Turbo codes for PCS applications

Turbo codes are the most exciting and potentially important development in coding theory in many years. They were introduced in 1993 by Berrou, Glavieux and Thitimajshima, and claimed to achieve near Shannon-limit error correction performance with relatively simple component codes and large interleavers. A required E/sub b//N/sub o/ of 0.7 dB was reported for BER of 10/sup -5/ and code rate of 1/2. However, some important details that are necessary to reproduce these results were omitted. This paper confirms the accuracy of these claims, and presents a complete description of an encoder/decoder pair that could be suitable for PCS applications. We describe a new simple method for trellis termination, we analyze the effect of interleaver choice on the weight distribution of the code, and we introduce the use of unequal rate component codes which yields better performance. Turbo codes are extended to encoders with multiple codes and a suitable decoder structure is developed, which is substantially different from the decoder for two-code based encoders.