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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. 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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  1. Trace-based Evaluation of Rate Adaptation Schemes in Vehicular Environments Kevin C. Lee WiVeC 2010, 5/17/10

  2. 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”

  3. Why Rate Adaptation? • Ideally, the transmission rate should be adjusted according to the channel condition 54Mbps Signal is good 12MbpsSignal is weaker Sender Receiver

  4. 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)

  5. 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

  6. 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

  7. Trace Collection • Traces from 3 different areas: City, Residential, and Highway

  8. Trace Collection Map

  9. Static Traffic Route • Car A centered at the mid point, stationary • Car B and C move back and forth toward and away from A

  10. Rate Adaptation Schemes Implementation • RRAA-DYN adjusts rates before the current estimation windowm

  11. Static Traffic Route Result • SNR from 440s to 540s • 40 seconds to complete one loop • Signal strength directly proportional to the distance between them

  12. 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

  13. Throughput in Different Transmission Rates • Throughput increases with transmission rate • ARF, RRAA-DYN, and RAM top 3 • AMRR and Sample bottom 2

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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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