  We measure several properties of the reionization process and the
corresponding low-frequency 21-cm signal associated with the neutral hydrogen
distribution, using a large volume, high resolution simulation of cosmic
reionization. The brightness temperature of the 21-cm signal is derived by
post-processing this numerical simulation with a semi-analytical prescription.
Our study extends to high redshifts (z ~ 25) where, in addition to collisional
coupling, our post-processed simulations take into account the inhomogeneities
in the heating of the neutral gas by X-rays and the effect of an inhomogeneous
Lya radiation field. Unlike the well-studied case where spin temperature is
assumed to be significantly greater than the temperature of the cosmic
microwave background due to uniform heating of the gas by X-rays, spatial
fluctuations in both the Lya radiation field and X-ray intensity impact
predictions related to the brightness temperature at z > 10, during the early
stages of reionization and gas heating. The statistics of the 21-cm signal from
our simulation are then compared to existing analytical models in the
literature and we find that these analytical models provide a reasonably
accurate description of the 21-cm power spectrum at z < 10. Such an agreement
is useful since analytical models are better suited to quickly explore the full
astrophysical and cosmological parameter space relevant for future 21-cm
surveys. We find, nevertheless, non-negligible differences that can be
attributed to differences in the inhomogeneous X-ray heating and Lya coupling
at z > 10 and, with upcoming interferometric data, these differences in return
can provide a way to better understand the astrophysical processes during
reionization.
