Allowing Errors in Speech over Wireless LANs Ian Chakeres, Hui - - PowerPoint PPT Presentation
Allowing Errors in Speech over Wireless LANs Ian Chakeres, Hui Dong, Elizabeth Belding-Royer, Allen Gersho and Jerry Gibson University of California, Santa Barbara Ian Chakeres Outline Motivation Related Work System model Design
Ian Chakeres
Ian Chakeres, Hui Dong, Elizabeth Belding-Royer, Allen Gersho and Jerry Gibson
University of California, Santa Barbara
Ian Chakeres
Motivation Related Work System model Design Evaluation Conclusions
Ian Chakeres
Wireless Erroneous channel Retransmissions Congestion Voice Significant error concealment available Improve capacity and maintain quality
Ian Chakeres
Voice encoding improvements
Bit rate, error correction, error and loss concealment
Additional protection
Redundant transmissions, retransmissions, packet size, wireless data rate
UDP Lite [Larzon 99]
Partial UDP checksum Requires lower layer support Wireless usage not examined
Ian Chakeres
Ian Chakeres
Encoder/decoder Bit stream Packetization Quality Delay, jitter, loss
Encoder Bit Rate G.711 64 kbps G.723.1 5.3, 6.3 kbps
Ian Chakeres
Ian Chakeres
Two state Markov model Bursty errors Experimentally determined values
Average (Avg) Noise Limited (NL) Interference Limited (IL) Frequency Selective Fading Limited (FSFL)
Model ABER Avg 1% NL 1% IL 8% FSFL 0.3%
Bad Good
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Protection methods MAC CRC: Entire packet IP checksum: IP header UDP checksum
Headers + payload or disabled
Typical CRC = T-CRC
MAC Header IP Header UDP Header MAC CRC Voice Data
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MAC Header CRC = M-CRC
MAC CRC - MAC header only UDP checksum off
Entire Header CRC = E-CRC MAC CRC - All headers UDP checksum off
MAC Header IP Header UDP Header MAC CRC Voice Data
Ian Chakeres
1
n
Wireless Communication
Node Node
Wireless Communication
Ian Chakeres
Encoding Bit Rate
Voice per Packet Bytes per Packet
G.723.1 6.3 kbps 30 ms 24 G.711 64 kbps 20 ms 160 G.711 64 kbps 25 ms 200 G.711 64 kbps 30 ms 240 G.711 64 kbps 35 ms 280 G.711 64 kbps 40 ms 320
Ian Chakeres
Ian Chakeres
Encoding Bit Rate
Voice per Packet Bytes per Packet
G.723.1 6.3 kbps 30 ms 24
G.711 64 kbps 25 ms 200 G.711 64 kbps 30 ms 240 G.711 64 kbps 35 ms 280 G.711 64 kbps 40 ms 320
Ian Chakeres
1 2 3 4 5 20 40 60 80 100 1 2 3 4 70 75 80 85 90 95 100 1 2 3 4 0.5 1.0 1.5 1 2 3 4 1.0 1.2 1.4 1.6 1.8 2.0
T-CRC M-CRC E-CRC Number of Calls Number of Calls Number of Calls % Bits in Error E-CRC
Packet Delivery Ratio (%) Delay (sec) Transmissions per Packet Delivered CDF
Ian Chakeres
1 2 3 4 5 6 7 8 9 101112 70 75 80 85 90 95 100 1 2 3 4 5 6 7 8 9 101112 0.5 1.0 1.5 1 2 3 4 5 6 7 8 9 101112 1.0 1.2 1.4 1.6 1.8 2.0
T-CRC M-CRC E-CRC Number of Calls Number of Calls Number of Calls
Packet Delivery Ratio (%) Delay (sec) Transmissions per Packet Delivered
Ian Chakeres
Ian Chakeres
20 25 30 35 40 95 96 97 98 99 100 20 25 30 35 40 0.05 0.10 0.15 0.20 0.25 20 25 30 35 40 1.0 1.2 1.4 1.6 1.8 2.0
Frame Size (ms) Frame Size (ms) Frame Size (ms)
Packet Delivery Ratio (%) Delay (sec) Transmissions per Packet Delivered
T-CRC M-CRC E-CRC
Ian Chakeres
5 10 15 20 25 30 20 40 60 80 100 1 2 3 4 70 75 80 85 90 95 100 1 2 3 4 0.5 1.0 1.5 1 2 3 4 1.0 1.2 1.4 1.6 1.8 2.0
T-CRC M-CRC E-CRC Number of Calls Number of Calls Number of Calls % Bits in Error E-CRC
Packet Delivery Ratio (%) Delay (sec) Transmissions per Packet Delivered CDF
Ian Chakeres
Allowing bit errors results in Lower delay More capacity Acceptable call quality Future work User studies Multihop networks Video and other multimedia
Ian Chakeres