Performance of turbo-codes for WCDMA systems in frequency selective fading channels

The original parallel concatenated convolutional codes (PCCC) known as turbo codes have been shown to yield very good performance 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 the WCDMA radio link based on the requirements of the wireless third generation (3G). Specifically here, we consider two different structures for the ¼ rate turbo codes. The first is the conventional structure in which three identical constituent encoders are used. This structure is named equal rate turbo code (ERTC). The second structure is a modified turbo code structure with an encoder consisting of two different constituent encoders (one of rate=1/2 and the other of rate=1/3). This structure is called unequal rate turbo code (URTC). The performance of the proposed URTC, conventional ERTC, and a convolutional code with the same decoding complexity are considered in AWGN as well as frequency selective fading channels