With the development of society and modern technology, the Internet of Things (IoT) has emerged and attracted the attention of many countries and people. The IoT is developed based on the existing internet. In addition to integrating networks, RFID technology, and information technology, it also introduces wireless technology, enabling deeper development of M2M (machine-to-machine) IoT. Furthermore, wireless sensor technology combines embedded system technology, sensor technology, modern networks, and wireless communication technology, making it a hot research area in itself. Today, we'll learn about wireless sensor networks.
Wireless sensor networks (WSNs) are distributed sensor networks whose endpoints are sensors capable of sensing and inspecting the external world. Sensors in a WSN communicate wirelessly, allowing for flexible network setup, easy relocation of devices, and wired or wireless connections to the internet. It forms a multi-hop, self-organizing network through wireless communication.
Wireless sensor network architecture
Wireless sensor network systems typically include sensor nodes, sink nodes, and management nodes.
A large number of sensor nodes are randomly deployed within or near the monitoring area, forming a network through self-organization. Data detected by each sensor node is transmitted sequentially along the path of other sensor nodes. During transmission, the data may be processed by multiple nodes, routed through multiple hops to a convergence node, and finally reach the management node via the internet or satellite. Users configure and manage the sensor network and publish monitoring data through the management node.
Sensor Networks
It has limited processing, storage, and communication capabilities and is powered by a small-capacity battery. In terms of network functionality, each sensor node, in addition to collecting and processing local information, must also store, manage, and fuse data forwarded from other nodes, and collaborate with other nodes to complete specific tasks.
aggregation node
The aggregation node has relatively strong processing, storage and communication capabilities. It is a gateway connecting the sensor network and the external Internet, realizing the conversion between the two protocols, issuing monitoring tasks from the management node to the sensor nodes, and forwarding the data collected by the WSN to the external network.
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.
Key features of wireless sensor networks
large-scale
To obtain accurate information, a large number of sensor nodes are typically deployed in the monitoring area, potentially reaching tens of thousands or even more. The large scale of sensor networks has two aspects: firstly, the sensor nodes are distributed over a large geographical area, such as in a vast virgin forest where a large number of sensor nodes are needed for forest fire prevention and environmental monitoring; secondly, the sensor nodes are deployed very densely, with a large number of sensor nodes densely deployed in a relatively small space.
The large scale of sensor networks has the following advantages: information obtained from different spatial perspectives has a higher signal-to-noise ratio; distributed processing of a large amount of collected information can improve the accuracy of monitoring and reduce the accuracy requirements of individual sensor nodes; the presence of a large number of redundant nodes gives the system strong fault tolerance; a large number of nodes can increase the coverage monitoring area and reduce caves or blind spots.
Self-organization
In sensor network applications, sensor nodes are typically placed in locations without infrastructure. Their locations cannot be precisely predetermined, and the neighbor relationships between nodes are unknown beforehand. Examples include deploying a large number of sensor nodes from airplanes into vast virgin forests or randomly placing them in inaccessible or dangerous areas. This necessitates that sensor nodes possess self-organizing capabilities, automatically configuring and managing themselves, and automatically forming a multi-hop wireless network system for forwarding monitoring data through topology control mechanisms and network protocols.
During the use of sensor networks, some sensor nodes fail due to energy depletion or environmental factors, while other nodes are added to the network to compensate for the failed nodes and increase monitoring accuracy. This results in a dynamic increase or decrease in the number of nodes in the sensor network, causing the network topology to change dynamically. The self-organizing property of a sensor network must be able to adapt to these dynamic changes in network topology.
Dynamism
The network topology may change due to the following factors:
① Sensor node failure or malfunction caused by environmental factors or power depletion;
② Changes in environmental conditions may cause changes in the bandwidth of wireless communication links, or even intermittent connection;
③The three elements of a sensor network—the sensor, the object being sensed, and the observer—may all be mobile;
④ The addition of new nodes. This requires the sensor network system to be able to adapt to such changes and have dynamic system reconfigurability.
reliability
WSNs are particularly well-suited for deployment in harsh environments or areas inaccessible to humans. Nodes may operate in open-air conditions, exposed to sunlight, wind, rain, and even damage from people or animals. Sensor nodes are often deployed randomly, such as by aerial seeding or artillery shelling to designated areas. All of these require sensor nodes to be extremely robust, resistant to damage, and adaptable to various harsh environmental conditions.
Due to the limitations of the monitoring area environment and the sheer number of sensor nodes, it is impossible to manually maintain each sensor node, making network maintenance extremely difficult, if not impossible. The confidentiality and security of sensor network communication are also crucial to prevent the theft of monitoring data and the acquisition of falsified monitoring information. Therefore, the hardware and software of sensor networks must be robust and fault-tolerant.
Data-centric
The Internet originated from computer terminal systems that were then interconnected to form a network. These terminal systems can exist independently of the network. In the Internet, network devices are identified by unique IP addresses. Resource location and information transmission rely on the IP addresses of network devices such as terminals, routers, and servers. To access resources on the Internet, one must first know the IP address of the server storing those resources. Therefore, the current Internet can be considered an address-centric network.
Sensor networks are task-oriented networks; discussing sensor nodes without considering the sensor network itself is meaningless. Nodes in a sensor network are identified by node numbers, and whether these numbers need to be unique across the entire network depends on the design of the network communication protocol. Because sensor nodes are randomly deployed, the relationship between the sensor network and the node numbers is completely dynamic, meaning there is no necessary correlation between node numbers and node locations. When a user queries an event using a sensor network, they directly notify the network of the event they are interested in, rather than notifying a node with a specific number. The network then reports the information to the user after receiving the specified event. This approach, using data itself as the query or transmission clue, is closer to the conventions of natural language communication. Therefore, sensor networks are generally considered data-centric networks.
For example, in sensor networks used for target tracking, the target may appear anywhere. Users interested in the target only care about its location and time of appearance, not which node detected it. In fact, as the target moves, different nodes must provide the target's location information.
Wireless sensor network security issues
Secure routing
In wireless sensor networks (WSNs), a large number of sensor nodes are densely distributed within an area. Messages may need to pass through several nodes to reach their destination. Furthermore, sensor networks are dynamic and multi-hop structures, requiring each node to have routing capabilities. Since each node is a potential routing node, it is more vulnerable to attacks, making the network insecure. Network layer routing protocols consider the entire wireless sensor network to provide critical routing services; secure routing algorithms directly impact the security and availability of wireless sensors. Secure routing protocols typically employ mechanisms such as link-layer encryption and authentication, multi-path routing, identity verification, bidirectional connection authentication, and authentication broadcasting to effectively improve the network's ability to resist external attacks and enhance routing security.
Security Protocol
In terms of security, there are two main methods: key management and secure multicast.
Key Management: Wireless sensor networks (WSNs) face numerous limitations, such as node capability constraints limiting their use to symmetric keys and techniques; power constraints necessitating minimal communication, as communication power consumption exceeds computational power consumption; and the need to reduce data redundancy through aggregation. Before deploying nodes, keys are pre-configured. Typically, pre-configured key schemes calculate session keys using pre-stored secret information. Due to node storage and energy limitations, pre-configured key management schemes must conserve storage space and minimize communication overhead.
Secure propagation: Wireless sensor networks may be set up in hostile environments. To prevent suppliers from injecting forged information into the network, secure multicast based on source authentication is required in wireless sensor networks.
