Combined source and channel coding based on multimode coding

A multimode source/channel coder which can dynamically control the balance of source and channel coding according to the channel quality is introduced. As an example of such a system, a 4.8-kb/s code excited linear predictive coder with three coding modes (A, B1, and B2), each of which has different bit assignments to source and channel coding, is presented. The optimum coding mode is selected in each frame, based on an evaluation of the spectral distortion (SN/sub LAR/) in reproduced speech. The threshold value of SN/sub LAR/ for mode decision is varied according to the channel error rate. Computer simulation shows that 2 dB and 3 dB of SNR/sub seg/ improvement is achieved at a bit error rate of 3*10/sup -3/ and 3*10/sup -2/ respectively, over conventional CELP without channel coding.<
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