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We investigate the design of a broadcast system in order to maximise thethroughput. This task is usually challenging due to the channel variability.Forty years ago, Cover introduced and compared two schemes: time sharing andsuperposition coding. Even if the second scheme was proved to be optimal forsome channels, modern satellite communications systems such as DVB-SH andDVB-S2 mainly rely on time sharing strategy to optimize the throughput. Theyconsider hierarchical modulation, a practical implementation of superpositioncoding, but only for unequal error protection or backward compatibilitypurposes. We propose in this article to combine time sharing and hierarchicalmodulation together and show how this scheme can improve the performance interms of available rate. We introduce the hierarchical 16-APSK to boost theperformance of the DVB-S2 standard. We also evaluate various strategies togroup the receivers in pairs when using hierarchical modulation. Finally, weshow in a realistic use case based on DVB-S2 that the combined scheme canprovide throughput gains greater than 10% compared to the best time sharingstrategy.

Combining Adaptive Coding and Modulation with Hierarchical Modulation in Satcom Systems