The Fixed Wireless Communications Coalition (FWCC) says a study backed by the likes of Apple, Facebook, Google, Microsoft, Intel, Qualcomm and others is badly flawed and should not be relied upon to allow for an array of unlicensed devices in the 6 GHz band.
Earlier this year, representatives from Apple, Broadcom, Cisco Systems, Hewlett Packard Enterprise, Facebook, Google, Intel, MediaTek, Microsoft and Qualcomm met with FCC representatives where they presented a study (PDF), prepared by RKF Engineering Solutions, that analyzed sharing between unlicensed operations in the 6 GHz band and existing services.
The upshot: The study showed that unlicensed services can successfully coexist with the primary services present in the 6 GHz band.
And that’s about where the FWCC says it went off the rails. The FWCC’s analysis showed that the uncontrolled distribution of unlicensed devices—in the numbers and at the power levels RKF studied—would indeed cause widespread harmful interference to fixed microwave receivers.
“If our results are correct, it follows that RKF’s analysis went badly off the rails,” the coalition said in its March 13 filing (PDF). “Unfortunately, RKF’s report is convoluted and hard to read in ways that make its assumptions and methods impossible to reverse-engineer.”
The organization said that fixed microwave systems often carry time-critical information: synchronizing the movement of railroad trains, controlling petroleum and natural gas pipelines, maintaining balance in the electric grid, providing backhaul to dispatch public safety and emergency vehicles and connecting commercial centers to real-time financial and market data. Systems must be engineered to high reliability, typically 99.9999% (30 seconds of outage per year from all causes) or 99.999% (five minutes of outage per year).
The 6 GHz bands at issue, having about 90,000 links nationwide, are widely used for links that must span tens of miles, according to FWCC, and high reliability is an engineering challenge, especially over long links.
The FWCC is a coalition of companies, associations and individuals involved in terrestrial fixed microwave communications. Its website doesn’t list individual companies, but its filing says its membership includes manufacturers of microwave equipment, fixed microwave engineering firms, licensees of terrestrial fixed microwave systems and communications service providers. Membership also includes railroads, public utilities, petroleum and pipeline entities, public safety agencies, cable TV providers and backhaul providers.
The backers of the RKF study said the interests of incumbents must be protected, which is why they worked on a thorough engineering analysis to study the impact. They noted that RKF directly addressed concerns about individual unlicensed devices situated on high floors, at close range, through a window or other corner-case geometries that may pose an unacceptable risk to fixed service receivers; it concluded that these kinds of corner cases were extremely rare. Even when they occurred, their impact was small and in no case did the interference cause any fixed service link to fall below its availability design.
One of the big reasons for the high-tech interest in 6 GHz is its proximity. The 5.925-7.125 GHz band is adjacent to current unlicensed U-NII bands, meaning existing technologies designed for the 5 GHz band can be rapidly deployed. The technology manufacturers signing onto the 6 GHz sharing proposal said they are committed to delivering 6 GHz-capable products and services to the market in a timely manner.
Last year the FCC’s called for comments on expanding flexible use in mid-band spectrum between 3.7 and 24 GHz, including the 3.7-4.2 GHz, 5.925-6.425 GHz, and 6.425-7.125 GHz bands.