Routing Improvement using Directional Antennas

CS525M 2006

Presented byGreg Ratner

Paper by Saha and Johnson

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Overview: Directional Antennas Paper

• Background• Protocol Details• Evaluation• Results• Other Application• Conclusion• Questions

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Background

• Primary concern: distance between mobile nodes

• Directional Antennas:– Longer transmission in one direction– Less interference to other nodes

• Previous research devoted to network throughput

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Background cnt.

• Dynamic Source Routing (DSR)– Forms a route on-demand – Uses source routing instead of relying

on the routing table at each intermediate device

– Source decides the entire sequence of hops to the destination

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Directional Antennas

• Idea:– Use of directional antennas to bridge

network• Permanent partitions• Non-permanent partitions

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Protocol Modification

• Mobility in Ad-Hoc networks might lead to partitioning

• Adaptively use directional antennas to bridge the gap

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Data Structure Modification

• Add 2 new flags to DSR header:– Trigger partition bridging

• Handles route requests differently

– Long hop• Sends packets directionally with higher

power

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Data Structure Modification cnt.

• Each node maintains Passive Acknowledgment Table (PAT):– Target Address– When (time) inserted– List of angular ranges

• Where to search for target address

– List of route request package• Different sources to a single destination

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Modifications to Route Discovery

• Long hop – distance between 2hops > than range of regular antenna

• Source node:– Checks local route cache

• If no Route Requests then send as DSR• If source already sent a Route Request,

send a new request with partition bridging flag

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Modifications to Route Discovery cnt.

• Reciving Node:– If PAT does not have a Route Request

• If partition bridging flag is not set, broadcast Route Request packet

• Else– Forward Rout Request omnidirectionaly– Enter target address into PAT– Record current time in ‘When’– Copy Route Request into a list of RR’s– Initialize directions to 240° opposite of arrival

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Modifications to Route Discovery cnt.

• If PAT contains an entry for Route Request– Node saves the list of Route Requests

for replying– Check ‘When’ field

• If < threshold list of directions is updated to exclude 60° on the direction of arrival of Route Request

• If > threshold no action is necessary since one or more long hop requests were sent

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Modifications to Route Discovery cnt.

• If ‘When’ time in PAT expires, angular ranges are checked

– For each range long hop request is sent

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Modifications to Route Discovery cnt.

• When Route Request arrives to its destination Route Reply is sent back

• Intermediate Node that gets Route Reply does the following:– Checks PAT and creates Route Reply to

all requests for the original target– Deletes the Route Request from the

PAT – If there is no entry for Request packet is

forwarded as DSR

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Modifications to Route Maintenance

• MAC layer handles long hops• If the hop is not long:

– Transmit the packet omnidirectionally– If not AKed consider a long hop and try

again– If still not aked or doesn’t have a

direction return an error

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Modifications to Route Maintenance

• Signal-to-interference-and-noise-ratio (SINR) is used to unset long hop flag– If SINR > threshold of suitable signal,

then unset long hop

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Analysis

• Evaluation– Packet delivery

ratio– 90th Percentile

Packet Latency– Packet Overhead

•Two scenarios:

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Results

• If node mobility is high protocol is less able to bridge the gap due to latency

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Repairing Broken Routing

• Instead of sending route errors, estimate the direction of next hop and send a directional request skipping broken link

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Conclusions

• Network bridging is especially effective with static end points

• Big performance gain in route repair• Direction accuracy does not have a

major effect

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Questions

• Equipment limitations?• Adjustment cost?• Stability?

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References

• Wikipedia– http://en.wikipedia.org/wiki/Dynamic_So

urce_Routing