Unequal power allocation to the turbo-encoder output bits with application to CDMA systems

Traditional turbo-codes with binary phase-shift keying modulation assign equal noise margins to the turbo-encoder output bits. It is shown that by using unequal power allocation (UPA) among the encoder output streams, one can improve the code performance especially for large block lengths. On the other hand, there has been a growing interest in the application of turbo-codes for signaling over a code-division multiple-access (CDMA) channel. A usual practice in CDMA systems for matching of rate is based on repeating the encoder output bits. This feature can be used to provide UPA with a negligible increase in the complexity. Simulation results are presented showing a noticeable improvement in the bit error rate performance.