What is Wireless Sensor Network, and Types of WSN?

Nowadays an efficient design of a Wireless Sensor Network has become a number one area of research. A Wireless Sensor Network is a technology that responds and detects some kind of input from both the physical or environmental conditions, like heat, pressure, light, etc.

The output of the sensor is an electrical signal that’s transmitted to a controller for further processing. You will understand the overview, types, and application of Wireless Sensor Network in this article.

What Is Wireless Sensor Network? 

WSNs stands for Wireless Sensor Networks can be defined as a self-configured and infrastructure-less wireless network to observe physical or environmental conditions, like temperature, pressure, motion, sound, vibration, or pollutants, and to directly pass their data or information through the network to a sink which is also called the main location where the information is often observed and analyzed.

A base station or sink seems like an interface between the users and the network. It can convert back some required information from the network by injecting some queries and gathering results from the sink. Typically a wireless sensor network contains many thousands of sensor nodes.

The sensory nodes can communicate with each other by using radio signals. The wireless sensor nodes are equipped with sensing and radio transceivers, computing devices, and power components.

A sensor node in a wireless sensor network is inherently resource-constrained, also it has limited processing speed, storage capacity, and communication bandwidth. After the sensor nodes are installed, they’re responsible for self-organizing an appropriate network infrastructure often with multi-hop communication with them.

Then the onboard sensors begin to collect information of their interest. And then the specifically designed devices of wireless sensor networks reply to those queries sent from a “control site” to perform specific instructions or provide sensing samples.

The working mode of the sensor nodes could also be either continuous or event-driven. GPS or Global Positioning System and LPA or local positioning algorithms can be used to obtain location and positioning information.

Wireless sensor devices are often equipped with actuators to “act” upon certain conditions. These networks are sometimes or normally called Wireless Sensor Network and Actuator Network. 

Types of Wireless Sensor Networks 

There are five types of Wireless Sensor Networks depending on the environment. Different Types of WSNs are:

1. Terrestrial Wireless Sensor Networks: Terrestrial WSNs are used for communicating base stations efficiently, and comprise thousands of wireless sensor nodes deployed either in an unstructured (ad hoc) or structured (Pre-planned) manner.

In an unstructured mode (ad hoc), the sensor nodes are randomly distributed within the target area that’s dropped from a set plane.

In WSNs, the battery power is limited, however, the battery is provided with solar cells as a secondary power source. The conservation of energy of the WSNs gets by using low duty cycle operations, optimal routing, minimizing delays, and so on. 

2. Underground Wireless Sensor Networks: In terms of deployment, maintenance, equipment cost considerations, and careful planning, underground wireless sensor networks are more expensive than terrestrial WSNs.

The Underground Wireless sensor networks UWSNs comprises several sensory nodes that are hidden in the ground to observe underground conditions.

 Additional sink nodes are located above the bottom to transfer information from the sensor nodes to the base station, These underground WSNs deployed into the ground are difficult to recharge.

The sensor battery nodes equipped with limited battery power are also difficult to recharge. Additionally, the underground environment makes wireless communication a challenge because of the high attenuation and signal loss level. 

3. Underwater Wireless Sensor Networks: About more than 70% of the earth’s planet is occupied with water. These networks contain several sensor nodes and vehicles deployed underwater. Autonomous underwater devices and vehicles are used to collect data from these sensor nodes.

A challenge of underwater communication may be a long propagation delay, and bandwidth and sensor failures. Underwater, WSNs are equipped with a limited battery that can’t be recharged or replaced.

The difficulty of energy conservation for underwater WSNs involves the development of underwater communication and networking techniques. 

4. Multimedia Wireless Sensor Networks: Multimedia wireless sensor networks are proposed to enable tracking and monitoring of events in the sort of multimedia, like video, imaging, and audio.

These networks contain low-cost sensor nodes equipped with cameras and microphones. These sensory nodes of Multimedia WSNs are interconnected together over a wireless connection for data retrieval, data compression, and correlation.

