Performance Testing of Rate
Adaptation Algorithms in WLAN
Author: Muhammad Sohail Khan
Supervisor: Prof. Rikku Jäntti
Comm Lab TKK
Wireless Local Area Networks
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Growing popularity and demand due to
mobility
Easy to deploy with low costs
Operates in Unlicensed band
Provide access to high speed data and
multimedia services
IEEE 802.11 Multirate Capability
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IEEE 802.11 standard is most mature and
accepted technology for broadband access
Current specifications provides multiple
transmission rates at PHY layer
802.11b PHY supports 1,2,5.5 and 11 Mbps
802.11a/g PHY support 6,9,12,18,24,36,48
and 54 Mbps
Optimal Data Rate Selection
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Different Modulation Schemes for the PHY
Data Rates
SNR and BER requirement
Highly volatile nature of Wireless channel due
to pathloss, fading and interference
Data rate selection in WLAN
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Fixed
Auto
Contribution to Thesis
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Experimental Testing of three Rate Adaptation
Algorithms
Designing of a realistic testbed
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Channel Simulator
802.11 Task Group n Channel Models
Analyze throughput performance under
varying channel conditions
Rate Adaptation Mechanism
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Selection of optimal PHY Data Rate according
to Varying wireless Channel conditions
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Estimation of channel
Data Rate selection
No specifications in 802.11 standard
Implementation manufacturer specific
Rate Adaptation Mechanisms
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Statistics Based Mechanisms
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Decision at sender
Estimators : frame errors, throughput calculation
Examples: ARF, AARF
SNR Based Mechanisms
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Decision at receiver
Estimators: SNR, RSSI
Examples: RBAR
Onoe
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Belongs to Statistics based mechanism
Uses credits as a function of number of Successful and
erroneous transmission/retransmission over an observation
period
Implementation detail
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starts at 24 Mbps for 802.11a/g and 11Mbps for 802.11b
Updates credits in fixed observation period of 1 second
Credits incremented if less then 10% packets needed retry else
decrease the credits
Switch to next higher Data Rate when credits value reaches 10
Sample Rate
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Throughput based mechanism
Increases throughput by sending packets at Data Rate with
minimum average transmission time
Implementation Detail
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Starts with highest Data Rate
If more then 4 retransmissions decrease until packet is sent
Periodically sends 10th packet at randomly selected Data Rate
Calculate average transmission time for probe packets
Switch to Data Rate with lowest average transmission time
AMRR (Adaptive Multi Rate
Retry)
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Retry Based Mechanism which adaptively increases threshold for
rate increase
Uses Binary Exponential Backoff to adapt length of period for
rate and transmission parameter
Implementation Detail
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Uses 4 pairs of Data Rate and Transmission Counters (r0/c0, r1/c1,
r2/c2 and r3/c3)
Starts with r0 and if transmission fails retry c0 times and switch to
r1
r3 always minimum rate
r1 and r2 set to immediate lower rate then r0
Experimental Testbed
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Reliable and Controlled test environment through use
of PROPSim C2 Channel Simulator
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Configurable
Repetitive
Open Source MadWiFi Drivers for WLAN Adaptors
Traffic generation tool IPerf
Experimental Testbed
Channel Models
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Channel Models Proposed by 802.11 Task Group n
Delay Profile of the Channel Models
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Model A: representative of a typical office environment, non-line
of sight (NLOS) conditions with 50 ns rms delay spread
Model B: representative of a large open space and office
environment, NLOS conditions with 100 ns rms delay spread.
Model C: representative of large open space (indoor and
outdoor), NLOS conditions with 150 ns rms delay spread.
Model D: representative of large open space (indoor and outdoor),
same as Model C, but for LOS conditions. A 10 dB spike at zero
delay with rms delay spread of 140 ns.
UDP Throughput vs Pathloss For
Channel Models A,B,C and D
8
8
SampleRate
AMRR
Onoe
7
6
Throughput (Mbps)
Throughput (Mbps)
6
5
4
3
4
3
2
1
1
63
66
69
72
75
Pathloss value (dB)
78
81
0
60
84
8
66
69
72
75
Pathloss value (dB)
78
81
84
SampleRate
AMRR
Onoe
7
6
Throughput (Mbps)
6
5
4
3
5
4
3
2
2
1
1
0
60
63
8
SampleRate
AMRR
Onoe
7
Throughput (Mbps)
5
2
0
60
SampleRate
AMRR
Onoe
7
63
66
69
72
75
Pathloss value (dB)
78
81
84
0
60
63
66
69
72
75
Pathloss value (dB)
78
81
84
Loss Ratio and TCP throughput vs
Pathloss for Channel Model C
100
8
SampleRate
AMRR
Onoe
80
SampleRate
AMRR
Onoe
7
Throughput (Mbps)
Loss Ratio (%)
6
60
40
5
4
3
2
20
1
0
60
63
66
69
72
75
Pathloss value (dB)
78
81
84
0
60
63
66
69
72
75
Pathloss value (dB)
78
81
84
Conclusions
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AMRR gives worst performance in terms of
throughput.
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Onoe Performs better at low pathloss value
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Switches between too many Data Rates
Conservative in nature.
Sample outperforms Onoe and AMRR at High
pathloss value
The End
Thank You!