Google’s “confidential” test might be a super-dense LTE network using Clearwire’s spectrum

Google filed an application at the FCC last week seeking permission to conduct testing of an experimental radio system.  Portions of the application and accompanying exhibits have been designated confidential and are thus not available to the public. Even the request for confidential treatment has been redacted. Let’s try to infer what’s happening from the information available.

An exhibit says that Google intends to construct a radio network in the vicinity of the Google corporate campus in Mountain View, California. Google plans to test up to 50 base stations and 200 user devices. Base stations will be indoors and outdoors, with the range of each 100-200 meters, and 500-1000 meters, respectively. Both directional and non-directional antennas will be used. The experiment is to take place within a two-mile radius, so this is a quite dense network, which could have very high capacity for carrying data.

The frequencies requested are 2524-2546 and 2567-2625 MHz. These are bands allocated to the Educational Broadband Service (EBS) and the Broadband Radio Service (BRS), which are used by Clearwire for its mobile broadband service.  (Google owned a stake in Clearwire, which it sold last year.) A cursory check of the FCC’s database (the accuracy of which varies) indicates that Clearwire, in the Mountain View area, might be leasing at least some of this spectrum from Stanford University. Generally, a licensee must consent to operation by others on its frequencies.

The output power of the devices is designated on the application form as “not applicable,” which doesn’t make sense. The power is a fundamental quantity that should be disclosed so others may independently assess the potential for interference from the experiment to their services. FCC staff should ask Google to supply this information. Because the area covered by the experiment is small, and there are many base stations, we can guess that the power of each is relatively low, on the order of a few watts or less (with device power even lower).

As with the missing power information, the information supplied for the emission designator is incomplete on the form (the “necessary bandwidth” is missing). The code supplied, “F9W,” is sometimes used for LTE, and it would be reasonable to expect LTE is being used in this test.

We don’t know yet exactly what Google is testing here. It might be devices it created. I suspect, though, that this is a test of a network architecture or service, using existing equipment. Google has been lobbying the FCC to approve the agency’s proposed shared-spectrum small-cell service in the 3550-3650 MHz band, and these test results might be relevant there.

This appears to be Google’s first experimental radio application using mobile broadband bands. Prior to this, Google’s requests for experimental radio authority have generally been confined to frequencies used for unlicensed devices (e.g., the 2.4 GHz band, 5 GHz band, and the 76-77 GHz band). There has also been experimentation on UHF TV frequencies for white-space device testing.


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