Minimum mean squared error interference suppression for direct-sequence spread-spectrum code-division multiple-access

Abstract

Demodulation of a direct-sequence spread-spectrum (DS/SS) code-division multiple-access (CDMA) signal in the presence of multiple-access interference is considered. The channel output is first passed through a filter matched to the chip waveform and then sampled at the chip rate. Because of the complexity and coefficient noise associated with such an adaptive filter when N is large, simpler structures with fewer adaptive components are proposed. In each case the multiple samples per symbol are combined via a trapped delay line, where the taps are selected to minimize the mean square error. It is shown that the complexity of both of these schemes are comparable, but that the first scheme is somewhat more effective in cancelling interference. Numerical results are presented for specific examples illustrating the efficacy of the proposed methods.