Efficient and Reliable Packet Forwarding by Utilizing Path Diversity in Wireless Ad Hoc Networks

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Efficient and Reliable Packet Forwarding by
Utilizing Path Diversity in Wireless Ad Hoc
Networks

• Jianfeng Wang, Hongqiang Zhai,
• Wei Liu and Yuguang Fang
• Department of Electrical and Computer Engineering
  
• University of Florida, USA

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Outline

• Background and Motivation
• To address small scale channel variations in
  multihop ad hoc networks
• Minimal cost multipath routing
• Opportunistic packet forwarding
• Performance evaluation
• Conclusion

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Background

• Time-varying wireless channel
• Fading and shadowing
• Negative effects of channel variations
• Head-of-Line blocking
• False link breakage, thus unnecessary rerouting
• Poor end-to-end TCP performance
• Three categories of solutions
• Rate Adaptation
• Power Control
• Utilize multipath diversity at the link layer

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Motivation

• Diversity based packet forwarding

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Motivation cont

• Issues left to well address in literatures1-4
• Route optimality
• MAC layer overhead
• Our objective
• Minimum cost based routing built over AODV
• CSMA/CA based any-casting MAC

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System model

• Fixed data rate and fixed power
• Link channel quality changes on the packet level
• Packet transmission time ltlt link life time
• ? Packet loss probability of each link maintains
  stable during the flow life time

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Desired resulted routing

• An end-to-end path is represented as certain
  number of virtual hops
• Each virtual hop includes a primary forwarding
  node and several alternative forwarding nodes
• Packet loss probability for each link connecting
  neighboring virtual hops is less than certain
  level

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Some notations
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Characterize routing cost
Cost from hop i to hop i1
where o(l) is the relative forwarding priority of
node l among candidate forwarding nodes of hop i.

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Route discovery - request
Note In case a node receives duplicated RREQ
messages, the node forwards the later one only if
it is marked less cost than previous ones
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Route discovery - reply
Note In case the destination receives several
RREQ messages, the destination will generate a
new RREP only if the later one is marked less
cost than previous ones. The source will
eventually use the least-cost virtual path
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Route maintenance
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Opportunistic packet forwarding

• Extend unicast RTS ( in de facto 802.11) to
  any-cast RTS
• Probe channel conditions of multiple candidate
  receivers simultaneously

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Opportunistic packet forwarding cont
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Simulation setting

• Ns-2 simulation tools, basic setting of 802.11b
  MAC
• Group-distributed chain topology
• Distance of each hop is 220m
• Ricean fading channel with factor K5, maximal
  velocity is 2 m/s
• Packet size 1000 bytes
• Comparison with 802.11 MAC plus single path
  routing

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UDP performance - case 1
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UDP performance case 2
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UDP performance case 3
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TCP performance
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Conclusion

• Utilize multipath diversity in ad hoc networks
  with the simple extension of AODV and IEEE 802.11
  MAC
• Provide a solution to address route optimality
• Present an efficient anycast MAC
• Simulation shows our scheme improves throughput
  and energy efficiency significantly

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Selected references

• 1 P. Larsson, Selection Diversity Forwarding
  in a multihop packet radio network with fading
  channel and capture, MC2R ,Vol. 5, No. 4, pp.
  47-54, 2001.
• 2 Sanjit Biswas and Robert Morris,
  Opportunistic Routing in Multi-Hop Wireless
  Networks, in Proc.of the 2nd workshop on Hot
  Topics in Networks (HotNets II),MIT, Nov, 2003.
• 3 Romit Roy Choudhury and Nitin Vaidya,
  MAC-Layer Anycasting in Wireless Ad Hoc
  Networks, in Proc.of the 2nd workshop on Hot
  Topics in Networks (HotNets II),MIT, Nov, 2003.
• 4 S. Jain, Yi Lv, and S. R. Das, Exploiting
  Path Diversity in the Link Layer in Wireless Ad
  Hoc Networks, Technical Report, WINGS Lab, July
  2003.