On a Subspace Training Method for Dispersive DS-CDMA Channels

A subspace training method has been proposed for dispersive direct-sequence code division multiple access (DS-CDMA) channels. Its performance was compared to a matched filter receiver. We think that it is not quite fair to compare a minimum mean square error (MMSE) based receiver to a matched filter receiver. For this reason, we further investigate the method demonstrating that its performance significantly falls short of the true MMSE receiver and that it suffers from error floor. We also illustrate that any attempt to fill the gap significantly increases the system complexity and drops the efficiency of the transmission, which were originally mentioned as the advantages of the proposed method.