Wireless Sensor Networks Technically And Its Application

Published Date: 02 Nov 2017

Navina Krsna(Author,Editor)

Student (Undergraduate)

Multimedia University, MMU

Cheras, Malaysia

[email protected]

Danish(Author)

Student (Undergraduate)

Multimedia University, MMU

Serdang, Malaysia

Abstract— a wireless sensor network (WSN) has many real life applications. Basically, wireless sensor network consist of spatially distributed autonomous sensors which monitors physical or environmental conditions. Figure 1 below shows the basic structure of Wireless Sensor Network.

Some of them are temperature, sound and pressure. What happens is it sends the data from one point to another point wirelessly. Nowadays, modern networks are said to be bi-directional, which means two way transmission and also there is control of the sensor activity. Besides, current sensors are smaller, cheaper and more intelligent. The development of wireless sensors began with the implementation in national security aspects such as the army and police. For instance, battlefield surveillance and in our modern world wireless sensors are used in many industries and consumer usage. The basis of the wireless sensor networks are the nodes which can range from a few to several thousands. These nodes are usually connected to sensors. The sensors are equipped with wireless interfaces which can communicate with each other to form a network. The sensor network normally consists of several parts which include a radio transceiver with an antenna, a memory unit, processors, sensors, Global positioning system (GPS) and power source. As shown in Figure 2 below.

The sensor node varies with size. Even the cost varies according to specifications. The topology of a wireless sensor network can range from an easy star network to a complex wireless mesh network. The transmission method between the networks can be routing or by flooding. The design process of wireless sensor networks depends vastly on the application of the sensors and other factors such as environmental, cost, hardware availability, system constraints. The reasoning towards this review research paper is to present a comprehensive review of the applications of wireless sensors networks currently in the modern world and present its features. Adhering to the top-down approach, we give an overview of what wireless sensors are all about and its applications and then give our suggestions on how to improve the application of various aspects of wireless sensor networks.

Keywords—

Introduction

In recent years, the desire for connectivity has caused continued growth in wireless communication networks. Specifically, wireless data networks, have led to this trend due to the increasing exchange of data in Internet services such as the World Wide Web (WWW), e-mail, and data file transfers. The need to deliver such service is spurred by the increasing need for data throughput in the network. Wireless Local Area Networks (WLANs) is a good example to further enhance this point. Besides that, there are other types of wireless networks which exist but, they have relaxed throughput requirements. An overview of the technical aspects and the applications of wireless sensor networks follows in later parts of this research paper.

Wireless sensor networks

A WSN can be defined as a network of devices which are commonly known as nodes, which has the capability to sense the environment and communicate. Then the information gathered from the monitored areas through wireless links are transmitted to a display. The data is transmitted via hops, to a sink which can be a monitor/controller that can use it on its own or is connected to other networks through a gateway. The nodes can either be static or mobile. Also it can be aware of its location or not. And it can be homogeneous or not.

The figure above shows what a common single-sink WSN looks like (see Figure 1, left part). This network suffers from the lack of scalability which means by increasing the number of nodes what happens is the amount of data gathered also increases concurrently and its capacity will be at its maximum. Thus, it’s not so practical. Hence, the network size cannot be augmented. The Medium Access Control (MAC) and routing aspects means network performance cannot be considered independent of the network size. Then there are multiple sinks in the network (see Figure 1, right part). The density of the node, larger number of sinks will decrease the occurrences of isolated clusters of node which will not be able to deliver data due to unfortunate signal propagation conditions. In contrast, a multi-sink WSN can be scalable which means the same performance can be obtained even by increasing the number of nodes in a network but, the same cannot be done for a single-sink network. From the point of a network engineer, a multi-sink WSN is not an extension of a single-sink network. Generally, nodes send the data collected to one of the sinks selected among many, which then will forward the data to the gateway, to the end user (see Figure 1, right part). Taking the protocol point of view, what it means is that selection take place, based upon a suitable criteria like least delay, highest throughput, and least number of hops. Comparatively, multi-sinks provide far better network performance to single-sink assuming the same number of nodes utilized at a particular area but, the protocols to be used needs to be designed using suitable criteria.

Applications of wireless sensor networks

The variety of possible applications of WSNs in the real world is practically unlimited, from environmental monitoring, health care, positioning and tracking, to logistic, localization, and so on. Do take note that it’s vital that the application strongly depends on the choice of the wireless technology to be used. Once requirements are set, the designer will choose the appropriate technology which allows satisfying these requirements. Therefore, the understanding of the features, pros and cons of the many different technologies is fundamental for the application of wireless sensor networks in the practical world. What follows are the applications of WSNs.

