Real-time implementation of a scaleable channel coding scheme for mobile transmission of G.723.1 speech bitstream

This paper describes the implementation of the scaleable channel coding scheme (Annex C) for ITU-T G.723.1 speech coder. Speech parameter bits from the encoded frame are reordered and allocated to bit classes of differing sensitivity. Each class is then coded by a rate compatible punctured convolutional code. A rate control algorithm provides scaleability by determining the number of bits and the puncture code per class according to the available channel capacity and speech frame type. At the receiver the bitstream is decoded and errors corrected by a Viterbi decoder and the recovered bitstream reordered back into the original speech frame parameters. Flags, which are generated depending on the error conditions, are passed to the speech decoder to enhance error concealment thereby improving the perceptual performance for the listener. A real-time DSP implementation of this scaleable channel coder is presented. The system is implemented on a TMS320C5X fixed-point DSP chip and integrated together with the speech codec. Efficient architectures are used for implementing the rate control algorithm, convolutional encoder and Viterbi decoder.