Wireless Sensor Networks : Types & Their Applications

In recent years an efficient design of a Wireless Sensor Network has become a leading area of research. A Sensor is a device that responds and detects some type of input from both the physical or environmental conditions, such as pressure, heat, light, etc. The output of the sensor is generally an electrical signal that is transmitted to a controller for further processing. This article discusses an overview of types of wireless sensor networks, classification, types of attacks, types of mobility & routing protocols.

What are Wireless Sensor Networks (WSNs)?

A Wireless sensor network can be defined as a network of devices that can communicate the information gathered from a monitored field through wireless links. The data is forwarded through multiple nodes, and with a gateway, the data is connected to other networks like wireless Ethernet.

WSN is a wireless network that consists of base stations and numbers of nodes (wireless sensors). These networks are used to monitor physical or environmental conditions like sound, pressure, temperature, and co-operatively pass data through the network to the main location as shown in the figure.

WSN Network Topologies

For radio communication networks, the structure of a WSN includes various topologies like the ones given below.

Star Topologies

Star topology is a communication topology, where each node connects directly to a gateway. A single gateway can send or receive a message to several remote nodes. In instar topologies, the nodes are not permitted to send messages to each other. This allows low-latency communications between the remote node and the gateway (base station).

Due to its dependency on a single node to manage the network, the gateway must be within the radio transmission range of all the individual nodes. The advantage includes the ability to keep the remote nodes’ power consumption to a minimum and simply under control. The size of the network depends on the number of connections made to the hub.

Tree Topologies

Tree topology is also called as a cascaded star topology. In tree topologies, each node connects to a node that is placed higher in the tree, and then to the gateway. The main advantage of the tree topology is that the expansion of a network can be easily possible, and also error detection becomes easy. The disadvantage with this network is that it relies heavily on the bus cable; if it breaks, all the network will collapse.

Mesh Topologies

The Mesh topologies allow transmission of data from one node to another, which is within its radio transmission range. If a node wants to send a message to another node, which is out of the radio communication range, it needs an intermediate node to forward the message to the desired node. The advantage of this mesh topology includes easy isolation and detection of faults in the network. The disadvantage is that the network is large and requires huge investment.

Types of Wireless Sensor Networks

Depending on the environment, the types of networks are decided so that those can be deployed underwater, underground, on land, and so on. Different types of WSNs include:

1. Terrestrial WSNs
2. Underground WSNs
3. Underwater WSNs
4. Multimedia WSNs
5. Mobile WSNs

Terrestrial WSNs

Terrestrial WSNs are capable of communicating base stations efficiently, and consist of hundreds to thousands of wireless sensor nodes deployed either in an unstructured (ad hoc) or structured (Pre-planned) manner. In an unstructured mode, the sensor nodes are randomly distributed within the target area that is dropped from a fixed plane. The preplanned or structured mode considers optimal placement, grid placement, and 2D, 3D placement models.

In this WSN, the battery power is limited; however, the battery is equipped with solar cells as a secondary power source. The Energy conservation of these WSNs is achieved by using low duty cycle operations, minimizing delays, and optimal routing, and so on.

Underground WSNs

The underground wireless sensor networks are more expensive than the terrestrial WSNs in terms of deployment, maintenance, and equipment cost considerations and careful planning. The WSNs networks consist of several sensor nodes that are hidden in the ground to monitor underground conditions. To relay information from the sensor nodes to the base station, additional sink nodes are located above the ground.

The underground wireless sensor networks deployed into the ground are difficult to recharge. The sensor battery nodes equipped with limited battery power are difficult to recharge. In addition to this, the underground environment makes wireless communication a challenge due to the high level of attenuation and signal loss.

Under Water WSNs

More than 70% of the earth is occupied with water. These networks consist of several sensor nodes and vehicles deployed underwater. Autonomous underwater vehicles are used for gathering data from these sensor nodes. A challenge of underwater communication is a long propagation delay, and bandwidth and sensor failures.

Underwater, WSNs are equipped with a limited battery that cannot be recharged or replaced. The issue of energy conservation for underwater WSNs involves the development of underwater communication and networking techniques.

Multimedia WSNs

Multimedia wireless sensor networks have been proposed to enable tracking and monitoring of events in the form of multimedia, such as imaging, video, and audio. These networks consist of low-cost sensor nodes equipped with microphones and cameras. These nodes are interconnected with each other over a wireless connection for data compression, data retrieval, and correlation.

The challenges with the multimedia WSN include high energy consumption, high bandwidth requirements, data processing, and compressing techniques. In addition to this, multimedia contents require high bandwidth for the content to be delivered properly and easily.

Mobile WSNs

These networks consist of a collection of sensor nodes that can be moved on their own and can be interacted with the physical environment. The mobile nodes can compute sense and communicate.