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The challenges with the Multimedia WSNs include high bandwidth requirements, high energy consumption, processing, and compressing techniques. Additionally, multimedia contents need high bandwidth for the content to be delivered properly and easily.

5. Mobile Wireless Sensor Networks MWSNs: Mobile WSNs networks comprise a group of sensor nodes that can be moved on their own and can be interacted with the physical environment. The mobile nodes can also compute sense and communicate respectively.

Mobile wireless sensor networks are way more versatile than static sensor networks. The benefits of Mobile WSNs over Static WSNs include better and improved coverage, superior channel capacity, better energy efficiency, and so on.

Classification of Wireless Sensor Networks 

Classification of Wireless Sensor Networks are as follows:

1. Static and Mobile WSN: All the sensor nodes are connected without movement and these are static networks in many applications. Some applications especially in biological systems- mobile sensor nodes are needed. These are called mobile networks. An example of a mobile network is animal monitoring. 

2. Deterministic and Nondeterministic WSN: In deterministic wireless sensor networks, the sensor node position is calculated and fixed.

The deployment of sensor nodes is possible in a limited number of applications. The position of sensor nodes determination isn’t possible because of several factors like harsh environments or hostile operating conditions. Such kinds of networks are non-deterministic and need a complex system. 

3. Single Base Station and Multi Base Station WSN: In single base station WSNs, only one base station is used that is found close to the sensor node region.

All the nodes communicate with this base station, in the case of a multi-base station WSNs, more than one base station is used and a sensor node can transfer data to the closest base station. 

4. Static Base Station and Mobile Base Station WSN: It is similar to sensor nodes, even base stations of the WSN are often either static or mobile. A static base station contains a fixed position usually close to the sensing region.

A mobile base station WSN moves around the sensing region because a load of sensor nodes is balanced. 

5. Single-hop and Multi-hop WSN: In single-hop WSNs, the sensor nodes are directly connected to the base station. And in the case of multi-hop WSNs, peer nodes and cluster heads are used to relay the information to reduce energy consumption. 

6. Self Reconfigurable and Non- Self Configurable WSN: In non-Self Configurable WSNs, the sensor networks cannot organize themselves in a network and consider a control unit to gather data.

In many WSNs, the sensor nodes can be able to organize and maintain the connection and work collaboratively with other sensor nodes to accomplish the task. 

7.Homogeneous and Heterogeneous WSN: In the case of homogeneous WSNs, all the sensor nodes have the same energy consumption, storage capabilities, and computational power.

And in the case of heterogeneous WSNs, some sensor nodes have higher computational power and energy requirements than others and also the processing and communication tasks are divided accordingly. 

Structure of Wireless Sensor Network 

The structure of WSNs includes different types of topologies for radio communications networks.

1. Star Network: A star network is also called a single point-to-multipoint is a communications topology where one base station can send and receive a message to a variety of remote nodes. The remote nodes aren’t permitted to send messages.

The benefit of these kinds of networks for wireless sensor networks includes simplicity, ability to keep the remote node’s power consumption to a minimum. It allows low-power communications between the remote node and the base station.

The disadvantage of such a network is that the base station must be within the radio transmission range of all the individual nodes and isn’t as robust as other networks because of its dependency on a single node to manage the whole network. 

2. Mesh Network: A mesh network allows transmitting data from one node to another in the network that’s within its radio transmission range.

This enables what is called multi-hop communications, i.e. if a node wants to send a message to a different node that’s out of radio communications range, it can use an intermediate node to forward the message to the particular node.

This topology has the power of redundancy and scalability. When an individual node fails to work, a remote node still can communicate to the other node in its range, which successively, can forward the message to the specified location.

Additionally, the range of the network isn’t necessarily limited by the range in between single nodes, it can simply be extended by adding more nodes to the system. 

3. Hybrid Star: A hybrid Star is a combination between the star network and a mesh network that provides a strong and versatile communications network while maintaining the ability to keep the wireless sensor node’s power consumption to a minimum.

In network topology, the sensor nodes with the lowest power aren’t enabled with the ability to forward messages. This permits for minimal power consumption to be maintained.

