Routing Improvement using Directional Antennas Presented by Greg - - PowerPoint PPT Presentation

Routing Improvement using Directional Antennas

CS525M 2006

Presented by Greg 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

• n 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 2

hops > 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
• ne 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