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Smart Antenna Basics and Models 199 the networking challenges that arise due to the deployment of such antennas in ad hoc networks. 7.2.1 Antennas in Brief Omni-directional antennas are those antennas that radiate or receive energy equally well in all directions. Traditionally these antennas have been considered (or implicitly assumed) for studies related to ad hoc networking. Since these antennas dissipate energy in all directions, they impose limitations on the extent to which the wireless spectrum may be re-used in the network. In [15], it was shown that the capacity of an ad hoc network that uses omni-directional antennas is limited. Smart antennas, naively speaking, have the ability to receive/transmit energy in a particular direction as compared to other directions. The energy dissipated in the directions other than the desired direction can be quelled when transmitting and filtered out while receiving. Smart antennas also null out the interference caused by other transmissions. The antenna is complemented by an adaptive array processor that decides on the amount of power to be used on each antenna element so that the signals combine together to form a specific antenna pattern. The lack of such signal processing techniques causes energy to be dissipated in directions other than the desired one. An antenna that simply beamforms the energy in a particular direction is often referred to as a directional antenna. Most of the work to date has looked primarily at the use of directional antennas in ad hoc networks. Figure 7.1 depicts the antenna patterns of (a) an omni-directional antenna and (b) a directional antenna. The antenna footprint of a directional antenna contains a main lobe and side lobes as shown in the figure. The Yagi antenna [13] is a well known directional antenna often used in cellular networks. It has been shown that the capacity of ad hoc networks can be increased significantly by using directional antennas [18]. We further classify directional antennas systems into switched beam (or sectorized) antenna systems and steerable beam systems. In switched beam systems only multiple fixed beams are possible. As an example, space might be divided into four sectors of 45° each. A directional transmission would then cover one of these four fixed sectors. A given node in the network cannot focus its antenna beam on a particular neighborhood node so as to maximize the signal strength at that node. Clearly, for a switched beam antenna with K beams, the width of each beam is radians. In contrast, in a steered beam system, the main lobe of the antenna can be focused in practically any desired direction. Thus, if a given node is communicating with its neighbor, it can adaptively steer its beam so as to point the main lobe towards that neighbor in a mobile scenario as well.
200 Use of Smart Antennas in Ad Hoc Networks Figure 7.1. Footprint of (a) An Omni-directional Antenna and (b) A Directional Antenna The nomenclature smart antennas typically refers to more sophisticated antenna arrays. There are dynamic phased arrays that maximize the gain towards a target in the presence of multi-path effects and there are adaptive arrays that can produce nulls so as to eliminate the effects of simultaneously ongoing interfering transmissions. We point out that the antennas that we consider for deployment in ad hoc networks are electronically steerable antennas. High-gain aperture and horn antennas that are commonly used in satellite or microwave based terrestrial wireless networks are inappropriate for use in mobile terminals. These antennas will have to be mechanically steered and could be extremely expensive in terms of the energy consumed; this in turn could significantly increase the energy usage in the mobile terminal and could quickly cause its battery to die. 7.2.2 Important Antenna Parameters The gain of a directional antenna is typically higher than that of an omnidirectional antenna. Correspondingly directional antennas can have a higher reachability or in other words, a larger directional range as compared to an omni-directional antenna. The gain of a directional antenna is defined as [16]: where, is defined to be the efficiency of the antenna and accounts for the hardware related losses, is the energy in the direction and is the
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AD HOC NETWORKS Technologies and Pr
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AD HOC NETWORKS Technologies and Pr
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Contents List of Figures List of Ta
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Contents vii 4.7. Conclusions and F
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Contents ix 9.2. Potential Attacks
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List of Figures 1.1 Internet in the
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List of Figures xiii 6.3 COMPOW com
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List of Figures xv 9.1 9.2 An IDS a
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List of Tables 2.1 2.2 2.3 2.4 2.5
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Contributing Authors Samir R. Das i
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Preface Wireless mobile networks an
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Acknowledgments xxiii We wish to ex
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Chapter 1 AD HOC NETWORKS Emerging
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Introduction and Definitions 3 coul
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Introduction and Definitions 5 Secu
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Ad Hoc Network Applications 7 tunis
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Ad Hoc Network Applications 9 The d
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Ad Hoc Network Applications 11 Figu
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Design Challenges 13 example of cro
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Evaluating Ad Hoc Network Protocols
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Overview of the Chapters in this Bo
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Overview of the Chapters in this Bo
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Conclusions 21 1.6 Conclusions This
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Chapter 2 COLLISION AVOIDANCE PROTO
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Performance of collision avoidance
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Framework and Mechanisms for Fair A
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Conclusion 59 In the first part of
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Conclusion 61 [13] [14] [15] [16] [
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Chapter 3 ROUTING IN MOBILE AD HOC
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Flooding 65 vector and link state p
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Flooding 67 centralized approximati
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Proactive Routing 69 status of each
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Proactive Routing 71 Topology Broad
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On-demand Routing 73 reply packets
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On-demand Routing 75 during the lin
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Proactive Versus On-demand Debate 7
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Proactive Versus On-demand Debate 7
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Location-based Routing 81 to find a
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Location-based Routing 83 Figure 3.
