Continuous Advancements in Telecommunications Have Allowed Companies To Design Sensors With Low Power Consumption, Small Size, And Reasonable Price For Different Applications.

Wireless Sensor Network: These tiny sensors, capable of performing various tasks such as receiving, processing, and transmitting environmental information, have led to the formation of a new architecture called the Wireless Sensor Network (WSN). The network proved its most powerful presence in the 2021 Olympics in Japan.

All technology experts believe that wireless sensor networks will become an integral part of our lives in the future. They have broad applications in manufacturing, healthcare, environmental monitoring, and other industries. Wireless sensor networks are a great way to collect and send environmental information or information about an event to a central node.

The use of a wide range of nodes capable of teamwork and easily managed led to the definition of different applications for these networks in terms of simultaneous routing, environmental monitoring, and monitoring the health of structures or equipment of a system.

These networks are typically used in agriculture, medicine, industry, smart homes, traffic control, and device health monitoring. One of the most common applications of this technology is remote environmental monitoring.

What is a wireless sensor network?

A sensor network comprises wireless components installed in a comprehensive or limited environment and collects environmental data.
Typically, these networks are established based on a specific map in pre-identified locations. Still, the sensors are installed based on analyses performed at different places and find each other through radio waves.

Because wireless sensor network protocols and algorithms can self-organize, their irregular deployment in different locations does not pose a particular problem.

One of the unique features of sensor networks is the ability to cooperate and coordinate between nodes. Each sensor node has a processor on its board that, instead of sending all the raw information to the center of the node responsible for data processing, performs some basic and straightforward processing on the data and sends the semi-processed data to the data center.

Increasing advances in the integrated circuit industry, the downsizing of electronic boards, and the development of wireless communication technology have paved the way for implementing low-cost wireless sensor networks.

One of the primary uses of these networks is to connect with environments where humans cannot be present.

These include deserts, oceans, accurate pressure measurements of oil rigs and wells, or chemical-contaminated environments.

In wireless sensor networks, each node is connected to another node or node. Network sensors comprise various components such as receivers and radio transmitters with internal or external antennas, batteries, and microcontrollers.

A microcontroller is an electronic circuit that communicates sensors and power supplies. These networks are composed of low-cost sensor nodes with low processing power whose primary mission is to collect environmental data.

While each sensor alone has little processing power, combining hundreds of tiny sensors provides the processing power needed for fundamental data analysis. More precisely, the power of wireless sensor networks lies in the teamwork of self-organizing nodes.

Applications of wireless sensor networks

There are many uses for wireless sensor networks. For example, wireless sensor networks are the best option in commercial and industrial applications where using wired receivers to control data is difficult and expensive. For example, these networks can be installed in desert environments and services for a long time.

Another important application of these networks is alerting when unauthorized persons enter controlled environments and tracking attackers. Other applications of these networks include residential monitoring, moving targets, fire detection, traffic monitoring, and more.

Another application for wireless receivers is controlling or monitoring the environment. In environmental monitoring, wireless receivers are deployed in areas where events are more likely to occur.

For example, installing transmitter and receiver nodes at highway or terminal junctions instead of human agents or CCTV cameras can provide the traffic police, or the Ministry of Roads and Urban Development with accurate statistics on the number of vehicles crossing specific routes can exercise precise traffic control. Or if they need to renovate the asphalt of the roads.

Of course, to maximize the benefits of these sensors and receivers, information such as temperature, pressure, sound, light, vibration, etc., must be sent to the cloud infrastructure whenever it is collected.

The transmission process can be satellite-based, fiber-optic, or cellular. In this architecture, unlike older wired systems, which are expensive to configure and arrange and require thousands of meters of wire to be installed, small devices the size of a coin or smaller can be installed.

Typically, wireless sensor networks can implement ad hoc wireless networks. Each node uses a multi-hop routing algorithm so that many nodes forward a packet to the station.

Supervision in the field of healthcare

In healthcare, these sensors are connected to people’s bodies as wearable equipment. In interaction with the smartphone application, they collect instantaneous information such as heart rate, body temperature, and similar samples and send it to the cloud infrastructure. Then, they provide processing, reporting, or alerts to the individual or, if necessary, send signals to healthcare providers.

