In this paper we consider the use of hierarchical QAM constellations (Quadrature Amplitude Modulation) for Multimedia Broadcast/Multicast Service (MBMS) within WCDMA-based systems (Wideband Code Division Multiple Access). The constellations are incorporated into HS-DSCH (High Speed Downlink Shared Channel) of UMTS (Universal Mobile Telecommunications System). They are employed so as to increase transmission efficiency due to their ability to provide unequal error protection to different information bit streams. Nevertheless, these constellations are very sensitive to inter-symbolic interference introduced by multipath propagation, especially for large constellations, and have also high channel estimation requirements. For these reasons, we propose the use of an iterative receiver based on the turbo principle for joint detection and channel estimation. The proposed transmitter/receiver scheme is evaluated considering the presence of other parallel UMTS transmissions.
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