During the first billion years of the Universe, first stars and galaxies formed within the large-scale collapsed structures, marking the Cosmic Dawn (CD). These early sources emitted ultraviolet and X-ray radiation, heating and ionizing the intergalactic medium (IGM), with the epoch of reionization (EoR) ending by z ≈ 5.3. The redshifted 21-cm signal from neutral hydrogen offers a promising probe to study these epochs, encoding key information about the IGM’s temperature, ionization state, density and velocity gradient.

In this talk, I will present my work on the analytical and numerical modelling of the 21-cm signal from CD/EoR. Specifically, I will discuss the effects of ionization and X-ray heating, along with the role of Lyman- α photons in coupling, heating, and cooling the IGM. The statistical properties of this signal—such as the two-point correlation function, power spectrum, and bispectrum—provide key insights into the nature of the first luminous sources and the evolving IGM. Finally, I will highlight the observational prospects of detecting the 21-cm power spectrum and bispectrum with ongoing and upcoming experiments such as Hydrogen Epoch of Reionization Array (HERA), and the Square Kilometre Array (SKA).