Adaptive frequency-domain chip equalization for the MIMO CDMA downlink

In the CDMA downlink, equalization can restore the orthogonality lost in multipath channels, and exceed the performance attained by the RAKE receiver. Previous work showed that this concept also applies to multiple-input multiple-output (MIMO) CDMA channels, and that adaptive equalization with training based on pilot symbols is the basis of a practical implementation. We derive a new frequency-domain version of the adaptive MIMO equalizer updated at the symbol rate. Generalizing the stepsize matrix to include the spatial cross-spectra is shown to give a significant performance enhancement. The new algorithm offers reduced complexity and improved convergence time relative to the time-domain version.