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Ad Hoc Networks: IntroductionModule A.int.1
Dr.M.Y.Wu@CSEShanghai Jiaotong University
Shanghai, China
Dr.W.Shu@ECEUniversity of New Mexico
Albuquerque, NM, USA
© by Dr.Wu@SJTU & Dr.Shu@UNM
A.int.1-2
Ad Hoc networks: introductionAd Hoc network overviewAd Hoc network types
Sensor networksMesh networksMANETs
Design issuesLink layer and MACsSpectrum reuseRoutingCrosslayer design
End of Module A.int.1
© by Dr.Wu@SJTU & Dr.Shu@UNM
A.int.1-3
Ad-Hoc networks: overview
Peer-to-peer communications.Virtually fully connected
Since media is wireless anywayQuality of link varies a lot! Diagram never can be done accurately
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad Hoc networks: overview
CharacteristicsWithout using a pre-existing infrastructure
Wireless
Mobile (partial)
Multi-hop
Ad hoc deployment
BenefitsEasy and fast deployment
Eliminating dependency on infrastructure
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad Hoc networks: overview
ApplicationsPAN
Personal area networking, connecting with cell phones, laptop, wrist watch, etc
Military environmentsTanks, soldiers, planes, battlefield communications
Emergency operationsRescue, fire fightingSurveillance
Civilian environmentsTown hall meetingGathering, convention
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Multi-hop
From source to destinationMay need to traverse multiple hops
Every node capable of forwarding
Require routing algorithms
Impacts on MACMulti-hop aware MAC
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Assumptions and variations
Symmetric or asymmetric?All nodes have identical capabilities & responsibilitiesOr capacity variations in
Transmission ranges & bandwidthBattery lifeMobility & its speedProcessing capacity
Or capacity variation inElected as a leaderRouting and forwarding packetsCo-exist or co-operate with an infrastructure-based network
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Assumptions and variations
Variation with infrastructuresCoexistence with an infrastructure if any
Variations in traffic characteristicsBit rateRealtime or data orientedUnicast/multicast/geocastAddressing (host, content, capability)
Variation in mobilitylink failure/repair due to mobility may have different characteristics than those due to other causesRate of link failure/repair may be high when nodes move fast
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad Hoc networks: introductionAd Hoc network overviewAd Hoc network types
Sensor networksMesh networksMANETs
Design issuesLink layer and MACsSpectrum reuseRoutingCrosslayer design
End of Module A.int.1
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad hoc special: sensor networks
Ad hoc sensor networksNode equipped with sensing capabilityNode are severely power constrained Applications are most likely data driven
a large collection of tiny sensor devices
Limited resource with sensorsPower, processing, storage, communication
Deployment in harsh environmentsSelf-organize, self-healing
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad hoc special: mesh networksAd hoc mesh networks
Rapidly deployable wireless infrastructureLargely immobile nodes or stationary nodes
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad hoc special: MANETs
Ad hoc MANETHighly mobile nodesMobility causes route changes
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad hoc special: MANETs
IEFT MANET Working Groupto standardize an interdomain unicast routing protocol which provides one or more modes of operation, each mode specialized for efficient operation in a given mobile networking “context”, where a context is a predefined set of network characteristics.
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad Hoc networks: introductionAd Hoc network overviewAd Hoc network types
Sensor networksMesh networksMANETs
Design issuesLink layer and MACsSpectrum reuseRoutingCrosslayer design
End of Module A.int.1
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Design issues
Link layer designChannel access and frequency reuseReliabilityRoutingNetwork issuesPower/energy management
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Link layer design
Modulation and CodingRobustnessRate requirementsPerformanceAdaptive techniques: rate, power, BER, code, framing, etc.
Power controlMultiuser DetectionAntenna design
Smart antennas and MIMO.
© by Dr.Wu@SJTU & Dr.Shu@UNM
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MAC design
Nodes need a decentralized channel access methodMinimize packet collisions while increasing channel utilization
Collisions course significant delay
Aloha w/ CSMA/CD have hidden/exposed terminals
802.11 uses four-way handshakeCreates inefficiencies, especially in multihop setting
HiddenTerminal
ExposedTerminal
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Design issues
Scalability issuesTradeoff
energy consumption vs. latencyStandard issues
protocol deployment and incompatibility standardsSecurity issues
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Spectrum reuse
Static channel allocation, multiple channelsPoor connectivity
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Spectrum reuse
Static channel allocation, single channelPoor interference
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Spectrum reuse
Dynamic channel allocation, single interfaceGood Connectivity and Controlled Interference
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Spectrum reuse
Dynamic channel allocation, mulitple interfacesComplicated control
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Ad hoc routing
AD-HOC MOBILE ROUTING PROTOCOLS
ON-DEMAND-DRIVEN REACTIVE
HYBRIDDSDV
CGSR
TABLE DRIVEN/ PROACTIVE
DSR
AODV
ZRP
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Ad hoc routing
Flooding, broadcast-basedInefficientRobust for fast changing topologies.Little explicit overhead
Point-to-point routingRoutes follow a sequence of linksConnection-oriented
Explicit end-to-end connectionLess overhead/less randomnessHard to maintain under rapid dynamics.
ConnectionlessPackets forwarded towards destinationLocal adaptation
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad hoc routing
Table-drivenDestination-sequenced distance-vectorClusterhead gateway switch routingWireless routing protocol
On-Demand RoutingOn-demand distance vector routingDynamic source routingTemporally ordered routingAssociativity-based routingSignal stability routing
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Ad hoc routing
Proactive Routing Protocol:continuously evaluate the routesattempt to maintain consistent, up-to-date routing information
when a route is needed, one may be ready immediatelywhen the network topology changes
the protocol responds by propagating updates throughout the network to maintain a consistent view
Reactive Routing Protocol:on-demandEx: DSR, AODV
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Ad hoc route dissemination
Route computed at centralized nodeMost efficient route computation.Can’t adapt to fast topology changes.BW required to collect and disseminate information
Distributed route computationNodes send connectivity information to local nodes.Nodes determine routes based on this local information.Adapts locally but not globally.
Nodes exchange local routing tablesNode determines next hop based on some metric.Deals well with connectivity dynamics.Routing loops common.
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Reliability
Packet acknowledgements neededMay be lost on reverse linkNeed negative ACKs?
Combined ARQ and codingRetransmissions cause delayCoding may reduce data rate
Hop-by-hop acknowledgementsExplicit ACKsEcho ACKs
Transmitter listens for forwarded packet More likely to experience collisions than a short ACK.
Hop-by-hop or end-to-end or both.
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Crosslayer design
ApplicationNetworkAccessLink/MACHardware
Delay ConstraintsRate RequirementsEnergy Constraints
Mobility
Optimize and adapt across design layers
Provide robustness to uncertainty
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Crosslayer design?
The technical challenges of future mobile networks cannot be met with a layered design approach.QoS cannot be provided unless it is supported across all layers of the network.
The application must adapt to the underlying channel and network characteristics.The network and link must be application aware
Interactions across network layers must be understood and exploited.
© by Dr.Wu@SJTU & Dr.Shu@UNM
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Summary
Ad-hoc networks provide a flexible network infrastructure for many emerging applicationsAdvances in communication techniques should be incorporated into ad-hoc network designDesign issues traverse all layers of the protocol stack, and cross layer designs are needed
Protocol design in one layer can have unexpected interactions with protocols at other layers.
Many new issues to be addressed