  We have carried out semianalytic simulations to build redshifted 21-cm maps
in the dark ages. An entropy-floor model is adopted for planting protogalaxies
in simulated minihaloes. The model allocates gas quantities such as baryonic
mass and temperature to every $N$-body particle and extensively exploits the
particle nature of the data in the subsequent analysis. We have found that the
number density of simulated minihaloes in the early universe is well described
by the Sheth & Tormen function and consequently the signal powers of simulated
minihaloes are far greater than the Press & Schechter prediction presented by
Furlanetto (2006b). Even though the matter power spectrum measured in the halo
particles at $z=15$ is about an order of magnitude smaller than the
intergalactic medium (IGM), the 21-cm signal fluctuations of haloes are, to the
contrary, one order of magnitude higher than the embedding adiabatic IGM on
scales, $k\lesssim 10 h{\rm Mpc}^{-1}$. But their spectral shapes are almost
same to each other. We have found that the adiabatic signal power on large
scales lies between the linear predictions of the infinite spin-temperature
model ($T_s\gg T_{\rm cmb}$) and the model with the uniform spin temperature
equal to background value ($T_s = T_s^{bg}$). Higher preheating temperature (or
higher background entropy) makes the power spectrum of signals more flattened
because the hotter IGM signals are more thermally broadened and minihalo
fluctuations dominating on small scales are more severely suppressed by the
higher background entropy. Therefore, this model-dependent power spectrum slope
measured on the scale of $100\le k \le 1000 ~h{\rm Mpc}^{-1}$ will enable us to
easily determine a best-matching halo + IGM model in future observations.
