United States radio spectrum frequency allocations chart as of 2003 (Photo credit: Wikipedia)

On August 12, 2013 the FCC, in [ET Docket No 07-113] amended the outdoor use for the 60 GHz spectrum. The changes were prompted by the industry to make the spectrum more useful. This spectrum is more commonly known as the millimeter spectrum, meaning it has a very short wavelength and operates between 57 GHz and 64 GHz. Radios at high frequencies like this have very short antennae which are typically built into the unit.

The spectrum is used today in two applications, a) as outdoor short-range point-to-point systems used in place of fiber, such as connecting two adjacent buildings, and b) as in-building transmission of high-speed data between devices for functions such as transmitting uncompressed high-definition (HD) video between devices like blu-ray recorders, cameras, laptops and HD televisions.

The new rules modify the outside usage to increase power and thus increase the distance of the signal. The FCC is allowing an increase in emissions from 40 dBm to 82 dBm which will increase the outdoor distance for the spectrum up to about 1 mile. The order further eliminates the need for outside units to send an identifying signal, which now makes this into an unlicensed application. This equipment would be available to be used by anybody, with the caveat that it cannot interfere with existing in-building uses of the spectrum.

One of the uses of these radios is that multiple beams can be sent from the same antenna site due to the very tight confinement of the beams. One of the drawbacks of this spectrum is it is susceptible to interference from heavy rain, which is a big factor in limiting the distance.

Radios in this spectrum can deliver up to 7 Gbps of ethernet (minus some for overheads) and so this is intended an alternative to fiber drops to buildings needed less bandwidth than that limit. A typical use for this might be to connect to multiple buildings in a campus or office park environment rather than having to build fiber. The FCC sees this mostly as a technology to be used to serve businesses, probably due to the cost of the radios involved.

Under the new rules the power allowed by a given radio is limited to the precision of the beam created by that radio. Very precise radios can use full power (and get more distance) while the power and distance are limited for less precise radios.

The FCC also sees this is an alternative for backhaul to 4G cellular sites, although the one mile limitation is a rather short one. Most 4G sites that are already within a mile of fiber have largely been connected.

This technology will have a limited use, but there will be cases where using these radios could be cheaper than installing fiber and/or dealing with inside wiring issues in large buildings. I see the most likely use of these radios to get to buildings in crowded urban environments where the cost of leasing fiber or entrance facilities can be significant.

The 60 GHz spectrum has also been allowed for indoor use for a number of years. The 60GHz band when used indoors has a lot of limitations related to both cost and technical issues. The technical limitations are 60 GHz must be line-of-sight and the spectrum doesn’t go through walls. The transmitters are also very power consumptive and require big metal heat sinks and high-speed fans for cooling. Even if a cost effective 60 GHz solution where to be available tomorrow battery operated devices would need a car battery to power them.

One issue that doesn’t get much play is the nature of the 60 GHz RF emissions. 60 GHz can radiate up to 10 Watts with the spectrum mask currently in place for indoor operation. People are already concerned about the 500mW from a cell phone and WiFI and it is a concern in a home environment to have constant radiation at 10 Watts of RF energy. That’s potentially 1/10 the power of a microwave oven radiated in your house and around your family all of the time.

Maybe at some point in the distant future there may be reasonable applications for indoor use of 60 GHz in some vertical niche market, but not for years to come.