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Understanding millimeter-band propagation and how it can be used for 5G, 6G, and beyond

September 12, 2022

Last month, NTIA’s research laboratory, the Institute for Telecommunication Sciences (ITS), released NTIA Technical Report TR-22-561, “Outdoor Propagation Measurements in the 37–40 GHz Band in Boulder, Colorado.” The measured data summarized in this report will be provided to NTIA’s Office of Spectrum Management (OSM) to be used to validate the 3rd Generation Partnership Project (3GPP) and other millimeter-wave propagation prediction models that are essential to further development of advanced fifth generation (5G) wireless technologies.  

5G wireless networks and technologies promise not only an enhanced consumer experience of cellular connectivity, but also revolutionary new applications such as smart electrical grids, smart cities, telehealth, autonomous vehicles, and many more. These new applications depend on very high connection speeds, very low latency, enormous data capacity, and ubiquitous connectivity. Fully achieving the promise of 5G technologies requires access to radio spectrum frequencies in what is known as the millimeter wave band (above 24 GHz) that have not previously been widely exploited for telecommunications services.  

Planning for these new millimeter-wave networks will depend heavily on the propagation prediction models that calculate how far a signal will travel and what is likely to stop or slow the signal. The past decade has seen a flurry of research—much of it proprietary—aimed at updating millimeter wave propagation models. But there is still a lack of fully validated propagation models at these frequencies, due in part to a shortage of current, publicly available, millimeter-wave propagation measurement data. 

The objective of the effort described in this latest report was to begin to remedy that shortage by performing and reporting the results of a set of outdoor mobile millimeter-wave propagation measurements in a small downtown environment (downtown Boulder, Colorado). Downtown Boulder represents a small business district with many closely spaced tall buildings that form a set of urban canyons—a typical topography for a profitable commercial 5G deployment. To take these measurements, ITS had to first develop a new high-precision measurement system incorporating many custom components. 

Measurements were taken when receiver and transmitter were in line of sight, and when they were not. The report compares the measured data to the predictions of two publicly available propagation models. In general, the measured signal loss did not agree well with the predicted signal loss.  

These comparisons can be used to develop more accurate models, which are especially crucial to planning the deployment of the urban microcells needed to realize the full potential of data-rich 5G cellular technologies.