Cognition in Wireless Sensor Networks

“Cognition in wireless sensor networks”

(Next generation smart networks-A WAY AHEAD)

Nidhi Joshi AnchalAirwan

() ()

Abstract-In this paper we are describing the basics of cognition in wireless sensor networks.As the name indicates itself“cognition” i.e about adapting the environ-ment as per the need and change its network parameters.Cognition in wsn basically deals with the environment sensing through which the networks can detect the parameters according to the conditions.Cognitive net- works are the next generation networks used for spectrum sensing.Spectrumsensing is a concept to overcome the interference problem due to the fixed spectrum allocation in the frequency bands for wireless systems.These kind of networks are used for higher transmission rate and most effecti- vely energy efficient transmission.In this article the main design principles,potential advantages,application areas of CRSNs are introduced.We also discuss the basic challenges,attacks and ideas to overcome these.

Introduction-Cognitive wireless sensor networks are the next generation networks which leads toward self-adapting ability.It detects the best wireless channels available in its vicinity.These kind of networks detect channels available in the wireless spectrum for the reliability then accordingly changes its transmission and reception parameters to allow more concurrent communication in a given spectrum band.With these capabilities cognitive radio can operate in licensed as well as unlicensed bands.In licensed bands wireless users with a specific license to communicate over the allocated band (the primary users,PUs)have the priority to access the channel.Cognitive radio user, called secondary users (SUs),can access the channel as long as they does not cause interference to the PUs.

When a PU starts communication,the cognitive radio user must detect the potentially vacant bands(spectrum sensing), decide onto which channel to move (spectrum decision),and then finally adapt its transceiver so that the active communication is continued over the new channel(spectrum handoff).This sequence of operation outlines a typical cognitive cycle which can also be applied over an unlicensed band by all cognitive radio users.Due to these actions of performance cognitive wsn has several advantages over simple wsns which are described as follows-

(1)-Dynamic Spectrum Access-Dynamic spectrum access is the phenomenon which specify dynamic allocation of the spectrum bands for the users.In simple wsns the spectrum allocation is fixed with the unlicensed spectrum users which leads toward overcrowded spectrum and hence provide breaks in communication.DSA technique provides dynamic access of the spectrum for the simple wsn.

(2)-Handling of busty traffic-Cognitive sensors worked on reliable data transfer mechanism.If the spectrum for the present user get busy at the time of communication, channel uses cognitive feature of wsn that provides reliability.It uses the white space of spectrum i.e unused part of the licensed band.

(3)-Low Power Consumption-CWSN havi- ng the ability to switch over licensed and unlicensed bands at the time of traffic handling.This switch over deals with energy efficiency in the network which is the most important feature as regard to the communication network.

(4)-Improved the consumption of limited radio spectrum resources-In CWSN the primary users and secondary users both have licensed and unlicensed band allocation which consumed the uses of white space i.e unused part of the licensed spectrum.Every user has a dynamic spectrum allocation so that the spectrum band can be used efficiently to overcome the problem of jamming due to large no. of users for the same wireless channel in the spectrum.

Characteristics of Cognitive WSN-There are mainly two characteristics of cognitive wireless sensor networks which are described as follows-

(a)-Cognitive Capability-This feature mainly deals with the ability of sensing the spectrum at the time of congestion.Cognitive capability defines the ability of CWSNs to learn from its radio environment.There are three steps which are followed in cognitive capability part to detect the dynamically changing parameters-

(i)-Spectrum Sensing-A cognitive radio monitors the available spectrum bands, captures their information and then detects the spectrum holes.

(ii)-Spectrum Analysis-The characteristics of the spectrum holes that are detected through spectrum sensing are estimated.

(iii)-Spectrum Decision-A cognitive radio determines the data rate,the transmission mode and the bandwidth of the transmission. Then,the appropriate spectrum band is chosen according to the spectrum characteri- stics and user requirements.

Fig-1.1 Cognitive Cycle

(b)-Reconfigurability-The cognitive capab- ility provides spectrum awareness whereas reconfigurabilityenables the radio to dyna-mically change its parameters according to its radioenvironment.The reconfigurability refers to the ability to dynamically vary the modulation scheme,transmission power,time and frequency.The main parameters which are considered to be changed and observed in the dynamic environment i.e modulation,transmission power and operating frequency

Performance-There are several features which makes CWSNs advantageous over simple WSNs.Cognitive Wireless Sensor Network(CWSN) is a network mainly used to overcome the defects of simpleWSNs.CWSNs are the networks working on the phenomenon of self-adaptation which is a key benefit towards the negatives of simple WSNs.As WSNs have less memory storage,energy consumption and higher information loss which leads towards failure of the networks in large area of applications.Some of the performance aspects of CWSNs over the simple WSNs are as follows-

(i)-Data Reliability:In simple WSNs reliability of data is a major problem as sensors are battery enabled devices used to gather the data from the environment.In the large areas of application sensors are not able to work for long duration of time period as consume more energy for the operations which is not possible to be increased as WSNs are randomly deployed in a specific region and energy is predefined.CWSNs are the substitutes to overcome with this problem of simple WSNs,it uses the concept of cognition i.e users can use the unused part of the spectrum as per there requirement without any kind of interruption in the services.This concept provides reliability in data transfer.

