Wireless Sensor Networks Technicallys

Published Date: 02 Nov 2017

Navina Krsna(Author)

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—component; formatting; style; styling; insert (key words)

Introduction

In recent years, the desire for connectivity has caused continued growth in wireless communication. Wireless data networks, in particular, 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 services are 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. Some of the applications for instance are industrial control and monitoring; home automation and consumer electronics; security and military sensing, asset tracking and supply chain management and intelligent agriculture and health monitoring. 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, denoted as nodes, which can sense the environment and communicate the information gathered from the monitored field through wireless links [1–9]. 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, the amount of data gathered by the sink increases and once its capacity is at its maximum. 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) [13]. The level of node density, a larger number of sinks will decrease the probability of isolated clusters of nodes that cannot deliver their data owing to unfortunate signal propagation conditions. In contrast, a multi-sink WSN can be scalable which means the same performance can be achieved even by increasing the number of nodes in a network, while does not apply for a single-sink network. However, a multi-sink WSN does not represent a minor extension of a single-sink case for the network engineer. 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, this means that a selection can be done, based on a suitable criteria that could be, for example, minimum delay, maximum throughput, and minimum number of hops. Thus, multi sinks provides better network performance with respect to the single-sink assuming the same number of nodes is deployed over the same area but, the protocols 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 [14], health care [15], positioning and tracking [16], to logistic, localization, and so on. A possible classification for applications is provided in this section. It is important to underline that the application strongly affects the choice of the wireless technology to be used. Once application requirements are set, in fact, the designer has to select the technology which allows satisfying these requirements. To this aim the knowledge of the features, advantages and disadvantages of the different technologies is fundamental.

Applications of wireless sensor networks:

Industrial control and monitoring

A large, industrial facility typically has a relatively small control room, surrounded by a relatively large physical plant. The control room will have indicators and displays that describe the state of the plant like the state of valves , the condition of equipment , the temperature and pressure of stored materials. As well as input devices that control actuators in the physical plant(valves, heater,etc.) that effect the observed state of the plant. The sensors describing the state of the physical plant, their 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 armored cable that must be used to communicate between them in a wired installation. Significant cost savings may be achieved if an inexpensive wireless means were available to provide this communication. Because the information being communicated is the state information, if often changes slowly. Thus, in the normal operation , the required data throughput of the network is relatively low, but the required reliability of the network is very high. A wireless sensor network of many nodes , providing multiple message routing paths of multi-hop communication, can meet these requirements.

An example of wireless industrial control is the control of commercial lighting. Much of expense in the installation of lights in a large building concerns the control of light – where the wired switches will be , which lights will be turned on and off together, dimming of the lights,etc. A flexible wireless system can employ a handheld controller that can be programmed to control a large number of lights in a nearly infinite variety of ways, while still providing the security needed by a commercial installation.

A further example is the use of wireless sensor networks for industrial safety applications. Wireless sensor networks may employ sensors to detect the presence of noxious, poisonous , or otherwise dangerous materials, providing early detection and identification of leaks or spills of chemicals or biologically agents before serious damage can result (and before the material can reach the public).Because the wireless networks may employ distributed routing algorithms, have multiple routing paths, and can be self healing and 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 otherwise moving machinery is another area suitable for wireless sensor area networks. In such applications, wired sensor and actuators are often impractical, yet it may be important to monitor the temperature, vibration , lubrication flow, etc. of the rotating components of the machine to optimize the time between maintenance periods, when the machine must be taken off-line. To do this, it is important that the wireless sensor system be capable of operating for the full interval between maintenance periods; to do otherwise defeats the purpose of the sensors. This, in turn, requires the use of a wireless sensor network with very low energy requirements. The sensor node often must be physically small and inexpensive as well. Wireless sensor networks may be of particular use in the prediction of component failure for aircraft, where these attributes may be used to particular advantage.

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 number of these thermostats and humidistats is limited, however, by the costs associated with their wired connection to the rest of the HVAC system. In addition, the air handlers and dampers that directly control the room environment are also wired; for the same reasons, their numbers are also limited.

