A constant modulus approach to multiple access interference rejection

Joaquín Míguez, Luis Castedo

Abstract: This paper addresses the problem of blind Multiple Access Interference (MAI) suppression in Direct Sequence (DS) Code Division Multiple Access (CDMA) systems. The Constant Modulus (CM) criterion is used to devise a blind adaptive DS CDMA receiver that achieves the same performance as the Minimum Mean Square Error (MMSE) receiver for high values of the Signal to Noise Ratio (SNR). The main limitation of the CM receiver is that an interferent user may be extracted instead of the desired one. Two approaches are investigated that practically overcome this problem when an estimate of the desired user code is available. The first one is an adequate choice of the adaptive receiver initial conditions and the second one is the incorporation of linear constraints.