Optimum Windowing for Multicarrier CDMA Systems with MMSE Receivers

The windows for achieving good multiple-access performance of multicarrier code-division multiple-access (MC-CDMA) systems employing minimum mean-squared error (MMSE) receivers are studied. The optimization objective, mean-squared error (MSE) minimization, is examined in the time domain. In a simplified two-user system, the optimization problem is shown to be equivalent to the problem of selecting the chip waveform in an asynchronous DS-CDMA system employing a matched filter. The rectangular window is shown to be optimum, while regarded as an inferior window in OFDM systems due to high spectral sidelobes and slow spectral rolloff.