1.1.2 Home automation and consumer electronics

The home is very large application space for wireless sensor networks. Many of the industrial applications just described have parallels in the home. For example, a home HVAC system equipped with wireless thermostats and dampers can 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 only a single, wired thermostat. However, many other opportunities are available.

One application is the "universal" remote control, a personal digital assistant (PDA)-type device that can control not only the television, DVD player, stereo, and other home electronic equipment, but the lights, curtains, and locks that are also equipped with a wireless sensor network connection. With the universal remote control, one may control the house from the comfort of one’s armchair. 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. With the scale and personal computer both connected via a wireless sensor network, one’s weight may be automatically recorded without the need for manual intervention ( and the possibility of stretching the truth "just this once").

A major use of wireless sensor networks in the home is expected to be for personal computer peripherals, such as wireless keyboard and mice. Such applications take advantage of the low cost and low power consumption that are the sine qua non of wireless sensor networks. Another application in the home is sensor-based information appliances that transparently interact and work symbiotically together as well as with the home occupant.

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 (save a few night lights),turns on outdoor security light, and sets the home’s HVAC system to nighttime(sleeping) 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.

Outside of the home, the location-aware capabilities of wireless sensor networks are suitable for a diverse collection of consumer-related activities, including tourism and shopping. In these applications, location can be used to provide context-specific information to the consumer. In the case of the tourism guide, the user is provided only information relevant to his present view; in the case of the shopping guide, the user is provided information relevant to the products before him, including sale items and special discount and offers.

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 (the " panic button" sensor requesting immediate assistance).

As with many technologies, some of the ealiest 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 (or the civilian population afterward ). 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 (i.e.,without a single point of failure), a feature that makes them difficult to destroy in battle. The use of spread spectrum techniques, combined with the bursty transmission format common to many wireless sensor networks (to optimize battery life), can give them a low probability 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 are empty and in storage, 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 in such a situation; by placing sensors on each container, its location can always be determined.

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 to quickly and accurately identify the location of material to be sold.knowing where a product is can mean the difference between making or not making a sale, but knowing the status of the entire supply chain – from raw materials through components to final product – can help a business operate more efficiently . for example, transferring axcess 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 tomanufacture 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 bingable 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 alredy 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 monitorthe 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 Sattelite (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 (aslow as one bit – "yes or no"- in response to the "Did it rain today?"query), and the message latency can be on the order of minutes. Yet, costs must be low, and power consumption must be low enough 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 application 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.

Wireless sensor networks may also be used for low-power sensing of environmental contaminants such as mercury. Integrated microcantilever sensors sensitive to particular contaminants can archieve parts-per-trillion sensitivities. Sensors can be attached with wireless transceiver in a standard complementary metal oxide semiconductor (CMOS) process, providing a very low- cost solution to the monitoring of chemical and biological agents.

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" is usually defined as "monitoring of non-life-critical health information," to differentiate It from medical telemetry, although the definition is broad and nonspecific, and some medical telemetry applications can be considered for wireless sensor networks.

Two general classes of health monitoring applications are available for wireless sensor networks. One class is athletic performance monitoring, for example, tracking one’s 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 and recording by a 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 inpharmaceuticals and medical care.

A developing field in the health monitoring market is that of implanted medical devices. In the United States, the Federal Communications Commission (FCC) established regulations governing the Medical Implant Communications Service, In January 2000,"for transmitting data in support of diagnostic or therapeutic functions associated with implanted medical devices. These types of systems can be used for a number of purposes,from monitoring cardiac peacemakers to specialized drug delivery systems.

