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Southern Company, a utility company serving parts of seven states, has asked the FCC to conduct further testing involving potential interference in the 6 GHz band, which the FCC freed up in April 2020 for unlicensed operation.

Southern Company operates microwave transmission equipment in the 6 GHz band and therefore is among the incumbent users that FCC 6 GHz transmission rules adopted in April were designed to protect. The company conducted testing that it says shows that unlicensed devices operating in the 6 GHz band according to the April FCC rules do cause interference to incumbent users.

If proven valid, the Southern Company’s concerns could jeopardize plans to use the 6 GHz band to support gigabit Wi-Fi.

A letter to the FCC from Southern Company notes that the Consolidated Appropriations Act adopted by Congress on December 27 includes a requirement for the FCC to provide a report within 90 days about its “progress in ensuring rigorous testing related to unlicensed use of the 6 GHz band.”

Southern Company 6 GHz Concerns

The 6 GHz band includes 1200 MHz of spectrum between 5.925 and 7.125 GHz. In April, the FCC made the spectrum available for unlicensed use in two broad categories: standard power and low power

Standard power indoor and outdoor use is permitted for equipment controlled by an automated frequency controller (AFC) designed to prevent unlicensed equipment from operating where they could cause interference to incumbent users. Low power devices do not require the use of an AFC and are allowed for indoor use only.

Southern Company’s concerns relate to the low-power category. According to the company, testing shows that a single low-power device transmitting at power levels authorized by the commission in April would cause harmful interference to a licensed microwave link from as far as nine kilometers away.

The Southern Company letter also expresses concern about another category of unlicensed 6 GHz operation that the FCC has proposed but not yet adopted. If adopted, that category, known as very low power, would be allowed for indoor and outdoor use. But according to the Southern Company, a single very low power device transmitting at the proposed power level was found to cause harmful interference to a licensed microwave link from more than two kilometers away.

The FCC already has approved at least one device for unlicensed operation in the 6 GHz band, although an FCC press release about the first device approved – a transmitter from Broadcom — doesn’t indicate if the device is designed for low-power operation.

Southern Company in its letter urged the FCC to obtain some devices approved for unlicensed use for testing purposes.

If proven valid, the Southern Company’s concerns about very low power devices could derail plans to add that device category. The commission also had proposed to increase the allowed power level for low-power devices, which may now be a non-starter.

If the concerns about low-power devices operating at already approved power levels are proven valid, it’s unclear what the FCC might do to address them. Would devices be required to operate at lower power levels or to use an AFC? Could devices already manufactured be modified?

These are important issues to be explored as the FCC gets set to meet its statutory responsibility to conduct 6 GHz testing and report the results to Congress.

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