The multi-frequency angular power spectrum in parameter studies of the
  cosmic 21-cm signal
  The light-cone effect breaks the periodicity and statistical homogeneity
(ergodicity) along the line-of-sight direction of cosmological
emission/absorption line surveys. The spherically averaged power spectrum
(SAPS), which by definition assumes ergodicity and periodicity in all
directions, can only quantify some of the second-order statistical information
in the 3D light-cone signals and therefore gives a biased estimate of the true
statistics. The multi-frequency angular power spectrum (MAPS), by extracting
more information from the data, does not rely on these assumptions. It is
therefore better aligned with the properties of the signal. We have compared
the performance of the MAPS and SAPS metrics for parameter estimation for a
mock 3D light-cone observation of the 21-cm signal from the Epoch of
Reionization. Our investigation is based on a simplified 3-parameter 21cmFAST
model. We find that the MAPS produces parameter constraints which are a factor
of $\sim 2$ more stringent than when the SAPS is used. The significance of this
result does not change much even in the presence of instrumental noise expected
for 128 hours of SKA-Low observations. Our results therefore suggest that a
parameter estimation framework based on the MAPS metric would yield superior
results over one using the SAPS metric.
