We investigate the design of a broadcast system where the aim is to maximise
the throughput. This task is usually challenging due to the channel
variability. Forty years ago, Cover introduced and compared two schemes: time
sharing and superposition coding. The second scheme was proved to be optimal
for some channels. Modern satellite communications systems such as DVB-SH and
DVB-S2 mainly rely on time sharing strategy to optimize throughput. They
consider hierarchical modulation, a practical implementation of superposition
coding, but only for unequal error protection or backward compatibility
purposes. We propose in this article to combine time sharing and hierarchical
modulation together and show how this scheme can improve the performance in
terms of available rate. We present the gain on a simple channel modeling the
broadcasting area of a satellite. Our work is applied to the DVB-SH standard,
which considers hierarchical modulation as an optional feature.