A 2.35 kbps joint-detection CDMA speech transceiver

The speech encoded bits generated by the proposed 2.36 kbps prototype waveform interpolated (PWI) speech coder are channel-coded using turbo codes or convolutional codes and transmitted using a joint-detection code-division multiple access (JD-CDMA) scheme. The speech codec combines Zinc basis function excitation (ZFE) and mixed-multiband excitation (MMBE), in order to model the mixed voiced/unvoiced speech segments at the highest possible quality. At the receiver, a joint detection algorithm is used to separate the information of the different up-link users. It is demonstrated that for channel signal-to-noise ratios (SNR) in excess of about 9 dB near-unimpaired speech quality is achieved, virtually independently of the number of users supported, as long as the number of users does not exceed half of the spreading factor. Furthermore, due to the limited acceptable turbo interleaver latency the more complex turbo coded system did not outperform the convolutionally coded scheme.