1. Link Rate Estimation and Adaptation for VoWLAN with Mobility
Student: Yann-Huei Li
Advisor: Dr. Ying-Dar Lin
2019/5/18
Speed Lab

2. Outline Background Problem statement Related works Solution
VoWLAN – Voice over WLAN
Sustainable Rate
Metrics – MOS and Medium Consumption
Problem statement
Related works
Solution
Estimating Sustainable Rate: RTQ
Adapting Retransmission Rate: RTQ
Performance Evaluation
Conclusions
Future Works
Reference
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3. Background – VoWLAN: VoIP over WLAN
Concerns of VoWLAN
Transmission quality? MOS
Service capacity? Medium consumption
Rate selection (for quality maintenance):
Sustainable rate determination
Initial & retransmission rate selection
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4. Background – Metrics: MOS and Medium Consumption
MOS (Mean Opinion Score):
Quality of received media after transmission.
Range 1 to 5, 5 = best quality.
Range for VoIP: 3.5~4.2
Medium Consumption (MC):
(function)
Lower MC --> more capacity
Tradeoff between link rate & MC
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5. Background - Sustainable Rate
Sustainable rate (Rs): the transmission rate with satisfied quality and highest utilization of the channel.
Let Rt represent current rate,
If Rt > Rs: error rate↑, retransmissions↑, MC↑, MOS↓.
If Rt < Rs: MOS is fine, but MC↑.
Value of Rs varies due to mobility
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Speed Lab

6. Problem statement Environment: Goal: VoWLAN with mobility
Selecting the rate closest to sustainable rate, i.e. satisfying certain MOS with minimum MC, as fast as possible.
Current rate unsuitable, select better rate.
Rate adaptation based on Traffic Quality (RTQ).
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7. Initial rate selection
Related Works
Passive
Active
# of
Succ. TX
# of Failure TX
RTT
Congestion
Medium condition
Initial rate selection
Sample rate
Increase rate
ARF, Onoe (with credit), PLC
Vega like ARC
Decrease rate
ARF, Onoe (with credit)
Maintain rate
PLC
Notation:
ARF: Auto Rate Fallback PLC: Packet Loss Classification ARC: Audio Rate Control
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8. Step 1 – Sustainable rate discovery (RAVTQ)
By simulations,
Given factors: distance (SNR), Link rate R
Calculated factors: MOS value, MC
(in % of the medium capacity) MC
MOS factor
Link rate
(at fixed voice codec)
1Mbps
2Mbps
1Mbps
Link rate
(at fixed voice codec)
2Mbps
Distance
Distance
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9. Step 1 – Sustainable rate discovery (RAVTQ) (cont.)
Need to find R, such that
At certain SNR,
MOS = 3.5~4.2 and minimum MC
Link Rate (in Mbps)
SNR
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10. Simulation - Input Traffic
NS-2’s traffic input requirement:
Packet send time
Packet size
Popular VoIP codec:
G.711: 8kHz sampling, 32kbps stream
G.723.1: 8kHz sampling, 5.6/6.3kbps stream
G.729: 8kHz sampling, 8kbps stream
CBR, Exponential on/off
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11. Rates’ MOS vs Distance
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12. Rates’ MOS vs SNR
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13. Rates’ MC vs Distance
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14. Rates’ MC vs SNR
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15. Sustainable Rate VS Distance
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16. Sustainable Rate VS SNR - Rs(SNR)
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17. Step 2 – Initial & Retransmission rate selection (RTQ)
Initial rate = Rt = Rs(SNR)
Retransmission rate:
Rate adjustment based on current MOS.
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18. Performance Evaluation - Fixed distance
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19. Performance Evaluation - with Mobility
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20. RBAR thresholds
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21. Rate Variance with Mobility
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22. MOS Variance with Mobility
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23. Conclusions Fixed distance: Mobility condition: RAVTQ MOS ≒ ARF MOS
RAVTQ MC < ARF MC (mostly)
Mobility condition:
RAVTQ MC < ARF MC
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24. Future Works - MOS of Different Codec
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25. Future Works – MC of Different Codec
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26. Future Works - Comparison of Average Rate under multiple MS nodes
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27. Reference
T. Branskich, N. Smavatkul, and S. Emeott, “Optimization of a Link Adaptation Algorithm for Voice over Wireless LAN Application,” IEEE Communications, 2005.
C. W. Huang, A. Chindapol, J. A. Ritcey, and J. N. Hwang, “Link Layer Packet Loss Classification for Link Adaptation in WLAN,”.
S. Pal, S. R. Kundu, K.Basu, and S. K. Das, “IEEE Rate Control Algorithms: Experimentation and Performance Evaluation in Infrastructure Mode,”.
A. Trad, Q. Ni, and H. Afifi, “Adaptive VoIP Transmission over Heterogeneous Wired/Wireless Networks,” 2004.
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28. Reference (cont.)
M. Lacage, M. H. Manshaei, and T. Turletti, “IEEE Rate Adaptation: A Practical Approach,” Oct 2004.
J. Matta, C. Pepin, K. Lashkari, and R. Jain, “A Source and Channel Rate Adaptation Algorithm for AMR in VoIP Using the Emodel,” June 2003
M. Bandinelli, F. Chiti, R. Fantacci, D. Tarchi, G. Vannuccini, “A Link Adaptation strategy for QoS support in IEEE e-based WLANs,” IEEE Communications, 2005
Z. Qiao, L. Sun, N. Heilemann, and E. Ifeachor, “A new method for VoIP Quality of Service Control use combined adaptive sender rate and priority marking,” IEEE Communications, 2004
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