology, and can collaboratively monitor, sense, and collect network distribution areas in real time The information of various environments or monitoring objects within the system, and process the information to obtain detailed and accurate information and transmit it to users who need this information.
Due to the huge application value of WSN, it has attracted wide attention from military departments, industry and academia in many countries in the world, and is widely used in military, industrial process control, national security, environmental monitoring and other fields.
The wireless sensor network integrates sensor technology, embedded computing technology, modern network and wireless communication technology, distributed information processing technology and other fields, and is the current research hotspot of computer network.
1. Development Overview
As early as the 1970s, there was a prototype of a sensor network that used traditional point-to-point transmission and connected sensor controllers, and we classified it as the first generation sensor network. With the continuous development and progress of related disciplines, the sensor network also has the comprehensive processing ability to obtain a variety of information signals, and through the connection with the sensor controller, a sensor network with information synthesis and processing capabilities is formed. It is the second generation sensor network. Since the end of the last century, fieldbus technology has been used in sensor networks. People use it to build intelligent sensor networks. A large number of multi-function sensors are used and connected using wireless technology. Wireless sensor networks are gradually formed.
Wireless sensor network is a new generation of sensor network, which has a very broad application prospect. Its development and application will bring far-reaching impact on various fields of human life and production. Developed countries such as the United States attach great importance to the development of wireless sensor networks. IEE (E is working hard to promote the application and development of wireless sensor networks. Boston University (BostonUniversity) also recently established the Sensor China Measurement and Control Network Association (SensorNetworkConsortium), hoping to promote sensors Networking technology development. In the United States, "Technology Review" magazine listed wireless sensor networks as the first future emerging technology when discussing the ten emerging technologies in the future. Among the four new technologies predicted by Business Week, wireless sensors The network is also included. It can be expected that the widespread of wireless sensor networks is an inevitable trend, and its appearance will bring great changes to human society.
Second, the definition and characteristics of wireless sensor networks
The wireless sensor network can be regarded as composed of three parts: data acquisition network, data distribution network and control management center. Its main components are nodes integrated with sensors, data processing units and communication modules. Each node forms a distributed network by itself, and then transmits the collected data to the information processing center through radio waves after optimization. The developer of the wireless sensor network operating system TIny0S141, Dr. Jason Hill defined WSN as: Sensing + CPU + Radio = ThousandsofpotenTIalapplicaTIon
Professor Li Jianzhong of Harbin Institute of Technology defines WSN as: WSN is a wired or wireless network composed of a group of sensor nodes in a self-organized manner. Its purpose is to cooperatively sense, collect and process information of the sensing object in the geographical area covered by the network And publish it to the observer. From the hardware point of view, the WSN node is mainly composed of a data acquisition unit, a data processing unit, a wireless data transceiver unit, and a small battery unit. It is usually small in size and has the characteristics of low cost, low power consumption, and multi-function. From a software perspective, It uses the built-in sensors in the node to effectively detect the environmental parameters such as temperature, humidity, light intensity, pressure and physical parameters such as the voltage and current of the object to be measured, and transmits the detection information to the data aggregation center for processing through the wireless network. , Analysis and forwarding.
WSN has obvious advantages compared with traditional sensors and measurement and control systems. It adopts point-to-point or point-to-multipoint wireless connection, which greatly reduces the cost of cables. It incorporates analog signal / digital signal conversion, digital signal processing and network communication functions at the sensor node. The node has self-checking function, system performance and reliability Significantly improved sex and significantly reduced costs.
The wireless sensor network has the following characteristics:
1. Limited hardware resources. The WSN node uses an embedded processor and memory, and its computing power and storage capacity are very limited. Therefore, it is necessary to solve the problem of how to carry out collaborative distributed information processing under the condition of limited computing power.
2. The power supply capacity is limited. In order to measure the specific values ​​of the real world, each node will be densely distributed in the area to be measured, and the method of artificial energy supplementation is no longer applicable. Each node must reserve energy for long-term use, or draw energy from itself (solar energy). When the energy of the battery carried by itself is exhausted, it is often discarded, and even the network is interrupted. Therefore, any WSN technology and protocol research must be based on energy saving.
3. No center. In the wireless sensor network, the status of all nodes is equal, there is no pre-specified center, it is a peer-to-peer network. The nodes coordinate with each other through a distributed algorithm. In the case of unattended operation, the nodes can automatically organize a measurement network. And because there is no center, the network will not be damaged by the detachment of a single node. Nodes can join or leave the network at any time. The failure of any node will not affect the operation of the entire network and is very resistant to destruction.
4. Self-organization. The network deployment and deployment do not depend on any preset network facilities. Nodes coordinate their respective behaviors through layered protocols and distributed algorithms. After the nodes are turned on, they can quickly and automatically form an independent network.
5. Multi-hop (MulTI-hop) routing. WSN nodes have limited communication capabilities, covering only tens to hundreds of meters, and nodes can only communicate directly with their neighbors. If you want to communicate with nodes outside its radio frequency coverage, you need to route through intermediate nodes. Multi-hop routing in WSN is done by ordinary network nodes.
6. Dynamic topology. WSN is a dynamic network, and nodes can move around; a node may quit the network due to battery exhaustion or other failures; it may also be added to the network due to work needs. These will make the topology of the network change at any time, so the network should have the function of dynamic topology organization.
7. The number of nodes is large and the distribution is dense. The number of WSN nodes is large and the distribution range is wide, making it difficult to maintain or even unmaintainable. Therefore, it is necessary to solve how to improve the robustness and fault tolerance of the sensor network.
8. Limited transmission capacity. The wireless sensor network performs data transmission through radio waves. Although it saves the trouble of wiring, low bandwidth becomes its inherent defect compared to the wired network. At the same time, there is mutual interference between the signals, the signal itself is constantly attenuating, and so on. However, because the amount of data transmitted by a single node is not too large, this shortcoming can still be tolerated.
9. Security issues. Wireless channels, limited energy, and distributed control make wireless sensor networks more vulnerable to attacks. Passive eavesdropping, active intrusion, and denial of service are common methods of these attacks. Therefore, security is crucial in the design of the network.
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