  The Tunka Radio Extension (Tunka-Rex) is a radio detector at the TAIGA
facility located in Siberia nearby the southern tip of Lake Baikal. Tunka-Rex
measures air-showers induced by high-energy cosmic rays, in particular, the
lateral distribution of the radio pulses. The depth of the air-shower maximum,
which statistically depends on the mass of the primary particle, is determined
from the slope of the lateral distribution function (LDF). Using a
model-independent approach, we have studied possible features of the
one-dimensional slope method and tried to find improvements for the
reconstruction of primary mass. To study the systematic uncertainties given by
different primary particles, we have performed simulations using the CONEX and
CoREAS software packages of the recently released CORSIKA v7.5 including the
modern high-energy hadronic models QGSJet-II.04 and EPOS-LHC. The simulations
have shown that the largest systematic uncertainty in the energy deposit is due
to the unknown primary particle. Finally, we studied the relation between the
polarization and the asymmetry of the LDF.
