PowerPoint Template

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Chorus Collision Resolution for Efficient
Wireless Broadcast
?? ? ???????? ??? ? ? ?
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?? ??

• ??
• Chorus Collision Resolution for Efficient
  Wireless Broadcast
• ?? Xinyu Zhang and Kang G. Shin
• Department of Electrical Engineering and Computer
  Science
• The University of Michigan
• ?? CSMA/CA ? ??? ??
• ????
• CSMA/CR Collision Resolution ??

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ABSTRACT

• CSMA/CA ? ?? multiple concurrent unicasts? ? ??
  ?????? ????? ????
• ?? ?? ?? ?? and links are lossy ? ??

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ABSTRACT

• ? ??? Chorus ?? ??? ????? ??
• IDEA ?? ??(Collisions)? ???? MAC ?????
  ?????? ???? Efficiency ? scalability ? ??
• ??? Overlap ? ? ?? ????? observation ?? ?????
  detect, decode
• Collision-tolerant ????? wireless broadcast ??
  transmission diversity ? spatial reuse? ???? ??
  ??
• network-level ?? ns-2 ? ?? CSMA/CA ? ?? ??

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?? ??

• ??????? ???? ??
• Multi-Hop ?? ???? ??? ??? ????? ???? ??
• ????? ????? ??? ???? ?? High PDR(packet-delivary
  ratio) ? Low latency ? ?? ???? ?????? ????? ???
  ??.

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?? ?? (PDR ? Delay)

• ???? ???? ??? ???
• PDR ? ????? ??
• ??? ??? ??? ??? ?? ??? ?? ??? ?? ?
• ??? PDR ??? ?? ??? ???? ???? ?? ??? ??? (Latency
  ? ???)
• PDR ? Delay ??? ???? ???? ?? ????

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Related Work

• ?? ?? CSMA/CA MAC-layer ?? ???? ?? ??
• R. Gandhi, S. Parthasarathy, and A. Mishra,
  Minimizing Broadcast Latency and Redundancy in
  Ad Hoc Networks, in Proc. of ACM MobiHoc, 2003.
• S.-H. Huang, P.-J. Wan, X. Jia, H. Du, and W.
  Shang, Minimum-Latency Broadcast Scheduling in
  Wireless Ad Hoc Networks, in Proc. of IEEE
  INFOCOM, 2007.
• S. Huang, P. J. Wan, J. Deng, and Y. Han,
  Broadcast Scheduling in Interference
  Environment, IEEE Trans. on Mobile Computing,
  vol. 7, no. 11, Nov 2008.
• W. Lou and J. Wu, Toward Broadcast Reliability
  in Mobile Ad Hoc Networks with Double Coverage,
  IEEE Trans. on Mobile Computing, vol. 6, no. 2,
  2007.
• ? ???? ?????? ?????? ???? ? ??? ??
• ? ??? ??? ???? scheme? ??? ??? ??? ??
  opportunity? ?? ??? ???
• ????????? ????? ??

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CSMA/CA ? ???

• CSMA/CA ? S ??? ?? ??? ????? ??? 3 TIME ??? ??
• ?? ??(Same packet) ?? ???? A,B ? ??? ?? ??
• D? ?? ??? ??? C ?? E ? A,B ??? ???? ???? ?
• ??? ??? ????? A,B ? D ? ?? ??? ?? ?? ??? ????
  ???? ?
• ??? CSMA/CA ??? ???
• ?? ?? ?? ??? ?? Back off ???

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CSMA/CR ? ??

• ??? ?????? ???? Chorus!!
• CSMA/CR(Collision resolution)? ??
• Chorus ? ?? ??
• ?? ?? ??? ?? ? ?? ????? overlap ??? ? ???
  ??(detect), ???(decode) ? ??
• ?? ?????? ?? ??? ???? ????? Resolve(??)
• A? B ? ??? ??? ????? ?? ? ??.

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CSMA/CA ? CSMA/CR ??
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Chorus ?? ?????? ??? ??

• The broadcast packet format in Chorus.

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Collision resolution scheme ?? ??

• lt??gt
• D ? CHORUS ? A,B??? ? ? ?? ??? ??? decode ??
  Collision Resolution? ??
• ? ??? ?? ????? ????? 2?? ?? ???? ??
• Reuse Spatial
• lt??gt
• ??? unreliable ? ? A,B ??? ? ? ???? ??? ???? ??
  ?? ?? ?? transmit diversity ? ????.(??? ???? D ?
  ??)
• Improve Diversity

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Collision resolution scheme ?? ?? -?? ??-

• ??? ??? transmit diversity ??
• R. Mudumbai, D.R. Brown, U. Madhow, and H.V.
  Poor, Distributed Transmit Beamforming
  Challenges and Recent Progress, IEEE
  Communications Magazine, vol. 47, no. 2, 2009.
• ?? ?? ??? ??? ?? ???? ??? ??
• ??? Chorus ? ? ??? ???? ??.
• ??? Symbol level ?? ???? ??? A,B ? ???? ???
• Chorus ? Overlapping ?? ????? ??? ??? ????
  ????? ??

