Joint detection for OFDM-CDMA communications in multipath fading channels

This paper proposes and compares four block joint detection algorithms for the orthogonal frequency division multiplexing (OFDM)-code division multiple access (CDMA) communication systems. The performance of the proposed OFDM-CDMA joint detectors with orthogonal and non-orthogonal spreading sequences are investigated in mobile radio channels. The proposed OFDM-CDMA detectors are zero forcing (ZF) and minimum mean square error (MMSE) detectors with decision feedback (DF) structures. The proposed joint detectors do not require discrete Fourier transform (DFT) or fast Fourier transform (FFT) operations and can be used to compensate the channel distortion. Hence for hardware implementation, the proposed detectors are more efficient than the conventional methods. The channel sorting method offers approximately 2 dB gain for the DF joint detectors and reduces the impairing effect of error propagation. The bit error rate (BER) performance of orthogonal codes is better than that of non-orthogonal ones in time varying channels. Simulation examples are given to demonstrate the effectiveness of the proposed detectors.