Location Awareness in Ad Hoc Wireless Mobile Neworksirchen/6204/paper/TSE01-slide.pdf(AODV): – An...

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11/14/2001 Mobile Computing, Fall 2001 1

Location Awareness

in Ad Hoc Wireless

Mobile Neworks

Lijuan Ai

Wenyu Wang

Yi Zhou


PART IPART I

INTRODUCTION TO MANET

&

LOCATION-AWARE COMPONENTS

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Mobile Ad Hoc NetworkMobile Ad Hoc Network(MANET)(MANET)

• A mobile ad hoc network that consists of a set of mobile hosts that roam at will and communicate with one another.

• Different from traditional wireless networks– Dynamic changing topology.– No base-station support, no fixed routers.– Multihop communication capability.


Figure 1. Typical MANET, a mobile ad hoc network consisting of a set of mobile hosts that roam at will and communicate with one another.

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MANETMANET

• A mobile host has to work as a router and cooperate with other hosts to find routes and relay messages.

• Example applications of MANET are emergency search-and-rescue operations, meetings or conventions where users need to deploy networks immediately, without base stations or fixed network infrastructure


Current research on MANET:Current research on MANET:

• Unicast.

• Collective communications.

• Quality-of-service routing.

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UnicastUnicast

• MANET finds a routing path from a source to destination host.

• Such protocols must deal with typical limitations of MANET, e.g.:– High power consumption.– Low bandwidth.– High error rates.


Routing ProtocolsRouting Protocols

• Proactive: constantly updates the routing table at each node to maintain a nearly global view on the network topology.

• Reactive: makes on-demand searches for a path, which can be less costly when host mobility is high.

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Proactive Routing ProtocolProactive Routing Protocol

• Destination-Sequenced Distance Vector (DSDV):– Every host maintains a routing table. – Each entry is marked with a sequence number

which enables hosts to find the freshest route.– Routing table updates are periodically transmitted

throughout the network.– Reacts slowly to mobility in large networks.


Reactive Routing ProtocolReactive Routing Protocol

• Ad Hoc On-Demand Distance Vector (AODV):– An improvement on the DSDV algorithm.– A source host initiates a path discovery process to

locate the destination if it doesn’t have a valid route to that destination.

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• Dynamic Source Routing (DSR):– Route discovery similar to AODV.– Routes maintained in route cache.– Each packet carry full routing information.– Overhead is potentially larger than AODV because

AODV packet only contains the destination address and sequence number.



• Zone Routing Protocol (ZRP):– A hybrid reactive/proactive protocol.– Each host proactively maintains the topological

information within its local neighborhood (routing zone).

– Reactively requires routes to destination beyond the routing zone.

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Collective CommunicationCollective Communication

• More than one destination, e.g. multicast.– Flooding-based protocol: distributes the multicast

message all around the network.– Tree-based protocol: establishes a multicast tree

among the multicast members that comprises a wireless network.

– The task of keeping the tree structure up-to-date is nontrivial!


QualityQuality--ofof--Service RoutingService Routing

• Supports real-time applications such as audio and video communications.– The protocol must establish a route that satisfies

certain QoS constrains such as delays and bandwidth.

– A ticket-based approach avoids unwise blind flooding by using tickets to limit the number of route-searching packets.

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Location AwarenessLocation Awareness

• Each mobile host uses a positioning device to determine its current physical location.

• The geometric relationship among mobile hosts can be accurately described with the knowledge of their location information.


LocationLocation--Aware ComponentsAware Components

• A Location-aware device uses an attached receiver to catch outside signal analyze and determine the current location.

• Outdoor positioning.– GPS.

• Indoor positioning.– Infrared sensors.– Short-range radios.

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Global Positioning System (GPS):Global Positioning System (GPS):

• 24 satellites in six orbital planes operating in circular, 10,900-nautical-mile orbits at an inclination angle of 55 degrees in a 12-hour period.

• Satellites transmit navigation messages that contain their orbital elements, clocks, and statues which a receiver uses to determine its position and roaming velocity.


GPSGPS

• 3 satellites are required to determine the receiver’s longitude and latitude. Adding a 4th can determine the receiver’s altitude.

• Positioning accuracy in the 15-meter range.

• Drawback: satellite signals can be blocked.

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Infrared SensorsInfrared Sensors

• Infrared transmitters automatically sending their own Ids can be hang from various places on a building.

• A computing device with an infrared receiver uses these signals to determine its current position.

• Low cost and low power consumption.


ShortShort--Range RadiosRange Radios

• Infrared signals are directional and can easily be blocked by intervening objects.

• Radio transmission is omnidirectional.

