Cosmological 21cm experiments: Searching for a needle in a haystack
  There are several planned and ongoing experiments designed to explore the
Epoch of Reionization (EoR), the pivotal period during which the gas in the
intergalactic medium went from being entirely neutral to almost entirely
ionized. These experiments will probe the EoR, through the redshifted 21 cm
line from neutral hydrogen, using radio arrays: e.g. Low Frequency Array
(LOFAR) and Murchinson Widefield Array (MWA). Unfortunately however, the
cosmological 21 cm signal is highly contaminated by astrophysical foregrounds
and by non-astrophysical and instrumental effects. Therefore, to reliably
detect the cosmological signal, it is essential to understand very well all
data components, their influence on the desired signal and explore additional
complementary or corroborating probes of the EoR. These proceedings give an
overview of observational constrains of the foregrounds, present theoretical
efforts to model the foregrounds, and discuss a problem of the foreground
removal. The major results are presented for the LOFAR-EoR experiment.
