Source dependent channel coding with error protection

• US 5,091,945 A
• Filed: 09/28/1989
• Issued: 02/25/1992
• Est. Priority Date: 09/28/1989
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.), Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: Kleijn, Willem B.
• Primary Examiner(s): Shaw, Dale M.
• Assistant Examiner(s): Knepper, David D.
• Application Number:
  US07/414,155
• Time in Patent Office: 880 Days
• Field of Search: 381/29-40, 364/513.5
• US Class Current: 704/219
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders

Abstract

A parameter communication arrangement where a parameter that is transmitted over a channel using m-bit codewords or labels is quantized before transmission as one of only p levels, where, significantly, p<k=2^m. Since only p labels are needed to transmit the p levels, the unused k-p labels are advantageously available to provide redundancy. The receiver decodes the redundant labels in accordance with an error routine. An encoding table mapping from the p levels to p labels and a decoding table inverse mapping from the p labels to p levels are obtained using an optimization procedure to minimize the effect of channels errors. The optimization is based on the probability distribution for the p levels such that a relatively high proportion of the error protection made available by having redundant labels inures to the benefit of parameter levels which are more likely to be transmitted. The optimization procedure is a well known technique referred to as simulated annealing which is for the first time applied to source dependent channel coding.

Claims

1. Speech processing apparatus comprising

speech analyzer means responsive to input speech signals from a source of input speech signals for generating a plurality of parameter signals representing said input speech signals in accordance with a speech model, at least one of said parameter signals being quantized as one of p levels,

channel encoder means comprising

encoder memory means for storing an encoding table defining a mapping from each of said p levels to a unique one of p, m-bit label signals, where p<

k=2^m, and

means responsive to said speech analyzer means for transmitting, over a channel to a destination, the one of said p label signals that is associated with said one of said p levels in said encoding table,

channel decoder means comprising

decoder memory means for storing a decoding table defining the inverse of said encoding table mapping and

means, responsive to a label signal received at said destination from said channel, for decoding said received label signal as the one of said p levels associated with said received label signal in said decoding table inverse mapping when said received label signal is one of said p label signals, and for decoding said received label signal in accordance with an error routine when said received label signal is one of the k-p, m-bit label signals other than said p label signals, and

speech synthesizer means responsive to said decoding means for synthesizing speech based at least in part on said decoded label signal,

wherein said encoding table mapping stored by said encoder memory means and said decoding table inverse mapping stored by said decoder memory means are obtained to minimize the effect of channel errors and are obtained using simulated annealing based on a probability distribution of said p levels for said one parameter signal.

2. Speech processing apparatus in accordance with claim 1 wherein said encoder memory means further stores other mappings and said decoder memory means further stores other inverse mappings, said other mappings and said other inverse mappings being for use in communication of other parameter signals from said source over said channel to said destination, said other mappings and said other inverse mappings being obtained, concurrently with said encoding table mapping and said decoding table inverse mapping, using said simulated annealing.

3. Speech processing apparatus in accordance with claim 2 wherein said simulated annealing minimizes an overall error measure for said one parameter signal and said other parameter signals.

4. Speech processing apparatus in accordance with claim 1 wherein

said decoding table stored by said decoder memory means defines an additional mapping from each of said k-p label signals,

said decoding means decodes said received label signal in accordance with said additional mapping when said received label signal is one of said k-p label signals, and

said decoding table additional mapping is also obtained using said simulated annealing to minimize the effect of channel errors based on said probability distribution.

5. Speech processing apparatus in accordance with claim 4 wherein said inverse and additional mappings are obtained concurrently using said simulated annealing.

6. Speech processing apparatus in accordance with claim 1 wherein

said decoding means decodes said received label signal as a default level when said received label signal is one of said k-p label signals.

7. Speech processing apparatus in accordance with claim 1 wherein

said decoding means decodes said received label signal based on information received over said channel other than said received label signal when said received label signal is one of said k-p label signals.

8. Speech processing apparatus in accordance with claim 1 wherein

said decoding means decodes said received label signal as the same level that was obtained from a previous communication of said one parameter signal over said channel when said received label signal is one of said k-p label signals.

9. Speech processing apparatus in accordance with claim 1

said decoding table stored by said decoder memory means defines an additional mapping from each of certain ones of said k-p label signals,

said decoding means decodes said received label signal in accordance with said additional mapping when said received label signal is one of said certain ones of said k-p label signals, and

said decoding means decodes said received label signal as a default level when said received label signal is one of said k-p label signals other said certain ones.

10. Speech processing apparatus in accordance with claim 1

said decoding table stored by said decoder memory means defines an additional mapping from each of certain ones of said k-p label signals,

said decoding means decodes said received label signal in accordance with said additional mapping when said received label signal is one of said certain ones of said k-p label signals, and

said decoding means decodes said received label signal based on information received over said channel other than said received label signal when said received label signal is one of said k-p label signals other said certain ones.

