Performance of OFDM/CDMA system with turbo coding in a multipath fading channel

The performance of an OFDM/CDMA system with turbo coding is analyzed and simulated in a multipath fading channel. The bit error probability is derived for a frequency-selective Rayleigh fading channel. In the OFDM/CDMA system, OFDM and CDMA are combined to exploit the advantages of both techniques. For decoding the turbo code, a MAP decoding algorithm is employed. Implementation issues are discussed for OFDM, a CDMA system, and a turbo decoding procedure. From the simulation results, it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding/decoding complexity. Also, it is shown that the BER performance is substantially improved by increasing the interleaver length for a fixed code rate and the increasing number of iterations used in the decoding process. The results in the paper can be applied to the design of OFDM-based CDMA system.