Waveform speech coding for wideband CDMA radio system
Yumi Takizawa, Atsushi Fukasawa, Chiharu Yamano, R.E. Fisher · 2002
This paper describes the environment and an evaluation of a robust ADPCM for a wideband CDMA system. The environmental conditions of the speech codec are first considered. Random error is assumed for the radio environment. Bit error rate (BER) is clear channel, 1/spl times/10/sup -3/ (typical point), and 3/spl times/10/sup -3/ (overload point). The speech quality evaluation method is then considered. The equivalent Q value is utilized to provide the reliability for evaluation. The modulated noise reference unit (MNRU) is first prepared, and then decoded speech is evaluated by mean opinion score (MOS). Finally an equivalent Q value is obtained based on the above MOS scores of MNRU and decoded speech. The evaluation is performed using waveform codecs of the proposed ADPCM, conventional ADPCM, PCM, and LD-CELP. The robust ADPCM proposed by the authors is found to provide toll quality of speech under a BER 1/spl times/10/sup -3/. The advantage is also confirmed compared to conventional waveform codecs of PCM, ADPCM, and LD-CELP.