Wireless Sensor Networks: Applications and Forms

Wireless Sensor Ne 2rks Applications and Forms1 Wireless Sensor NetworkIn this chapter, wireless sensing element mesh (WSN) principles are cosmos shortly introduced and discussed. In order to increase the level of consciousness for analyzing Wireless Sensor Network (WSN) placements it is useful to study the engine room behind them the technologies which are presented in this section.Wireless Sensor Networks (WSNs) are distributed and independent sensors that are committed and worked together to measure quantities such as temperature, humidity, pressure, noise levels or vibrations 5. WSNs goat measure vehicular movement (velocity, location, etc.) and monitor conditions such as lightning condition, soil get hold ofup and motion 5. Nowadays, WSNs are utilized in m each common screenings such as vehicle applications. Some of vehicle applications are vehicle tracking and breakion, tire pressure monitoring, vehicle speed detection, vehicle direction indicator, traffic control, reversing aid sensors etc. such(prenominal) applications do- nonhing be split in major categories such as safety, gage, environment and logistics.To implement WSN in an application and have an efficient system, first we motivation to consider about WSN technology, comp atomic number 53nts and communication topology and protocols. Therefore, first, in this chapter, basic information about WSN comp whizznts, the communication devices and process unit of WSN bequeath be described. Then, the chapter will be followed by a description of the WSN topologies and protocols emphasizing on mesh WSN technology with ZigBee Protocol.1.1 Wireless Sensor Network percentageTo provide comprehensive view of WSN hardware, understanding of WSN components structure is required. Wireless sensors are small(a) micro control conditions equipped with wireless communication device and an postal code supplier. The computer architecture of WSNs is illustrated in prefigure 31 .As Figure 31 shows the comp onents of WSNs are sensing unit, processing unit, part supplier and communication device. The sensing unit consists of sensors and Analog to Digital Converters (ADCs). ADCs are amen competent for gathering the omens and converting them into digital signals info and transfer them done to each one other using communicate topology to the processor unit. In the sensing unit, each sensor is called an end client and varies in size and cost. The mission of these multifunction sensor nodes are to sense, process entropy and collaborate with other nodes 8. Wireless sensor network can be positioned in two ways, every using a complex technique with the large sensors far from the object or using several sensors with an engineered radiation diagram on position and topology 5. In addition, each node provided with a wireless communication transceiver as a communication component.In the process unit, the controller and small memory storage are creditworthy for managing the collaboration w ithin the sensors to achieve the assigning task. In addition, the communication device with a transceiver makes the network tie-in. preceding(prenominal) all, the essential component of WSN is the power unit, which supports the power for all units 5.One of the unique characteristics of sensor networks is that they are equipped with an on-board processor. This feature enables them to locally process some transparent computations and broadcast only necessary processed data 5. Network communication is really complicated and desires years of study 8, but to be able to implement WSN, we need to know some basic primary concepts of communication technology such as network topologies, network protocol and their bars and specifications.1.2 intercourse technologyTo cover technical aspects of WSN, network topology and network protocol studying is needed. This study will help to provide information about reliableness, robustness, security and stableness and of WSNs software aspect to answ er the research questions RQ. 1 ,RQ. 2 and RQ. 3 .1.2.1 Topologies in WSN conversationIn network communication, the big issue is how data transfers through nodes and nodes interconnect with each other. Several basic network topologies may be used for transmitting to and receiving from a node. The Alliance for Telecommunications Industry Solutions (ATIS) the standards organization of telecommunication perseverance explained the network topology as The material, real, logical or virtual arrangement of the nods/elements of a network 9. The topology shows the diameter and the number of nodes between any two nodes. Moreover how a data process and the data routing complexities are relied on the chosen topology. Consequently, some characteristics of a sensor networks such as latency, robustness and mental ability are changed by their topology 10.Figure 32 is a graphic mapping of networks topology which shows the links of one or to a greater extent nodes and explains the personal topo logy of the network. Despite having the same topology, two networks can differ in transmission rates be designer of their corporal interaction, signal types and distance between nodes 9. Table 31 describes the polar types of network topology.Table 31 Topology TYPES 9.Since Mesh topology is a main topic in the thesis, it is studied much in-depth in this section1.2.1.1 Mesh Wireless NetworkWireless mesh network is a term used when all