Mobile wireless sensor networks are much more versatile than static sensor networks. The advantages of MWSN over static wireless sensor networks include better and improved coverage, better energy efficiency, superior channel capacity, and so on.

Classification of Wireless Sensor Networks

The classification of WSNs can be done based on the application but its characteristics mainly change based on the type. Generally, WSNs are classified into different categories like the following.

• Static & Mobile
• Deterministic & Nondeterministic
• Single Base Station & Multi Base Station
• Static Base Station & Mobile Base Station
• Single-hop & Multi-hop WSN
• Self Reconfigurable & Non-Self Configurable
• Homogeneous & Heterogeneous

Static & Mobile WSN

All the sensor nodes in several applications can be set without movement so these networks are static WSNs. Especially in some applications like biological systems uses mobile sensor nodes which are called mobile networks. The best example of a mobile network is the monitoring of animals.

Deterministic & Nondeterministic WSN

In a deterministic type of network, the sensor node arrangement can be fixed and calculated. This sensor node’s pre-planned operation can be possible in simply some applications. In most applications, the location of sensor nodes cannot be determined because of the different factors like hostile operating conditions & harsh environment, so these networks are called non-deterministic that need a complex control system.

Single Base Station & Multi Base Station

In a single base station network, a single base station is used and it can be arranged very close to the region of the sensor node. The interaction between sensor nodes can be done through the base station. In a multi-base station type network, multiple base stations are used & a sensor node is used to move data toward the nearby base station.

Static Base Station & Mobile Base Station

Base stations are either mobile or static similar to sensor nodes. As the name suggests, the static type base station includes a stable position generally close to the sensing area whereas the mobile base station moves in the region of the sensor so that the sensor nodes load can be balanced.

Single-hop & Multi-hop WSN

In a single-hop type network, the arrangement of sensor nodes can be done directly toward the base station whereas, in a multi-hop network, both the cluster heads & peer nodes are utilized to transmit the data to reduce the energy consumption.

Self Reconfigurable & Non-Self Configurable

In a nonself configurable network, the arrangement of sensor networks cannot be done by them within a network & depends on a control unit for gathering data. In wireless sensor networks, the sensor nodes maintain and organize the network and collaboratively work by using other sensor nodes to accomplish the task.

Homogeneous and Heterogeneous

In a homogeneous wireless sensor network, all the sensor nodes mainly include similar energy utilization, storage capabilities & computational power. In the heterogeneous network case, some sensor nodes include high computational power as well as energy necessities as compared to others. The processing & communication tasks are separated consequently.

Types of Attacks in WSNs

There are different types of attacks against wireless sensor networks. These attacks can be faced by a variety of measurements. Attacks are classified into two types the active attacks and passive attacks.
In the active type attack, an attacker attempts to modify or detach the transmitted messages over the network. An attacker can give a reply to old messages and also insert his own traffic to interrupt the network operation otherwise to cause a rejection of service.

The passive attack can be restricted to listening & examining exchanged traffic. So this kind of attack can be easier to recognize & it is complex to notice. As the attacker does not make any change on exchanged data. The goal of the attacker is to get confidential information otherwise the significant nodes data within the network by examining routing data.

• Tampering
• Identity replication attack
• Blackhole
• Wormhole attack
• Selective forwarding
• Exhaustion
• Sybil attack
• Blackmail attack
• HELLO flood attack
• Jamming

Types of Mobility in Wireless Sensor Networks

In ad hoc networks, mobility is a basic feature for all nodes. In WSNs, mobility exists generally to separate the elements of the network & more specifically it depends on the application. Wireless sensor network applications have been involving in different fields but in many fields, there is no involvement of mobility. So mobility plays a key role where wireless sensor networks are used. In WSNs, we can differentiate three different types of mobility like the following.

• Sensor nodes mobility
• Sin nodes mobility
• Monitored object or event mobility

The first type of mobility like sensor nodes mobility mainly occurs whenever the sensor node’s slightest element is mobile. The best examples of this type of mobility are once sensor nodes go away & freely move within the monitored area. These are set up on animals for monitoring & tracking of animals.

The second type of mobility refers to a condition where sink nodes are capable of separately moving within the monitored area for collecting information from the sensor network. Lastly, the third type of mobility mainly happens once a wireless sensor network is used for tracking/monitoring purposes & functions under the event-driven data model.

In the same way, once the wireless sensor network is used for tracking target, movement of target modeling is extremely useful for guessing the pattern & amount of produced data within the network throughout tracking the target.

Types of Routing Protocols in Wireless Sensor Networks

The routing protocol can be defined as it is one kind of a process used to choose the appropriate lane for the data to move from basic to end. This process faces numerous difficulties while choosing the route. Here, this route depends on the type of network, the performance metrics & channel characteristics.