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PART IIPART II

LOCATION-AWARE ROUTING

PROTOCOLS


• Purpose of a routing protocol

– Source Node ---------------------> Destination Node

• Difficulties– dynamically changing topology– scarce wireless bandwidth– tradeoff between routing and location information

availability

LocationLocation--Aware Routing ProtocolsAware Routing Protocols

Shortest Path

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• Approach in developing routing protocols– Use extra location information provided by MHs

• Several routing-issue Optimizations– Location-aided routing (LAR)– Geographic distance routing (Gedir)– Grid– Zone-based two level routing

LocationLocation--Aware Routing ProtocolsAware Routing Protocols


• Requesting a route in DSR, ZRP, AODV– Initiate a route request packet

•waste a lot of bandwidth

•can initiate a broadcast storm

• Requesting a route in LAR– Use selective flooding

LocationLocation--Aided Routing (LAR)Aided Routing (LAR)

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• Requiring a route from source S to destination D

– System defines a smaller forwarding zone that covers both S and D

– Forwarding zone seeks the smallest rectangle that can bound S’s current location and D’s possible location

– Carefully choosing the forwarding zone saves bandwidth.




Figure 2. Forwarding zone optimizations confine the route-searching area:(a) rectangle, (b) bar W, © fan, and (d) dual fan

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• Work in a connectionless mode

• Send data packets directly without establishing

path a priori

Geographic Distance Routing (Gedir)Geographic Distance Routing (Gedir)


• Several approaches– X always picks as Y, the next host, the receiver that

has the smallest angle from X to Y and to thedestination

– X always picks as Y, the receiver closest to the destination

• Both approaches can lead to endless loop

• Second approach may create detour

Geographic Distance Routing (Gedir)Geographic Distance Routing (Gedir)

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Geographic Distance Routing (Gedir)Geographic Distance Routing (Gedir)First ApproachFirst Approach


Geographic Distance Routing (Gedir)Geographic Distance Routing (Gedir)Second ApproachSecond Approach

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• Concept of Grid– Partitioning the geographic area into several squares– There is at most one MH selected as the grid’s leader– Grid leaders is responsible for performing routing

• Fully location-aware

• Scalability

GridGrid


• Route discovery– Eliminate redundant route request packets– This filtering mechanism suitable for a crowded

environment

• Packet relay– Grid ID represents a route, not a host ID– Each entry in routing table records the next grid that

will lead to the destination– Stronger, more resilient route maintenance

GridGrid

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• Route maintenance– Highly resilient to host mobility

– In other protocols, when an intermediate host in a

route roams outside its neighbor’s range, the route

breaks

– Leader election protocol

– Routing table handoff via broadcast

GridGrid


GridGrid

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• Concept of two-level– Peer - to - peer but hierarchical– Geographic area is divided into zones– Each MH knows its current position and thus zone ID– Distributes link states throughout network

• Intrazone and interzone– Propagation of any change in connectivity inside a

zone is limited to within zone itself

ZoneZone--based twobased two--level routinglevel routing



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• Gateway– MH connects to one or more hosts in other zones– Local changes causes global flooding only if it changes interzone connectivity

• Routing– Use information exchange and routing tables– Search for a route



• Three issues for a manet routing protocol– Route discovery– Packet relay– Route maintenance

• Categories– Non-location aware– Partially location aware– Fully location aware

Protocol ComparisonProtocol Comparison

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Protocol ComparisonProtocol Comparison


PART IIIPART III

LOCATION-AWARE SERVICES

& CONCLUSION

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•Navigation/ Position identification

•Geographic messaging/ advertising

•Neighbor-and-service discovery

LocationLocation--Aware ServicesAware Services


LocationLocation--Aware ServicesAware Services

LAR unicast

Geocast

Grid

Geogrid

TORA

Geotora

Protocolsto provide geographic services

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GeocastGeocast

•Differs from traditional multicast– multicast group vs. geographic region

•Uses two approaches– Forwarding Zone– Distance to the center of geocast region


GeogridGeogrid

•Differs from traditional multicast– multicast group vs. geographic region

•Uses two approaches– Forwarding Zone– Distance to the center of geocast region

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GeotoraGeotora

•Derives from TORA

•Uses modified DAG created in TORA

•Requires two-phase geocasting– inside/outside geocast region


DAG and TORADAG and TORA

•Directed Acyclic Graph– graph/directed link/height/sink

•Temporally Ordered Routing Algorithm– creates a route by using DAG

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Two Two DAGsDAGs


GeotoraGeotora

•Derives from TORA

•Uses modified DAG created in TORA

•Requires two-phase geocasting– inside/outside geocast region

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Geogrid vs. GeotoraGeogrid vs. Geotora

•Geogrid– connectionless– forwarding zone plus grid leader prohibition

•Geotora– connection oriented– costly if mobility is high– worthwhile if sending large amount of data


LocationLocation--aware Tour Guideaware Tour Guide

•GPS receiver connected to a laptop

•Software part implemented by Java– 2D map– 3D virtual world– Web page information– Interact with other guide users

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Interface of the tourInterface of the tour--guide systemguide system


ConclusionConclusion

•Location information– is natural and inevitable to be exploited

•Challenges– positioning accuracy– mapping location to web data

Location Awareness in Ad Hoc Wireless Mobile Neworksirchen/6204/paper/TSE01-slide.pdf(AODV): – An...

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