Codebook

About: Codebook is a research topic. Over the lifetime, 8492 publications have been published within this topic receiving 115995 citations.

Improved hochwald construction of unitary matrix codebooks via eigen coordinate transformations

Abstract: A method of deriving a codebook including deriving a first codeword P, in Euclidean coordinates, transforming the first codeword into eigen-coordinates, applying Hochwald construction to the first codeword in eigen­ coordinates to derive a plurality of codewords in eigen­coordinates and transforming the plurality of codewords in eigen-coordinates into a plurality of codewords in Euclidean coordinates to form the codebook.

Fast search algorithm for VQ-based recognition of isolated words

Abstract: This paper presents a fast search algorithm for vector quantisation (VQ)-based recognition of isolated words. It incorporates the property of high correlation between speech feature vectors of consecutive frames with the method of triangular inequality elimination to relieve the computational burden of vector-quantising the test feature vectors by full codebook search, and uses the extended partial distortion method to compress the incomplete matching computations of wildly mismatched words. Overall computational load can therefore be drastically reduced while the recognition performance of full search can be retained. Experimental results show that about 93% of multiplications and additions can be saved with a little increase of both comparisons and memory space.

The capacity for a discrete-state code division multiple-access channel

Abstract: One of the proposed techniques for the third generation of mobile communications is code division multiple access (CDMA). Some attributes of CDMA which are important to indoor systems include desirable anti-multipath properties, the lack of a need for frequency management or assignment, coexistence with other systems and suitability for micro-cell and in-building systems. The anti-multipath feature turns out to be a key issue for indoor systems and derives from the property that a signal with path delay greater than one chip interval is treated much like an interfering user. The number of users that share the same spectrum, and still maintain an acceptable performance, is determined by the interference generated by the set of remaining users and leads to soft degradation as the number of users increases. This work describes and analyzes a model for the discrete-input continuous-output Gaussian multiple-access channel, that uses spread spectrum techniques. The notion of sum capacity is used to characterize the system performance. Bounds on the sum capacity of this essentially binary input, continuous output channel, where the variance of the output noise is dependent on the number of users present, are obtained. The users are noncooperative in that no common codebook or synchronization is assumed. A novel feature of the work is the use of the modeling of the activity of the user community as a birth-death process. An information theoretic approach is used and the sum capacity is then considered in light of the various regimes to determine the effect of this modeling. >

Speech encoding method and apparatus

Abstract: In encoding in which an adaptive codebook such as PSI-CELP or a fixed codebook is used on switching selection, waveform distortion caused by selection of the fixed codebook in case input speech frequency components are changed significantly is diminished. An output of an adaptive codebook 21 or an output of a fixed codebook 22 is selected by a changeover selection switch 26 and summed to an output of noise codebooks 23, 24 so as to be sent to a linear prediction synthesis filter 16. A switching control circuit 19 for controlling the switching of a changeover control switch 26 operates in response to a prediction gain which is a ratio of the linear prediction residual energy to the initial signal energy from a linear prediction analysis circuit 14 so that, if the prediction gain is smaller than a pre-set threshold value, the switching control circuit 19 judges the input signal to be voiced and controls the changeover control switch 26 for compulsorily selecting the output of the adaptive codebook 21.

Comments on "modified K-means algorithm for vector quantizer design"

Abstract: Previously a modified K-means algorithm for vector quantization design has been proposed where the codevector updating step is as follows: new codevector=current codevector+scale factor (new centroid-current codevector). This algorithm uses a fixed value for the scale factor. In this paper, we propose the use of a variable scale factor which is a function of the iteration number. For the vector quantization of image data, we show that it offers faster convergence than the modified K-means algorithm with a fixed scale factor, without affecting the optimality of the codebook.