A dual-rate algebraic CELP-based speech transceiver

A novel high-quality, low-complexity dual-rate 4.7/6.5 kbits/s algebraic code excited linear predictive (ACELP) codec is proposed for adaptive speech communicators, which can drop their source rate and speech quality under network control in order to invoke a more error resilient modem amongst less favourable channel conditions. Source-matched binary Bose-Chaudhuri-Hoequenghem (BCH) codecs combined with unequal protection diversity- and pilot-assisted 16and 64-level quadrature amplitude modulation (18-QBM, 64-QAM) are employed In order to accommodate both the 4.7 and the 6.5 kbits/s coded speech bits at a signalling rate of 3.1 kBd. In a bandwidth of 200 kHz 32 time slots can be created, which allows to support in excess of 50 users, when employing packet reservation multiple access (PRMA). Good communications quality speech is delivered in an equivalent bandwidth of 4 kHz, if the channel signal-to-noise ratio (SNR) and signal-to-interference ratio (SIR) are in excess of about 15 and 25 dB for the lower and higher speech quality 16-QAM and 64-QAM systems, respectively