Industrial control and monitoring

A large, industrial facility typically will have a small control room, surrounded by a massive physical plant. The control room will normally have indicators and displays that describe the current state of the monitored plant like the state of valves, the temperature and pressure the substances. Not only that the control actuators in the physical plant also affects the state of the plant. These wireless sensors which show the state of the physical plant, the displays in the control room, the control input device and the actuators in the plant are often all relatively inexpensive when compared with the cost of the wired cables that must be used in order to communicate between devices in a wired network. Hence, there are significant cost savings that can be achieved if wireless sensors are used to provide this link of communication. Since the information being transmitted is the state information, if often changes slowly. Thus, in the normal operation, the required data throughput of the network is quite low, but a very high reliability is required for the network. Given a WSN network with many nodes, providing multiple message routing paths of multi-hop communication then it can meet these requirements. As an example of wireless sensors used in industrial environment is the control of commercial lighting. Much of expense in the installation of lights in a large building concerns the control of light. Typically, it concerns where the wired switches will be, which lights can be on/off, and dimming of the lights. A wireless system can be used concurrently with a handheld controller that can be programmed to control a large number of lights in a nearly infinite variety of ways.

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Another relevant example is the use of wireless sensor networks for industrial safety systems. Wireless sensor networks are deployed to detect the presence poisonous or hazardous materials, giving early detection and identification of leaks or spills of chemicals or biologically agents before serious damage can result. Since the wireless networks can use routing algorithms and at the same time have multiple routing paths, and can be self-maintaining, they can be resilient in the face of an explosion or other damage to the industrial plant, providing officials with the critical plant status information under very difficult conditions.

The monitoring and control of rotating or moving machinery is another area wireless sensor networks are utilized. In such applications, wired sensor are not practical, yet it may be important to monitor the temperature, vibration and lubrication flow of the rotating components of the machine to determine the time between maintenance periods such as when the machine should be off-line. In order to do so, it is vital that the wireless sensor system to be operating the whole cycle between maintenance periods. Subsequently, this system requires deployment of wireless sensor network with very low energy requirements. Besides, the sensor node should be sufficiently small and inexpensive. Wireless sensor networks can be useful in the prediction of component failure for aircrafts too.

Still another application in this area for wireless sensor networks is the heating, ventilating, air conditioning (HVAC) of buildings. HVAC systems are typically controlled by a small number of strategically located thermostat and humidistat. The thermostat and humidistat are normally a few units. In addition, the air handlers and dampers that directly control the room environment are also wired networks and they are also limited in numbers since the cost is quite high. Hence, wired networks are always more expensive compared to cost effective and wireless network.

1.1.2 Home and consumer electronics

The home is very large application space for wireless sensor networks. Some of the industrial applications also have parallels for home usage. For instance, a home installed with the HVAC system equipped with wireless thermostats will keep the rooms on the sunny side of the house comfortable-without chilling the occupants on the shady side of the house-more effectively than a home equipped with a single, wired thermostat.

One very useful application is the "universal" remote control, a personal digital assistant (PDA)-type device that can control few devices such as the television, DVD player, stereo, and other home electronic equipment. And it’s not limited to that but, the lights, curtains, and locks can also be controlled using sensors. By using the universal remote control, users can have complete control of the house from the comfort of their chair. Its most intriguing potential, however, comes from the combination of multiple services, such as having the curtains close automatically when the television is turned on, or perhaps automatically muting the home entertainment system when a call is received on the telephone or the doorbell rings. These features ease human effort.

Subsequently, wireless sensor networks at home will connect computer peripherals, such as wireless keyboard and mouse. Such applications take advantage of the low cost and low power consumption. Another application in the home is sensor-based information appliances that transparently interact and work symbiotically together as well as with the home occupant.

As for children toys represent another large market for wireless sensor networks. The list of toys that can be enhanced or enabled by wireless sensor networks is limited only by one’s imagination, and range from conventional radio-controlled cars and boats to computer games employing wireless joysticks and controllers. A particularly intriguing field is personal computer (PC)- enhanced toys , which employ the computing power of a nearby computer to enrich the behavior of the toy itself. For example, speech recognition and synthesis may be performed by placing the microphone and speaker in the toy, along with the appropriate analog-to-digital and digital-to-analog converters, but employing a wireless connection to the computer, which performs the recognition and synthesis functions. By not placing the relatively expensive yet limited speech recognition and synthesis circuits in the toy, and using the (much more powerful) computing power already present in the computer, the cost of the toy may be significantly reduced, while greatly improving the capabilities and performance of the toy. It is also possible to give the toy complex behavior that is not practical to implement in other technologies.

Another major home application is an extension of the key Remote Keyless Entry (RKE) feature found on many automobiles. With wireless sensor networks, wireless locks, door and window sensor, and wireless light controls, the homeowner may have a device similar to a key job with a button. When this button is pressed, the device locks all the doors and windows in the home, turns off most indoor lights, turns on outdoor security light, and sets the home’s HVAC system to nighttime mode. The user receives a reassuring "beep" once this is all done successfully, and sleeps soundly, knowing that the home is secure. Should a door be left open, or some other problem exists, a small display on the device indicates the source of the trouble. The network may even employ full home security system to detect a broken window or other trouble.