(ii)-Energy Efficiency:As in simple WSNs energy of each and every sensor device is defined at the time of deployment.Due to this sensor devices are less energy efficient as they require more energy to charge it up in case of discharge of batteries.In CWSNs as the users work on a concept of spectrum sensing energy efficiency get improvised throughout the network.As the network breakdown is very low and hence energy consumption of every user is low i.e highly energy efficient.

(iii)-Transmission Rate:Discharging of sensor devices concluded in interruption of services.This interruption degrades the performance of WSNs as the transmission of data disturbed.In CWSNs the user occupy the spectrum which is unused at the time of interference of users so it improvises the transmission rate of the data.

(iv)-Delays:Higher transmission rate decrea- ses the delays in between information gathering and processing.In WSNs the delays are increased by means of lower energy efficient devices but in CWSNs the devices have large scale of energy efficiency which provides lower delays and low network failures during information exchange.

(v)-Communication Efficiency:WSNs are less communication efficient as there are higher delays and storage of data is very low.CWSNs overcome with better communication efficiency as there are better spectrum uses,hence lower delays and information loss.

(vi)-Spectrum Usage:WSNs utilizes less spectrums results in breakage of informa- tion.To overcome the problem of WSNs, CWSNs better use the spectrum by not interrupting the primary users i.e licensed users.

Application Areas-CWSNs has several application areas,some of them are discussed below:

1.4.1.1 Emergency

CWSNs are the advance versions of WSNs but the areas of application remains the same.Public safety and emergencynetworks are another area in which CWSN networks can be implemented.In the case of natural disasters,which may temporarily disable or destroy existing communication infrastru- cture,emergency personnelworking in the disaster areas need to establish emergencynetworks.Since emergency networks deal with the critical information,reliable comm- unicationshould be guaranteed with minimum latency.In addition,emergency communication requires a significantamount of radio spectrum for handling hugevolume of traffic including voice,video and data.CWSN networks can enable the usage of the existing spectrumwithout the need for an infrastructure and bymaintaining communication priority and responsetime.

1.4.1.2 Multimedia Applications

Reliable and timely delivery of event features in the form ofmultimedia by resource-constrained sensor nodes under varyingchannel conditions is an extremely challenging objectivedue to the inherent high bandwidth demands of multimedia.CRSNs may provide sensor nodes the freedom to dynamicallychange communication channels according to the environmentalconditions and application-specific QoS requirements in terms of bandwidth,bit error rates,and access delay.For example,as the packet travels through multiple hops,eachrelaying node may use higher frequencies and the highest possibledata rate to provide required bandwidth.

1.4.1.3 Military

One of the most interesting potential applications of a CWSN network is in a military radio environment.CWSN networks canenable the military radios choose arbitrary,intermediate frequency (IF) band- width,modulation schemes,and coding sche- mes,adapting to the variableradio envi- ronment of battlefield.Also militarynet- works have a strong need for security and protectionof the communication in hostile environment.CWSN networks could allow military personnelto perform spectrum handoff to find secure spectrumband for themselves and their allies.

1.4.1.4 Environment

Environmental monitoring of large areas can be done through CWSN networks.In present scenario it is very much important to gather the information regarding to the changes in parameters of environment.There are several kind of climate changes which leads toward heavy disasters like landslides and hence it is really very important to monitor it in every possible cases.It is not possible to monitor the habits of several creatures as their eating,breeding etc in the remote areas.To detect all the possibilities sensors are deployed in the remote region to gather the information.Monitoring vast areas such as great forests or oceanic areascould be impossible without WSNs.Moreover, the numerous sensors provide informationof many variables that can help to prevent certain natural disasters.All ofthat while minimizing the environmental impact of the human activities.

1.4.1.5 Healthcare

Health is the major concern with respect to human being so it is really very important to track the conditions of an individuals.To take the data samples of any person sensors are deployed in form of wearable and non- wearable devices to monitor different kind of parameters regarding to several diseases.Due to the easy integration in small devices,WSNs will improve the controlof patients’s vital signs and act consequently if there is any variation on them.It canbe considered one of the most promising fields of actuation as long as the devicesbecome smaller.

