Analysis of MMSE beamformer for DS-CDMA systems

The performance of two commonly used criteria to obtain the optimum beamforming weights in adaptive antenna arrays, namely, the chip-based mean-squared-error (MMSE) criterion and the symbol-based MMSE criterion, is investigated and a qualitative explanation for the difference in their performance is given. In the first criterion, spatial diversity is exploited in the determination of the beamforming weights. In the second, code separation and spatial diversity are utilized. It is shown that the utilization of code separation in the determination of beamforming weights leads to less noise magnification resulting from interference rejection. Analysis and simulation results show that the symbol-based MMSE criterion offers a better performance than the chip-based MMSE criterion in the presence of multiple access interference.