MMSE interference suppression for timing acquisition and demodulation in direct-sequence CDMA systems

It has been recently shown that minimum-meansquared-error (MMSE) demodulators are effective means of interference suppression in code-division multiple-access (CDMA) systems. The MMSE demodulator can be implemented adaptively using an initial training sequence, followed by decision-directed adaptation. This requires that the symbol-level timing of the desired user be known prior to training. In this paper we remove this requirement by providing a method for timing acquisition in which the output of the acquisition process is a near–far-resistant demodulator which automatically accounts for the delays and amplitudes of both the desired signal and the interference without explicitly estimating these parameters. The only requirements are a training sequence for the desired user and a finite uncertainty regarding the symbol timing. The latter condition can be realized by using a periodic training sequence even if the absolute timing uncertainty is arbitrarily large.