  Fifth-generation (5G) cellular systems are likely to operate in the
centimeter-wave (3-30 GHz) and millimeter-wave (30-300 GHz) frequency bands,
where a vast amount of underutilized bandwidth exists world-wide. To assist in
the research and development of these emerging wireless systems, a myriad of
measurement studies have been conducted to characterize path loss in urban
environments at these frequencies. The standard theoretical free space (FS) and
Stanford University Interim (SUI) empirical path loss models were recently
modified to fit path loss models obtained from measurements performed at 28 GHz
and 38 GHz, using simple correction factors. In this paper, we provide similar
correction factors for models at 60 GHz and 73 GHz. By imparting slope
correction factors on the FS and SUI path loss models to closely match the
close-in (CI) free space reference distance path loss models, millimeter-wave
path loss can be accurately estimated (with popular models) for 5G cellular
planning at 60 GHz and 73 GHz. Additionally, new millimeter-wave beam combining
path loss models are provided at 28 GHz and 73 GHz by considering the
simultaneous combination of signals from multiple antenna pointing directions
between the transmitter and receiver that result in the strongest received
power. Such directional channel models are important for future adaptive array
systems at millimeter-wave frequencies.
