High-quality signal transmission techniques for personal communication systems-novel coherent demodulation and ADPCM voice transmission with click noise processing

The paper proposes high-quality signal transmission techniques for personal communication systems. A novel coherent demodulator-variable carrier filter and hang-up free clock recovery coherent demodulator (VCHACE)-is proposed. The carrier recovery circuit uses a reverse-modulation scheme with variable bandwidth carrier filter. By employing the proposed scheme, the FER (frame error rate) performance is improved by 2 dB compared with the differential detection scheme in typical Rayleigh fading environments. An ADPCM voice transmission scheme that employs a click noise suppressor is also proposed. It achieves a voice quality improvement of 0.5 points in an MOS evaluation (3 dB improvement in required Eb/No) compared with conventional muting schemes in fading environments.