An Iterative Receiver for WCDMA Systems with MIMO Transmissions and Hierarchical Constellations

In this paper we consider the use of M-QAM hierachical constellations (quadrature amplitude modulation) and MIMO (multiple input multiple output) for the transmission of multicast and broadcast services in the downlink connection of a WCDMA (wideband code division multiple access) 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. Due to the more demanding channel estimation requirements and the higher sensitivity to interference resulting from the usage of several antennas and hierarchical constellations, an enhanced receiver based on the turbo concept is developed and evaluated. It is shown that high transmission bit rates can be achieved even in high delay spread environments