Auxiliary-vector filters and adaptive steering for DS/CDMA single-user detection

Abstract

Single-user detectors for direct-sequence code-division multiple-access (DS/CDMA) systems are characterized by their architecture, the design optimality criterion, the optimization computational complexity, and ultimately by their average bit error rate (BER) performance. With a fixed tap-weight architecture that implies zero optimization cost, the conventional signature-matched correlator positions itself as the low-cost low-performance solution. This paper submits a proposal that maintains the same tap-weight architecture and introduces the concept of maximum cross-correlation auxiliary-vector filtering associated with minimum BER adaptive steering. Calculation of the auxiliary vector taps involves standard sample average estimation of the data autocorrelation matrix, and no matrix inversion operation is required. The resulting scalar parametrized filter is optimized adaptively in the minimum BER sense by a fast stochastic approximation recursion on /spl Rscr/. Simplicity and BER comparisons place the proposed receiver competitively on the cost versus performance curve. Numerical results under realistic small sample support scenarios support the theoretical developments and indicate that performance-wise the receiver compares favorably not only to the conventional matched-filter correlator, but also to the minimum-output-energy (MOE) detector the LMS-implemented minimum-mean-square-error (MMSE) filter, and the multiuser decorrelating receiver that assumes perfectly known interfering user population.