Vector coding method, encoder using the same and decoder therefo

Details Vector coding method, encoder using the same and decoder therefo Vector coding method, encoder using the same and decoder therefo

1997-04-23

1998-10-20

Hoff, Marc S.

Coded data generation or conversion

Digital code to digital code converters

Adaptive coding

395 231, G01G 918, H03M 730

Patent

active

058253114

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a vector coding method that is used to encode speech, images and various other pieces of information and is particularly suited to encoding of information that is transmitted over an error-prone channel such as a mobile radio channel and encodes an input vector through the use of a plurality of codebooks each composed of plural representative vectors. The invention also pertains to a vector encoder using the above-mentioned vector coding method and a vector decoder for decoding codes encoded by the vector encoder.
Methods that have been proposed to transmit vectors over channels prone to channel errors set representative vectors in anticipation of possible channel errors and take into account the channel errors when labeling representative vectors. These methods are disclosed in Kumazawa, Kasahara and Namekawa, "A Communication of Vector Quantizers for Noisy Channels," Transactions of the Institute of Electronics, Information and Communication Engineers of Japan , Vol. J67-B, No. 1, pp. 1-8, 1984, Zeger and Gersho, "Pseudo-Gray Coding," IEEE Trans. on Comm., Vol. 38, No. 12, pp. 2147-2158, 1990, and other literature. These methods hold all representative vectors directly in one codebook, and hence require large storage capacity for storing the codebook.
As a method that does not need large storage capacity in transmitting vectors over channels prone to channel errors, it has been proposed to transmit vectors after quantizing them through the use of two structured codebooks. This is disclosed in Moriya, "Two-Channel Vector Quantizer Applied to Speech coding," Transactions of the Institute of Electronics, Information and Communication Engineers of Japan, IT87-106, pp. 25-30, 1987 and other literature. This method has two small-scale codebooks and uses two representative vectors in combination to reduce the storage capacity needed and transmits two labels indicative of the two representative vectors to lessen the influence of channel errors. This method will be described with reference to FIGS. 1A and 1B. The representative vectors of the codebooks are generated beforehand by learning, for instance. In an encoder depicted in FIG. 1A, one representative vector Z.sub.1i is fetched from a codebook CB1 and one representative vector z.sub.2j from a codebook CB2, then they are added together in a vector combining part 3 to generate a vector sum Y.sub.ij =z.sub.1i +z.sub.2j, and the distance, d(X,y.sub.ij), between the combined representative vector y.sub.ij and an input vector X via an input terminal 4 is calculated, as distortion, in a distance calculating part 5. A control part 6 controls representative vector select switches 7 and 8 for the codebooks CB1 and CB2 and searches them for the representative vectors z.sub.1i and z.sub.2j that minimize the output d(X,y.sub.ij) from the distance calculating part 5. The control part 6 provides, as encoded outputs to an output terminal 9, labels i and j of the representative vectors z.sub.1i and z.sub.2j that provides minimum distance.
In a decoder shown in FIG. 1B, the control part 6 controls representative vector select switches 13 and 14 in accordance with the labels i and j in the input code via an input terminal 11 and reads out representative vectors z.sub.1i and z.sub.2j from codebooks CB3 and CB4, respectively. The thus read-out representative vectors z.sub.1i and z.sub.2j are combined in a vector combining part 17 into a reconstructed vector y.sub.ij =z.sub.1i +z.sub.2j, which is provided to an output terminal 18. Incidentally, the codebooks CB3 and CB4 are identical to CB1 and CB2, respectively.
The method described above in respect of FIGS. 1A and 1B reduces the storage capacity of the codebooks needed for storing the representative vectors and lessens the influence of channel errors by combining the vectors in the decoder through utilization of the two labels corresponding thereto.
With this method, however, if an error arises in the labels during transmission over the channel, then distortion will

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