Since the beginning of the 21st century, with the rapid development of perceptual recognition technology, information automatic generation devices represented by sensors and intelligent identification terminals can sense, measure and monitor the physical world in real time. The development of microelectronics, computer technology and wireless communication technology has promoted the rapid development of low-power, multi-function sensors, and has now developed miniature sensors with sensing capabilities, computing capabilities and communication capabilities. The networking needs of the physical world and the expanding needs of the information world have created a new type of network—sensor networks (abbreviated as sensor networks).
Sensor network integrates sensors, embedded computing, micro-electromechanical, modern network and wireless communications, information processing and other technologies, across the computer, semiconductor, embedded, network, communications, optics, micro-mechanics, chemistry, biology, aerospace, medicine Many fields, such as agriculture, can enable people to obtain a large amount of accurate and reliable information at any time, place and in any environment, so as to truly realize ubiquitous computing concepts. Sensor network is a new type of information acquisition and processing technology. It changes the way humans interact with nature and expands the human ability to recognize the world. US Business Weekly believes that sensor network is one of the world's next four high-tech industries and one of the 21 most influential 21 technologies in the 21st century. In 2003, MIT's Technical Review magazine listed sensor networks as the top ten emerging technologies that have a profound impact on the future of human life.
The sensor network is composed of a large number of sensor nodes with wireless communication and computing capabilities deployed in the active area. These nodes constitute a sensor network through self-organization. The purpose of the sensor network is to cooperatively perceive, collect, and process sensor information in the geographical coverage of the network. And released to the observer.
Sensor node architectureThe sensor node is a basic component of the wireless sensor network. According to different application requirements, the specific requirements that the sensor node must meet are also different. Sensor nodes may be small, inexpensive or energy-efficient, must be equipped with suitable sensors, have the necessary computing and storage resources, and require adequate communication facilities [6, 7]. A typical sensor node consists of a sensing unit, a processing unit (including processor and memory), a communication unit, an energy supply unit, and other application-related units. The architecture of the sensor node is shown in Figure 1-1.
In Figure 1-1, the sensing unit is mainly used to collect various information in the real world, such as temperature, humidity, pressure, sound, and other physical information, and converts the analog information collected by the sensor into digital information and sends it to the processing unit. deal with. The processing unit is responsible for the data processing and operation of the entire sensor node, storing the collected data of the node and the data sent by other nodes. The communication unit is responsible for wireless communication with other sensor nodes, exchanging control messages, and sending and receiving data. The energy supply unit provides the energy required for the operation of the sensor node and is one of the most important units of the sensor node. In addition, in order to accurately locate the nodes and manage the mobile state, the sensor nodes need corresponding application support units, such as a location search unit and a mobile management unit.
The sensor node is usually a miniature embedded system, and its processing power, storage capacity and communication capacity are limited. Nodes need to work properly and require the close cooperation of hardware and software systems. The composition of the hardware system refers to Figure 1-1. The software system consists of five basic software modules, which are the operating system (OS) microcode, sensor driver, communication processing, communication driver, and data processing mini-app software module. All software modules of the OS microcode control node support various functions of the node. TinyOS is an operating system designed specifically for embedded wireless sensor networks. The sensor driver module manages the basic functions of the sensor transceiver; in addition, the type of the sensor may be a module or a plug-in type. According to the different types and complexity of the sensor, the module also needs to support the corresponding configuration and setting of the sensor. The communications processing module manages communications functions including routing, packet buffering and forwarding, topology maintenance, media access control, encryption, and forward error correction. The communication driver module manages the radio channel transmission links, including clock and synchronization, signal encoding, bit count and recovery, signal classification, and modulation. The data processing mini-app module supports node data processing, including the storage and operation of signal values ​​or other basic applications.
Sensor network network structureThe sensor network consists of a large number of sensor nodes, and the nodes communicate with each other through wireless transmission. A typical sensor network architecture is shown in Figure 1-2 and typically includes sensor nodes, aggregation nodes, and task management nodes. Sensor nodes are scattered within the monitoring area. These nodes can collect data, analyze the data, and route the data to a specified aggregation node.
