ON QAM SPEECH TRANSMISSION SCHEMES FOR MICROCELLULAR MOBILE PCNS

On the way towards third generation personal communication networks (P CN) the deployment of 16-level quadrature amplitude modulation (QAM) s chemes is investigated via flat microcellular Rayleigh-fading mobile r adio channels having mild co-channel interference with and without div ersity. Our proposed differentially coded non-coherent 16-QAM scheme r equires no pilot symbol assistance, no automatic gain control (AGC) an d no carrier recovery. High speech quality associated with a mean opin ion score of about four (MOS almost-equal-to 4.0) is ensured at a sign alling rate of 6.2 kBd for channel signal to noise ratios (SNR) above 20 - 25 dB and signal to interference ratios (SIR) above 25 - 30 dB by the 13.4 kbit/s medium complexity regular pulse excited (RPE) speech codec, when carefully matched twin-class low complexity binary Bose-Ch audhuri-Hocquenghem (BCH) error correction coding and 16-QAM combined with second order diversity are deployed. The overall speech delay is about 40 ms and the user bandwidth is 9.3 kHz, which allows us to acco mmodate 21 users in a 200 kHz channel slot.