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Compensating for Packet Loss in Real-Time Applications - Strategies for Reducing Loss of Speech Data

This workshop on compensating for packet loss in real-time applications discusses signal processing and networking techniques to reduce packet loss in VoIP transport. It explores the use of techniques such as saving and processing corrupted speech data, employing robust header compression (ROHC), and using UDP-Lite for arbitrary checksum coverage. Simulations and evaluations demonstrate the effectiveness of these strategies in improving speech quality and reducing packet losses.

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Compensating for Packet Loss in Real-Time Applications - Strategies for Reducing Loss of Speech Data

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  1. ETSI STQ Workshop on “Compensating for Packet Loss in Real-Time Applications“ February 11th, 2003 Reducing Packet Loss by Employing Damaged Speech Data Florian Hammer Hammer@ftw.at

  2. Overview • Signal Processing and Networking Techniques • Three Strategies for VoIP Transport • Simulations • Conclusions

  3. Dropping Damaged IP-packetsConsidered Harmful • Links with bit errors currently result in IP-packets being dropped • Quality of speech signals is severely degraded by dropped packets • Approach: Save corrupted speech data • Combination of signal processing and networking techniques • AMR codec provides uneven level protection (ULP) • UDP-Lite allows for arbitrary checksum coverage • What can be gained by using RObust Header Compression (ROHC)?

  4. Speech data bits (ULP) A B C High Low Perceptual importance Signal Processing • Quality related algorithms: • Speech coding • Packet loss concealment • De-jitter buffers • Unequal level protection ULP; E.g., 3GPP Adaptive MultiRate (AMR) codec 81 Bits 163 Bits 60 Bits

  5. IP UDP RTP A B C UDP checksum coverage IP UDP RTP A B C UDP checksum coverage Networking • Avoid packet drops caused by bit errors • RTP/UDP/IP Bit error -> entire packet lost! • RTP/UDPlite/IP Error at less important bits -> packet saved!

  6. Robust Header Compression (ROHC) • Headers -> huge overhead • RTP/UDP/IP (12/8/20 Bytes) Headers A B C 330 : 256* [Bits] • ROHC (e.g., 4 Bytes) cHdrs A B C 42 : 256* [Bits] *AMR 12.2 kb/s, 1 frame per packet, RTP bandwidth efficient mode

  7. Strategy 2 Strategy 3 Transmission Strategies IP UDP RTP A B C Strategy 1

  8. Simulations Bit error rate Bitstreams for 3 strategies MatLab Simulator Codec Decoder Reference speech sample Evaluation (PESQ) Degraded speech samples Speech Database Estimated speech-quality [PESQ-MOS]

  9. Bit Error Model • Simulation of • Additive White Gaussian Noise Channel (xDSL) • Binary Symmetric Channel (UMTS) • Number of bit errors X within actual packet: • Binomial distribution X » B(N,p) • N...Packet size [Bits] • p...Bit Error Rate • Error locations LX within the packet: • Uniform distribution

  10. Results: No Header-Compression

  11. Results: with Header-Compression

  12. Packet Loss Analysis • Use of corrupted payload avoids packet losses: 43.6% 33.6% 28.0%

  13. Packet Loss Analysis Contd.Compressed Headers • Less than 5% packet loss at a BER of 10-3 25% 11.5% 4.1%

  14. Conclusions • Dropping packets degrade the speech-quality much more than bit errors • Using techniques like UDP-Lite and ROHC improves the speech-quality by reducing packet losses • For example, using traditional IP-transport with a BER 10-4 we get a PESQ-MOS of 3.0, while using UDP-Lite and ROHC the quality increases to 3.7

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