Wireless Sensor Networks : Technology, Protocols, and Applications

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BACKGROUND 285 data relaying, and so on. This topology can result in more efficient routing, but the topology formation is an energy-consuming task and also increases the complexity of sensor nodes. In ad hoc mode, sensor nodes self-organize into a flat and unstructured topology, and all nodes perform the task of sensing and relaying. A sensor node will become dysfunctional if its energy is depleted and recharging is not possible. In a multihop environment, multiple paths exist between a source and the sink, which lead to route redundancy and therefore flexible routing. When the number of dysfunctional nodes accumulates to a certain level, the topology will be disjointed and service failure may occur. The movement of sensor nodes in some cases (such as when installed in tanks on the battlefield) still makes this topology variable. In summary, the topology of sensor networks can be well structured or ad hoc. The topology is usually variable and has multiple paths from the source nodes to the sink. These attributes influence the design of routing protocols in WSNs. Most traffic in WSNs flows starlike from sensor nodes to the sink. If there are multiple sinks, multiple traffic flows will be generated between sensor nodes and the sink. The sensor nodes gather data and report to the sink according to the preconfigured rules. This many-to-one traffic flow is called convergecast [11.24], which means many-to-one traffic flow from sensor nodes to the sink. Therefore, sensor nodes closer to the sink have the heavier burden for relaying, and due to higher energy consumption they might become dysfunctional sooner. A helpful way to get around this problem is to deploy more densely around the sink or to perform in-network processing (e.g., data aggregation) to reduce traffic flow. The traffic flow and specific functional requirements of the sensor deployment can be used to optimize networking protocols. The basic service provided by WNSs is to detect certain events and report them. The data related to the events are usually small, usually just a few bytes and in many cases just a few bits. Therefore, it may be possible to transmit more than one event in a single data unit if the application reporting frequency allows it. Other factors that affect WSN design are listed in (Table 11.1). These factors have a direct impact on the system performance of WSNs. TABLE 11.1 Design Factors for Wireless Sensor Networks [11.1] Factor Node deployment Mobility Network topology Coverage Connectivity Network size Communications Options Random, manual, one-time, iterative Immobile, partly, all; occasional, continuous; active, passive Single-hop, star, networked stars, tree, graph Sparse, dense, redundant Connected, intermittent, sporadic Hundred, thousand, more Laser, infrared, radio-frequency (narrowband, spread spectrum, UWB) Source: [11.1].
286 PERFORMANCE AND TRAFFIC MANAGEMENT The remainder of this chapter is organized as follows. In Section 11.3 several design issues are described as they affect system performance. In Section 11.4 we present the metrics of system performance and in Section 11.5, a simple model to compute system lifetime. Section 11.6 concludes the chapter. In this section we highlight briefly networking protocols for wireless sensor networks, including MAC, routing, and transport protocols, from a performance point of view. These protocols heavily influence the overall performance of WSNs. 11.3 WSN DESIGN ISSUES 11.3.1 MAC Protocols MAC protocols affect the efficiency and reliability of hop-by-hop data transmission. Existing MAC protocols such as the IEEE 802 series standard may not be completely suitable for WSNs because of energy efficiency. General MAC protocols can result in a waste of energy in the following ways [11.12]: Since a wireless channel is shared in a distributed manner, packet collision cannot be avoided. The collided packets require retransmission and result in energy waste. Most distributed wireless MAC protocols require control messages for data transmission (e.g., request-to-send/clear-to-send in the IEEE 802.11 distributed coordination function). Control messages consume energy. Overhearing and idle listening can also result in energy waste. Overhearing means that a node receives packets destined for other nodes. Idle listening refers to a situation where nodes there need to listen on the channel to get its status. MAC protocols for wireless sensor networks emphasize energy efficiency through design of effective and practical approaches to deal with the foregoing problems. For example, S-MAC [11.13] designs an adaptive algorithm to let sensor nodes sleep at a certain time. The approach of Tay et al. [11.14] devises a nonuniform contention slot assignment algorithm to speed up collision resolution and reduce latency while in the idle state. Typical parameters used to measure performance of MAC protocols include collision probability, control overhead, delay, and throughput. 11.3.2 Routing Protocols As we have seen in earlier chapters, routing protocols in WSNs are for setting up one or more path(s) from sensor nodes to the sink. Since sensor nodes have limited resources, routing protocols should have a small overhead, which may result from control message interchange and caching. Therefore, the traditional address-centric routing protocols for Internet (e.g., the routing information
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WIRELESS SENSOR NETWORKS Technology
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WIRELESS SENSOR NETWORKS Technology
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CONTENTS Preface xi About the Autho
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CONTENTS vii 5.4 MAC Protocols for
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CONTENTS ix 9.3 Traditional Network
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xii PREFACE text provides thorough
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xiv ABOUT THE AUTHORS communication
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1 INTRODUCTION AND OVERVIEW OF WIRE
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INTRODUCTION 3 in the wireless case
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INTRODUCTION 5 In this book we emph
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INTRODUCTION 7 and low-power-consum
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INTRODUCTION 9 1. The typical mode
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INTRODUCTION 11 Commercial applica
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BASIC OVERVIEW OF THE TECHNOLOGY 13
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REFERENCES 31 Standards As implied
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REFERENCES 33 [1.22] D. Minoli, W.
