Wireless Network Coding

1
Wireless Network Coding

• Martin Xu

2
Outline

• Introduction
• New Solutions
• COPE
• ANC
• Conclusions

3
Introduction

• Wireless mobility
• Problem severe throughput limitation
• Solutions
• COPE
• ANC
• Lets take a look at traditional wireless

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Traditional Wireless
Router
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Traditional Wireless
Router
4 transmission required
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Traditional Wireless
Router
4 time slots required
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COPE

• Katti, S., Rahul, H., Hu, W., Katabi, D., Médard,
  M., and Crowcroft, J. 2006. XORs in the air
  practical wireless network coding. In Proceedings
  of the 2006 Conference on Applications,
  Technologies, Architectures, and Protocols For
  Computer Communications (Pisa, Italy, September
  11 - 15, 2006). SIGCOMM '06. ACM Press, New York,
  NY, 243-254.
• Forward multiple packets in a single transmission
• Lets take a look at how COPE deals with the
  aforementioned example

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COPE
Router

XOR
9
COPE
Router
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COPE
Router

XOR

XOR
Higher throughput (3 transmissions required)
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COPE

• Transparent coding layer between IP and MAC
• Forward multiple packets in a single transmission
• Never delay packets
• HOW?
• Opportunistic Listening
• Opportunistic Coding
• Learning neighbor state

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COPE - Listening

• Broadcast in a small neighbor
• Each node stores overheard packets for a limited
  time
• Pseudo broadcast
• Broadcast results in poor reliability and lack of
  backoff
• Pseudo broadcast unicast packets that are meant
  for broadcast

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COPE - Coding

• To transmit n packets, p1, ..., pn, to n
  nexthops, r1, ..., rn, a node can XOR the n
  packets together only if each next-hop ri has all
  n - 1 packets pj for j i.

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COPE - data structure

• Reception report
• Reports are piggybacked on packets
• If no packets to send, periodically send reports
• Output queue (FIFO)
• Two per-neighbor virtual queue
• packet-size distribution in the Internet is
  bimodal with peaks at 40 and 1500 bytes
• Packet info

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COPE - Performance

• With no hidden terminals, TCPs throughput can
  increase by 38
• flows, COPE increases UDP throughput by 3-4x

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ANC

• Katti, S., Gollakota, S., and Katabi, D. 2007.
  Embracing wireless interference analog network
  coding. In Proceedings of the 2007 Conference on
  Applications, Technologies, Architectures, and
  Protocols For Computer Communications (Kyoto,
  Japan, August 27 - 31, 2007). SIGCOMM '07. ACM
  Press, New York, NY, 397-408.
• Strategically exploit interference instead of
  avoiding it
• Interfered signal is not exactly the sum
• Channel distorts signals
• Two signals are never synchronized

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ANC - Algorithm

• Decode small part of uninterfered signal (MSK)
• Decode interfered signal
• Decomposition using amplitudes of the original
  ones and the interfered
• Four possible angles
• Choose the 90 degree one
• Decode the rest of the uninterfered signal

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ANC - Performance

• For the example used at the beginning, median
  throughput gain of ANC over routing 70, COPE 30
• For X-topology, median throughput gain over
  routing is 65, over COPE 28
• For chain topology, median throughput gain over
  routing is 37

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Conclusion

• Both implementation that yields large throughput
  gains
• COPE
• Simple and practical
• ANC
• Embrace Broadcast and Interference