Wireless Sensor Networks
First A. Author1,2,*, Second B. Author2, and Third C. Author3
1SRON Netherlands Institute for Space Research, Groningen, the Netherlands2University of Groningen, Kapteyn Astronomical Institute, Groningen, the Netherlands3California Institute of Technology, Pasadena, CA 91125, USA*Contact: [email protected], phone +31-50-363 4074
Abstract— Wireless Sensor networks (WSNs) have become one of the most interesting areas of research in thepast few years. A WSN is composed of a number of wireless sensor nodes which form a sensor field and a sink.These large numbers of nodes, having the abilities to sense their surroundings, perform limited computation andcommunicate wirelessly form the WSNs. Recent advances in wireless and electronic technologies have enableda wide range of applications of WSNs in military, traffic surveillance, target tracking, environment monitoringhealthcare monitoring, and so on. There are many new challenges that have surfaced for the designers of WSNsin order to meet the requirements of various applications like sensed quantities, size of nodes, and nodes’ autonomy. Therefore, improvements in the current technologies and better solutions to these challenges are required. The future developments in sensor nodes must produce very powerful and cost effective devices, so that they may be used in applications like underwater acoustic sensor systems, sensing based cyber physical systems,time critical applications, cognitive sensing and spectrum management, and security and privacy management.This paper also describes the research challenges for WSNs.
Key words: Future trends, recent advances, research challenges, wireless sensor networks
With the advances in the technology of microelectromechanical system (MEMS), developments inwireless communications and WSNs have also emerged. WSNs have become the one of the most interestingareas of research in the past few years. Here, we look into the recent advances and future trends in WSNs.WSNs are usually composed of small, low cost devices that communicate wirelessly and have the capabilities ofprocessing, sensing and storing. The development of WSNs was motivated by military applications such as battlefield surveillance. WSN are being used in many industrial and civilian application areas, including industrialprocess monitoring and control described by Kay and Mattern (2004), machine health monitoring described byTiwari (2007), environment and habitat monitoring, healthcare applications, home automation, and traffic control presented well by Kay ; Mattern (2004) and Hadim (2006). A WSN generally consists of a base station(also called as gateway sometimes) that can communicate with a number of wireless sensors via a radio link.Wireless sensor nodes collect the data, compress it, and transmit it to the gateway directly or indirectly with thehelp of other nodes. The transmitted data is then presented to the system by the gateway connection. This paperdiscusses the recent advances in WSNs that enable a wide range of applications and future development in applications like underwater acoustic sensor systems; sensing based cyber physical systems, time critical applications, cognitive sensing and spectrum management, and security and privacy management. Rest of the paper isorganized as follows. Section 2 describes the recent advances in WSNs. We discuss future trends in WSN inSection 3. Section 4 describes the research challenges for WSN. Finally Section 5 presents the conclusion. Page Layout
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Recent advances in wireless and electronic technologies have enabled a wide range of applications ofWSNs in military sensing, traffic surveillance, target tracking, environment monitoring, healthcare monitoring,and so on. Here we describe such type advances in WSN and their applications in various fields. Page Style
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Sensor Localization and Location Aware Services
Smart Home/Smart Office: A Smart home environments can provide custom behaviours for a given individual. Considerable amount of research has been devoted to this topic. The research on smart homes is now starting to make its way into the market. It takes a considerable amount of work and planning to create a smart home. There are many examplesof products currently on the market which can perform individual functions that are considered to be part of asmart home. Several useful applications which take advantage of information collected by WSN are presentedby Hussain et al. (2009).
Military: New and emerging technologies, such as networks, support military operations by delivering critical information rapidly and dependably to the right individual or organization at the right time. This improves theefficiency of combat operations. The new technologies must be integrated quickly into a comprehensive architecture to meet the requirements of present time. Improvement in situation awareness (ChienChung Shen, 2001)is must requirement. Doumit and Agrawal (2002) described some other important application is detection ofenemy units’ movements on land/sea, sensing intruders on bases, chemical/biological threats and offering logistics in urban warfare. Command, control, communications, computing, intelligence, surveillance, reconnaissance, and targeting systems are well described by Akyildiz (2002).
Industrial & Commercial: New Since the long-time wireless transmission of data is being done in industrial applications, but recently it has gained importance. Successful use of wireless sensors in systems such as supervisory control and data acquisition has proved that these devices could effectively address the needs of industrial applications. The critical process applications of WSNs in industry are monitoring temperature, flow level, and pressure parameters. With the rapidly increasing technological advances in wireless technology and its subsequently decreasing prices, numerous wireless applications are being developed in industry. WSN in manufacturing industries can monitor and optimize quality control.
Traffic Management and Monitoring: Every big city is suffering from traffic congestion around the world. A sincere effort is being made tosolve the traffic congestion. Congestion can be alleviated by planning managing traffic. A real time automatictraffic data collection must be employed for efficient management of rush hour traffic. Research on this topic isconsidered as part of the Intelligent Transport System (ITS) research community. Chinrungrueng (2006) explained ITS to be the application of the computers, communications, and sensor technology to surface transportation. The vehicle tracking application is to locate a specific vehicle or moving object and monitor its movement. This work also describes design of WSN for vehicular monitoring. As the power source (battery) is limited, it is important that a design of sensor node is power efficient.
