radiation in the universe which appeared during the “cosmic dawn” is at the forefront of modern observational astronomy. It is believed that these sources formed within the dark matter haloes sometime around redshifts $z \sim 15 - 20$ [@2007ApJ...665..899W; @2010ApJ...716..510G; @2011ApJ...731...54P; @wise2012]. Observing these first sources will not only reveal their unknown properties but also help us in understanding their influence on the formation and evolution of astrophysical objects during later epochs. In recent times a large number of galaxies have been detected at redshift $z \gtrsim 6$ using the broad-band colour [@Ellis13; @Bouwens15] and the narrow-band ${\rm {Ly{\alpha}}}$ emission [e.g., @Ouchi10; @Hu10; @Kashikawa11]. In addition, a significant number of bright quasars have been detected at high redshifts through various surveys [@Fan06b; @Venemans15]. New space missions in the near future, e.g., the James Webb Space Telescope ($JWST$)[^2], are expected to detect the most faint sources at even higher redshifts.

In addition to the above, 21-cm radiation from the neutral hydrogen ([H [i ]{}]{}) in the intergalactic medium (IGM) can also be used as a probe to detect the very early sources. Motivated by this fact, many of the present low-frequency radio telescopes like the Low Frequency Array (LOFAR)[^3] [@van13], the 