On QAM Speech Transmission Schemes for Microcellular Mobile PCNs
Transactions on Emerging Telecommunications Technologies
On the way towards third generation personal communication networks (PCN) the deployment of 16-level quadrature amplitude nlodulation ( Q A W schemes is investigated via flat microcellular Rayleiph-fading mobile radio channels having mild co-channel interference with and without diversity. Our proposed differentially coded non-coherent 16-QAM scheme requires no pilot symbol assistance. no automatic gain control (AGC) and no carrier recovery. High speech quality associated with a mean opinion
... re of about four (MOS = 4.0) is ensured at a signalling rate of 6.1 kBd for channel signal to noise ratios tSNR) above 30 -25 dB and signal to interference ratios (SIR) above 75 -30 dB by the 13.4 kbit/s medium complexity resular pulse excited (a) Also with Multiple Access C~rnrnunicnrions Lfd. Enterprise Rd.. Chilworth Research Cenlrr. Sautharnplon SO1 7NS. U.K. ted by deploying 16-level quadrature amplitude modulation (IBQAM), which lowers the signalling rate by a factor of four and hence quadruples the signalling interval's duration. Therefore the relative effects of signal dispersion are mitigated and the need for channel equalization can be removed. The paper is organised as follows. Section 2 gives a brief overview of QAM research for both Gaussian and Rayleigh fiiding channels and highlights the key features of two previously proposed QAM-based mobile communication schemes for PCN in contrast to the presently suggested system. Section 3 hishlights our proposed non-coherent differentially coded 16-QAM modem. Section 4 concentrates on the RPE speech codec and after a theoretical treatise it provides a rigourous bit sensitivity analysis based on a sensitivity measure derived from the amalgamation of segmental SNR (SEG-SNR) and cepstral distance (CD) measures. Section 5 deals with aspects of channel coding. while Section 6 describes the combined transceiver scheme proposed. Lastly. Section 7 summarises our results and provides some discussions.