Frequency-domain approach to multiuser detection in DS-CDMA communications

By introducing a new spreading approach and employing orthogonal signature sequences over the frequency domain, we propose a new category of near-optimum multiuser detectors, whose complexity is as low as the detector in point-to-point communications, in the asynchronous additive white Gaussian noise (AWGN) channels. These newly proposed schemes do not have to maintain synchronous CDMA operations and are mathematically proved to be equally well-performed in asynchronous operations.