Improved constrained optimization method for CDMA systems

The constrained optimization method has been shown to be applicable for direct CDMA receiver design. However, due to the presence of additive noise and multipath distortion, the optimal constraint is a biased estimate for the channel, resulting in some performance loss of the constrained receiver compared with the MMSE receiver. This loss becomes more significant for the lower SNRs. It is shown in this paper that constrained optimization is closely related to the subspace method which can give a good estimate for the channel. Motivated by this result, a modified cost function is proposed to obtain the constraint with less complexity than the subspace method and better performance than the previously proposed constrained method.