Ad Hoc Networks: Introduction - SJTUxue-gt/wireless/Online Course... · Ad Hoc Networks: Introduction Module A.int.1 Dr.M.Y.Wu@CSE Shanghai Jiaotong University Shanghai, China Dr.W.Shu@ECE

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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

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Ad Hoc networks: introductionAd Hoc network overviewAd Hoc network types

Sensor networksMesh networksMANETs

Design issuesLink layer and MACsSpectrum reuseRoutingCrosslayer design

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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


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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


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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


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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


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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


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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


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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


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Ad hoc special: mesh networksAd hoc mesh networks

Rapidly deployable wireless infrastructureLargely immobile nodes or stationary nodes


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Ad hoc special: MANETs

Ad hoc MANETHighly mobile nodesMobility causes route changes


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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.


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Design issues

Link layer designChannel access and frequency reuseReliabilityRoutingNetwork issuesPower/energy management


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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.


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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


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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


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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


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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.


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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.


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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


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Documents

Ad Hoc Networks: Introduction - SJTUxue-gt/wireless/Online Course... · Ad Hoc Networks: Introduction Module A.int.1 Dr.M.Y.Wu@CSE Shanghai Jiaotong University Shanghai, China Dr.W.Shu@ECE