  The process of heating and reionization of the Universe at high redshift
links small scale structures/galaxy formation and large scale inter-galactic
medium properties. Even if the first one is difficult to observe, an
observation window is opening on the second one, with the promising development
of current and future radio telescopes. They will permit to observe the 21cm
brightness temperature global signal and fluctuations. The need of large scale
simulations is therefore strong to understand the properties of the IGM that
will be observed. But at the same time the urge to resolve the structures
responsible of those process is important. We introduce in this study, a
coupled hydro-radiative transfer simulations of the Cosmic Dawn and
Reionization with a simple sub-grid star formation process developed and
calibrated on the state of the art simulation CoDaII. This scheme permits to
follow consistently dark matter, hydrodynamics and radiative transfer
evolution's on large scales, while the sub-grid models bridges to the galaxy
formation scale. We process the simulation to produce 21cm signal as close as
possible to the observations.
