Joint self and multiuser interference reduction for reliable synchronization of DS-CDMA systems over frequency-selective fading channels

This paper deals with the reduction of both self interference (SI) due to multipath, and multiuser interference (MUI) due to multiple access for synchronous DS-CDMA communications over frequency-selective fading channels. We are concerned with the down-link where the base station transmits all the users information synchronously and any mobile receiver must perform a reliable demodulation. In this scenario, the user receiver´s tasks involving synchronization and single detection are severely degraded by the high interference level. Our proposal intends to reduce this error source by using subspace blind detectors with a structure similar to the Generalized Side Lobe Canceller (GSLC) exploiting the canonical representation for the desired user linear detector. The orthogonality condition between both components is imposed by the proper design of the blocking matrix in the unknown multipath environment. Working at chip rate rather than baud rate, a multirate structure at the lower branch provides an almost MUI/SI free signal for time synchronization and multipath optimum combining.