Near-far resistant channel estimation for CDMA systems using the linear decorrelating detector

The well-known linear decorrelating detector (LDD) for direct-sequence code-division multiple-access (CDMA) systems provides near-far resistant performance when the timing of each user is accurately known. Traditional CDMA acquisition techniques suffer from high differences in power levels. The estimation accuracy for a user overwhelmed by stronger ones is likely to be unsatisfactory; at the same time, the interference from a user undergoing acquisition or tracking is not removed by the standard LDD. In this paper, a fully near-far resistant technique for acquisition and tracking for asynchronous CDMA systems applying the LDD is proposed, considering realistic band-limited signals. This technique is based on the adoption of a pair of special sequences equivalent to a dedicated access channel and is shown to provide a relatively fast and robust means to perform channel estimation both in case of single- and multipath channels