Chapter 5 Ad Hoc Wireless Network

Jang Ping Sheu

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Introduction

Ad Hoc Network is a multi-hop relaying networkALOHAnet developed in 1970Ethernet developed in 1980In 1994, Bluetooth proposed by Ericsson to develop a short-range, low-power, low-complexity, and inexpensive radio intefaceWLAN 802.11 spec. is proposed in 1997

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Cellular and Ad Hoc Wireless Networks

Cellular Wireless Networks: infrastructure dependent networkAd Hoc Networks: multi-hop radio relaying and without support of infrastructure

Wireless Mesh networksWireless Sensor networks

The major differences between cellular networks and ad hoc networks as summarized in Table 5.1

Cellular Wireless Networks Hybrid WirelessNetworks

Wireless MeshNetworks

Wireless SensorNetworks

Infrastructure Dependent(Single-Hop Wireless Networks)

Ad Hoc Wireless Networks (Multi-Hop Wireless Networks)

Figure 5.1. Cellular and ad hoc wireless networks.

Switching Center+

Gateway

BBA

C

DE

Base Station Mobile Node Path from C to E

Figure 5.2. A cellular networks.

Mobile Node

BBA

C

DE

F

Mobile Node Wireless Link Path from C to E

Figure 5.3. An ad hoc wireless networks

Table 5.1 Differences between cellular networks and ad hoc wireless networks

Cellular Networks Ad Hoc Wireless Networks

Fixed infrastructure-based Infrastructure-less

Single-hop wireless links Multi-hop wireless links

Guaranteed bandwidth (designed for voice traffic)

Shared radio channel (more suitable for best-effort data traffic)

Centralized routing Distributed routing

Circuit-switched (evolving toward packet switching)

Packet-switched (evolving toward emulation of circuit switching)

Seamless connectivity(low call drops during handoffs)

Frequency path breakdue to mobility

High cost and time of deployment Quick and cost-effective deployment

Reuse of frequency spectrum through geographical channel reuse

Dynamic frequency reuse based on carrier sense mechanism

Easier to achieve time synchronization Time synchronization is difficult and consumes bandwidth

Easier to employ bandwidth reservation Bandwidth reservation requires complex medium access control protocols

Application domains include mainly civilian and commercial sector

Application domains include battlefields, emergency search and rescue operation, and collaborative computing

High cost of network maintenance(backup power source, staffing, etc.)

Self-organization and maintenance properties are built into the network

Mobile hosts are of relatively low complexity Mobile hosts require more intelligence (should have a transceiver as well as routing/switching capacity)

Major goals of routing and call admission are to maximize the call acceptance ratio and minimize the call drop ratio

Man aim of routing is to find paths with minimum overhead and also quick reconfiguration of broken paths

Widely deployed and currently in the third generation

Several issues are to be addressed for successful commercial deployment even though widespread use exists in defense

Table 5.1 Differences between cellular networks and ad hoc wireless networks (cont.)

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Applications of Ad Hoc Wireless Networks

Military ApplicationsRequirements: secure communication, reliability, multicasting routing, efficiency

Collaborative and Distributed Computing: Mobile learningEmergency OperationsWireless Mesh Networks

Wired Network

A house with rooftop transceiver

Transmission range

Wired link to the Internet

Wireless link

Figure 5.4. Wireless mesh networks operating in a residential zone

Gateway node

Internet

Wired link to the Internet

Multi-hop radio relay link Lamp

Radio relay node

Figure 5.5 Wireless mesh network covering a highway

Coverage area

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Applications of Ad Hoc Wireless Networks

Wireless sensor networks:Mobility of nodes, size of network, density of deployment, power constraints, data/information fusion, traffic distribution

Hybrid wireless NetworksHigher capacityIncreased flexibility and reliability in routingBetter coverage and connectivity in holes

Switching Center+

Gateway

BBA

C

D

E

Mobile NodeBase Station MCN communication

Figure 5.6. MCN architecture.

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Issues in Ad Hoc Wireless Networks

Medium access schemeRouting, Multicasting, TPC protocolPricing scheme, QoS, Self-organizationSecurity, energy managementAddressing and service discoveryDeployment considerations

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Medium Access Scheme

Distributed operation and synchronizationHidden terminals and exposed terminalsThroughput and access delayFairness, real-time traffic supportResource reservationPower control and adaptive rate controlDirectional antennas

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Routing

Mobility: frequent path break, packet collision, resource reservationBandwidth constraintError-prone and share channel: high bit error rateLocation-dependent contention: load balanceLoop-free routingProvisioning of QoSSecurity and privacy

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Multicasting

Robustness: recover and reconfigure quicklyEfficiencyControl overheadQoSEfficient group managementScalabilitySecurity

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Security

Denial of service: DoS attackResource consumption

Energy depletionBuffer overflow: filling unwanted data, routing table attack (filling nonexistent destinations)

Host impersonationInformation disclosure: support useful traffic patternInterference: create wide-spectrum noise

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Energy Management

Transmission power management: RF hardware design ensure minimum power consumptionUses variable power MAC protocolLoad balance in network layerReducing the number of retransmissions at the transport layerApplication software developed for mobile computers

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Energy Management (cont.)

Battery energy management: extending the battery life by taking chemical properties, discharge patternsProcessor power management: CPU can be put into different power saving modes Devices power management: can be done by OS by selectively powering down interface devices

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Ad Hoc Wireless in Internet

Gateways: entry points to the wired InternetAddress mobility: similar to the Mobile IP Routing: major problem in ad hoc wireless InternetTransport layer protocolLoad balancing, pricing/billing, security, QoSService, address, and location discovery

Application Layer(HTTP, TELNET, SMTP,

etc.)

Transport Layer(TCP/UDP)

Network Layer(IPv4/IPv6)

802.11/HIPERLAN

Network Layer(IPv4/IPv6)

802.11HIPERLAN

802.3/802.4/802.5

InternetAd hoc wireless Internet gateway connected to a subnet of the Internet

Mobile node that can relay packets to any mobile node running ad hoc wireless routing protocol

Multi-hop wireless part of ad hoc wireless Internet Traditional wired Internet

Flow of an IP packet from the wired Internet to a mobile node

Transceiver antenna

Application Layer(HTTP, TELNET, SMTP,

etc.)

Transport Layer(TCP/UDP)

Network Layer(IPv4/IPv6)

802.11/HIPERLAN

Application Layer(HTTP, TELNET, SMTP,

etc.)

Transport Layer(TCP/UDP)

Network Layer(IPv4/IPv6)

802.3/802.4/802.5

Mobile node that can be connected to any AP running ad hoc wireless routing protocol

TCP/IP protocol stack TCP/IP protocol stack TCP/IP protocol stack

Figure 5.7. A schematic diagram of the ad hoc wireless Internet

Internet

A house with rooftop transceiver Transmission range

Wired link to the Internet

Wireless link

Figure 5.8. An illustration of the ad hoc wireless Internet implemented by a wireless mesh network

Gateway Node

A

Path 1Path 2

Homework

5, 6, 10, 11

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