  Reverberation mapping technique is an important milestone in AGN
demographics, kinematics and the structure of the Broad Line Region (BLR) based
on the time-delay response between the continuum and emission line. The time
delay is directly related to the size of BLR which is related to the continuum
luminosity of the source, producing the well-known Radius-Luminosity (RL)
relation. The majority of sources have been monitored for their H$\beta$
emission line in low redshift sources ($z<0.1$), while there are some attempts
using the MgII line for higher redshifts. We present a recent MgII monitoring
for the quasar CTS C30.10 ($z=0.90$) observed with the 10-meter SALT, for which
RL scaling based on MgII holds within measurement and time-delay uncertainties.
One of the most important advantages of reverberation mapping technique is the
independent determination to the distant source, and considering the large
range of redshifts and luminosities found in AGNs, their application to
cosmology is promising. However, recently it has been found that highly
accreting sources show the time delays shorter than expected from RL relation.
We propose correction for this effect using a sample of 117 H$\beta$
reverberating-mapped AGNs with $0.02<z<0.9$, recovering the low scatter along
with the relation. We are able to determine the cosmological constants,
$\Omega_m$ and $\Omega_\Lambda$ within 2$\sigma$ confidence level. We present
the first steps in modelling of light curves for H$\beta$ and MgII and discuss
the quasar selection in the context of photometric reverberation mapping with
Large Synoptic Survey Telescope (LSST). With the onset of the LSST era, we
expect a huge rise in the overall quasar counts and redshift range covered
($z\lesssim 7.0$), which will provide a better constraint of AGN properties
with cosmological purposes.
