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Isolating Physical PER for Smart Rate Selection in 802.11. Malik Ahmad Yar Khan and Darryl Veitch ARC Special Centre for Ultra-Broadband Information Networks (CUBIN) The University of Melbourne, Australia IEEE Infocom 2009 (acceptance rate = 19.65%). Outline. Introduction The core idea

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isolating physical per for smart rate selection in 802 11

Isolating Physical PER for Smart Rate Selection in 802.11

Malik Ahmad Yar Khan and Darryl VeitchARC Special Centre for Ultra-Broadband Information Networks (CUBIN)The University of Melbourne, AustraliaIEEE Infocom 2009(acceptance rate = 19.65%)

  • Introduction
  • The core idea
  • RCA modification
    • Fragmentation implementation
    • RTS/CTS implementation
  • Performance
  • Conclusion
  • Rate selection algorithms in use in 802.11 suffer from a fundamental problem
    • Implicity or explicity make decisions bases on total Packet Error Rate (PER)
  • False rate decision lowers the system throughput
  • Total PER = PPER + CPER
    • PPER: Physical PER
    • CPER: contention PER
  • It is often the case CPER dominates PPER
    • Poor latency, loss and throughput
goal of the paper
Goal of the paper
  • Providing a novel way to isolate the physical error
  • Providing a modular way of isolating the contention error which any rate adaptation algorithm can be enhanced
  • Only consider a packet is fragmented into 2 frames
  • The fragment 2 is sent out only after an SIFS after the final ACK
    • Provided there are no hidden terminals
  • If the first fragment is lost, for nay reason, the second will not even be sent
  • Observation: the loss of a second fragment on the first transmission attempt
    • Physical error
rts cts
  • Once the RTS-CTS exchange is completed, the data packet will have the channel reserved, and will only encounter error for physical reasons
block reservation in 802 11e
Block reservation in 802.11e
  • An option in IEEE 802.11e
  • The second data packet of such blocks could be used to directly measure PPER
main concept
Main concept
  • Not to use these methods all the time in practice
  • Only trigger their use often enough to gather good statistics on PPER
fragmentation implementation
Fragmentation implementation
  • Only descriptors of second fragments are passed to the RCAs
  • A mechanism is needed to trigger the fragmentation of selected packets
    • Maintains a simple ON/OFF variable
rts cts implementation
RTS/CTS implementation
  • RTS/CTS protection is switched on by a per-packet decision
  • Use Long Retry Count (LRC) to record the statistic of RTS/CST transmission
  • Two main metrics
    • Weighted mean rate summaries
    • IP throughput
  • All experiments are run in IEEE 802.11a in testbed
    • Full rate set:{6,9,12,18,24,36,48,54}
    • Packet size: 1500 bytes
    • 10 stations if no further explanation
the wireless testbed
The wireless testbed
  • St[1-13] are stations, Sniff[1-2] are sniffers
two implementation protocols
Two implementation protocols
  • SampleRate
    • A MIT master thesis
    • Implemented on MadWifi
  • AMRR
    • A multi-rate algorithm also implemented on MadWifi
  • The paper investigates two ways to isolate Physical PER
    • RTS/CTS
    • MAC level packet fragmentation
  • Higher channel rates were used when PPER was in fact low, even when contention is present