Combined speech and channel coding for mobile radio applications

The authors present the combined speech and channel coding scheme for half rate (8 kbps/user) digital cellular application. The speech coding algorithm is code-excited linear prediction (CELP) and the channel codes used are punctured Reed-Solomon codes. A preliminary study on combining CELP and rate-compatible convolutional codes was also conducted. Unequal error protection of different speech elements is employed. The error-protected digits are sent through the digital cellular channel via π/4-QPSK modulation. The channel is assumed to introduce Rayleigh flat fading and additive Gaussian noise. The received signal is demodulated through differential detection. The performance of the codec has been studied for different received SNR, fade rates, and interleaving delays