An LSF quantizer for the North-American half-rate speech coder

Abstract

The design of the half-rate coder for the North-American cellular communication standard poses a challenging problem. The desired speech quality is that of the full-rate coder, but the total bit rate specified for the half-rate is only 6.5 kb/s. Since the mobile communication channel is very noisy, the use of error-correcting codes is necessary, which leaves only about 4 kb/s for the actual speech information. This very restricted bit budget requires that fewer than 30 b be allotted to the quantization of the LSF parameters, which precludes the use of scalar quantization. In this work, a quantizer design procedure which is tailored for the transmission frame structure of the North-American (TIA) cellular communication standard is presented. It is basically a split vector quantizer which makes use of interframe prediction to lower the number of bits required for quantization. Since the prediction is performed only on every other frame, the error propagation is limited. The quantization technique yields good performance in the 26-27 blfiame range, and the complexity of its implementation is less than 0.5 Mip.

Performance of LSF vector quantizers for VSELP coders in noisy channels

“…In order to avoid this performance loss when a moderately complex split VQ is desired, in [5] it was proposed that advantage be taken from the high interframe correlation presented by the LSF coefficients. The scheme introduced in [ 5 ] actually applies prediction on every other frame so as to avoid error propagation and slope overload. Specifically.…”

“…Following the suggestion in [5]. a value of M = 4 was adopted in this work and bit distribution for the frame which is absolutely quantized (frame A ) and the frame which is predicted (frame B ) is as shown in Table 1. Codebook design was performed, following the procedure outlined in [ 5 ] . using the previously mentioned speech data base.…”

“…Such a measure should reflect both the cost and power requirements of a real time implementation. In this work it was adopted the measure described in [ 5 ] . This measure takes into account the number of operations, with weight factors associated to each type of operation, and also the data memory requirements both in terms of static and dynamic memory.…”

Joint inter-frame and intra-frame predictive coding of LSF parameters

“…To exploit this, several predictive schemes have been proposed in the past ( [2], [7], [9]). We refer to these methods as inter-frame correlation based predictive methods (1-D methods).…”

Sistema de codificão de vídeo baseado em transformadas tridimensionais, rápidas e progressivas

“…Outras formas de avaliação dos codificadores de vídeo analisam, por exemplo, a complexidade computacional dos algoritmos implementados, tais como as apresentadas em [26] e [27]. As medidas calculadas nestes artigos estabelecem pesos para cada tipo de operação aritmética realizada no algoritmo e levam em consideração as quantidades de memória física e dinâmica das máquinas em que os algoritmos estão sendo executados.…”