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Collision resolution scheme ?? ??

• Chorus ? 802.11 CSMA ? MAC ????
• cognitive sensing ? scheduling module ?
  ADD
• ???? ??? ????? ?? AIR ?? ??? ??? sensing ??? ??
  back off.
• ???? detect, decode

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COLLISION RESOLUTION (?? ???)A. Detecting
Collided Packets

• ??? ?? Detect
• ?????? known random sequence ? ??? preamble? ADD
• ???? Matched filter ? ?? ??
• Preamble ? detect ? overlapping ??? ?
• ?? ?? 32 bit pseudo-random preamble ? ??? ?? ??
  ??? 98
• S. Gollakota and D. Katabi, ZigZag Decoding
  Combating Hidden Terminals in Wireless Networks,
  in Proc. of ACM SIGCOMM, 2008.

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COLLISION RESOLUTION (?? ???) B. Iterative
Collision Resolution

• Iteratively decoding two collided packets
  carrying the same data.
• ?? ???????? ? ??? ??
• ltwhile to endgt
• 1. ?????? ?? S? combine
• 2. P1 ? A? ?? ?? ???? A ? A ? ?? ?? ??
• 3. A ? ???? Reconstruct
• 4. S ? ?? A? subtract

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COLLISION RESOLUTION (?? ???) C. Using Packet
Combination to Improve Diversity

• Fortunately, such error propagation(????) stops
  if the actual bits of A' and C are the same.
• A ? C ? ?? ?? ?? ??? ??(?? ???? ??)
• ?? ??? ??? ??? ?????? ???? ?? transmit
  diversity ? ???

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COGNITIVE SENSING AND BROADCAST SCHEDULING (MAC
???) MAC Layer Cognitive Sensing and Scheduling

• CSMA ???? ??
• carrier sensing ? backoff ? ??
• Congnitive sensing ??(Chorus header)
• ??? identitiy ??
• ?????? ??? ID
• ?? sequence ??
• CRC

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COGNITIVE SENSING AND BROADCAST SCHEDULING (MAC
???) MAC Layer Cognitive Sensing and Scheduling

• The MAC layer control flow in Chorus. seq
  denotes the sequence number of the packet on the
  air.

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COGNITIVE SENSING AND BROADCAST SCHEDULING (MAC
???) MAC Layer Cognitive Sensing and Scheduling

• lt??gt
• ??? ?? Iterative decoding ??
• ??? CRC ?? / ?? ??? BACK
• lt??gt
• R1 ??? idle ?? ??? Forward ??
• R2 ??? busy ?? ??? transmit queue ? ?? ??
  ??? transmitting.
• R3 ??? busy ?? preamble ? detect ?? ???
  ??? header field ? decode ?? ??? ??
  ??? AIR? ???
• backoff ?? 802.11 (Chorus ? ???? ??)

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COGNITIVE SENSING AND BROADCAST SCHEDULING (MAC
???) MAC Layer Cognitive Sensing and Scheduling

• R1 ???? CSMA ????
• R2 CSMA/CR ? ??? ??.
• ?? ??? Overlapping ?? ??? ???? ??
• CSMA/CA ? ??? busy ? ??? ?? back off
• ???? overhead
• 802.11 ?? ???? 20 bit ??
• Chorus preamble header 80 bit ? ??

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EXPERIMENTAL EVALUATION -??-

• Chorus CR ? ???? ???? ?? Symbol-level ????? ???
  ???? ???? ?? ??? ??
• ??? ?????? Chorus ? ????? ???? ?? ns-2 ? ?? ?????
  ???? ?????
• ??
• CSMA/CR MAC ? ?????? ????? ??
• Chorus? CSMA/CA ? ?? ??
• Chorus ? Latency ? PDR ? ???? ??? ???

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EXPERIMENTAL EVALUATIONNetwork-Level Performance

• The impact of link quality (reflected by o) on
  latency and PDR. The error bars indicate
  variation over 30 random topologies.
• DCB Double Coverage Broadcast / ns-2 802.11b ?
  MAC / CSMA/CA
• PDR packet-delivery ratio
• e edge reception probability (?? ?? ?? /
  transmission range? ??)

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EXPERIMENTAL EVALUATIONNetwork-Level Performance

• Scalability of the broadcast protocols as the
  topology size (number of nodes) grows.

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EXPERIMENTAL EVALUATIONNetwork-Level Performance

• Sensitivity to source rate, which indicates the
  maximum supportable throughput of a broadcast
  protocol.

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EXPERIMENTAL EVALUATIONNetwork-Level Performance

• Impact of packet sizes, which range from 64 to
  2048 bytes.

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CONCLUSION

• Chorus? ?? ?? ??? ?? ???(roughly)? ??? ?,
• ???????? ???? ??? ????
• iterative ?? decoding ? ??
• Transmit diversity Spatial reuse ? ??
• Chorus ? ?? ?? (large-scale ??????)

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???

• CR? ?? CSMA/CA ? ??
• ???? ??? ??
• ??? ????? ??? ???? ?????
• ?? vs ML

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?? ??
?? ? ????? ??? ? ? ?