Environmental monitoring

Other applications of this technology include monitoring forest pollution, forest fires, landslide monitoring, water pollution, and climate change monitoring to prevent and reduce the consequences of natural disasters such as floods and storms.

Supervision in the field of industry

We monitor the performance and health of machines, systems, other network sensors, data centers, and engineering structures, among other industry applications of this technology.

Ad hoc Network

Case wireless networks consist of several sensors located in a specific geographical area. Each sensor can communicate wirelessly, has enough intelligence to process signals, and can network.

These networks are based on mobile devices that communicate with each other via wireless links. Traditional wired networks are not suitable in environments where unpredictable events are likely to occur, centralized networks are impossible to implement, and there is insufficient reliability.

In such environments, wireless networks are the best choice. Nodes in mobile case networks are equipped with wireless receivers and transmitters and use antennas capable of transmitting signals in a broadcast or peer-to-peer manner. Of course, wireless networks have their security requirements and problems.

The most critical challenges in this regard are the following:

• Lack of infrastructure: Wireless networks do not have centralized and integrated structures such as servers, routers, and other equipment, so the security solutions of this network model are decentralized, distributed, and based on the cooperation of all network nodes.
• Using a wireless link: In a wireless network, common defense mechanisms such as firewalls are not possible, so hackers may target any node without the need for physical access to communications.
• Multiprocessing: In most wireless routing protocols, nodes act as routers, and packets have several different hops. In this case, each node may be manipulated by error or data, and the nodes may not perform the routing properly due to incorrect configuration or cyber-attacks.
• Node autonomy in relocation: Mobile nodes in a wireless network are difficult to detect due to redirection, especially in large networks.
• Lack of standard alignment: Each manufacturer can use its topology. An unstable topology can cause inconsistencies and problems with resource use.

Requirements for wireless sensor networks

One of the essential requirements of sensor networks is synchronous service. The importance of time in sensor networks has caused the synchronization of sensors to interfere with the operation of the entire network.
For example, hackers can disrupt the web in various ways, preventing synchronous messages from reaching, changing, or forging them, delaying the receipt of time-sensitive messages, and sending wrong synchronous messages on the network.

Despite introducing several synchronization methods for sensor networks in recent years, no comprehensive synchronization method has been proposed to meet these networks’ security and efficiency requirements.

Routing

In wireless sensor networks, network nodes do not have prior knowledge of the network topology in which they are located and must discover the network’s destination location to communicate with other nodes.

The basic idea is that a new node will voluntarily publish its presence on the network and listen to its neighbors. In this way, the node acquires information about its nearby nodes and learns how to reach them. In the same way, all nodes know each other and know at least one way to go them.

Routing protocols

Routing on these networks is complex because each node can move randomly and leave the network over time. For example, an optimal path may not be available for a few seconds at one time. In general, the following protocols are used in a wireless sensor network:

Table-based protocols: In this method, each node obtains routing information by storing the local information of other nodes in the network. The report is used to transfer data through different nodes.

Request path protocols: Path updates are rarely performed in a wireless sensor network, and the paths created are used. However, sometimes conditions require you to use custom paths to transfer data and request path protocols are used for this purpose.

These protocols find the requested path by sending a flood of identifier packets. Disadvantages of these protocols include the long time it takes to find the direction and volume of the packages sent, the possibility of congestion, and disruption of network performance.

• Hybrid protocols combine the above two protocols. They use the vector-distance routing method to find the shortest distance and report routing information only when the network topology changes. Each node in the network has its routing area, and a record of routing information is maintained in those areas.
• Table routing protocols (active): These protocols maintain a list of the latest destinations and their routing methods by periodically updating and distributing routing tables. They are maintained. Disadvantages of these protocols include the significant amount of data that must be stored and distributed and network structure, rebuilds, and failures.
• Reactive routing protocols (on demand): These protocols also function similarly to the requested routing protocols and send paths by sending large tracking packets. However, it can be problematic to spend a lot of time finding the direction and volume of packets sent.
• Active and responsive routing protocols: These protocols combine the strengths of dynamic and responsive routing. These protocols initially create a series of default energetic paths and find the courses requested for the added active nodes by sending a basic response algorithm. The performance of these protocols depends on the number of active nodes.