1.1.3 Security and military sensing

The wireless security system described above for the home can be augmented for use in industrial security applications. Such systems, employing proprietary communication protocols, have existed for several years. They can support multiple sensors relevant to industrial security, including passive infrared, magnetic door opening, smoke, and broken glass sensors, and sensors for direct human intervention like panic buttons. As with many technologies, some of the earliest proposed uses of wireless sensor networks were for military applications. One of the great benefits of using wireless sensor networks is that they can be used to replace guards and sentries around defensive perimeters, keeping soldiers out of harm’s way. In this way, they can serve the same function as antipersonnel mines, without the attendant hazard mines represent to allied personnel during the battle. In addition to such defensive applications, deployed wireless sensor networks can be used to locate and identify targets for potential attack, ant to support the attack by locating friendly troops and unmanned vehicles. They may be equipped with acoustic microphones, seismic vibration sensors, magnetic sensors, ultra wideband radar, and other sensors.

Wireless sensor networks can be small, unobtrusive, and camouflaged to resemble native rock, trees, or even roadside litter. By their nature, multi hop networks are redundant. These networks have distributed control and routing algorithms a feature that makes them difficult to destroy in battle. The use of spread spectrum techniques, combined with great transmission format common to many wireless sensor networks, would give low chances of detection by electronic means. The relative location determination capability of many ad hoc wireless sensor networks can enable the network nodes to be used as elements of a retro directive array of randomly distributed radiating elements; such an array can be used to provide exfiltration of the sensor network data. The relative location information is used to align the relative carrier phase of the signals transmitted by each node; with this information, the exhilarated data may be transmitted not just in the direction of the incoming signal, but in any desired direction. Beam forming techniques can also be applied to the sensors themselves, to enhance their sensitivity and improve detection probabilities.

Wireless sensor networks can also be effective in the monitoring and control of monitoring populations with the use of optical, audio, chemical, biological, radiological sensors to track individuals and groups. The control of wireless sensor networks and the data they produce in a free society, while an important public policy discussion, is outside the scope of this text.

1.1.4 Asset tracking and supply chain management

A very large unit volume application of wireless sensor networks is expected to be asset tracking and supply chain management. Asset tracking can take many forms. One example is the tracking of shipping containers in a large port. Such port facilities may have tens of thousands of containers, some of which could be empty and full capacity, while others are bound for many different destinations. The containers are stacked, both on land and on ship. An important factor in the shipper’s productivity (and profitability) is how efficiently the containers can be organized so that they can be handled the fewest number of times and with the fewest errors. For example, it is important that the containers next needed be on top of a nearby stack instead of at the bottom of a stack 1km away. An error in the location record of any container can be disastrous; a "lost" container can be found only by an exhaustive search of a very large facility. Wireless sensor networks can be used to advantage by placing sensors on each container so that its location can always be known.

Similar situations involving large numbers of items that must be tracked occur in rail yards, where thousands of railroads cars of all types must be organized, and in the manufacture of durable goods, such as cars and trucks, that may sit in large lots or warehouses after manufacture, but before delivery to a retailer. A related application is that of supply chain management. An item in a large warehouse, but its with precise location unknown, is practically lost because it is unavailable to be used or sold. This represents inventory shrinkage, even though the item is physically on the premise, and is therefore a business expense. In a manner similar to that of the asset tracking application described. Previously, wireless sensor networks can be used to reduce the cost; however, additional benefits may be obtained. In a large distribution chain, one of the most vexing problems facing the distributors is to quickly and accurately identify the location of material to be sold. Thus, knowing where a product is can mean the difference between purchasing and not purchasing, but knowing the status of the entire supply chain from raw materials through components to final product will help a business to operate successfully. For example, transferring access product from Division X (where it is selling slowly) to Division Y (where it is selling briskly) can help a company avoid the purchase of component parts to manufacture more products for division Y. Wireless sensor networks placed along the supply chain enable everyone in the business to make better decision because more information about product in the supply chain is available.

This information can also be used as a competitive advantage; by being able to tell a customer exactly where his product is (or even where the components parts of his product are) in the supply chain, the customer’s confidence of on-time delivery (and opinion of the seller’s competence) rises. This has already been used extensively in the package shipping industry, so much so that the customer expect this service as a matter of course-a shipper that cannot tell a customer where his package is at any given time is rarely reused. The use of wireless sensor networks for the tracking of nuclear materials has already been demonstrated in the Authenticated Tracking and Monitoring System (ATMS). The ATMS employs wireless sensor (including the state of the door seal, as well as infrared, smoke, radiation, and temperature sensors) within a shipping container (e.g., a railroad car) to monitor the state of its contents. Notification of sensor events are wirelessly transmitted within the shipping container to a mobile processing unit, connected to both a Global Positioning System (GPS) receiver and an International Maritime Satellite (INMARSAT) transceiver. Through the INMARSAT system, location and status of each shipment may be monitored anywhere in the world.

