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Modern cosmology mainly deals with the origin and evolution of the Universe. Various observational detections (e.g., CMBR, galaxy survey) can probe the Universe at different time stages. The 21-cm signal from neutral hydrogen is another important tool that can be used to study the Universe over a large time period. It also contains a wealth of cosmological and astrophysical information, such as the properties of the first stars and galaxies. But, the problem is particularly challenging due to the presence of strong foregrounds. In this talk, I will present the global effort towards the detection of this faint 21-cm signal using radio telescopes. We have also developed a novel estimator (namely Tapered Gridded Estimator: TGE) to detect this 21-cm signal in the presence of the bright foreground sources. I will discuss the formalism and the effectiveness of the TGE, which is relevant for the present and future 21-cm studies. |