A Re-Configurable Speech Transceiver
Jason Woodard, Lajos Hanzo · ePrints Soton (University of Southampton) · 1995
A 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 Bose-Chaudhuri-Hocquenghem (BCH) codecs combined with unequal-protection diversity and pilot-assisted 16- and 64 level quadrature amplitude modulation (16-QAM, 64-QAM) are employed in order to accommodate both the 4.7 and the 6.5 kbits/s coded speech bits at a signaling rate of 3.1 kBd. In a bandwidth of 200 kHz 32 time slots can be created, which allows us to support i n 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.