  We determine the sharp constants for the fractional Sobolev inequalities
associated with the conformally invariant fractional powers
$\mathcal{L}_{s}(0<s<1)$ of the sublaplacian on H-type groups. From these
inequalities we derive a sharp log-Sobolev inequality by considering a limiting
case and a sharp Sobolev trace inequality. The later extends to this context
the result of Frank, Gonz\'alez, Monticelli and Tan (Adv. Math, 2015).
