Adaptive channel equalization and interference suppression for CDMA downlink

In the synchronous CDMA downlink using orthogonal codes, the intracell multiple access interference (MAI) is essentially caused by the frequency selective multipath channel. Therefore, intracell MAI may be suppressed by simple linear channel equalization. Similarly, intercell interference can be suppressed by means of linear space-time filtering. We compare two different adaptive receiver algorithms in the context of one or several receive antenna elements. The first one is based on adaptive LMMSE chip estimation, whereas the other one performs simple interchip interference cancellation by adaptive chip separation. The presented receiver structures are suitable for systems with long code scrambling, such as 3rd generation wideband CDMA standard. The results show considerable performance gains when compared to the conventional RAKE receiver.