Blind adaptive interference suppression for the near-far resistantacquisition and demodulation of direct-sequence CDMA signals

• Authors: U. Madhow
• Venue: IEEE Transactions on Signal Processing
• Year: 1997

Two key operations required of a receiver in a direct-sequence (DS) code division multiple access (CDMA) system are the timing acquisition of transmissions that are starting up or have lost synchronization, and the demodulation of transmissions that have been acquired. The reliability of both these operations is limited by multiple-access interference, especially for conventional matched filter-based methods, whose performance displays an interference floor and is vulnerable to the near-far problem. Recent work has shown that, provided timing information is available for a given transmission, it can be demodulated reliably using blind or training-sequence-based adaptive interference suppression techniques. These techniques are near-far resistant, unlike the matched filter demodulator, and do not require explicit knowledge of the interference parameters, unlike nonadaptive multiuser detectors. In this paper, we present a blind adaptive interference suppression technique for joint acquisition and demodulation, which has the unique feature that the output of the acquisition process is not simply the timing of the desired transmission, but a near-far resistant demodulator that implicitly accounts for knowledge of the timing and amplitudes of all transmissions to suppress the multiple-access interference. The only knowledge required by the scheme is that of the desired transmission's signature sequence, so that it is amenable to a decentralized implementation. On the other hand, it can be efficiently implemented as a centralized scheme in which the bulk of the computations for the adaptation are common to all transmissions that need to be acquired or demodulated