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Concluding Remarks 85 relative meri
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Concluding Remarks 87 [14] [15] [16
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Concluding Remarks 89 [42] [43] [44
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Chapter 4 MULTICASTING IN AD HOC NE
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Introduction 93 The mobility of the
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Classifications of Protocols 95 red
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Multicasting Protocols 97 this sect
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Multicasting Protocols 99 as close
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Multicasting Protocols 101 In ODMRP
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Multicasting Protocols 103 hoc netw
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Multicasting Protocols 105 A member
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Multicasting Protocols 107 Figure 4
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Broadcasting 109 “talk” to a ra
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Broadcasting 111 broadcasted packet
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Protocol Comparisons 113 are cluste
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Overarching Issues 115 is user data
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Overarching Issues 117 and RTS/CTS
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Conclusions and Future Directions 1
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Conclusions and Future Directions 1
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Chapter 5 TRANSPORT LAYER PROTOCOLS
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TCP and Ad-hoc Networks 125 Modifie
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TCP and Ad-hoc Networks 127 mechani
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TCP and Ad-hoc Networks 129 timeout
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TCP and Ad-hoc Networks 131 to freq
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TCP and Ad-hoc Networks 133 Figure
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Transport Layer for Ad-hoc Networks
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Modified TCP 137 MAC layers without
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Modified TCP 139 Figure 5.6. TCP-EL
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TCP-aware Cross-layered Solutions 1
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Ad-hoc Transport Protocol 147 in it
Page 174 and 175: Ad-hoc Transport Protocol Figure 5.
Page 176 and 177: Summary 151 References [1] [2] [3]
Page 178 and 179: Chapter 6 ENERGY CONSERVATION Robin
Page 180 and 181: Energy Consumption in Ad Hoc Networ
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Page 184 and 185: Communication-Time Energy Conservat
Page 200 and 201: Idle-time Energy Conservation 175 a
Page 202 and 203: Idle-time Energy Conservation 177 T
Page 204 and 205: Idle-time Energy Conservation 179 k
Page 206 and 207: Idle-time Energy Conservation 181 F
Page 210 and 211: Idle-time Energy Conservation 185 t
Page 212 and 213: Idle-time Energy Conservation 187 c
Page 216 and 217: Conclusion 191 [6] [7] [8] [9] [10]
Page 218 and 219: Conclusion 193 [33] [34] [35] [36]
Page 220 and 221: Conclusion 195 [59] [60] [61] [62]
Page 222 and 223: Chapter 7 USE OF SMART ANTENNAS IN
Page 226 and 227: Medium Access Control with Directio
Page 242 and 243: Routing with Directional Antennas 2
Page 248 and 249: Broadcast with Directional Antennas
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Page 252 and 253: Summary 227 [4] [5] [6] [7] [8] [9]
Page 254 and 255: Chapter 8 QOS ISSUES IN AD-HOC NETW
Page 256 and 257: Introduction 231 The concept of ad-
Page 258 and 259: Physical Layer 233 The 802.11a stan
Page 260 and 261: Medium Access Layer 235 neighbors,
Page 262 and 263: Medium Access Layer 237 Figure 8.5.
Page 264 and 265: QoS Routing 239 where is the number
Page 266 and 267: QoS at other Networking Layers 241
Page 268 and 269: Inter-Layer Design Approaches 243 8
Page 270 and 271: Conclusion 245 are specifically des
Page 272 and 273: Conclusion 247 [13] S. Mangold, S.
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Chapter 9 SECURITY IN MOBILE AD-HOC
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Potential Attacks 251 attacks, such
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Attack Prevention Techniques 253 9.
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Intrusion Detection Techniques 255
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Conclusion 265 an important and sti
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Conclusion 267 [24] [25] [26] [27]
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Index Ad hoc network multicast rout
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