Coded data generation or conversion – Digital code to digital code converters – With error detection or correction
Patent
1994-10-14
1996-08-27
Gaffin, Jeffrey A.
Coded data generation or conversion
Digital code to digital code converters
With error detection or correction
375350, H03M 1300
Patent
active
055505430
ABSTRACT:
A method and apparatus for improving the performance of coding systems in the presence of frame erasures or lost packets. The encoded signal is modified after transmission but prior to decoding by a decoder preprocessor. The preprocessor recognizes that a given frame has been corrupted and modifies the encoded signal so that the decoding thereof will result in improved coding system performance. Specifically, based on the decoding process and on a predetermined target signal, the encoded signal is modified so that the decoding thereof will generate an approximation to the target signal. In a first illustrative embodiment, a CELP speech coder is used and the target signal is an excitation signal comprised of all-zero excitation vectors. In this case, the portion of the corrupted excitation signal indices which identify the corresponding gain factors are set to values which represent a low gain factor. In a second illustrative embodiment, a CELP speech coder is used and the target signal comprises an extrapolation of the excitation signal represented by the encoded signal for one or more previous frames. In this case, the preprocessor encodes the extrapolated excitation signal using the best codebook matches available. In either case, the effect of corrupted frames in the reconstructed speech signal is minimized.
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Chen Juin-Hwey
Watkins Craig R.
Brown Kenneth M.
Gaffin Jeffrey A.
Kost Jason L. W.
Lucent Technologies - Inc.
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