Google says tests prove large exclusion zones are unnecessary in 3.5 GHz band

Google (NASDAQ: GOOG) says its testing reveals that LTE and Wi-Fi networks can work in close proximity to radar systems in the 3.5 GHz band, proving it is unnecessary to establish large exclusion zones to protect commercial wireless systems from harmful radar interference.

The experiments focused on SPN-43 radar systems, which are used by the Naval Air Systems Command for air traffic control. Google conducted the tests in cooperation with the U.S. Department of Defense and Navy. Virginia Polytechnic Institute and State University and Federated Wireless partnered with Google on the tests.  

In an FCC filing, Preston Marshall, principal systems architect at Google Access Services, recounted an Aug. 28 meeting he and a colleague had with John Leibovitz, deputy chief of the FCC's Wireless Telecommunications Bureau, and Julius Knapp, chief of the Office of Engineering and Technology. At that meeting, Google's representatives suggested the FCC should establish interference protection requirements for periods when radar is in operation and vulnerable to interference from secondary users but also stressed that the commission should avoid attempting to protect secondary users, which Google said "would constrain innovation."

The FCC intends to use spectrum sharing to create a Citizens Broadband Radio Service (CBRS) in the 3550-3650 MHz spectrum band and is also pondering extending the service to 3700 MHz, providing a total of 150 MHz of spectrum for the CBRS. The FCC's three-tiered access and sharing model would be comprised of federal and non-federal incumbents, priority access licensees (PALs) and general authorized access (GAA) users, which would basically be an unlicensed tier. Some proposed use cases for the CBRS spectrum include carrier-grade small cell deployments and backhaul.

The commission plans to have a centralized spectrum manager, or Spectrum Access System (SAS), assign channels dynamically. Google contends the controversial SAS, which the company supports in concept, "could easily develop the capability to protect incumbent radars and the method for doing so is similar to the approach for protecting in-band FSS [fixed satellite service] operation."

Further, the company says existing International Telecommunication Union (ITU) standards for protecting radar operations could provide basic criteria for protecting naval radars.

Google told the commission that commercial devices are likely to be deployed quickly in the 3.5 GHz band if the commission issues favorable rules. "There has been rapid growth in chipsets and equipment availability, driven largely by overseas deployment of LTE-TD in this band," Google added.

China Mobile, Datang and Huawei recently asked the FCC to allocate 3.5 GHz spectrum for TDD-based operations, saying that doing so would enable U.S. operators "to cooperate with operators in other countries and regions to develop the global TDD market on 3.5 GHz band."

For more:
- see this Google filing

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