  This paper analyzes the frequency dependency of the radio propagation
channel's root mean square (rms) delay spread (DS), based on the
multi-frequency measurement campaigns in the mmMAGIC project. The campaigns
cover indoor, outdoor, and outdoor-to-indoor (O2I) scenarios and a wide
frequency range from 2 to 86 GHz. Several requirements have been identified
that define the parameters which need to be aligned in order to make a
reasonable comparison among the different channel sounders employed for this
study. A new modelling approach enabling the evaluation of the statistical
significance of the model parameters from different measurements and the
establishment of a unified model is proposed. After careful analysis, the
conclusion is that any frequency trend of the DS is small considering its
confidence intervals. There is statistically significant difference from the
3GPP New Radio (NR) model TR 38.901, except for the O2I scenario.