wireless nodes are affiliated to each other within an ad-hoc multi-hob and mesh topology. In this network, any pair of nodes is able to communicate between each other within more than one manner. In this network each node is used as a router to forward packets to the neighbor nodes which they have linked to. That means all nodes communicate this instant or through other midway nodes without any manual configuration. Therefore, this network withal called a self-configuration and self-organized network 11 12.As described in Table 31, there are two t ypes of mesh topology Partially connected and Fully connected (See Figure 33). In a fully connected topology each node has the ability to communicate with all other nodes in the network and creates an interconnection links. By increasing the number of nodes in a mesh network, the number of links increases as well. On the other hand, in a partially connected topology, instead of direct interconnection between nodes, each node has two or more links to others to provide alternate routing and traffic balancing. Due to more links and indirect connections between nodes, traffic can flow through one or more router nodes to the destination 7 and create more reliable interconnections between nodes.Moreover, in partial network, the nodes are connected to either the node with higher rate of data transaction or the nearest neighbor node while in fully connected network all nodes have a direct links with each other. This multiple link path conducts a reliable communication. Therefore, whenever a connection fails or a node breaks down, the packages can automatically change their path by jumping from a disconnected node. This is often called the self-healing of the network. This means that the networks connection stability and reliability are not essentially affected by node failures 11.Due to the characteristics of wireless sensor network mesh, this network is self-configuring and self-organizing network in which each end-node is also used as a router (dual role- data originator /data router) to forward the signal packages all the way back of the main gateway.Therefore, due to the characteristics of mesh networks, this network is becoming one of the most implemented networks which able to have the flexible architecture for the network, easy self-configuration and robust crack tolerance connectivity 11 12. Additionally, the self-configuring characteristic of mesh WSN, bring the ability for the network to connect or disconnect nodes from the network. This brings the ability to grow/decrease the network by adding/removing nodes of a system.Mesh WSN has reliable self-healing and robust fault tolerance. This means if a node fails or breaks down the signal packages jump from the disconnected node and automatically conducts a new path through the nearest node. However, the new path imposes re-routing and re-organizing to the network 5, which consumes too a lot power from the system. Therefore, having a power-aware protocol and algorithm is necessary for mesh network. ZigBee protocol is one of the protocols which provides this ability for WSN.1.2.2 Protocols in WSN CommunicationWSN systems accommodate variety of protocols for communication. Protocols need to program in different architectural levels. One of these architectural standard is OSI (Open System Interconnection) framework. In this session a brief doorway of each protocol and OSI are delineated.Figure 34 shows the graphic overview of all wireless network technologies. This figure illustrated IEE E trash/LAN/MAN technologies and clearly shows how these standards and protocols can be used in different conditions. For instance, 3G protocol is used to cover a long range of audio information in a wide area network (WAN) while for the same information in a short range and personal area network (PAN), Bluetooth is better.The standard abstract rules set for data representation, data communication and shift detection across two ends in telecommunication, are called communication protocols. These abstract rules represent in different points of communication. There are different protocol stacks introducing different architectures for these stratums such as AppleTalk, Distributed Systems Architecture (DSA), Internet protocol suite (TCP/IP) and Open Systems Interconnect (ISO/OSI). Figure 35 (a) illustrates the different works of an OSI Model and their functionalities. The OSI model has seven layers and each layer provides services for the upper layer and requests services from th e lower layer. Figure 35 (b) shows the typical communication protocols layers. Each of these layers has to deal with different issues regarding the communication procedure.As the typical protocol stack model shows in Figure 35 the communication protocols should implement all layers from bottom to top. In addition, a solicitude protocol needs to be applied in each layer to manage power efficiency, robust connectivity and connection reliability (see Figure 35 b). Below, rules and functionality for each layer are described* Physical layer is creditworthy for signal processing and strong-arm interface connectivity between a device and bodily medium and used bit stream in its data unit. It acted as communication channel for sensing and actuation in cost-efficient and reliable manner. Some examples of this layer are IEEE 802.11b/g Wi-Fi, IEEE 802.15.1 Bluetooth, IEEE 802.15.4 ZigBee, etc. 7* Data link layer provides functionality toward channel sharing, Medium Access Control (MAC-Layer) , timing (e.g. data time arrival), local link and capacity. It is responsible for detecting and correcting the data errors in physical layer and control the locality data comparison. It follows the protocols such as point-to-point protocol (PPP) and IEEE 802 Local Link Control (LLC). 