OFDM and DS-CDMA approaches, analysis of performances on fading multipath channels

We show how orthogonality constraints for DS-CDMA spreading sequences yield directly to OFDM sequences. Having shown this duality we do a comparison of performances between these two waveforms in a multipath fading channel context. The comparison includes the MC-CDMA approach. We show how the cyclic prefix solution can be used for DS-CDMA in order to propose an MMSE optimal despreading solution. This first part of our study is based on a perfect channel estimation. The second part includes channel estimation uncertainty in the comparison. Parameters of simulations, presented in this paper, correspond typically to an UMTS downlink transmission.