Multiple-access interference suppression for OFDM systems based on Doppler shifts

We consider multiuser communications in an additive white Gaussian noise (AWGN) channel in the presence of significant Doppler shifts. It is well-known that the time asynchrony between users in a direct-sequence (DS) code-division multiple-access (CDMA) system allows for interference suppression. Similarly, the different Doppler shifts of received signals from a multiuser channel can be exploited in the frequency domain to achieve interference suppression. We show that this can be achieved with multicarrier CDMA (MC-CDMA). The relationship between the interference suppression capability and the Doppler shifts is studied in terms of signal-to-interference ratio (SIR).