Showing papers on "Enhanced Variable Rate Codec published in 1993"

QCELP: A Variable Rate Speech Coder for CDMA Digital Cellular

Abstract: Digital cellular telephone systems require efficient encoding of speech to achieve capacity improvements required of the next generation of cellular systems. The use of a variable rate speech coder can reduce the average data rate required to transmit conversational speech by a factor of two or more, while providing many other advantages. This reduction in average data rate leads to a factor of two increase in the capacity of a Code Division Multiple Access, or CDMA, based digital cellular telephone system by decreasing the mutual interference among users. This chapter describes “QCELP,” a variable rate speech coder which has been selected as the speech coding algorithm for the TIA North American digital cellular standard based on CDMA technology.

High Quality Coding of Wideband Speech at 24 Kbit/s

Abstract: This paper proposes a Wideband-CELP-Coding scheme (bandwidth 7kHz) at 24 kbit/s. The codec introduces a delay of just 10 ms. This fulfills the requirements of a possible codec candidate for wideband speech coding within DECT or video applications [1]. The analysis-by-synthesis structure of the proposed Wideband-CELP-Codec includes an alternative LPC analysis concept, where the autocorrelation function is calculated recursively [2]. This special LPC scheme provides an improved speech quality and a reduction of computational complexity in comparison to conventional algorithms for the LPC analysis. In addition a stochastic sparse codebook with extremely low computational effort is presented, comparable to the one presented in [12] resulting in a neglectable amount of storage. The CCITT G.722 standard was applied as reference codec, in order to compare the new coding scheme in terms of subjective quality. With the proposed Wideband-CELP a speech quality is achieved, which is equivalent to the reference codec operating at 56 kbit/s.

Variable rate speech coding for umts

Abstract: A variable rate speech codec with seven operating rates ranging from 400 bit/s to 16 kbit/s and a 10 ms algorithmic delay is presented in this paper. The current rate is chosen according to an open-loop speech classification followed by a closed-loop quality evaluation. The rate selection can be source-controlled or network-controlled. The codec is based on a CUP algorithm with a variable number of excitations. The innovations have a deterministic structure allowing a very efficient search procedure and are orthogonalized to the long-term contribution. The algorithm will be implemented in the testbed of one RACE II project: CODIT (COde DIvision Testbed) [1].

A Low Bit Rate Video Codec

Abstract: video coding, low bit rate, morphological segmentation, wavelet A video coding/decoding system for applications requiring low bit rate has been developed. This coding scheme uses an intraframe coder for the initial frame in the video sequence and subsequent frames are coded using an interframe coding method. A wavelet-based technique is used for intraframe coding. For interframe coding, displaced frame differences are computed and coded using a segmentation based method wherein the displaced frame is segmented into active and inactive regions. To meet the low bit rate requirements, the motion vectors are processed so as to reduce their contribution to the overall bit rate. Preprocessing techniques are also employed to generate a smooth motion-vector field. To reduce coding artifacts, post-processing techniques are developed for use at the decoder. Coding results for 30 fps CIF resolution sequences at 60 kbits/sec and 15 fps QCIF sequences at 16 kbits/sec are discussed in this report.

Speech Codec Systems

Abstract: This Chapter examines the development of efficient speech compression algorithms, with particular focus placed on new techniques developed over the past 10 years. The main emphasis is placed on techniques that are likely to have applications in narrowband satellite communications, developing the theory as well as describing practical aspects of design and performance evaluations.