Error protection for a 4.8 kbps VQ based CELP coder

An error protection scheme for a vector-quantization (VQ)-based code excited linear predictive (CELP) coder for mobile radio applications is proposed. To arrive at an appropriate error protection strategy, the sensitivity of the different parameters in the CELP coder are studied, and then unequal error protection is designed according to parameter sensitivities. Different levels of error protection are provided by the use of punctured convolutional codes. The mobile radio channel is modeled as a Rayleigh fading channel. A convolutional interleaving technique is used to combat fading. The combined source and channel codec for this application has a total bit rate of 6.4 kb/s, of which 1.6 kb/s is used for channel coding. Simulation result show that the resulting codec can provide good quality speech at a Doppler frequency of 48 Hz and a channel bit error rate as high as 10^-2