Structural Healthcare: Structures are inspected at regular time intervals, and repairing or replacing based on the time of use,rather than on their working conditions. Tiwari et al. (2004) has explained that sensors embedded into structuresenable condition based maintenance of these assets. Wireless sensing will allow assets to be inspected when thesensors indicate that there may be a problem. This will reduce the cost of maintenance and preventing harmfulfailure. These applications include sensors mounted on heavy duty bridges, within concrete and composite materials (Arms et al. 2001), and big buildings.
Agriculture: Wang and Wang (2006) stated that agriculture can also be benefited by the deployment of WSN to getthe information regarding soil degradation and water scarcity. With help of WSNs we can check the clean waterconsumed in irrigation and manage it.
Topology and Coverage Control
Topology control is one of the fundamental problems in WSNs. It has great importance for prolonglifetime, reducing radio interference, increasing the efficiency of media access control protocols and routingprotocols. It also ensures the quality of connectivity & coverage and increase in the network service as well. Asignificant progress in research can be seen in WSNs topology control. Many topology control algorithms havebeen developed till date, but problems such as lack of definite and practical algorithm, lack of efficient measurement of network performance and idealness of mathematical model still exist. Several graph models used intopology control, the present hot spots and the future trends on the research of topology control are presented byJardosh and Ranjan (2008).
Quality of Service (QoS) Provision
QoS support is challenging due to severe energy and computational resource constrains of wireless sensors. Various service properties such as the delay, reliability, network lifetime, and quality of data may conflict;for example, multipath routing can improve the reliability; however it can increase the energy consumption anddelay due to duplicate transmissions. Modeling such relationships, measuring the provided quality, and providing means to control the balance is essential for QoS support. There are various research opportunities in enhancing the QoS of WSNs. One of the researches is the project described by Abidin (2009) that analyzes andenhances the performance of a WSN by deploying a simple max min fairness bandwidth allocation technique.
Mobility is one of the most important issues in next generation networks. As WSNs are becoming thenext elements of the future Internet, it is crucial to study new models that also support mobility of these nodes.WSNs are applicable in variety of cases that make it difficult to produce a standard mobility scenario. Followingare some cases where the mobile support is necessary presented in Camilo (2008). Intra WSN device movementis probably the most common scenario in WSNs architectures, where each sensor node has the ability to changefrom its local position at run time without losing the connectivity with the sensor router (SR). In the case of interWSN device movement, sensor nodes move between different sensor networks, each one with its SR responsible to configure and manage all the aggregated devices. A research project of IETF working group NEMO, anexample of WSN movement is described in RFC3963 by Devarapalli (2005). Sensor network deployed in amoving bus is a real scenario of this type. It is possible to have a scenario where a sensor network can useanother sensor network in order to be connected through Internet. MANEMO (Wakikawa et al., 2007) project isalso an example.
The uses of WSNs in biomedical and medical are in growing phase. Biomedical wireless sensor networks (BWSNs) show the future opportunities for supporting mobility while monitoring vital body functions inhospital and home care. There is a requirement for BWSN to develop in order to cover security handling, improved signal integration and visualization. They can also be used to achieve extended mobility outside the surgery room, monitoring of several patients/persons at the same time, and further adaptations to medical expertsneeds for information. As the Internet usage has become popular among people, eservices for the healthcarewhich is commonly known as eHealth, have recently attracted significant attention within both the research society and industry.
The future developments in sensor nodes must produce very powerful and cost effective devices, sothat they may be used in applications like underwater acoustic sensor systems, sensing based cyber physicalsystems, time critical applications, cognitive sensing and spectrum management, and security and privacy management. In this section we will look into all possibilities of further development in WSN applications.
Cognitive sensor networks are used for acquiring localized and situated information of the sensing environment by the deploying a large number of sensors intelligently and autonomically. Managing a large number of wireless sensors is a complex task. As GuangZhong Yang (2008) described, a significant research interestcan be seen in bio inspired sensing and networking. Two well known examples of cognitive sensing are swarmintelligence and quorum sensing:1. Swarm intelligence is developed in artificial intelligence for studying the collective behavior of decentralized,self organized systems.2. Quorum sensing is an example of bioinspired sensing and networking. Quorum sensing is the ability of bacteria to communicate and coordinate behavior via signaling molecules.
As application of low power wireless protocols is increasing, we can envision a future in which wireless devices, such as wireless keyboards, power point presenters, cell phone headsets, and health monitoringsensors will be ubiquitous. But the pervasiveness of these devices leads to increased interference and congestionwithin as well as between networks, because of overlapping physical frequencies. Cognitive radios and multifrequency MACs are some approaches that have been developed to utilize multiple frequencies for parallelcommunication. A generic solution is provided by Zhou (2009) as SAS: a Self Adaptive Spectrum Managementmiddleware for WSNs, which can be easily integrated with an existing single frequency.