Routing Challenges

For WSN, the design task of routing protocols is pretty challenging due to several characteristics which distinguish them from wireless infrastructure with fewer networks. In WSNs, different types of routing challenges are available where some of them are discussed below.

It is approximately complex to assign a universal identifiers system for sensor nodes with high quantity. Thus, wireless sensor nodes are not capable of utilizing protocols based on classical IP. The information which is detected is essential from different sources to a particular base station. However, this does not happen in normal communication networks.

In most cases, the data which is created has important redundancy because several sensing nodes can produce similar data while detecting. So, it is necessary to use such redundancy through the routing protocols, the accessible bandwidth & energy.

Furthermore, wireless nodes are definitely restricted in bandwidth, transmission energy relations, storage, capacity & onboard energy. Because of these dissimilarities, the number of the latest routing protocols have been estimated to handle routing challenges within WSNs.

Design Challenges

There are some main design challenges in WSNs because of a lack of resources like bandwidth, processing storage & energy. When designing the latest routing protocols, then the following basics must be fulfilled through a network engineer.

• Efficiency of Energy
• Location of Sensor
• Complexity
• Transmission of Data & Transmission Models
• Scalability
• Strength
• Delay

Challenges of WSN

The different challenges in wireless sensor networks include the following.

• Fault Performance
• Scalability
• Production Cost
• Operation Environment
• Quality of Service
• Data Aggregation
• Data Compression
• Data Latency

Fault Performance

Some sensor nodes stop working because of power loss, so physical damage may occur. This shouldn’t affect the sensor network’s overall performance, so this is known as the issue of fault tolerance. Fault tolerance is nothing but the ability to maintain the functionalities of the sensor network without any interruption because of the failures of sensor nodes.

Stability

The number of nodes used in the detecting area may be in the order of thousands, hundreds & routing schemes should be scalable enough for responding to events.

Production Cost

The sensor networks include a number of sensor nodes where a single node price is very significant to validate the cost of the overall network and thus each sensor node’s price must be kept low.

Operation Environment

The arrangement of sensor networks can be done within large machinery, under the ocean, in the field of chemically or biologically contaminated. in homes, battlefields, connected to fast-moving vehicles, animals, for monitoring in forests, etc.

Quality of Service

The quality of service which needs by the application could be energy efficiency, lifetime length, and reliable data.

Data Aggregation

The combination of data from various sources with different functions like average, max, min, is known as data aggregation.

Data Compression

The data reduction is known as data compression

Data Latency

These are treated like the essential factors that influence the design of routing protocol. The data latency can be caused through data aggregation & multi-hop relays.

Issues in Wireless Sensor Networks

There are different issues occurred in wireless sensor networks like design issues, topology issues, and other issues. The design issues in different types of wireless sensor networks mainly include

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

The topology issues of wireless sensor networks include the following.

• Sensor Holes
• Geographic Routing
• Coverage Topology

The major issues of a wireless sensor network include the following. These issues mainly affect the design and performance of the WSN.

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

Limitations

The limitations of wireless sensor networks include the following.

1. Possess very little storage capacity – a few hundred kilobytes
2. Possess modest processing power-8MHz
3. Works in short communication range – consumes a lot of power
4. Requires minimal energy – constrains protocols
5. Have batteries with a finite lifetime
6. Passive devices provide little energy

Wireless Sensor Networks Applications

• These networks are used in environmental trackings, such as forest detection, animal tracking, flood detection, forecasting, and weather prediction, and also in commercial applications like seismic activity prediction and monitoring.
• Military applications, such as tracking and environment monitoring surveillance applications use these networks. The sensor nodes from sensor networks are dropped to the field of interest and are remotely controlled by a user. Enemy tracking, security detections are also performed by using these networks.
• Health applications, such as Tracking and monitoring of patients and doctors use these networks.
• The most frequently used wireless sensor network applications in the field of Transport systems such as monitoring of traffic, dynamic routing management, and monitoring of parking lots, etc., use these networks.
• Rapid emergency response, industrial process monitoring, automated building climate control, ecosystem and habitat monitoring, civil structural health monitoring, etc., use these networks.

This is all about the types of wireless sensor networks and their applications. We believe that the information about all the different types of networks will help you to know them better for your practical requirements. Apart from this, for additional information about wireless SCADA, queries, and doubts regarding this topic or electrical and electronic projects, and any suggestions, please comment or write to us in the comment section below.

Photo Credits

• Wireless Sensor Networks by dolcera
• Wireless Sensor Network Topologies by ni
• Underground WSNs by amrita
• Under Water WSNs by jurdak
• Multimedia WSNs by ohio-state
• Wireless Sensor Networks Applications by immateriel