A combined CELP/Reed-Solomon codec for mobile radio applications

The performance of an error-protected speech codec for mobile radio applications is investigated. The speech codec is a 4 kb/s variation of the proposed Federal Standard 1016 CELP. The major difference is the use of a trained codebook (as opposed to a stochastic codebook in the proposed standard). The channel codec on the other hand, consists of a bank of rate-compatible punctured Reed-Solomon (RS) codes. The two subsystems are combined in an optimal fashion, according to the sensitivity of the speech elements. This implies that the most sensitive bits are protected by the most powerful RS codes, while the least sensitive bits are (either uncoded or) protected by the least powerful code. The performance of such a combined codec under different sets of system parameters and channel conditions is studied. In all cases, though, the aggregate rate is fixed at about 6.4 kb/s. The simulation results show that under the condition that there is no interleaving delay, the resulting codec can provide good quality speech at a channel bit error rate as high as 10^-2