1.4.1.6 Security Monitoring

In many areas where security is the main point to monitor like banks,historical building and places of ancient things,museum.These kind of places require high level of security to monitor any suspicious acitivity.Restringed areas such as government buildings,nuclear plants or airports,where typical monitorization can not be placed,whereas WSNs can bediscreetly placed almost everywhere.It was one of the firsts application fields of thecurrent WSNs.

1.4.1.7 Domotics

Affordable technology for the next coming homes,WSNs will automatically act according to some user presets and taking into account the environmental issues as time,temperature,humidity or even the energy consumption.In addition,this technology is easy to deploy in the already existing homes,without requiring a great construction work because of the its wireless feature.Furthermore,this technology is likely to become cheaper than the wired one.

1.4.1.8 Industrial sensors

Some of the quality controls within the manufacturing industryare being done by WSNs since they can be placed easily and they accomplish theirtasks more efficiently than the traditional quality controls.

1.4.1.9 Automotive industry:

As a complement for the control cameras, WSNs can add informationof the situation of the car either locally by built-in sensors around the car,orglobally by getting live information of the state of our route, warning us from trafficincidents.

Security Challenges and problems in CWSNs-Due to CWSNs dynamic environment adaptability there are many challenges which has to be faced by the network users some of them are as follows-

(i)-Dynamic Environment-Dynamic envir-onment changes the parameters frequently in CWSNs so it is very challenging to maintain the parameters of the networks at every point of spectrum change.The dynamic nature of sensor networks means no structure can be statically defined.Cognitive approach includes new dynamic issues: communication protocol,modulation,freque- ncy,sensibility or emitted power.The attacker can use these powerful characteristics to affect the data transmissions between nodes with a concrete purpose.The goal could be from isolate a node to try to change the behaviour of entire network.Security schemes must be able to operate within this dynamic environment.

(ii)-Less Security due to hostile environment-Due to its dynamic environ- ment there are very high possibilities of attacking to thief the information gathered.In the dynamic environment it is very difficult to detect every change in parameter so as the information,it is very easy for the outside users to fetch the information.The hostile environment in which cognitive sensor nodes function,nodes face the possibility of destruction or capture by attackers.Since nodes may be in a hostile environment attackers can easily gain physical access to the devices.Attackers may capture a node,physically disassemble it,and extract from it valuable information(e.g. crypto graphic keys).Because of the capacity of change the communication protocol,a capture node can affect to the whole network.For example,a malicious node can order to the network use a specific modulation or cryptographic algorithm and capture all the data.Also node can provide wrong information to the network causing a bad configuration.The ability to have a profound effect on network performance and behaviour through simple spectral manipulation is very dangerous.The highly hostile environment represents a serious challenge for security researchers.

(iii)-Wireless Medium-The wireless medium is inherently less secure because its broadcast nature makes eavesdropping simple.Any transmission can easily be intercepted,altered or replayed by an adversary.The wireless medium allows an attacker to easily intercept valid packets and easily inject malicious ones.Cognitive features allow a dynamic reconfiguration to avoid these attacks.However,malicious nodes can use the dynamic reconfiguration to create new attacks such us PUE(Primary User Emulation).CWSNs have to adapt traditional wireless problems to cognitive networks.

Scalability of security mechanism-Cognitive networks are not only hundreds of sensors;they can also include different wireless interfaces and integrate a myriad of nodes in the same network.Providing security over such a network is equally challenging.Security mechanisms must be scalable to very large networks with different radio interfaces while maintaining high computation and communication efficiency.

Attacks on CWSNs-Due to its hostile environment there are several kind of activities can be get done by the outside users which leads toward several kind of attacks which are discussed below-

(a)-Primary User Emulation Attacks

In the DSA paradigm,when a primary user is

detected in a given band,all secondary users should avoid accessing that band.However, when a secondary user is detected,other secondary users may choose to share that same band.In other words,primary users have higher priority than secondary users in accessing spectrum resources.In a PUE attack,a malicious secondary tries to gain priority over other secondary users by transmitting signals that emulate the characteristics of a primary user’s.An illustration of a PUE attack is shown in Fig. 1.2.Due to the reconfigurability of CRs,it is possible for an adversary to modify the radio software of a CR to change its emission characteristics(i.e.,modulation,frequency,po-wer,etc.)so that the emission characteristics resemble those of a primary user.The potential impact of the PUE attacks depends on the legitimate secondary users’s ability to distinguish the attacker’s signal from actual primary signals while conducting spectrum sensing.