11. Speech processing apparatus in accordance with claim 1

said decoding table stored by said decoder memory means defines an additional mapping from each of certain ones of said k-p label signals,

said decoding means decodes said received label signal in accordance with said additional mapping when said received label signal is one of said certain ones of said k-p label signals, and

said decoding means decodes said received label signal as the same level that was obtained from a previous communication of said one parameter signal over said channel when said received label signal is one of said k-p label signals other said certain ones.

12. Speech processing apparatus in accordance with claim 1 wherein said p label signals are selected from k, m-bit label signals as a result of said simulated annealing.

13. Speech processing apparatus in accordance with claim 1 wherein said model is a code excited linear prediction model.

14. Speech processing apparatus in accordance with claim 1 wherein said encoding table mapping and said decoding table mapping are obtained to minimize distortion in said synthesized speech.

15. Speech processing apparatus in accordance with claim 1 wherein p>

2^m-1.

16. Speech processing apparatus comprising

speech analyzer means responsive to input speech signals from a source of input speech signals for generating a plurality of parameter signals representing said input speech signals in accordance with a speech model, at least one of said parameter signals being quantized as one of p levels,

channel encoder means comprising

encoder memory means for storing an encoding table defining a mapping from each of said p levels to a unique one of p, m-bit label signals, where p<

k=2^m, and

means responsive to said speech analyzer means for transmitting, over a channel to a destination, the one of said p label signals that is associated with said one of said p levels in said encoding table,

channel decoder means comprising

decoder memory means for storing a decoding table defining the inverse of said encoding table mapping and defining an additional mapping from each of certain ones of the k-p, m-bit label signals other than said p label signals and

means, responsive to a label signal received at said destination from said channel, for decoding said received label signal as the one of said p levels associated with said received label signal in said decoding table inverse mapping when said received label signal is one of said p label signals, and for decoding said received label signal as defined by said additional mapping when said received label signal is one of said certain ones of said k-p label signals, and

speech synthesizer means responsive to said decoding means for synthesizing speech based at least in part on said decoded label signal,

wherein said encoding table mapping stored by said encoder memory means and said decoding table inverse mapping stored by said decoder memory means are obtained to minimize the effect of channel errors and are obtained based on a probability distribution of said p levels for said one parameter signal,

wherein said inverse and additional mappings are such that at least one of said p label signals differs in b bits, 1<

=b<

m, from a label signal which maps into the same level as said at least one of said p label signals and which also differs in b bits from a label signal which maps into a level other than said same level.

17. Speech processing apparatus in accordance with claim 16 wherein

said decoding means decodes said received label signal as a default level when said received label signal is one of said k-p label signals other than said certain ones.

18. Speech processing apparatus in accordance with claim 16 wherein

said decoding means decodes said received label signal based on information received over said channel other than said received label signal when said received label signal is one of said k-p label signals other than said certain ones.

19. Speech processing apparatus in accordance with claim 16 wherein

said decoding means decodes said received label signal as the same level that was obtained from a previous communication of said one parameter signal over said channel when said received label signal is one of said k-p label signals other than said certain ones.

20. Speech processing apparatus in accordance with claim 16 where p>

2^m-1.

21. Speech processing apparatus in accordance with claim 16 wherein said model is a code excited linear prediction model.

22. Speech processing apparatus in accordance with claim 16 wherein said encoding table mapping and said decoding table mapping are obtained to minimize distortion in said synthesized speech.

23. Speech processing apparatus comprising

speech analyzer means responsive to input speech signals from a source of input speech signals for generating a plurality of parameter signals representing said input speech signals in accordance with a speech model, at least one of said parameter signals being quantized as one of p levels,

channel encoder means comprising

encoder memory means for storing an encoding table defining a mapping from each of said p levels to a unique one of p, m-bit label signals, where p<

=k=2^m, and

means responsive to said speech analyzer means for transmitting, over a channel to a destination, the one of said p label signals that is associated with said one of said p levels in said encoding table,

channel decoder means comprising

decoder memory means for storing a decoding table defining the inverse of said encoding table mapping and

means, responsive to a label signal received at said destination from said channel, for decoding said received label signal as the one of said p levels associated with said received label signal in said decoding table inverse mapping when said received label signal is one of said p label signals, and

speech synthesizer means responsive to said decoding means for synthesizing speech based at least in part on said decoded label signal,

wherein said encoding table mapping stored by said encoder memory means and said decoding table inverse mapping stored by said decoder memory means are obtained to minimize the effect of channel errors and are obtained using simulated annealing based on a probability distribution of said p levels for said one parameter signal.

24. Speech processing apparatus in accordance with claim 23 wherein said model is a code excited linear prediction model.

25. Speech processing apparatus in accordance with claim 23 wherein said encoding table mapping and said decoding table mapping are obtained to minimize distortion in said synthesized speech.