Does 16-QAM Provide an Alternative to a Half-Rate GSM Speech Codec?

Download

PDF Download (492Kb)

Description/Abstract

The computational complexity, speech-quality, spectral efficiency and robustness trade-offs of speech transmission schemes for personal communications networks (PCNs) are addressed. Differentially encoded star 16-QAM arrangements with and without oversampling and diversity are compared in terms of robustness to the parallel frequency division multiplex (FDM) 16-QAM system to find the most appropriate modern scheme. The 13.4 <i>kbps</i> regular pulse <i>RPE-LTP</i> speech codec is subjected to rigorous bit sensitivity analysis in terms of both cepstral distance (CD) and segmental signal to ratio (SEGSNR) degradations. A twin-class embedded binary Bose-Chaudhuri-Hocqunghem (BCH) bit protection scheme is devised to improve robustness. The 6.2 kBd system proposed guarantees low-complexity, high-quality speech transmissions in a bandwidth of 12 kHz for vehicular speeds of 30 mph and channel signal to ratios (SNRs) in excess of 25 dB, a value readily maintained in microcellular PCNs. Wehn using diversity, our system has similar robustness to the 11.4 kbps quadruple-complexity, lower speech-quality code excited linear predictive speech codec/convolutional coding/minimum shift keying (CELP/CC/MSK) benchmarker utilised. Yes, 16-QAM does provide an attractive alternative to half-rate speech coding.