  This paper presents millimeter-wave propagation measurements for urban
micro-cellular and indoor office scenarios at 28 GHz and 73 GHz, and
investigates the corresponding path loss using five types of path loss models,
the singlefrequency floating-intercept (FI) model, single-frequency closein
(CI) free space reference distance model, multi-frequency alpha-beta-gamma
(ABG) model, multi-frequency CI model, and multi-frequency CI model with a
frequency-weighted path loss exponent (CIF), in both line-of-sight and
non-line-of-sight environments. Results show that the CI and CIF models provide
good estimation and exhibit stable behavior over frequencies and distances,
with a solid physical basis and less computational complexity when compared
with the FI and ABG models. Furthermore, path loss in outdoor scenarios shows
little dependence on frequency beyond the first meter of free space
propagation, whereas path loss tends to increase with frequency in addition to
the increased free space path loss in indoor environments. Therefore, the CI
model is suitable for outdoor environments over multiple frequencies, while the
CIF model is more appropriate for indoor modeling. This work shows that both
the CI and CIF models use fewer parameters and offer more convenient closedform
expressions suitable for analysis, without compromising model accuracy when
compared to current 3GPP and WINNER path loss models.