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REFERENCES 35 [1.58] S. Lindsey et
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REFERENCES 37 [1.89] J. M. Kahn et
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BACKGROUND 39 static routing over t
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BACKGROUND 41 The WNs have computat
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RANGE OF APPLICATIONS 43 TABLE 2.1
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RANGE OF APPLICATIONS 49 expect wit
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EXAMPLES OF CATEGORY 2 WSN APPLICAT
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ANOTHER TAXONOMY OF WSN TECHNOLOGY
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REFERENCES 71 In aggregating system
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REFERENCES 73 [2.25] ‘‘Short Di
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3 BASIC WIRELESS SENSOR TECHNOLOGY
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SENSOR NODE TECHNOLOGY 77 2. Detect
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SENSOR NODE TECHNOLOGY 79 Hardware
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Figure 3.3 Some of the networking p
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Very small (10 1 mm 3 ) Ultrasmall
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WN OPERATING ENVIRONMENT 85 TABLE 3
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WN TRENDS 87 aggregated, fused, and
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WN TRENDS 89 TABLE 3.4 Partial List
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REFERENCES 91 to those sensors so t
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4 WIRELESS TRANSMISSION TECHNOLOGY
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RADIO TECHNOLOGY PRIMER 95 Ionosphe
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RADIO TECHNOLOGY PRIMER 97 TABLE 4.
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RADIO TECHNOLOGY PRIMER 99 TABLE 4.
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RADIO TECHNOLOGY PRIMER 101 citizen
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AVAILABLE WIRELESS TECHNOLOGIES 103
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APPENDIX A: MODULATION BASICS 131 s
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APPENDIX A: MODULATION BASICS 133 T
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APPENDIX A: MODULATION BASICS 135 T
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APPENDIX A: MODULATION BASICS 137 P
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REFERENCES 139 algorithm, although
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REFERENCES 141 [4.36] C. Berrou, A.
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BACKGROUND 143 therefore be shared
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FUNDAMENTALS OF MAC PROTOCOLS 145 T
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FUNDAMENTALS OF MAC PROTOCOLS 147 q
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FUNDAMENTALS OF MAC PROTOCOLS 149 T
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FUNDAMENTALS OF MAC PROTOCOLS 151 d
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FUNDAMENTALS OF MAC PROTOCOLS 153 w
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FUNDAMENTALS OF MAC PROTOCOLS 155 F
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FUNDAMENTALS OF MAC PROTOCOLS 157 A
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MAC PROTOCOLS FOR WSNs 159 A B C D
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MAC PROTOCOLS FOR WSNs 161 multihop
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MAC PROTOCOLS FOR WSNs 163 can be o
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MAC PROTOCOLS FOR WSNs 165 of nodes
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SENSOR-MAC CASE STUDY 167 services
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SENSOR-MAC CASE STUDY 169 Nodes are
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SENSOR-MAC CASE STUDY 171 to secure
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IEEE 802.15.4 LR-WPAN 173 Sender RT
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IEEE 802.15.4 LR-WPANs STANDARD CAS
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REFERENCES 193 residing within 30 f
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REFERENCES 195 [5.25] K. Sohrabi, J
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6 ROUTING PROTOCOLS FOR WIRELESS SE
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DATA DISSEMINATION AND GATHERING 19
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ROUTING CHALLENGES AND DESIGN ISSUE
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ROUTING STRATEGIES IN WIRELESS SENS
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REFERENCES 225 first two faces and
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REFERENCES 227 International Confer
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7 TRANSPORT CONTROL PROTOCOLS FOR W
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TRADITIONAL TRANSPORT CONTROL PROTO
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TRADITIONAL TRANSPORT CONTROL PROTO
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Page 276 and 277: EXISTING MIDDLEWARE 257 tools and s
Page 278 and 279: REFERENCES 259 8.5 CONCLUSION In th
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Page 282 and 283: TRADITIONAL NETWORK MANAGEMENT MODE
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Page 292 and 293: 10 OPERATING SYSTEMS FOR WIRELESS S
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Page 302 and 303: 11 PERFORMANCE AND TRAFFIC MANAGEME
Page 306 and 307: WSN DESIGN ISSUES 287 WSNs Routing
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Page 323 and 324: 304 INDEX Code-division multiple ac
Page 325 and 326: 306 INDEX NEMS, 28 Network design,
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