Speech Transmission Using Rate - Compatible Trellis

| This paper presents bandwidth-eecient speech transmission systems using rate-compatible channel coders and variable bitrate embedded source coders. Rate-compatible punctured convolutional codes (RCPC) are often used to provide unequal error protection (UEP) via progressive bit puncturing. RCPC codes are well suited for constellations for which Euclidean distance and Ham-ming distance are equivalent (BPSK and 4-PSK). This paper introduces rate compatible punctured trellis codes (RCPT) where rate compatibility and UEP are provided via progressive puncturing of symbols in a trellis. RCPT codes constitute a special class of codes designed to maximize residual Euclidean distances (RED) after symbol puncturing. They can be designed for any constellation, allowing for higher throughput than when restricted to using 4-PSK. We apply RCPC and RCPT coding schemes to two embedded source coders: a perceptual subband coder and the ITU embedded ADPCM G.727 standard. Error sensitivity analysis is used to determine the protection level needed to keep the eeect of channel impairment imperceptible. Different operating modes with distinct source/channel bit allocation and UEP are deened. Each operating mode is optimal for a certain range of AWGN channel SNRs. Performance results using an 8-PSK constellation clearly illustrate the wide range of channel conditions at which the adaptive scheme using RCPT can operate. For the same constellation sizes and transmission rates, RCPT codes are compared to RCPC used with bit interleaved coded modulation codes (RCPC-BICM). We also compare performance to RCPC codes used with a 4-PSK constellation.