1.1.5 Intelligent agriculture and environmental sensing

A textbook example of the use of the wireless sensor networks in agriculture is the rain gauge. Large farms and ranches may cover several square miles, and they may rain only sporadically and only on some portions of the farm. Irrigation is expensive, so it is important to know which fields have received rain, so that irrigation may be omitted, and which fields have not and must be irrigated, such an application is ideal for wireless sensor networks. The amount of data sent over the network can be very low like 0 or 1 (yes/no) and the response period will be of low latency. Yet, cost has to be minimized, and power consumption should be as efficient as possible for the entire network to last an entire growing season.

The wireless sensor network is capable of much more than just soil moisture measurement, however, because the network can be fitted with a near-infinite variety of chemical and biological sensors. The data that is provided by such a network is capable of providing the farmer with a graphical view of soil moisture; temperature; the need for pesticides, herbicides, and fertilizers; received sunshine; and many other quantities. This type of application is especially important in vineyards, where subtle environmental changes may have large effects on the value of the crop and how it is processed.

The location determination features of many wireless sensor networks also may be used in advanced control systems to enable more automation of farming equipment.

Many applications of wireless sensor networks are also used on ranches. Ranches may use wireless sensor networks in the location determination of animals within ranch and, with sensors placed on each animal, determine the need for treatments to prevent parasites. Dairy farmers may use wireless sensors to determine the onset of estrus in cattle, a labor intensive manual process at present. Hog and chicken farmers typically have many animals in cooled, ventilated barns. Should the temperature rise excessively, many thousands of animals may be lost. Wireless sensor networks can be used to monitor the temperature throughout the barn, keeping the animals safe.

1.1.6 Health monitoring

A market for wireless sensor networks that is expected to grow quickly is the field of health monitoring. Health monitoring basically means the monitoring of non-life-critical health information. Two general classes of health monitoring applications are available for wireless sensor networks. One class is athletic performance monitoring like the tracking of athlete pulse and respiration rate via wearable sensors and sending the information to a personal computer for later analysis. The other class is at-home health monitoring, for example, personal weight management. The patient’s weight may be wirelessly sent to a personal computer for storage. Other examples are daily blood sugar monitoring for patients of diabetic and remote monitoring of patients with chronic disorders. The use of wireless sensor networks in health monitoring is expected to accelerate due to the development of biological sensors compatible with conventional CMOS integrated circuit processors. These sensors, which can detect enzymes, nucleic acids, and other biological important materials, can be very small and inexpensive, leading to many applications in pharmaceuticals and medical care. A developing field in the health monitoring market is that of implanted medical devices.

A developing field related to both health monitoring and security is that of disaster relief. For example, the wireless sensors of the HVAC system in a collapsed multistory building (perhaps the result of an earthquake) can provide victim location information to rescue workers if acoustic sensors, activated automatically by accelerometers or manually by emergency personnel, are included. Water and gas sensors also could be used to give rescuers an understanding of the conditions beneath them in the rubble. Even if no additional sensors were included, the identities and pre- and post-collapse locations if the surviving network nodes can be used to help workers understand how the building collapsed, where air pockets or other survivable areas may be, and can be used by forensic investigators to make future buildings safer.

Wireless disaster relief systems, in the form of avalanche rescue beacons, are already on the market. Avalanche rescue beacons, which continuously transmit signals so that rescuers can be use them to locate the wearer in time of emergency, are used by skiers and other mountaineers in avalanche prone areas. But, these systems have their limitations, however; principal among these is that they provide only location information and give no information about the current state and health of the victim. In a large avalanche, when emergency personnel can detect several beacons, they have no way to decide who should be assisted first. It was recently proposed that these systems be enhanced by the addition of health sensors, so that would-be rescuers would be able to perform triage in a large avalanche, identifying those still alive under the snow.

Area monitoring is a common usage of WSNs. For area monitoring the WSNs is usually deployed over a region where some activity is to be monitored. It is usually for military use like the use of sensors to detect enemy presence in secured areas. For example, the intrusion of enemy fighter pilots or submarines. This is a major factor in the safety of a particular nation as it consists of the security of a nation. Besides, other security monitoring is for oil refineries and highly secured research laboratories.