Underwater Acoustic Sensor Systems
Akyildiz et al. (2005) presented a complete survey in underwater sensor networks. Underwater sensornetworks are designed to enable applications for oceanographic data collection, pollution monitoring, offshoreexploration, disaster prevention, assisted navigation and tactical surveillance applications. Underwater sensorsare also being in use for exploration of natural undersea resources and gathering of scientific data. So a need ofunderwater communications among underwater devices arises. Underwater sensor nodes and vehicles should becapable of coordinate their operation, exchanging their location and movement information and hence relay monitored data to an onshore base station. A new research paradigm of underwater wireless sensor networks(UWSNs) poses challenges like large propagation delays, node mobility and high error probability of acousticunderwater channels, compared to the ground based WSNs. A protocol named DUCS (Distributed UnderwaterClustering Scheme) described by Domingo and Prior (2008), is a GPS free routing protocol. It minimizes theproactive routing message exchange and does not use flooding techniques. It also uses data aggregation to eliminate redundant information.
Coordination in Heterogeneous Networks
Since the sensor nodes are energy constraints so the main obstacle in the coordination with other networks is limited energy of sensor nodes. Sensor networks are very useful for applications like health monitoring,wildlife habitat monitoring, forest fire detection and building controls. To monitor the WSN, the data producedby sensor nodes should be accessible. This can be done by connecting the WSN with existing network infrastructure such as global Internet, a local area network or private internet. Liutkevicius (2010) described two typeof interconnection techniques: gateway based interconnection technique and overlay based interconnectiontechnique.
Time Critical Applications
A new generation of distributed embedded systems, with a broad range of real time applications, suchas fire monitoring, border surveillance, medical care, and highway traffic coordination, can be represented byWSNs. Due to severe resource limitations in highly dynamic environments these systems face new kinds of timing constraints. Many classical approaches to real time computing like wireless networking protocols, operatingsystems, middleware services, data management, programming models, and theoretical analysis are challengedby WSNs. The design of complex time critical systems includes different types of information and communication technology systems, such as wireless (mesh) sensor networks, to carry out control processes in real time.
Experimental Setup and New Applications
There are huge opportunities to deploy WSNs for real life applications and experimental setups. WSNsare being deployed in various application scenarios, including rural and forest environments. Sanchez (2010)designed a WSN based system for generic target (animal) tracking in the surrounding area of wildlife passages.That is built to establish safe ways for animals to cross transportation infrastructures. This deployment is designed on the basis of the IEEE 802.15.4 standard
New Models and Architectures
WSN is a self organized network of battery powered wireless sensors that can sense, process, andcommunicate. We have discussed many technical challenges so far that deserve sincere consideration. Thesechallenges are not limiting the progress in WSNs so much as lack of perfect WSN architecture. Some of recentlydeveloped architectures are discussed here: the environment adaptive and energy efficient capabilities should beintegrant for WSN architecture. A hierarchical structure and subfacets functions architecture model EAWNA isproposed by L. Liu (2010) that also has other objectives like scalability, customized services, environment adaptive and energy efficiency. Conventional network architecture designs are based on layering approach. Holes Problem
Holes are one of the challenges in deployment of WSNs in a large area. Holes generally considered as acommunication gap among sensor nodes. Khan and Javed (2008) described various types of holes like Coveragehole, Routing hole, Jamming hole, Sink/Black hole, and Worm hole in their survey work.
1. Power: Power is always been a challenge for WSNs designs. One of the ways to prolong the network lifetimeis to design the energy efficient algorithms and hardware that uses power intelligently.2. Hardware Cost: One of the main challenges is to produce low cost and tiny sensor nodes. Current sensornodes are mainly prototypes with respect to these objectives. Low cost of sensor nodes can be achieved by recent and future progress in the fields of MEMS.3. Security: Security is one of the major challenges in WSNs. Most of the attacks that are performed on WSNare insertion of false information by compromised nodes within the networks. Development of security schemesfor WSN also faces challenges related to constrained environment.4. System Architecture: Researches in the field of WSN is going on around the world but still there is no unified system and network architecture, on the top of that different application can be built.5. Real World Protocols: protocols need to be developed for real world problems considering the theoreticalconcepts and synthesizing novel solutions into a complete system wide protocol for real world application.6. Analytical and Practical Results: Till date very few analytical results exists for WSNs. All new applicationsonly get confidence when it is tested & analysed practically and results are compared with existing schemes.
The inherent nature of WSNs makes them deployable in a variety of circumstances. They have the potential to be everywhere, on roads, in our homes and offices, forests, battlefields, disaster struck areas, and evenunderwater in oceans. This paper surveys the application areas where WSNs have been deployed such as military sensing, traffic surveillance, target tracking, environment monitoring, and healthcare monitoring as summarized in Table 2. The paper also surveys the various fields where WSNs may be deployed in the near future asunderwater acoustic sensor systems, sensing based cyber physical systems, time critical applications, cognitivesensing and spectrum management, and security and privacy management. These application areas are beingresearched extensively by various people across the industry and academician.
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