  5G and beyond networks will use, for the first time ever, the millimeter wave
(mmWave) spectrum for mobile communications. Accurate performance evaluation is
fundamental to the design of reliable mmWave networks, with accuracy rooted in
the fidelity of the channel models. At mmWaves, the model must account for the
spatial characteristics of propagation since networks will employ highly
directional antennas to counter the much greater pathloss. In this regard,
Quasi-Deterministic (QD) models are highly accurate channel models, which
characterize the propagation in terms of clusters of multipath components,
given by a reflected ray and multiple diffuse components of any given Computer
Aided Design (CAD) scenario. This paper introduces a detailed mathematical
formulation for QD models at mmWaves, that can be used as a reference for their
implementation and development. Moreover, it compares channel instances
obtained with an open source NIST QD model implementation against real
measurements at 60 GHz, substantiating the accuracy of the model. Results show
that, when comparing the proposed model and deterministic rays alone with a
measurement campaign, the Kolmogorov-Smirnov (KS) test of the QD model improves
by up to 0.537.