Similarly, the various other nodes on the network are having multi-hop capability, allowing them to forward messages from the low power nodes to another on the network.

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The nodes whose having the multi-hop capability are of a higher power, and if possible, are often plugged into the electrical mains line. 

Applications of wireless sensor network 

Wireless sensor networks have been used widely over the world. The applications of wireless sensor networks are: 

• Military applications: The military domain isn’t only the primary field of human activity that is used by WSNs but it’s also considered to have motivated the initiation of sensor network research.

Tracking and environment monitoring surveillance applications use these kinds of networks. The sensor nodes from sensor networks are dropped to the sector of interest and are remotely controlled by a user.

Security detections and enemy tracking are also performed by using these networks.

• Health applications: These networks are generally used by doctors to track and monitor patients.

• Transport systems: Most frequently used wireless sensor networks are in the transport systems like dynamic routing management, monitoring of traffic, and monitoring of parking lots, etc., use these networks.

• Environmental trackings: Wireless Sensor Networks have been used widely in the field of environment changes and their tracking.

Forest detection, animal tracking, weather prediction, flood detection, forecasting, and also commercial applications like seismic activity prediction and also monitoring are using these networks like Air pollution monitoring, water quality monitoring, etc.

• Threat detection: The Wide Area Tracking System (WATS) is a device and a prototype network for detecting a ground-based nuclear device such as a nuclear bomb, and many other WSNs are also used for threat detection.

• Industrial process monitoring, rapid emergency response, automated building climate control, area monitoring, civil structural health monitoring, ecosystem, and habitat monitoring, etc., use these networks to monitor things. 

Characteristics of Wireless Sensor Network  

Some basic characteristics of Wireless Sensor Networks are as follows:

• Power consumption constraints for nodes using energy harvesting or mainly batteries are used.
• Examples of suppliers are ReVibe Energy and Perpetuum
• Having the ability to deal with node failures (resilience)
• Having some mobility of nodes (for highly mobile nodes see Mobile Wireless Sensor Networks)
• Scalability to the large scale of deployment
• Ability to resist harsh environmental conditions
• Heterogeneity of nodes
• Homogeneity of nodes
• Easy to use
• Cross-layer optimization

Issues in Wireless Sensor Networks 

Various issues are occurring in wireless sensor networks WSNs such as design issues, topology issues, and other issues.

The complications in design in different types of wireless sensor networks include:

• Low latency
• Transmission Media
• Fault
• Coverage Problems
• Scalability

The complications in the topology of wireless sensor networks include the following.

• Sensor Holes
• Coverage Topology
• Geographic Routing

The big issues of a wireless sensor network WSNs include the following. These issues mainly affect the design and performance of wireless sensor networks.

• Operating System & Hardware for WSN
• Schemes for Medium Access
• Deployment
• Middleware
• Characteristics of Wireless Radio Communication
• Architecture
• Calibration
• Database Centric and Querying
• Network Layer
• Localization
• Sensor Networks Programming Models
• Synchronization
• Transport Layer
• Data Dissemination & Data Aggregation 

The Advantages and Disadvantages of wireless sensor networks: 

The advantages of wireless sensor networks WSNs are as follows:

• It is suitable for non-reachable places like over the sea, mountains, rural areas, or deep forests.
• It avoids lots of wiring.
• It might accommodate new devices at any time.
• It can also be accessed by using a centralized monitor.
• Flexible if there’s a random situation when the additional workstation is required.
• Implementation pricing is affordable.
• It’s flexible to undergo physical partitions.

The disadvantages of Wireless sensor networks are as follows:

• Less secure because hackers can enter the access point and obtain all the data.
• Lower speed as compared to a wired network.
• It’s easy for hackers to hack it we couldn’t control the propagation of waves.
• It is even more complicated compared to a wired network.
• Easily troubled by surroundings (walls, microwave, large distances because of signal attenuation, etc).
• Comparatively low speed of communication.
• Gets distracted by various elements like Blue-tooth.
• Still Costly (most importantly).