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 that rescuers can be use to locate the wearer in time of emergency, are use by skiers and other mountaineers in avalanche prone areas. The oresent systems have their limitations, however; principal among these is that they provide only location information, and give no information about the 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, including oximeters and thermometers, so that would-be rescuers would be able to perform triage in a large avalanche, identifiying 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 area 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. For instance, the temperature at the mountain or under the deep sea and the humidity of the particular area. 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 which can lead to intoxification. 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. And variations of different aspect which may occur during or 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 reliablilty. 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 instance, monitoring the temperature of the fridge or the level of water in the coolants of nuclear powered stations. 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 ID 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 gathered in the network. Almost any application, in fact, could be classified into two categories: event detection (ED) and spatial process estimation (SPE). In the first case sensors are deployed to detect an event, for example a fire in a forest, a quake, etc. [17–19]. Signal processing within devices are 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 while maintaining a low rate of false alarm. The detection of the phenomenon of interest (POI) could be performed in a decentralized (meaning that sensors, together with the sink, cooperatively undertake the task of identifying the POI. However, there are greater challenges which exist in a WSN setting. There are power constraints for each 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 a bi-dimensional random process. In this case the main issue is to obtain the estimation of the entire behavior of the spatial process based on the samples taken by sensors that are typically placed in random positions [20–23]. The measurements will then subject to proper processing which might be performed either in a distributed manner by the nodes, or centrally at the supervisor. The estimation error is strictly related to nodes density as well as on the spatial variability of the process. Higher nodes density lead to a more accurate scalar field reconstruction at the expense of a larger network throughput and cost. In the recent literature, different works addressed the estimation of a scalar field using random WSNs. As an example, [20] presents a distributed algorithm able to estimate the gradient of a generic smooth physical process (energy constraints and nodes failure are not considered there); in [21] 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 for efficient data acquisition and reconstruction are derived. Distributed source coding techniques can be successfully exploited to reduce the amount of data to be transmitted and hence to improve the network energy efficiency [24]. There exist also applications that belong to both categories. As an example, environmental monitoring applications could be ED- or SPE-based. To the first category belong, for example, the location of a fire in a forest, or the detection of a quake, etc. (see Figure 2). 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 may be few hundreds of square meters 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 impairments encountered in open environments. The system should respond to environment changes as quick as possible. The environment to be observed will mostly be inaccessible by the human all the time. Hence, robustness plays an important role. 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 efficient buildings. In this application, in fact, sensor nodes could aim at estimating a process (SPE), but also events (ED). In this case the WSN is distributed in buildings (residential or not) to manage efficiently the energy consumption of all the electric appliances. Consequently, nodes have 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 wide variety of possible applications of WSNs, system requirements could change significantly. For instance, in case of environmental monitoring applications, the following requirements

are typically dominant: energy efficiency, nodes are battery powered or have a limited power supply; low data rate, typically the amount of data to be sensed is limited; one-way communication, nodes act only as sensors and hence the data flow is from nodes to sink(s); wireless backbone, usually in environmental monitoring no wired connections are available to connect sink(s) to the fixed network. Significantly different are the requirements of a typical industrial application where wireless nodes are used for cable replacement: reliability, communication must be robust to failure and interference; security, communication must be robust to intentional attacks; inter-operability, standards are required; high data rate, the process to be monitored usually carries a large amount of data; two-way communication, in industrial applications nodes typically act also as actuators and hence the communication between sink(s) and nodes must be guaranteed; wired backbone, sinks can be connected directly to the fixed network using wired connections. Even if requirements are strongly application dependent, one of the most important issues in the design of WSNs, especially in such scenarios where power supply availability is limited, is energy efficiency. High energy efficiency means long network lifetime and limited network deployment and maintenance costs. Energy efficiency can be achieved at different levels starting from the technology level (e.g., by adopting low consumption hardware components), physical layer, MAC, routing protocols up to the application level. For example, at physical and MAC layers, nodes could operate with low duty cycle by spending most of their time in sleeping mode to save energy. This poses new problems such as that nodes may not wake up at the same time, due to the drifts of their local clocks, thus making the communication impossible. Suitable network synchronization schemes are mandatory in this case [8, 25].

Main Features in Wireless Sensor Networks Design

The main features of wireless sensor networks, can be deduced as scalability of the networks, self-organization, energy efficiency of networks, degree of connectivity among nodes, the complexity of networks, low cost and size of nodes. Protocol architectures and technical solutions providing such features can be considered as a potential framework to design such networks but, the definition of such a protocol architecture and technical solution is not as simple, and more research is still needed [5].

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 and its applications. We would like to take this opportunity to thank 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 understand of the course data communication and 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 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