Properties of the single-bit single-user MMSE receiver for DS-CDMA systems

The single-bit single-user minimum mean-squared error (MMSE) receiver for direct-sequence code-division multiple access systems is studied in great detail. It is shown that the MMSE receiver is near-far resistant and asymptotically optimum as the interference or noise disappear (i.e., in interference or noise dominated scenarios). It is experimentally shown that the popular Gaussian approximation of the error probability is reasonable for the MMSE receiver over a broad range of operating conditions-i.e., signal-to-noise ratios and interference situations-even though this may not be the case for the standard matched-filter receiver. The concept of dimension reduction is introduced to reduce the complexity of the adaptive part of the receiver and the optimum dimension reduction transform is derived. Unfortunately, the optimum transform is dependent on unknown side-information and is, therefore, of limited practical use. However, several practical schemes are proposed (one which is asymptotically optimum). The schemes are shown to outperform previously known methods.