7* Network layer is responsible for network routing functionality, network security, energy and power efficiency and reliability of the communication. It implys the network topology management and manages the information and detects errors in data transfer from router to router. A number of protocols is address in this layer such as Internet protocol (IP), Threshold Sensitive Energy Efficient Sensor Network Protocol and etc. 7.* Transport layer provides lengthways transportation (distributing and gathering) of data between end users. It includes storage and responds for caching and controlling the data to recover them back to the initial message that has been sent. Best-known protocols for this layer are transmission system Control Protocol (TCP) and User Datagram Protocol (UDP) 7.* Upper layers The Upper Layers are responsible for application processing, external query processing and etc. Upper layers include presentation layer session layer and application layer 7.The summary of these standards and protocols are shown in Figure 36Among all the standard and protocols, IEEE PAN/LAN/MAN technologies are the ones applied in the majority of commercialWSNs to support physical layer and link-data layer signal transmission. As SOHRABY and ZNATI (2007) mentioned, the most common known protocols are (1) the IEEE 802.15.1 (also known as Bluetooth) (2) the IEEE 802.11a/b/g/n series of wireless LANs (3) the IEEE 802.15.4 (ZigBee) (4) the MAN-scope IEEE 802.16 (also known as WiMax) and (5) radio-frequency identification (RFID) tagging 7. Each of these protocols has their own benefits and constraints. The comparisons between IEEE technologies are mentioned in Table 32. As Table 32 shows th e IEEE 802.15.4 standard provides data rate of 20 to 250 kbps and operates in the 2.4-GHz ISM band. This standard covers signals in range of 10 m and requires the lowest power among other IEEE class. While IEEE 802.11a/b/g/n transmits the data in the rate of 54 Mbps exaltation for wireless internet connections and operates in the 2.4-GHz ISM (Industrial, Scientific and Medical) radio band as well as the 5-GHz ISM / 5-GHz U-NII (Unlicensed National Information Infrastructure) radio band. However, it requires much higher power consumption than IEEE 802.15 7.Recently, researchers put much effort to develop a cost-effective standards-based wireless networking solution that supports low-to medium data rates, has low power consumption, and guarantees security and reliability 7. ZigBee Alliance is an association of companies which aims to provide such a standard for WSN consumers. Their mission is to have a simple, reliable, low-cost, low-power and standards-based wireless syllabus1.2.2. 1 ZigBee standardThe ZigBee standard builds on IEEE 802.15.4 and is suitable for remote monitoring and controlling applications. Although it has lower-data-rates than the other standards, its reliability, security, long life battery with less complexity mechanism make it ideal for edifice automation in industrial network applications. The architecture of the ZigBee stack is established on the Open System Interconnection (OSI) model. The IEEE 802.15.4 defines the physical layer (PHY) and medium portal control (MAC) sub-layer and In addition, ZigBee Alliance defines other functionalities for upper layers 7. Figure 37 is a graphic overview of ZigBee protocol stack and shows the responsibility areas of IEEE 802.15.4, ZigBee Alliance platform and users applications 7. This picture also shows the basic functionality of each layer.The data transmission service is provided by PHY layer and the protocol in this layer enables the connection between data units and the physical radio channel. ZigBee provides three different frequency band options for PHY layer. First, the transmission data-rate of 250kbps in 16 channels at 2.45GHz (Global) frequency. Second, with 40Kbps in 10 channels at 915MHz (Americas). And the last one, with 20kbps in 1 channel at 868MHz (Europe). The higher data-rate causes a higher order in modulation design and the lower frequency cause a larger cover area and better sensitivity. Depending on the power output, the transmission distance rate can change from 1 to 100 meters. (For more detail information see Table 71 in Appendix A)ZigBee WSN has the ability to have static or dynamic network/component with either star or mesh topology and it has three types of nodes a ZigBee Coordinator (ZC), ZigBee Routers (ZR), and ZigBee End-Devices (ZED).In order to have a communication protocol and physical connection both PHY layer and MAC sub-layers of the architecture should be defined upon agreement between server and clients. These layers require manual adm inistrative procedures setting for server/client gateway.The next three levels namely the network layer, security protocol and transport layer are defined by ZigBee alliance platform automatically. The last layer, application layer, has to interact with the user-interface and other applications it ought to be programmed with high-level language so that integration