Environmental monitoring consists of wireless sensors which are deployed to monitor the environment. The core usage is in the earth science research field whereby the sensors monitor volcanoes for scientific research and eruption signs. The ocean is also monitored for weather patterns and sea levels. Besides that, the glaciers and the forest are some of the examples where environmental monitoring applies. One of the major areas is the air quality monitoring whereby sensors are used to protect the environment, animals and humans from being affected by air pollution. Since air pollution is a real-time occurrence the need for real-time monitoring is vital. Data collected will then be termed as air pollutant index (API). It’s an interesting application of sensors since the conditions can change dramatically easily in hazardous areas which could result in serious consequences. Therefore, the wireless sensors act as a potential safety barrier to protect humans for such hazardous environments. Then, there are the environmental magnitudes such as the temperature, humidity and light. These magnitudes can be easily obtained by using wireless sensors to monitor them. Furthermore, there are also gas and particle concentration sensors. They basically perform the task of monitoring gaseous and particles which can range from hazardous to non-hazardous. This simplifies the task of humans as they need not be exposed to such harsh environment which would be harmful to health. For example, monitoring the concentration of Carbon Monoxide gas (CO) which is a toxic gas can lead to intoxication. Then there is ambient monitoring which monitors rainfall, wind speed, wind direction, UV levels and Atmospheric pressure. It is vital to use wireless sensors to measure these as it is easier to do so and the accuracy is higher. This aids human work and is more practical. The ambient sensors are normally used by weather forecasters to aid their forecasting. Next, comes the interior and exterior monitoring sensors. Interior monitoring measures the gas levels at hazardous environments as such the durability and the accuracy of such equipment must meet the industrial regulations. Since, hazardous environments need accurate measurements to ensure the safety of humans or living things in that particular environment. This is followed by exterior monitoring. Whereby the outdoor air quality requires the use of accurate wireless sensors but, it has to be durable enough to withstand rain, wind and probably other harsh conditions. Besides that, the sensor also has to be self-sufficient in term that it needs the use of energy harvesting techniques that would ensure the sensors extended autonomy to equipment which most probably will be difficult to access. For example, sensors high in the Swiss Alps, considering the strong wind and harsh conditions up there, it’s obvious that the power supply is going to be a tough task to supply to altitude that high.

Air pollution Monitoring is currently being utilized at several major cities around the world like London and Brisbane in order to keep track of the concentration of dangerous gaseous for citizens. Air pollutants like Carbon Monoxide (CO) and haze are very harmful to citizens well being. The sensors are deployed by taking advantage of ad-hoc wireless links rather than wired installation which greatly improve the speed and the easy of usage. As a result, the monitoring sensors will be portable enough to obtaining readings in varying locations. In short, there are plenty of architectures that can be applied for air quality monitoring as well as alternate data analysis methods to further improve the outcome of the results.

Forest Fire detection basically works using the nodes which carry sensors which can be installed in forest to detect whenever a fire has started. They sensors which can be equipped can range from measurements of temperature, humidity and types of gases produced by forest fires. These sensors play an important role as they are crucial for early detection in order for firefighters to be successful in their actions of saving properties, humans, animals and crops. Provided the wireless sensor network is deployed efficiently firefighters will be able to know the moment the fire is started and the rate it is spreading so they can curb the losses to the minimum.

A Landslide detection system also uses the aid of wireless sensor networks to detect slight movement on or in the earth crust, if there are any variations of different aspects to the crust before a landslide. Given the data provided by the sensors it is easier to identify landslide prone areas and take early precaution. This can avoid lives being lost and property damage in the long term.

Water quality monitoring system involves analyzing water properties in streams, lakes, oceans, as well as underground reservoirs. The system functions with the use of many wireless sensors distributed which enables the formation of a precise map of the water status. This also acts as a permanent deployment for monitoring stations which have tough access without the need for manual retrieval. Therefore, it is easier to identify whether the water is contaminated or the presence of harmful elements which would make the water unsuitable for consumption. And it eases the burden of detecting water levels in the reservoirs underground.

The application of wireless sensor networks can effectively prevent natural disasters like flash floods, earthquakes and volcanic eruptions.

The sensors function with the usage of wireless nodes which have been successfully deployed in rivers and on the earth crust. So that the sensor can monitor the changes in water level and movement under the earth crust in real-time.

Then, there is Industrial monitoring. Where the machine health monitoring system uses wireless sensor networks to check the condition of the machine based on maintenance. Therefore, these sensor systems offer significant cost savings and better reliability. Besides, in wired systems the usage of sensors is often limited since the cost for wiring is very high. As such previously inaccessible locations like hazardous, restricted areas with rotating machinery can be reached using the current high technology wireless sensors.

Moreover, sensor networks are also used for data logging. As the term states it collects data for monitoring environmental information. For example, to monitor the temperature of the fridge. The statistic can then be used to explain how certain systems function. The major asset using wireless sensor networks is the real-time or live data feed. Since, the data will be always up-to-date.

This is followed by industrial sense and control applications. Currently, there are plenty of wireless sensor network communication protocols which have been developed. In the past, the industrial focus was mainly towards saving energy but nowadays it’s more towards aspects such as wireless reliability, real time capabilities and quality of service provided. So, the priority for all these aspects makes the industrial performance more efficient. Therefore, by replacing the old wire based networks with the wireless networks more productivity can be obtained.

On another note, WSNs are also applied for water/wastewater monitoring systems. They involve aspects such as the quality of surface or underground water, to the monitoring of the country’s water infrastructure. The 3 major systems are water quality magnitudes which monitor temperature, pH value, specific electrical conductance (EC) and dissolved Oxygen (O2). These aspects are very important for human water consumption and all living things. Followed by the water distribution network monitoring which monitors the flow and pressure levels of water, leakage detection, water levels and remote metering. These aspects would be very helpful for underground reservoirs and water supply systems. It aids the delivery process of water supply to the common household till industrial sites. Finally there is the natural disaster prevention system which monitors for flood and drought and give an early warning so necessary precautions can be taken.

