Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Patent
1998-03-12
1999-11-09
Hudspeth, David R.
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
704226, H04L 120, H03M 1300
Patent
active
059831740
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present application is concerned with transmission of data using convolutional codes and is particularly, though not exclusively, concerned with the transmission of digitally coded speech signals.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a method of decoding signals by processing received signals to provide confidence measure signals and using a soft decision decoder to decode the received signal values, the method comprising: signal value statistics for the received known signals differ from a logarithmic representation of the error statistics of the received known signals; the received unknown signals, the correction factors being derived from the said stored data, so as to reduce the extent to which the confidence measure signal value statistics differ from the said logarithmic representation;
In another aspect the invention provides an apparatus for decoding signals comprising: signal values; measure signal values so as to reduce the extent to which the confidence measure signal value statistics differ from a logarithmic representation of the error statistics of the received signals; and
In a preferred embodiment the correction factors are derived from tests performed by: signals for the received known signal value statistics differ from a logarithmic representation of the error statistics of the received known signals.
The apparatus may also include period of the signal and indicating the quality of the frame.
In another aspect the invention provides signal values; period of the signal; indicating the quality of the frame.
Preferably the apparatus may include means operable in response to the said signal indicating the quality of the frame to suppress further processing of those which are of a lower quality than that determined by the said threshold.
A further aspect of the invention provides a method of transmitting data bits comprising, for each of successive frame periods, formatting the bits into a frame sequence, coding the bits by means of a convolutional coder, including generating error check bits which are a function of (a) bits formatted into the beginning of the frame sequence and (b) bits formatted into the end of the frame sequence.
Preferably the bits (a) may be taken from the first 50% of the frame and the bits (b) may be taken from the last 25% of the frame.
BRIEF DESCRIPTION OF THE DRAWINGS
Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram of an apparatus for the transmission of speech signals;
FIGS. 2 and 3 show graphically the results of error tests on the speech coder used in the apparatus of FIG. 1;
FIGS. 4 and 5 show graphically the results of error tests on the convolutional codes used in the apparatus of FIG. 1;
FIGS. 6, 7, 8 and 9 are block diagrams of, respectively, the reordering unit 4, convolutional coder 6 masking unit 8 and CRC unit 5 of the apparatus of FIG. 1 and FIG. 10;
FIG. 10 is a block diagram of an apparatus for receiving speech signals and
FIG. 11 shows a typical plot of the likelihood of a bit error against the confidence measure for that bit.
FIG. 12 shows inter-frame interleaving and deinterleaving.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
In FIG. 1, speech signals are received in digital form at an input 1 and are supplied to a digital speech coder 2. The preferred coder is a codebook excited linear predictive (CELP) coder, operating at 8 kbit/s, in accordance with standard G.729 of the International Telecommunications Union. However, other types of coder may be used, and, indeed, simple p.c.m. is not excluded.
The coder 2 analyses each 10 ms frame of speech samples and, for each, produces 79 bits representing a number of parameters (enumerated below) which serve, at a receiver to drive a decoder which synthesises received speech signals. Certain of these parameters are re-coded using Gray code, in a unit 3.
These bits are to be formatted into a bit-serial frame
REFERENCES:
patent: 5144644 (1992-09-01), Borth
IEEE International Conference on Communications Supercomm/ICC 1994, New Orleans, US, vol. 3, May 1, 1994, IEEE, New York, US pp. 1236-1241 "Hoeher, Unequal Error Protection for Digital Mobile DS-CDMA Radio Systems".
ITG Fachbericht 118.9 Fachtagung Horrundfunk (Audio Broadcasting), Mannheim, vol. 118, Feb. 18, 1992, Vde Verlag, Berlin/Offenbach, 1992, DE, pp. 109-112, Weck, "Optimierung der Empfangsqualitat durch angepassten Fehlerschutz bei DAB".
IEEE Transactions on Vehicular Technology, vol. 43, No. 4, Nov. 1994, New York, US, pp. 1078-1087, Shi et al, "Combined Speech and Channel Coding for Mobile Radio Communicatons".
L. H. C. Lee and P. G. Farrelll, "Concatenated Coding and Interleaving for Half-Rate GSM Digital Mobile Radio System," Electronics Letters, vol. 27, No. 14, pp. 1274-1276, Jul. 4, 1991.
Hong Shi, Paul K. M. Ho, and Vladimir Cuperman, "Combined Speech and Channel Coding for Mobile Radio Communications,"IEEE Trans. on Vehicular Technology, vol. 43, No. 4, pp. 1078-1087, Nov. 1994.
Wong Danny Yuk-Kun
Wong Wing Tak Kenneth
British Telecommunications public limited company
Hudspeth David R.
Smits Talivaldis Ivars
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