with any existing devices applications becomes more conveniently practical.The ZigBee stack in gateway is responsible for all the network functionality such as network process management, authentication of the joined nodes, binding nodes and routing the messages throughout the network. ZigBee stack as a standard protocol, has clusters and libraries for up(a) the implementation process, therefore, using ZigBee compare to other protocols makes the system (including both hardware and software) development process much faster and easier. On the other hand, such calibration provides easiness of adopt with third party sensors regardless of manufacturer, which might be attached to the network later.2 Software AspectsTo address the research question regarding the reliability, robustness, and security of any WSN application, it is essential to investigate the software architecture of that network. For convenience in description of the architecture of a WSN application, it is divided into three segments Physical devices (such as lamps, sensors, nodes), Communication Protocol (terminals and servers, bridge, switch, network topology and standard) and Carried Information (application, functions, etc.).Any attempts to retain a precise design on software architecture for each part will cause an effective data transmission, which ensures reliability and security of the system 7. so achieving any desired data transmission precision level in a WSN, network management (NM) techniques are applicable. Such techniques assist in network status monitoring, reliability and security amendment, and cooperation supervision b etween components 7. NM techniques could also detect and resolve network faults in addition to restoring the system respectively 7.In practice, designing WSN application necessitates tailoring NM techniques for each architectural segment. Various NM techniques regarding each segment are summarized as follows 7 12 5a) Physical architectureSensing and processing management, operation and administration, fault tolerance, keep, energy efficiency management, configuration management, movement management, security management, network element management.b) Communication architectureNetwork management, networking protocols, network topology, function management, monitoring functions, fault management, performance management, security management, service management and communication, maintenance management, network configuration and organization, network behavior, data delivery model, sensor mobility, naming and localization, sensing coverage area, communication coverage area energy effici ency managementc) Information architectureReal-time information management, mapping management, service management, analyze information, control application, business application management report management, sending and receiving commands or response, naming, localization, maintenance, fault toleranceAforementioned NM techniques enhance quality of the system. According to ISO 9126-1 software quality model Table 41 13 14 15, the quality characteristics of a system could be divided into six fundamental properties functionality, reliability, usability, efficiency, maintainability, and portability. According to the same documentation, these characteristics are broken to sub-characteristics such as suitability, security, maturity, fault tolerance, adaptability, analyzability, stability, testability and so on 13. However, way on all subcategories collectively exceeds the time horizon of this research, from this stance three dimensions namely reliability, robustness and security are brou ght into attention.This section will be divided to two subsections describing the architecture issues and NM techniques for (1) Reliability and Robustness, (2) Security, of WSN and other characteristics is relegated to future studies.2.1 Reliability and RobustnessIn WSNs context, the probability that a network functions properly and aggregates trustworthy data without any breaking continuously, is usually referred to as reliability characteristic of the network 23 20. According to ISO 9126-1 software quality documentation, reliability characteristic shows the capability of a network to maintain or re-built (re-start) the service in certain period of time 13. So, it is important that during long sensing, the network has to service up continuously. Reliable service of a network includes precise and proper sensing, delivering and sending acceptable data to the base station. In other words as Taherkordi et al. (2006) put The less loss of enkindle data, leads us to higher reliability o f a system. Systematic approach perceives reliability as probability of data delivery to the base station quite a than point-to-point reliability 16.Robustness defined by Sohraby et al. (2007) as a combination of reliability, availability, and dependability requirements, reflects the degree of the protocol insensitivity to errors and misinformation. Achieving system robustness in WSN, necessitates system capability to detect, tolerate and confine errors as well as reconfigure and restart the network respectively 7. According to the given definition by Sohraby et al. (2007), it is apprehensible that reliability and robustness share commonalities with each other this is the main rational behind discussing these two attributes together in this section 7.Considering the nature of communication in WSN, a network