A coded modulation scheme for a broadcast AWGN channel

This paper proposes a coded modulation scheme for transmission of two classes of information on a broadcast AWGN channel. The scheme is based on multilevel coding with a nonstandard partition of a 32-QAM constellation. The QAM constellation consists of four groups of 8-PSK subconstellations instead of 8-QAM subconstellations. This results in a constellation with reduced peak-to-average power ratio. As component codes of the multilevel construction only one binary convolutional code and a punctured version of it are used. The nonstandard partition allows parallel decoding of the component codes in a multistage decoding algorithm. The error performance of the proposed scheme is obtained. In comparison with Wei's scheme with similar parameters, the proposed scheme achieves higher coding gains for the most important class at the cost of a small degradation in performance for the less important class. Although only results for a specific constellation are presented, the design principles can be easily extended to other QAM constellations.