The deployment of wireless sensor networks in agriculture based industry is a common thing nowadays. Since, it frees the farmers of the need to maintain wirings in difficult environments. The usage of gravity feed water systems can be monitored by using pressure sensors to monitor water levels and water pumps can be operated using input/output devices. So, all of these will be automated and gives less burden to farmers. This enables efficient water usage and prevents wastage. So the efficiency is very high.

Another vital usage of WSNs is for Greenhouse monitoring. Wireless sensors are used to control the temperature and humidity levels inside man made greenhouses. Provided there is a temperature drop or humidity variance the sensor notifies the system which triggers other systems like misting systems, air vents and turning on fans which automatically controls the temperature of the greenhouses without the need for manual actions.

Finally, there is structural monitoring which involves the aspects of engineering and architecture. It is mainly used to monitor the movements of infrastructures such as buildings, highway flyovers, tunnels underground and bridges. These structures need to be monitored real-time as it involves infrastructures which need constant monitoring to ensure the safety of the general public. Besides that, monitoring assets remotely enables engineers to monitor infrastructures without the need for costly onsite inspections. As an advantage there is real-time database which can be referred to in the future if there is any mishap. In contrast, according to traditional method data is usually collected on a weekly or monthly basis using physical site visits, which involves site closure in some cases. On another note, the data collected is far more accurate using wireless sensor networks compared to manual on the site inspections. Also some of the useful uses of WSNs are for structural health monitoring like the amount of load the structure can handle, the vibration level, the formation of cracks and the fatigue of structures. Besides that, wireless sensor network also has the capability to monitor the wind and weather condition. For example, the humidity level outside and the wind direction affecting the infrastructure. Some sensor networks also monitor the traffic situation to warn motorist of traffic congestions and also sensors which can monitor the pollution levels to warn the general public on the potential air pollution. The major structural monitoring involves the monitoring of bridges. It’s important that for bridges measurements of loads and the effects the load has on the bridge. This can help to identify possible fatigues of the structure and engineers can take early precautions to avoid any mishaps. Another use of wireless sensors is for passive localization and tracking purposes. For example, tracking people with tags and identification cards. So these, things can be monitored wirelessly. They are normally connected by wireless links in a mesh wireless sensor infrastructure. Finally, there is smart home monitoring whereby wireless sensors are used to monitor the security of the compound and the presence of human in unauthorized areas. This gives real-time security. Some sensors are even embedded in objects to form a WSN which enables network activity support services.

Applications Classification

Applications are differentiated by the type of data that must be collected in the network. Most common networks can be classified into two categories: event detection (ED) and spatial process estimation (SPE). In the first case sensors are deployed to detect say a fire in a forest, an earthquake and so on. Signal processing within devices need to be simple purely due to the fact that each device has the capability to compare the measured quantity with a given threshold and to send the binary information to the sink(s). The nodes need to make sure that the information is detected and transmitted to the sink(s) with a suitable success rate. This avoids unnecessary false alarm. The detection could be performed in a decentralized method meaning that sensors together with the sink can cooperatively undertake the task of identifying areas. However, there are greater challenges which exist in a WSN setting. For instance, there are constrains in power for each set of node, communication channels between nodes and the fusion center are severely bandwidth-constrained and no longer have issues such as fading, noise and, external sources of interference. In the context of decentralized detection, cooperation of nodes allows interchange of information among sensor nodes to continuously update the database until a consensus is reached across the nodes. In SPE the wireless sensor network aims to estimate the given physical phenomenon such as atmospheric pressure, the ground temperature, which is then interpreted as two dimensional random processes. Hence, the main priority here is to obtain the estimation of the entire behavior of the spatial process based on the data obtained. The measurements will then be subject to further processing which could be carried out either in a distributed manner by the nodes, or centrally controlled by the supervisor. The error estimation is purely correlated to nodes density and also the spatial variability of the process. Obviously, the higher the node density the more accurate the scalar field reconstruction at the expense of a larger network throughput and cost. Different network address the estimation of a scalar field using random WSNs. As an example, the presence of distributed algorithm will be able to estimate the smoothness of the process. The relationship between the random topology of a sensor network and the quality of the reconstructed field is investigated and some guidelines on how sensors should be deployed over a spatial area can be deduced. On the other hand, distributed source coding techniques can be applied to reduce the amount of data to be transmitted and hence to improve the network energy efficiency overall. Subsequently, there exist applications that utilize to both categories. In environmental monitoring applications there can be both ED and SPE. For example, the location of a fire in a forest is the first category. Alternatively, the estimation of the temperature of a given area belongs to the second category. In general, these applications are for monitoring indoor or outdoor environments, where the supervised area can range to hundreds or thousands of square kilometers for a long period of time. Natural disasters such as floods, forest fires, and earthquakes can be identified beforehand by installing network embedded systems at places prone to natural disasters. Such systems cannot rely on a fixed infrastructure and have to be very robust, because of the inevitable condition to be encountered in harsh open environments. The system should have the capability to respond to environment changes as rapid as possible. The case being the environment to be observed will be almost inaccessible for humans all the time judging by the safety reasoning. Therefore, the robustness of the sensors plays a vital role in such a demanding application. Also security systems have vital requirements such as real-time monitoring and high security. Another application that could belong to both the above defined categories is devoted to the realization of energy saving structures. In this application, sensor nodes could use a process (SPE), but also events (ED). In this case the WSN is distributed in buildings throughout to manage efficiently the energy consumption of all the electrical appliances. As a result, nodes have to be able to continuously monitor the energy consumed by all appliances connected to the electrical grid. Therefore, sensors have to estimate and process these data. As an example, sensors could detect the arrival of a person in a room to switch on some electrical appliances.

