  We study the design of a DVB-S2 system in order to maximise spectrum
efficiency. This task is usually challenging due to channel variability. Modern
satellite communications systems such as DVB-SH and DVB-S2 rely mainly on a
time sharing strategy to optimise the spectrum efficiency. Recently, we showed
that combining time sharing with hierarchical modulation can provide
significant gains (in terms of spectrum efficiency) compared to the best time
sharing strategy. However, our previous design does not improve the DVB-S2
performance when all the receivers experience low or large signal-to-noise
ratios. In this article, we introduce and study a hierarchical QPSK and a
hierarchical 32-APSK to overcome the previous limitations.We show in a
realistic case based on DVB-S2 that the hierarchical QPSK provides an
improvement when the receivers experience poor channel condition, while the
32-APSK increases the spectrum efficiency when the receivers experience good
channel condition.
