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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

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
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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