IMPROVED ADPCM VOICE SIGNAL TRANSMISSION EMPLOYING CLICK-NOISE DETECTION SCHEME FOR TDMA-TDD PERSONAL COMMUNICATION-SYSTEMS

In personal communication systems, better voice quality and lower term inal price are essential requirements, and adaptive differential pulse -code modulation (ADPCM) codecs are one of the voice codec candidates that have good voice quality and reasonable cost, However, in slow fad ing environments, burst errors induce click noise in ADPCM voice signa l transmission, This paper proposes a novel error-concealment scheme t o improve the ADPCM voice signal transmission quality of time division multiple access-time division duplex (TDMA-TDD) personal communicatio n systems in slow fading environments, The proposed scheme employs an improved error-detection technique with PCM differential detection and overflows detection coupled with a cyclic redundancy check (CRC) code , To compensate for residual click noise, an expanded ORC error-detect ion signal is used, Erroncous PCM signals are adaptively suppressed ac cording to the click-noise detection information. Hardware simulation results show that these techniques significantly improve. ADPCM voice signal transmission quality by 0.5 points and 1.0 compared to that of the conventional ADPCM muting scheme and no processing, respectively, with the mean opinion scoring (MOS) test in the slow fading environmen ts typical of personal communication systems.