Iterative turbo multipath interference cancellation for WCDMA systems with non-uniform modulations

In this paper we consider the use of non-uniform QAM constellations (quadrature amplitude modulation) for the transmission of multicast and broadcast services in the downlink connection of a WCDMA (wideband code division multiplexing) system. The objective is to increase the efficiency of the transmission by splitting the information in classes with different importance and mapping the bit streams of these classes to more or less protected positions of the modulation symbols. With this strategy, the most important information streams can be received by all users while the less relevant information will only be extracted by users with good propagation conditions. It is shown that the multipath interference introduced by the channel induces a severe performance loss for these modulations. A low complexity iterative turbo multipath interference canceller (MPIC) that uses feedback information from the turbo-decoder is proposed for suppressing this interference. Computer simulation results are presented, showing that a considerable performance gain can be obtained with the use of the iterative MPIC.