Trace based evaluation of rate adaptation schemes in vehicular environments
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Trace-based Evaluation of Rate Adaptation Schemes in Vehicular Environments. Kevin C. Lee WiVeC 2010, 5/17/10. Rate Adaptation Overview. The 802.11 a/b/g/n standards allow the use of multiple transmission rates 802.11b, 4 rate options (1,2,5.5,11Mbps)

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Trace-based Evaluation of Rate Adaptation Schemes in Vehicular Environments

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Trace based evaluation of rate adaptation schemes in vehicular environments

Trace-based Evaluation of Rate Adaptation Schemes in Vehicular Environments

Kevin C. Lee

WiVeC 2010, 5/17/10


Rate adaptation overview

Rate Adaptation Overview

  • The 802.11 a/b/g/n standards allow the use of multiple transmission rates

    • 802.11b, 4 rate options (1,2,5.5,11Mbps)

    • 802.11a, 8 rate options (6,9,12,18,24,36,48,54 Mbps)

    • 802.11g, 12 rate options (11a set + 11b set)

  • The method to select the transmission rate in real time is called “Rate Adaptation”


Why rate adaptation

Why Rate Adaptation?

  • Ideally, the transmission rate should be adjusted according to the channel condition

54Mbps

Signal is good

12MbpsSignal is weaker

Sender

Receiver


Motivation

Motivation

  • MANY rate adaptation algorithms yet no fair comparison

    • Unrealistic propagation (unrealistic)

    • Dynamic changing conditions (non-repeatable)

    • Long system setup and device driver implementation (impractical)


Framework goal

Framework & Goal

Repeatable evaluation of rate adaptation schemes

Implementation of different application

Application Layer

Rapid deployment independent of hardware spec

Implementation of various rate adaptations schemes

MAC Layer

Realistic SNR to reflect the environment

Use field-collected SNR to replace synthetic value

Physical Layer


Physical layer

Physical Layer

  • Collect SNR traces from moving cars

    • Server broadcasts @ 6Mbps

    • 2 Clients receive and record SNR

  • Increase range and power of signal with an external 7dBM antenna

  • Replace SNR logic with SNR from the field

  • Derive BER and then bit error probability


Trace collection

Trace Collection

  • Traces from 3 different areas: City, Residential, and Highway


Trace collection map

Trace Collection Map


Static traffic route

Static Traffic Route

  • Car A centered at the mid point, stationary

  • Car B and C move back and forth toward and away from A


Rate adaptation schemes implementation

Rate Adaptation Schemes Implementation

  • RRAA-DYN adjusts rates before the current estimation windowm


Static traffic route result

Static Traffic Route Result

  • SNR from 440s to 540s

  • 40 seconds to complete one loop

  • Signal strength

directly proportional to the distance between them


Instantaneous throughput for all algorithms

Instantaneous Throughput for All Algorithms

  • Packet-based rate adaption schemes react similarly to the SNR-based scheme (RAM)

  • Sample rate plateau from 460-470s and 500-530s


Throughput in different transmission rates

Throughput in Different Transmission Rates

  • Throughput increases with transmission rate

  • ARF, RRAA-DYN, and RAM top 3

  • AMRR and Sample bottom 2


Rate distribution for all schmes

Rate Distribution for All Schmes

  • 6Mbps occupies the largest fraction for top 3 schemes but there are other rates => short-term lossy channel

  • Sample & AMRR can’t adapt to short-term fluctuation


Success of arf

Success of ARF

  • Comes from the fact that rate increases conservatively and decreases drastically

  • Not too good if the channel condition does not change frequently

  • Conclusion: Packet-based scheme does a subpart job because of fixed parameters of packet statistics; adaptive parameters to improve


Impact of environments

Impact of Environments

  • Throughput degradation from residential, highway, city; speed & traffic density play a factor

  • RRAA-DYN beats

    RRAA & RRAA-BASIC

    => changing trans-

    mission wind. helps

    improve responsive-

    ness


Impact of propagation model

Impact of Propagation Model

  • Rayleigh has higher throughput b/c it considers fading where there is no dominant propagation along a line of sight between transmitter and receiver

  • A more accurate

    prop. model to use

    b/c lead car and

    trailing car are often

    separated by cars in

    between


Conclusion

Conclusion

  • An integrated framework that utilizes empirical data collected from the testbed to objectively compare different rate adaption schemes

    • Repeatable

    • Rapid

    • Realistic


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