Steven J. Crowley, P.E.
On October 13 Google filed two experimental radio applications with the FCC. The first seeks permission to test in the 3.5 GHz band in Mountain View, California and in suburban Washington D.C. The second is for testing in the 5.8, 24, 72, and 82 GHz bands in Mountain View and San Mateo County, California. The applications are redacted. Most technical detail is unavailable, but here’s what’s visible.
One application form and redacted supporting exhibit covers testing in the 3.550-3.575 GHz band in Mountain View, California, and in Arlington and Reston, Virginia. Two general types of signals are indicated: a narrowband unmodulated signal carrying no information, and a 10 MHz wide signal carrying data transmissions. The unmodulated signal may be for propagation testing. Three different antenna types are proposed, two directional and one non-directional.
Google’s testing in the 3.5 GHz band isn’t a surprise, given its general support for the FCC’s proposed rules allowing commercial operation in the 3.550-3.650 GHz band.
5.8, 24, 72, and 82 GHz
In the other application form and redacted exhibit, Google requests permission to test on 5.775-5.825, 24.19988-24.20012, 72.500-72.550, and 82.500-82.550 GHz in Mountain View and San Mateo County, California.
On all frequencies, Google intends to transmit narrowband unmodulated carriers. These are not data transmissions, and may be used for propagation testing. Google has some discussion saying that, based on the relative low powers and highly directional antennas used, interference to other users is unlikely.
The 5.8 GHz operation falls in the U-NII-3 band in which operation is normally permitted under Part 15 of the FCC’s Rules. Google notes the following with regard to the 24 GHz band:
Google’s proposed testing in the 24 GHz band similarly will avoid harmful interference to other users of the band. There are three classes of non-federal users in the 24.05-24.25 GHz band: Part 18 ISM users, Part 90 private land mobile radio users, and Part 97 amateur radio users. Based on a query of the FCC’s universal licensing system, there are no active, licensed Part 90 or Part 97 users in either San Mateo or Santa Clara County in the spectrum between 24.05 GHz and 24.25 GHz. Operations in other counties are unlikely to experience interference: The transmitter will be located in the southern part of San Mateo County, close to the Santa Clara County border. San Mateo County extends west to the Pacific Ocean, and Santa Clara County extends east to the San Francisco Bay.
Google’s proposed operations likewise will avoid interference with Part 18 users, who do not need a license to operate their equipment. Although Google’s test will exceed the field strength limitations set forth in 47 C.F.R. §15.249 for fixed, point-to-point operations in the 24.2 GHz band, the transmissions will employ extremely directional, narrow bandwidth transmissions. Indeed, the full beamwidth of the antenna proposed for operation at 24.2 GHz is only 1.4 degrees, making it extremely unlikely that unaffiliated transmissions will pass through the main beam of the antenna. And as with the 5.8 GHz transmissions, all of the 24.2 GHz transmitters [REDACTED].
Google is prepared to coordinate with the National Telecommunications and Information Administration (NTIA) to ensure that testing does not interfere with any earth exploration satellites services (EESS) in this band.
Google notes the following with regard to the 72 and 82 GHz bands:
Google’s proposal complies with the technical specifications set forth in Part 101 for commercial millimeter wave operations in the 71-76 GHz and 81-86 GHz band and Google believes no experimental authorization is necessary. Nevertheless, because [REDACTED], Google requests Special Temporary Authority to conduct its test operations in the band to the extent that the Commission determines such experimental authority is necessary. Prior to commencing test operations, Google will register its proposed links with an authorized third-party database manager for these bands.
UPDATE (10/16): I’ve had a few questions about where, more exactly, these tests are taking place for the millimeter-wave experiment (the second application referenced above). Beyond the general areas of San Mateo County and Mountain View, California, the exhibit specifies three sites defined by geographic coordinates, with not all frequencies being transmitting from all locations (see the bottom of the application form for those details):
The tests will use point-to-point communications between between three sites located in the Bay Area. The locations are as follows:
Location 1: 37°20’40’’ N, 122°12’56’’ W
Location 2: 37°25’3’’ N, 122°4’39’’ W
Location 3: 37°25’33’’ N, 122°04’20’’ W
Using Google Maps (of course), Locations 2 and 3 plot to Google buildings in Mountain View, about a half-mile apart. Location 2 is Google Building 1675, at the northeast corner of the intersection of N. Shoreline Blvd. and Space Park Way. Location 3 is Google Building CL2; there’s no clear address, but you could say north of Crittenden Lane about 1/4 mile east of N. Shoreline Blvd.
Location 3 is roughly 9 miles southwest of Locations 2 and 3, and plots to what appears to be the grounds of the Thomas Fogarty Winery south of Woodside, an elevated location about 1600 feet above sea level.