A technique is presented to reduce the multiple-access interference in the forward link of a direct-sequence code-division multiple-access system. For each symbol period, an energy-constrained nonlinear transformation is applied at the transmitter output to minimize the mean-squared error at the receiver, subject to a constraint on the peak transmitted energy. The proposed algorithm can be implemented with existing optimization techniques that solve the quadratic trust-region problem. It is shown that in the presence of forward error-correction codes, the proposed method results in a significant gain over earlier known techniques at the cost of a modest increase in computational complexity at the base station. Another advantage of the proposed precoder is that it caps the peak energy (while earlier methods cap the average energy), requiring less sophisticated power amplifiers.

This article presents a technique to reduce multiple access interference in the forward-link of a conventional DS-CDMA system by applying an energy constrained transformation to the transmitter output. For each symbol period, a new transformation is selected which minimizes the mean-squared error at the output of a bank of matched-filter detectors. This selection is subject to a constraint on total transmitted energy. It is shown that the proposed method results in substantial advantages over earlier similar techniques. The proposed algorithm can be implemented efficiently at the transmitter with existing optimization techniques that solve the quadratic trust-region subproblem.