The sensor nodes form a network through self-organizing, and can intelligently adopt different network topology structures as required. The monitoring data of the sensor node may be processed by multiple nodes, usually hop by hop along other nodes in a multi-hop manner, and after routing to other intermediate nodes for data fusion and forwarding to reach the convergence node, and finally reach users through the Internet or satellites. Operational task management nodes, task management nodes can configure and manage sensor networks.
The computational and storage capacity of the sensor node is weak, and the communication bandwidth is narrow. The battery is powered by its own battery, so the energy is limited. The sensor node not only needs to process the local information, but also stores, manages, merges, and forwards the data forwarded by other nodes. The aggregation node's processing capability, storage capacity, and communication capability are relatively strong. It is mainly responsible for sending the task management node's monitoring task, collecting data and forwarding it to the Internet and other external networks to realize the communication between the sensor network and the external network. The aggregation node can be a sensor node with enhanced capabilities, with more memory, computing resources, and energy provision, or it can be a special gateway device with only a wireless communication interface.
Sensor networks are often deployed in unattended, harsh environments or areas that are out of reach of the body, so networks need to be self-maintaining. When some nodes of the network fail due to intrusion, failure, or battery depletion, they cannot affect major tasks such as data transmission and network monitoring.
Sensor network node compositionSensor node
The processing power, storage capacity, and communication capabilities are relatively weak and are powered by small capacity batteries. The sensor node is composed of a large number of inexpensive miniature sensor modules deployed near the sensing object. Its purpose is to cooperatively sense, collect, and process the information of the sensing object in the network coverage area and send it to the aggregation node. Each module forms a multi-hop self-organizing network system through wireless communication, and the data collected by the sensor nodes is transmitted hop by hop along other sensor nodes to the convergence node. A WSN system usually has a large number of small, low-cost sensor nodes. From the aspect of network functions, each sensor node not only performs local information collection and data processing, but also stores, manages, and merges the data forwarded by other nodes, and cooperates with other nodes to complete certain tasks.
Aggregation node
The aggregation node's processing capability, storage capacity, and communication capability are relatively strong. It is a gateway that connects the sensor network and the external network such as the Internet, realizes the conversion between the two protocols, and simultaneously issues monitoring tasks from the management node to the sensor nodes. The data collected by the WSN is forwarded to the external network. The aggregation node can be either a sensor node with enhanced functions, enough energy supply and more, all information in the Flash and SRAM is transferred to the computer, and the acquired information can be conveniently converted into assembly by the assembly software. The file format is used to analyze confidential information such as program code, routing protocol, and key stored in the sensor node. At the same time, the program code can be modified and loaded into the sensor node.
Management node
The management node is used to dynamically manage the entire wireless sensor network. The owner of the sensor network accesses the resources of the wireless sensor network through the management node.
Phase 1: Military sensor networks during the Cold War
During the Cold War, the United States used expensive acoustic networks to monitor submarines. At the same time, the National Oceanic and Atmospheric Administration of the United States used some of these sensors to monitor ocean seismic activity.
Phase 2: DARPA Initiative
In the early 1980s, the research of sensor networks made significant progress under the support of the US Department of Defense Advanced Research Projects Agency (DARPA) funded project. On the premise that there are many low-cost spatially distributed sensor nodes, distributed sensor networks (DSNs) operate in a self-organizing, cooperative manner to determine whether the newly developed TCP/IP protocol can be used in the sensor network. The ARPA network (the predecessor of the Internet) comes in a way to communicate.
Phase 3: Military Application Development and Deployment in the 1980s and 1990s
In the 1980s and 1990s, based on the DARPA-DSN research and experimental platform, sensor network technology was used in the military field, making it a key component of the network center battle. Sensor networks can improve detection and tracking performance through multiple observations, extended detection ranges, and faster response times.
Phase 4: Today's sensor network research
In the late 1990s and early 2000s, the development of computing and communications led to the emergence of a new generation of sensor network technologies. Standardization is the key to any large-scale deployment of technologies, including wireless sensor networks. With the development of IEEE 802.11a/b/g wireless networks and other wireless systems such as ZigBee, reliable connections have become ubiquitous. The emergence of low-power, low-cost processors allows sensors to be deployed in more applications.
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