1. Juan J. Ramos-Muñoz, Angel M. Gómez, Juan M. Lopez-Soler Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver Signal Theory, Telematics and Communications Department

2. 2 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Outline  Introduction  Basic and Multi-flow Block Interleavers Algorithms  Intelligibility Estimation  Experimental Results  Conclusion

3. 3 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Introduction  Background  Bursts degrade the perceived quality in Voice over IP  VoIP services are extremely delay concerned  Enhanced VoIP services must be subjectively evaluated

4. 4 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Introduction  In this work  We contribute to demonstrate some perceptual benefits that can be obtained by using active routers in VoIP  We propose a new delay-aware interleaver to mitigate the bursty-error-prone nature of IP  We evaluate the service performance by using Automatic Speech Recognition

5. 5 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Basic and Multi-flow Block Interleavers Algorithms  Given and an interleaver is defined by  Basic TypeI(s): to face bursts of length equal to s packets, with the minimum incurred delay, an (s x s) matrix is required  Packets are written by rows, from left to right and from top to bottom.  Packets are read by columns, from bottom to top and from left to right.  Type I(s) maximum interleaver delay is given by  Type I(s) is limited to such that  For typical VoIP values and TypeI(s) is restricted to bursts with length s < 5

6. 6 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Basic and Multi-flow Block Interleavers Algorithms  We interleave packets from different flows to face consecutive losses by introducing a tolerable delay  We use the reference TypeII(n f ) and propose TypeII(n f,s) where  n f is the number of available flows and  s is the maximum expected burst length  Round-robin interleaver (TypeII(n f )) is suited for n f ≥ s  it requires one (n f x 1) interleaver matrix  to write the matrix each row will be assigned to a single flow.  the matrix will be read from bottom to top  if no switching delay is assumed then  Drawback: when n f < s, TypeII(n f ) interleaver does not isolate all the packet losses

7. 7 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Basic and Multi-flow Block Interleavers Algorithms  The proposed TypeII(n f,s) assures the isolation of losses for a given (n f,s) pair of values, even when n f < s, with tolerable (bounded) delay  Memory requirements  If s is a multiple of n f then one (s x s) matrix is required.  Otherwise, n f squared (s x s) matrices are needed.

8. 8 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Basic and Multi-flow Block Interleavers Algorithms  Let us define R i j as the number of consecutive rows that the flow i will be assigned for matrix j. rem(a,b) as the remainder of the integer division a/b. int(a) largest integral value not greater than a.  TypeII(n f,s) matrix writing procedure  First matrix:  R i 1 = int(s/n f ), for i = { 1, 2, …, n f - rem(s,n f )}.  R j 1 = int(s/n f ) + 1 for j = { n f -rem(s,n f ), n f -rem(s,n f )+1, …, n f }  Next j = 2, …, n f matrices and flows i = 2, …, n f  If R i (j-1) = int(s/n f )+1 and R (i-1) (j-1) = int(s/n f ) then R i j = int(s/n f ) and R (i-1) j = int(s/n f )+1  Type II(n f,s) matrix reading procedure  Packets are read by columns, from bottom to top and from left to right.

9. 9 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Basic and Multi-flow Block Interleavers Algorithms  TypeII(n f,s) maximum delay D max is given by D max =º where r = rem(s,n f ) d = int((s-r) / n f )  For typical VoIP values and for the best case TypeII(n f,s) interleaver scatters bursts up to s < 15 favorably compared to TypeI(s) limited to s < 5 s·(r·(d +1)-1-(r - 1)·d) if r  (n f - r) s·(r·(d +1)-1-((r - 1)·d+2·r - n f -1))if r > (n f - r)

10. 10 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Intelligibility Estimation  For performance evaluation, we propose to use a high level end-user intelligibility estimation: ASR rate  Compared to MOS, ASR has lower cost and is more reproducible  For end-user intelligibility estimation ASR rate can be more suitable than other measures like PESQ (P.862) or the E-model  The Word Error Rate is defined by

11. 11 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Experimental Results  Experimental results were obtained by simulation.  We adopt a single error model based on a Markov chain (Yajnik et al [9]).

12. 12 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Experimental Results  For ASR evaluation we use the connected digit Project Aurora 2 database  The speech recognizer is based on eleven 16-state continuous Hidden Markov Models (HMM)  The HMM models are trained from a set of 8440 noise- free sentences, while the out-of-train-test set comprises 4004 noise-free sentences  More details are explained in the printed version of the paper

13. 13 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Experimental Results  WER and D max (seconds) obtained values

14. 14 Juan J. Ramos-Muñoz, Ángel M. Gómez, Juan M. Lopez-Soler University of Granada Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005. Conclusion  Compared to a single-flow approach, our proposed interleaver reduces the packet delay and makes it applicable under conditions where the reference scheme is unfeasible.  Compared to the round-robin multi-flow interleaver, our proposed scheme increases the perceived end-user intelligibility (WER)  With a slight penalty on the introduced delay  We propose to consider ASR as a tool to measure VoIP services enhancements.  Future work: by setting up mapping functions  for ASR rate to human intelligibility  for ASR rate to MOS score and using it together with AN technology, enhanced VoIP services can be envisaged. Thank you for your attention