The University of British Columbia

We study An application of hierarchical constellations (known also as nonuniform, asymmetric, and multi-resolution constellations) in conjunction with a retransmission strategy to multi-class data transmission over block fading channels. The basic idea is to assign different hierarchies of a hierarchical quadrature amplitude modulation (QAM) to different classes of data according to their transmission priorities (quantified through their average throughput and delay requirements) and then to apply a truncated retransmission scheme to each hierarchy (or equivalently each class of data) separately in order to meet the delay requirements of the various services. We present closed-form expressions for the average packet loss rate and the packet transmission rate of each class of data over Nakagami-m block fading channel. Some numerical results show that the proposed hierarchical scheme outperforms a classical time-multiplexing scheme employing power-controlled uniform QAM constellations for multi-class data transmission over block fading channels.