Blind direct multiuser detection for uplink MC-CDMA: performance analysis and robust implementation

We consider the problem of blind (i.e., without training sequences) linear mitigation of multiple-access interference in the uplink of quasi-synchronous multicarrier code-division multiple-access (MC-CDMA) systems. In the first part of the paper, we present the analytical performance assessment of the recently proposed blind two-stage multiuser detector, whose synthesis requires only the knowledge of the spreading code of the desired user. The analysis allows one to evaluate the actual performance when the receiver's parameters are estimated by resorting to a finite data record. Based on this analysis, in the second part of the paper, we propose to improve the performance of the two-stage detector by adding a quadratic constraint in the first stage synthesis, which exploits the knowledge of the spreading codes of the active users within the cell of interest. It is shown analytically that incorporation of such a quadratic constraint improves the receiver robustness against errors in the estimated statistics of the received data, although it slightly reduces the interference suppression capabilities of the two-stage detector. The effectiveness of the proposed receiver is further corroborated by computer simulation results