Robust vector quantization of line spectral frequencies
First Claim
1. A method for quantizing line spectral frequency (LSF) vectors in a digital communications system comprising:
- receiving an unquantized LSF vector;
searching each of a plurality of specialized codebooks and selecting from each of the plurality of specialized codebooks, a candidate quantized LSF vector resembling the unquantized LSF vector;
calculating a distortion measure for each of the candidate quantized LSF vectors using the unquantized LSF vector; and
selecting a quantized LSF vector from among the candidate quantized LSF vectors using the calculated distortion measures for each candidate quantized LSF vector.
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Abstract
A line spectral frequency (LSF) vector quantizer, having particular application in digital cellular networks (DCN), is provided for code excited linear predictive (CELP) speech encoders. The LSF vector quantizer is efficient in terms of bits employed, robust and effective in terms of performance across speakers and handsets, moderate in terms of complexity, and accommodates effective and simple built-in transmission error detection schemes. The LSF vector quantizer employs a minimum number of bits, is of moderate complexity and incorporates built-in error detection capability in order to combat transmission errors. The LSF vector quantizer classifies unquantized line spectral frequencies into four categories, employing different vector quantization tables for each category. Each quantization table is optimized for particular types of vectors. For each category, three split vector codebooks are used with a simplified error measure to find three candidate split quantized vectors. The three sets of three split vectors are combined to produce as many as 27 vectors from each category. The quantizer then makes a final selection of optimal category using a more complex error measure to achieve the robust performance across speakers and handsets. Split vector quantization follows a two stage constrained search procedure that results in an ordered set of quantized line spectral frequencies that is "close" to the unquantized set with moderate complexity within each category. Effective and simple transmission error detection schemes at the receiver are made possible by the split nature of the vector quantization and the constrained search procedure. Only twenty-six bits are required to encode ten line spectral frequencies.
22 Citations
46 Claims
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1. A method for quantizing line spectral frequency (LSF) vectors in a digital communications system comprising:
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receiving an unquantized LSF vector; searching each of a plurality of specialized codebooks and selecting from each of the plurality of specialized codebooks, a candidate quantized LSF vector resembling the unquantized LSF vector; calculating a distortion measure for each of the candidate quantized LSF vectors using the unquantized LSF vector; and selecting a quantized LSF vector from among the candidate quantized LSF vectors using the calculated distortion measures for each candidate quantized LSF vector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A line spectral frequency (LSF) vector quantizer comprising:
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an input for receiving an unquantized LSF vector; a plurality of specialized codebooks of quantized (line spectral frequency) LSF vectors; means coupled to the input for searching each of the specialized codebooks and selecting from each of the specialized codebooks, a candidate quantized LSF vector resembling the input unquantized (line spectral frequency) LSF vector; means for calculating a distortion measure for each of the candidate quantized LSF vectors using the unquantized LSF vector; and means for selecting a quantized LSF vector from among the candidate quantized LSF vectors using the calculated distortion measures for each candidate quantized LSF vector. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for quantizing line spectral frequency (LSF) vectors in a digital communications system comprising:
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receiving an unquantized LSF vector; splitting the unquantized LSF vector into a plurality of unquantized split LSF vectors; searching a plurality of split codebooks for candidate quantized split LSF vectors resembling each of the unquantized split LSF vectors; calculating a first distortion measure for each candidate quantized split LSF vector using the corresponding unquantized split LSF vector; selecting a subset of candidate quantized split LSF vectors from among the candidate quantized split LSF vectors based on the first distortion measure calculated for each candidate quantized split LSF vector; combining candidate quantized split LSF vectors chosen from among the subset of candidate quantized split LSF vectors so as to produce a plurality of unsplit candidate quantized LSF vectors; calculating a second distortion measure for each of the unsplit candidate quantized LSF vectors using the unquantized LSF vector; and selecting a quantized LSF vector from among the unsplit candidate quantized LSF vectors using the second distortion measure calculated for each unsplit candidate quantized LSF vector. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. A line spectral frequency (LSF) quantizer comprising:
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a plurality of split codebooks of quantized split LSF vectors; an input for receiving an unquantized LSF vector; means for splitting the unquantized LSF vector into a plurality of unquantized split LSF vectors; means coupled to the input for searching the plurality of split codebooks for candidate quantized split LSF vectors resembling each of the unquantized split LSF vectors; means for calculating a first distortion measure for each candidate quantized split LSF vector using the corresponding unquantized split LSF vector; means for selecting a subset of candidate quantized split LSF vectors from among the candidate quantized split LSF vectors based on the first distortion measure calculated for each candidate quantized split LSF vector; means for combining candidate quantized split LSF vectors chosen from among the subset of candidate quantized split LSF vectors so as to produce a plurality of unsplit candidate quantized LSF vectors; means for calculating a second distortion measure for each of the unsplit candidate quantized LSF vectors using the unquantized LSF vector; and means for selecting a quantized LSF vector from among the unsplit candidate quantized LSF vectors using the second distortion measure calculated for each unsplit candidate quantized LSF vector. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38)
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39. A method for quantizing line spectral frequency (LSF) vectors in a digital communications system comprising:
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receiving an unquantized LSF vector; splitting the unquantized LSF vector into first, second and third unquantized split LSF vectors; searching a plurality of split codebooks for candidate quantized split LSF vectors most closely resembling each of the first, second and third unquantized split LSF vectors; calculating a first distortion measure for each of the first, second and third candidate quantized split LSF vectors using the corresponding unquantized split LSF vector; selecting a first, second and third quantized split LSF vectors from among the candidate quantized split LSF vectors based on the first distortion measure calculated for each candidate split LSF vector; combining candidate quantized split LSF vectors chosen from among the first, second and third quantized split LSF vectors so as to produce a plurality of unsplit candidate quantized LSF vectors; calculating a cepstral distortion measure for each of the unsplit candidate quantized LSF vectors using the unquantized LSF vector; and selecting a quantized LSF vector from among the unsplit candidate quantized LSF vectors using the cepstral distortion measure calculated for each unsplit candidate quantized LSF vector. - View Dependent Claims (40, 41, 42)
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43. A line spectral frequency (LSF) quantizer comprising:
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a plurality of split codebooks of quantized split LSF vectors; an input for receiving an unquantized LSF vector; means for splitting the unquantized LSF vector into first, second and third unquantized split LSF vectors; means coupled to the input for searching the plurality of split codebooks for candidate quantized split LSF vectors most closely resembling each of the first, second and third unquantized split LSF vectors; means for calculating a first distortion measure for each of the first, second and third candidate quantized split LSF vectors using the corresponding unquantized split LSF vector; means for selecting a first, second and third quantized split LSF vectors from among the candidate quantized split LSF vectors based an the first distortion measure calculated for each candidate split LSF vector; means for combining candidate quantized split LSF vectors chosen from among the first, second and third quantized split LSF vectors so as to produce a plurality of unsplit candidate quantized LSF vectors; means for calculating a cepstral distortion measure for each of the unsplit candidate quantized LSF vectors using the unquantized LSF vector; and means for selecting a quantized LSF vector from among the unsplit candidate quantized LSF vectors using the cepstral distortion measure calculated for each unsplit candidate quantized LSF vector. - View Dependent Claims (44, 45, 46)
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Specification