Adaptive interference suppression for joint acquisition and demodulation of direct-sequence CDMA signals

It has shown that adaptive interference suppression methods for the demodulation of CDMA signals provide immunity to the near-far problem, and perform much better than the conventional matched filter receiver even with perfect power control. Demodulation must, however, be preceded by acquisition of the timing of the desired signal, and conventional methods for acquisition are interference-limited and vulnerable to the near-far problem to the same extent as conventional demodulation. We present two interference suppression schemes for the joint acquisition and demodulation of direct sequence CDMA signals. Roughly speaking, the idea is to run several adaptive demodulation algorithms serially or in parallel, each under a different hypothesis regarding the desired transmission's timing, and to choose the one that gives the best performance. Thus, our schemes have the unique feature that the output of the acquisition process is not merely the timing of the desired transmission, but a near-far resistant demodulator which implicitly takes into account the timing and amplitudes of all transmissions in order to achieve interference suppression. Our acquisition schemes are amenable to efficient decentralized or centralized implementations, and are near-far resistant by virtue of the near-far resistance of the demodulation schemes on which they are based.