Comparison of convolutional and turbo codes for OFDM with antenna diversity in high-bit-rate wireless applications

This letter presents simulation results for the application of Turbo coding to an OFDM system with diversity. First, results are presented for convolu tional and Reed-Solomon codes. It is shown that even with short constraint lengths, convolutional codes have the potential to outperform Reed-Solomon codes, provided that sufficient precision is used in the soft decoder. We t hen evaluate the performance of Turbo codes under slow fading conditions an d study the effects of varying codeword size. Increasing codeword size theo retically provides better interleaving between the two component codes. How ever, this advantage is less clear when the fading rate is significantly lo wer than the symbol rate, which is typical of the high-data-rate systems co nsidered here. Under such conditions, the advantage of using two component convolutional codes in Turbo codes is limited, A single convolutional code with a long constraint length may be a better choice.