Protocols of the first method

• DSDV: These protocols are based on the classic Bellman-Ford algorithm. In this case, each node provides a list of all destinations and the number of jumps to each destination. In this method, each input is numbered with a number. 
• The incremental-packages approach solves the heavy traffic volume caused by updating the routes in the network. This protocol’s most important advantage is the avoidance of routing loops in networks, including mobile routers. Thus, route information is always provided regardless of whether the node currently needs to use the route.
• WRP: This protocol is based on the path-finding algorithm, except that it solves the counting problem of this algorithm indefinitely. In this protocol, each node has four spreadsheet optimization tables, a routing table, a link cost table, and a table of messages to be retransmitted. Changes to links are notified by sending and receiving messages between neighboring nodes.
• CSR: In this type of protocol, nodes are divided into groups. Each group has a group leader who can control and manage a group of hosts, among the features the categorization approach provides in allocating appropriate bandwidth and access to the channel. This protocol uses DSDV as its underlying routing protocol. 
• STAR: This protocol does not require constant path updating and does not attempt to find the optimal path between nodes.

Protocols of the second method

• SSR: This protocol selects paths based on the strength and power of the signals between nodes, so the chosen courses are more substantial. This protocol can be divided into two main models, DRP and SRP, as well as related submodels. The DRP is responsible for preparing and maintaining the routing and signal strength tables. The SRP examines incoming packets to send to higher layers if they have their node address.
• DSR: In this protocol, mobile nodes must have temporary memories for paths. It uses two main approaches: route discovery and route updating.
• TORA: Based on a distributed routing algorithm designed for dynamic mobile networks. This algorithm determines several paths for each pair of nodes and requires a synchronous clock. This protocol is based on a three-step pattern of creating a course, updating the system, and eliminating the path.
• AODV: The DSDV algorithm can save considerable bandwidth, as path detection only begins when there is no path between the two nodes.
• RDMAR: This protocol calculates the distance between two nodes through radio loops and distance detection algorithms. This protocol first specifies the search range before taking action to prevent unnecessary flood traffic on the network.

Multi-route routing

Some routing algorithms in a wireless sensor network perform routing operations in a multi-route manner, meaning they simultaneously establish multiple routes between source and destination. In general, the following advantages can be enumerated for multipath algorithms over multipath algorithms:

1.  Increase fault tolerance.
2.  I am balancing the load on the network and controlling congestion and traffic.
3.  Increase the bandwidth of the endpoints.
4.  Reduce endpoint latency.

Routing algorithms work in two ways. In the first case, one of the routes is selected as the main route to send information, and data is sent to the destination only through the main highway. The rest of the courses are kept as an alternative route in case of inefficiency or loss of the primary system. , Use one of them to send information.

This way, in case of failure, the network will have less latency. In the second case, the originator uses several routes to send information to the destination. Patient benefits such as load balancing in the network, traffic control, and congestion can be achieved.
Finally, this approach reduces the latency of the endpoints due to the parallel transmission of data. The most crucial multi-route routing algorithms are SMR, AOMDV, AODVM, ZD-AOMDV, and IZM-DSR.

last word

As you can see, Wireless Sensor Networks are a particular type of network that consists of a wide range of sensors that cover a specific area without the need for hardware infrastructure and perform tasks in interaction with each other. Coverage is one of the most critical issues in wireless sensor networks.

Sensors are classified into fixed and moving groups in terms of mobility. Intelligent algorithms should be used to detect gaps. More fixed sensors should be deployed in these areas, or mobile sensors should be used to improve the area covered by the sensors. Movable nodes perform better than selected nodes. However, the above networks are not without flaws.

The most critical problems around these networks are data processing, the required communication mechanisms, and energy consumption. However, because the wireless sensor network does not require a predefined structure or central management, and all nodes act as routers, their leadership is not very complex.
In addition, scalability is the most crucial reason for the increasing expansion of these networks, in which the role of demand-based routing protocols should not be overlooked.