is unpredictable and prone to fail caused by any physical damages in hardware devices, energy depletion, communication link error, information collapses in packages and etc. 17 16. Therefore, one of the critical issues in design phase of WSN is applying fault tolerance techniques to optimize the network so that reliability and robustness attained 17. These techniques enable the network to withstand and recover any upcoming failure and restart operation 13.Liu et al. (2009) categorized fault tolerance techniques into node placement, topology control, target and resolution detection, data gathering and aggregation, and sensor surveillance. Reminding from the beginning of this chapter architecture design divided into three segments. Table 42 depicted a summary of the believable related faults and their solutions in each segment. In the following, each aforementioned fault tolerance techniques are being discussed in each design segment.Table 42 The most probable fault and their fault tolerance solutions in WSN 17 7 182.1.1 Reliability and Robustness of Physical Architecture Fault any physical interruption in sensor surveillance Solution Node placement manage ment and signal-effect managementFirst item that should be considered in designing physical components architecture for reliability and Robustness is physical placement and signal-effect management. As it is mentioned in section 3, although the mesh network communication is self-organize topology and does not need any manual configuration to bind the network for mobile sensors, the physical architecture and the location schema of the hardware components, sensors and gateways need to be designed carefully 7.As a characteristic of mesh WSN, the sensors in network are free of any installation restrictions, even though, the placement should be far from any physical destruction or hostile locations. Inappropriate physical placement of sensor transmitters and gateway antenna can cause noise or significant woolly in signals 7. In addition, the signal coverage is decayed by surrounding objects and materials such as metal wall and the like. (E.g. exterior wooden, concrete, brick or gypsum f rame, block or wall). Especially in the case of vehicles, the main body can impose such problem and henceforth installation of the sensors in this manner would be delicate.Moreover, the signal vibrates might be faded and affected during the transmission, due to various physical phenomena such as reflection, diffraction or scattering 7. These effects would cause significant interruption in sensor surveillance. Therefore, it is important to manage these signal-effects in early stage of WSN physical architecture design.Reflection occurs when electromagnetic wave of signals is duplicated due to impinge of the wave on large object or surface such as walls, buildings and the Earth 7. Therefore, all the reflection of the walls and also the Earth should be acknowledged in physical architecture design.Diffraction refers to any defection and obstruction in waves caused by irregular sharp edges during the data transmission between the transmitter and receiver 7. In this case, designers have t o be prudent in sensors placements in the proximity of sharp edges and corner angels.Scattering refers to any deviation from straight line. Environmental obstacles in the file name extension path affect passing waves from their original structure. Even small irregular object such as street signs, and lampposts might encounter and scatter the wave. Hence WSN should be design to face with any irregular scattering during the wave transmission. Above all, the mobility of sensors and surrounding objects might fade the signals and add noises that should be considered in architecture design 7.These issues are the basic physical factors, which cause major fault in data aggregation of WSN and cut down reliability and robustness. These destructive signals need to be subtracted from the received signal paths 7 before sending the data to gateway. Therefore, reflection, diffraction and scattering should be considered not only by designers in the physical components placements, but also by progr ammers in network development. Fault Sensors failure Solution Hardware replacementThe next issue that needs to be considered in designing the physical architecture of a WSN is hardware failure. Sensors energy suppliers or any damages to the sensors and/or their transmitters are the sources of hardware failure. Regardless of source of failure, the WSN must be satisfactory of functioning as well as replacing and switching sensors when necessary. Additionally, any changes in the physical components, on one hand, needs an explicit and well-defied consideration on security issue to prevent any potential threats, and on the other hand, needs an adaptable and configurable communication connection network 18.2.1.2 Reliability and Robustness of Communication Architecture Fault communication link errors SolutionTopology control and event detection , Replicated services in communication model,Communication link error is an important concern in dealing with reliability and robustness of a netw ork in communication architecture. The sensors in WSN are prone to fail and make link errors in point-to-point reliability of communication protocol. Therefore, it is the network topology responsibility to detect the errors and guarantee the overall reliability of the syste