Examples of Application Requirements

Due to the varieties of possible applications of WSNs, system requirements would be significantly different. For instance, the environmental monitoring application has the following requirements like energy efficiency, nodes with restricted power supply; low data rate, limited data sensing capabilities; half duplex communication, nodes act only as sensors and as a result the data flow is from nodes to sink(s). Usually in environmental monitoring no wired connections will be used to connect sink(s) to the fixed network. Significantly the requirements are different for a typical industrial application where wireless nodes are used for cable replacement since it offers more reliability, withstand failure and interference; security, communication must be immune to intended attacks; inter-operability; high data rate flow, the process to be monitored usually carries huge amount of data; thus full duplex communication is needed, in industrial applications nodes typically act also as actuators and hence the communication between sink(s) and nodes must be reliable. The requirements are strongly application dependent, in order to design a wireless sensor network, especially scenarios where power supply could be constrained. Hence, high energy efficiency directly relates to long network lifetime and at the same time minimizes maintenance costs. Energy efficiency can be achieved at different levels starting from the technology level, physical layer, MAC, routing protocols up to the application level. For instance, nodes could operate with low duty cycle by spending most of their time in sleeping mode to save energy in the physical or MAC layer. This poses other problems such as nodes would not synchronize to awake, due to the differences to the nodes local clocks, therefore making the communication process impossible. Thus, suitable network synchronization schemes are mandatory in this case.

Main Features in Wireless Sensor Networks Design

Wireless Sensor Network challenges for applications

1.2.1 Power consumption

Wireless sensor network applications typically require network components with average power consumption that is substantially lower than currently provided in implementations of existing wireless networks such as Bluetooth. Applications involving the monitoring and control of industrial equipment require exceptionally long battery life so that the existing maintenance schedules of the monitored equipment are not compromised. Other applications, such as environmental monitoring over large areas, may require a very large number of devices that make frequent battery replacement impractical. Also, certain applications cannot employ a battery at all; network nodes in the applications must get their energy by mining or scavenging energy from the environment.

In addition to average power consumption, primary power sources with limited average power sourcing capability often have limited peak power sourcing capabilities as well; this factor should also be considered in the system design.

1.2.2 Cost

Cost plays a fundamental role in applications adding wireless connectivity to inexpensive or disposal products, and for applications with a large number of nodes in the network, such as wireless supermarket price tags. These potential applications require wireless links of low complexity that are low are in cost relative to the total product cost.

To meet this objective, the communication protocol and network design must avoid the need for high-cost components, such as discrete filters, by employing relaxed analog tolerances wherever possible, and minimize silicon area by minimizing protocols complexity and memory requirements. In addition, however, it should be recognized that one of the largest costs of many networks is administration and maintenance. To be a true low-cost system, the network should be ad hoc and capable of self-configuration and self-maintenance. An "ad hoc" network in this context is defined to be a network without a predetermined physical distribution or topology of the nodes. The term self-configuration can be defined as the ability of network to detect other nodes and organize the functioning network without human intervention. The term self-maintenance is defined as the ability of the network to detect and recover from faults appearing in other networks or communication links, again without human intervention.

1.2.3 Worldwide availability

Many of the proposed applications of wireless sensor networks, such as wireless luggage tags and shipping container location systems, implicitly require that the network capable of operation worldwide. Further, to maximize production, marketing, sales, and distribution efficiency of products that may have wireless sensor network devices embedded in them, and avoid the establishment of regional variants that must be individually monitored through (perhaps separate) distribution chains, it is desirable to produce devices capable of worldwide operation. Although, in theory, this capability may be obtained by employing Global Positioning System (GPS) or Global Navigation Satellite System (GLONASS) receivers in each network node and adjusting node behavior according to its location, the cost of adding a second receiver, plus the additional performance flexibility required to meet the varying worldwide requirements, makes this approach economically unviable. It is, therefore, desirable to employ a single band worldwide-one that has minimal variation in government regulatory requirements from country to country-to maximize the total available market for wireless sensor network.

