The millimeter wave regions (3 GHz to 300 GHz) mostly are unused today for communications purposes, mostly because, up to this point, they have been too difficult to harness. Because of distance limitations, line of sight requirements and infrastructure cost, millimeter waves have not been much used for end user access, though some firms always have used such frequencies for point-to-point services for some business customers.
Up to this point, only portions of the 24, 28, 31, and 39 GHz bands ever have been licensed to U.S. service providers, although many of those licenses have lapsed, as the primary business purpose has been point-to-point backhaul, and that market is relatively small, if important to some users.
But with rapid advances in signal processing, antenna technology, application sets and potential business models, much more attention is going to be focused on use of millimeter wave frequencies for communications.
The U.S. Federal Communications Commission, for example, is looking at commercialized use of a number of frequencies, including greater use of 24, 28, 31, and 39 GHz bands, plus new bands in the 37 GHz, 42 GHz, 60 GHz, 70 GHz and 80 GHz regions:
- 24 GHz Bands (24.25-24.45 GHz and 25.05-25.25 GHz)
- LMDS Band (27.5-28.35 GHz, 29.1-29.25 GHz, and 31-31.3 GHz)
- 39 GHz Band (38.6-40 GHz)
- 37/42 GHz Bands (37.0-38.6 GHz and 42.0-42.5 GHz)
- 60 GHz Bands (57-64 GHz and 64-71 GHz)
- 70/80 GHz Bands (71-76 GHz, 81-86 GHz)
Radio signals in those regions have variable attenuation (signal loss when passing through a medium), much as do light signals passing through an optical fiber. For that reason, some frequencies are better suited for communications purposes than others.
Millimeter wave signals perform better (have less attenuation) in the lower 20-GHz to 30 GHz regions; 60 GHz to 80 GHz and 200 GHz to 240 GHz regions, for example.
Optical attenuation is much better at 1300 nm and 1500 nm, for example, than at 1400 nm, which is why 1300 nm and 1550 nm are used for optical communication systems.
Traditionally, millimeter wave frequencies have not had much widespread use because they were so difficult to monetize (propagation issues limited use to higher power point-to-point links). That is expected to change as better technology and architectures, plus new demand drivers, begin to emerge.
On the demand side, the inexorable climb of end user capacity demands matches nicely with the much-higher bandwidth capability of millimeter waves, compared to lower-frequency alternatives.
All of that should mean more capacity will be available for mobile and untethered communications, which also should mean lower spectrum prices, going forward.