Transmitter/Receiver Method for Supporting Hierarchical Modulations in MBMS Transmissions

In this paper we consider the use of hierarchical Quadrature Amplitude Modulation (QAM) constellations for Multimedia Broadcast/Multicast Service (MBMS) within Wideband Code Division Multiple Access (WCDMA) based systems. These constellations are employed so as to increase the transmission efficiency, since they are able to provide unequal error protection to different information bit streams. With this strategy, the most important information can be received by all users while the less relevant information will only be extracted by users with good propagation conditions. However, these constellations are very sensitive to inter-symbolic interference introduced by multipath propagation, especially for large constellations. Moreover, large hierarchical constellations have also high channel estimation requirements. For these reasons, we propose an iterative receiver for joint detection and channel estimation. The proposed receiver takes advantage of the turbo-code present in the transmission system and uses feedback information from the turbo-decoder to estimate and suppress the interference, as well as to provide enhanced channel estimates.