XORS IN THE AIR: PRACTICAL WIRELESS NETWORK CODING

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XORS IN THE AIR PRACTICAL WIRELESS NETWORK CODING

• Athours
• Sachin Katti Hariharan Rahul Wenjun Hu?
  Dina Katabi Muriel Medard Jon Crowcroft?
• MIT CSAIL ?Univ. of Cambridge

SIGCOMM06
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OUTLINE

• Motivation
• Methodology - COPE
• Opportunistic Coding
• Understanding COPSs gains
• Coding MAC gain
• Experimental Results
• Pros and Cons

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MOTIVATION

• This paper proposes COPE, a new architecture for
  wireless mesh networks
• In addition to forwarding packets, routers code
  packets from different sources to increase the
  information content of each transmission
• COPE is run as a bundle layer between MAC layer
  and network layer
• This paper implements COPE on WiFi 802.11

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MOTIVATION
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MOTIVATION

• P1 01001 P2 10011
• gt P3 P1 xor P2 11010
• Alice P3 xor P1 10011 P2
• Bob P3 xor P2 01001 P1

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METHODOLOGY - OPPORTUNISTIC CODING
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METHODOLOGY - UNDERSTANDING COPSS GAINS

• (a) transmissions 4
• (b) transmissions 3
• gt Coding gain 4/3 1.33

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METHODOLOGY - CODING MAC GAIN

• Assuming all nodes continuously have traffic to
  send
• Because it tries to be fair, the MAC divides the
  bandwidth equally between the 3 contending nodes
  Alice, Bob, and the router.

1.5K
3K
3K
1.5K
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METHODOLOGY - CODING MAC GAIN

• Assuming all nodes continuously have traffic to
  send
• Because it tries to be fair, the MAC divides the
  bandwidth equally between the 3 contending nodes
  Alice, Bob, and the router.

1.5K
Received by Alice and Bob 3K
1.5K
1.5K
1.5K
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METHODOLOGY - CODING MAC GAIN
Received by Alice and Bob 6K

• Coding MAC gain 6K/3K 2

3K
3K
3K
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METHODOLOGY - GAIN

• Theoretical gains for a few basic topologies

Chain topology
X topology
Cross topology
Wheel topology
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EXPERIMENTAL RESULTS TEST BED
20 nodes locations for two floor of the testbed
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EXPERIMENTAL RESULTS - COPE IN GADGET TOPOLOGIES
TCP gain in the Alice-and-Bob topology
UDP gain in the Alice-and-Bob topology
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EXPERIMENTAL RESULTS - COPE IN GADGET TOPOLOGIES
TCP gain in the X-topology
UDP gain in the X-topology
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EXPERIMENTAL RESULTS - COPE IN GADGET TOPOLOGIES
TCP gain in the cross topology
UDP gain in the cross topology
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EXPERIMENTAL RESULTS TESTBED

• COPE provides 38 increase in TCP goodput when
  the testbed topology does not contain hidden
  terminals

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EXPERIMENTAL RESULTS TESTBED

• COPE can provide a several-fold (3-4x) increase
  in the throughput of wireless Ad hoc networks.
  Results are for UDP flows with randomly picked
  source-destination pairs, Poisson arrivals, and
  heavytail size distribution.

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PROS

• COPE provides enhancement of throughput without
  too much extra coding overhead
• COPE can not only apply on WiFi, but also other
  MAC protocols, such as WiMax, sensor networks.
• COPE doesnt optimize power usage

CONS
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