An adaptive antenna array for multiple received signals in direct-sequence code-division multiple-access communication systems

Direct-sequence spread-spectrum (DS-SS) has been under increasing scrutiny as a means to provide a multi-user communications channel via code-division multiple-access (CDMA). One of the issues which can impact the performance of a DS-SS communication system is the near-far effect. The near-far effect occurs when a powerful incident signal (desired or undesired) overwhelms desired DS-SS signals. One of several possible ways to lessen this effect is to use an adaptive antenna array at the DS-SS receiver. Of particular interest is the special case of a single receiver which must detect multiple desired signals. This might occur in commercial NAVSTAR GPS receivers and in mobile cellular base station receivers. This paper examines the steady-state performance of adaptive antenna arrays which are based on a minimum mean-squared error (MMSE) optimization criterion. The beamforming array is limited to a single feedback loop, and a single array output, which supports multiple received signals. It is shown that a single-loop MMSE array can level the output signal-to-noise ratios to nearly the same level and thus eliminate the near-far effect