Performance of turbo-codes for WCDMA systems in flat fading channels

Turbo-codes have drawn much attention due to its remarkable error correcting capability in digital communication systems for long block sizes. The performance of turbo codes for short block sizes suitable for real time communication systems has gained a lot of attention. We consider the applicability of such codes to a WCDMA radio link based on the requirements of the wireless third generation (3G) systems. We present unequal rate turbo codes (URTC) as an alternative to the conventional equal rate turbo code (ERTC) to obtain an overall code rate equal to 1/4. The URTC provides a reduction in the decoding complexity by almost 33%. This is because the unequal rate turbo decoder uses two soft output Viterbi algorithm (SOVA) decoders while the equal rate turbo decoder uses three SOVA decoders. The performance of the URTC, conventional ERTC, and a convolutional code with the same decoding complexity are considered in AWGN as well as flat fading channels.