(1) Large-scale
In order to obtain accurate information, many sensor nodes are usually arranged in the monitoring area, perhaps in the tens of thousands, or even more. The large-scale nature of the sensor network contains two implications: on the one hand, the sensor nodes are distributed in a large geographical area, such as the selection of sensor networks for forest fire prevention and environmental monitoring in the primeval forest, and the need to arrange a large number of sensor nodes; On the other hand, the sensor nodes are densely arranged, and in a small space, a lot of sensor nodes are densely arranged.
The large-scale nature of sensor networks has the following advantages: the information obtained through different spatial perspectives has a larger signal-to-noise ratio; The accuracy of monitoring can be improved by distributing a lot of collected information, and the accuracy requirements for a single node sensor can be reduced. The existence of many redundant nodes makes the system have strong fault tolerance. Many nodes can increase the area of masked monitoring, reducing caves or blind spots.
(2) Self-organization
In the application of sensor network, under normal circumstances, the sensor node is placed in a place without infrastructure, the orientation of the sensor node cannot be set accurately in advance, and the mutual neighborhood connection between the nodes is not known in advance, such as spreading many sensor nodes into a vast area of primeval forest through aircraft, or randomly placed in areas that are inaccessible or risky to people. In this way, the sensor node is required to have the ability to self-organize, can actively configure and manage, and actively form a multi-hop wireless network system for forwarding monitoring data through the topology control mechanism and network protocol.
In the process of sensor network application, some sensor nodes fail due to energy exhaustion or environmental elements, and some nodes are supplemented to the network in order to compensate for the failure nodes and add monitoring accuracy, so that the number of nodes in the sensor network is dynamically increased or reduced, so that the topology of the network is dynamically changed. The self-organization of sensor networks needs to be able to adapt to the dynamic changes in this network topology.
Dynamics
The topology of the sensor network may be changed due to the following elements: (1) the failure or failure of the sensor node caused by the exhaustion of environmental elements or power consumption; (2) changes in environmental conditions may result in changes in the bandwidth of wireless communication links, or even intermittent and time-to-time connections; (3) the sensors, sensing objects, and observers of the sensor network may all be mobile; (4) Participation of new nodes. This requires that the sensor network system can adapt to this change and have dynamic system reconfigurability.
reliability
WSN is particularly suitable for locations in harsh environments or areas that are inaccessible to humans, and nodes may work in the open air, exposed to sun, wind, rain, or even damage by humans or animals. Sensor nodes are often randomly arranged, such as by airplanes spreading or firing artillery shells into a designated area. All of this requires sensor nodes to be extremely robust, not easily damaged, and able to withstand a wide range of harsh environmental conditions.
Due to the constraints of the monitoring area environment and the huge number of sensor nodes, it is not possible to manually "take care" of each sensor node, and the protection of the network is difficult or even impossible. The confidentiality and security of the communication of the sensor network is also important to avoid the theft of monitoring data and the acquisition of fake monitoring information. Therefore, it is necessary for the software and hardware of sensor networks to be robust and fault-tolerant.
Data-centric
The Internet first has a computer terminal system, and then interconnects it into a network, and the terminal system can exist independently from the network. In the Internet, network devices are identified by a unique IP address in the network, and resource positioning and information transmission depend on the IP addresses of network devices such as terminals, routers, and servers. If you want to access a resource on the Internet, you must first know the IP address of the server where the resource is stored. It can be said that the existing Internet is an address-centric network.
Sensor networks are task-oriented networks, and there is no meaning in talking about sensor nodes apart from sensor networks. The nodes in the sensor network are identified by the node number, and whether the node number needs to be network-specific depends on the planning of the network communication protocol. Because the sensor nodes are randomly arranged, the connection between the sensor network and the node number is completely dynamic, which means that the node number is not necessarily related to the node orientation. When a user uses a sensor network to query things, they communicate the things they care about directly to the network, rather than to a node with a certain number. The network reports to the user after obtaining information about the specified thing. This kind of thinking, which uses the data itself as a clue for query or transmission, is closer to the habit of natural language communication. So generally speaking, the sensor network is a data-centric network.
For example, in a sensor network used for policy tracking, the tracking policy may be displayed anywhere, and the user who is interested in the policy only cares about the direction and time when the policy is presented, and does not care which node detects the policy. In fact, in the process of policy movement, the direction of the policy must be supplied by different nodes.
Wireless sensor network security issues
Secure routing
Generally, in the wireless sensor network, many sensor nodes are densely distributed in a region, and the audio may need to pass through several nodes to reach the destination, and the sensor network has a dynamic and multi-hop structure, requiring each node to have a routing function. Because each node is a potential routing node, it is more vulnerable to attacks and makes the network insecure. The network-layer routing protocol believes that the entire wireless sensor network provides key routing services, and the secure routing algorithm will directly affect the security and availability of the wireless sensor. Secure routing protocols generally use mechanisms such as link-layer encryption and authentication, multi-path routing, careful identity, two-way connection authentication, and authentication broadcasting, which can effectively improve the network's ability to resist external attacks and enhance the security of routing.
Security protocols
In terms of security assurance, there are two main methods: key management and security multicast.
Key management: Wireless sensor networks have many constraints, such as node constraints, so that they can only use symmetric key and technology; The power supply can be constrained, and the communication should be reduced as much as possible in the wireless sensor network, because the power consumption of communication will be greater than the calculated power consumption; Sensor networks should also consider issues such as aggregation to reduce data redundancy. In general, the pre-configured key plan calculates the session key through the pre-stored secret information, because of the constraints of node storage and energy, it is necessary to save storage space and reduce communication overhead for the pre-configured key management plan.
Secure communication: In order to prevent suppliers from injecting fake information into the network, secure multicast based on source-side authentication is required in the wireless sensor network.
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