1.2.4 Network Type

A conventional star network employing a single master and one or more slave devices may satisfy many applications. Because the transmit power of the network devices is limited by government regulation and battery life concerns, however, this network design limits the physical area a network may serve to the range of a single device (the master). When additional range is needed, network types that support multi-hop routing like mesh or cluster types must be employed; the additional memory and computational cost for routing tables or algorithms, in addition to the network maintenance overhead, must be supported without excessive cost or power consumption. It should be recognized that for many applications, wireless sensor networks are relatively large order (e.g., > 256 nodes); device density may also be high (e.g., in active supermarket price tag applications).

1.2.5 Security

The security of wireless sensor network has two facets of equal important-how secure the network actually is and how secure the network is perceived to be by users and (especially) potential users. The perception of security is important because users have a natural concern when their data (whatever it may be) is transmitted over the air for anyone to receive. Often, an application employing wireless sensor networks replaces an earlier wired version in which users could physically see the wires and cables carrying their information, and know, with reasonable certainty, that no one else was receiving their information or injecting false information for them to receive. The wireless application must work to regain that confidence to attain the wide market needed to lower costs. Often, the most important security goals are to ensure that any message received has not been modified in any way and are from the sender it purports to be. That is, if one has a wireless light and light switch in a home, there is often little to be gained by encrypting the commands "turn on light" and "turn off light."

Regarding security, the wireless sensor network designer faces three difficulties:

The length of the MIC, as well as the security plan in general, must be balanced with the typical length of data to be transmitted, and the desire for short transmitted messages. Although a 16-byte (128-bit) MIC is often cited as necessary for the most secure systems, it becomes unwieldy when single-bit data is being passed.

To minimize the cost of the network devices, the security features must be capable of implementation with inexpensive hardware, with a minimum addition of logic gates, random access memory (RAM), and read-only memory (ROM). Combination of low gate count, small memory requirements, and low executed instruction count limits the types of security algorithms that can be used.

Finally, perhaps the most difficult problem to solve in general is key distribution. Many methods are available, including several types of public key cryptography employing dedicated key loading devices and various types of direct user intervention.

1.2.6 Data throughput

Wireless sensor network have limited data throughput requirements when compared with Bluetooth (IEEE 802.15.1) and other WPANs and WLANs. For design purposes, the maximum desired data rate, when averaged over a one hour period, may be set to be 512b/s (64bytes/s), although this figure is somewhat arbitrary. The typical data rate is expected to be significant below this: perhaps 1b/s or lower in some applications.

This low required amount of data throughput implies that with any practical amount of protocol overhead, the communications efficiency of the network will be very low – especially when compared against a network sending TCP/IP packets that may be 1500 bytes long. No matter what design is chosen, the efficiency will be very low, and the situation, therefore, may be viewed in a positive light: the protocol designer has the ability to design free of the consideration of communications efficiency often a critical parameter in protocol design.

1.2.7 Message latency

Wireless sensor networks have very liberal Quality of Services (QoS) requirements, because in general, they do not support isochronous or synchronous communication, and have data throughput limitations that prohibit the transmission of real-time video and, in many applications, voice. The message latency requirements for wireless sensor networks is, therefore, very relaxed in comparison to that of other WPANs; in many applications, a latency of seconds or minutes is quite acceptable.

1.2.8 Mobility

Wireless sensor network applications, in general, do not require mobility. Because the network is therefore released from the burden of identifying open communication routes, wireless sensor networks suffer less control traffic overhead and may employ simpler routing methods than mobile ad hoc networks.

Main features:

The main features of wireless sensor networks can be deduced as scalability of the networks, self-organization, energy efficiency of networks, and degree of connectivity among nodes, and the complexity of networks, low cost and size of nodes. The framework for designing networks is the protocol architectures and technical solutions although, the design of such a protocol architecture and technical solution is not as simple, and more research is still needed.

8. Conclusions

The aim of this paper is to discuss some of the most relevant issues of WSNs, from the application, and technical features. The first part aims to explain in detail what wireless sensor networks are all about. The second part mainly presses on the applications of wireless sensor network in the current world we live in today. Finally, the paper provides a vision on future trends of the short- and long-term research on WSNs.

9. Acknowledgment

The main purpose of this review research paper is to have a further understanding on WSNs technically and its applications on the world we live today. Concurrently, we would like to take this opportunity to convey our gratitude and thank our lecturer Mr. Ayman Bin Salleh for his initiation in assigning us this assignment of writing a review research paper in order to improve and support our understanding of the course data communication and computer networking. By writing this review research paper a lot of research had to be done on the internet and also lots of reading and referring to Journal papers and topics related to WSNs. As such, we have gained a lot of knowledge in this topic related to data communication and computer networking. Finally, we have also got some experience in writing a review research paper which will surely aid us in our future undertakings.

10. References and Notes