Effective channel coding combined with low bit-rate speech coding for digital cellular system

A channel coding method for a half-rate speech codec is proposed. This method includes new error control techniques that effectively integrates a speech codec with a channel codec. It utilizes bit swelling technique for an efficient unequal error protection. Highly significant bits are swollen and combined with other significant bits. Combined bits are coded with a convolutional code. In addition, the Viterbi decoder employs temporal correlation in encoded speech data as well ail the redundancy of convolutional code, to improve its decoding performance. The paper shows the error correction ability for this method is higher than that for a conventional method. A subjective test shows that the speech quality for a half-rate speech codec combined with the proposed channel codec is considerably better than that for the full-rate VSELP codec on a fading channel