About Automated Frequency Coordination (AFC) for 6 GHz Wi-Fi
What is the problem?
The use of 6 GHz spectrum is an ongoing and complex area of collaboration internationally, particularly as cellular mobile network operators and Wi-Fi vendors make their case for a share of the valuable spectrum.
Note: the Federal Communications Commission (FCC) defines the 6 GHz band as being from 5925 MHz to 7125 MHz per [1].
Using the United States as an example, a look at a graphical representation of the the FCC’s Table of Frequency Allocations shows many existing uses of the 5925–7125 MHz range sought for Wi-Fi use. Adding to the mix of users in 6 GHz spectrum are incumbent fixed services such as point-to-point microwave links (in the U-NII-5 and U-NII-7 bands) and incumbent mobile services such as the Broadcast Auxiliary Service and the Cable Television Relay Service (both in the U-NII-6 band) [2].
This might sound somewhat familiar to another co-channel operation issue in Wi-Fi: that of radar and its Dynamic Frequency Selection (DFS) fix. Dynamic Frequency Selection (DFS), from IEEE 802.11h-2003, performs a “listen-before-transmit” passive scan on a Wi-Fi access point operating in the U-NII-2C band (5470 MHz to 5725 MHz) to detect radar emissions. If such transmissions are discovered it will use a frequency not affected by radar to avoid co-channel operation with detected radar systems. DFS is a decentralized system, able to operate independent of any established deconfliction infrastructure.
What is solution?
To help address the 6 GHz spectrum management challenge, Wi-Fi vendors and other interested parities introduced Automated Frequency Coordination (AFC) in 2021. The intent of AFC is to management spectrum allocation such that Wi-Fi can be used via standard power access points and fixed client devices without interfering with other Wi-Fi stations or incumbent 6 GHz spectrum users. Standard power is up to 4 watts effective radiated power (EIRP) [3].
Just over a month ago via public notice DA-24–166, OET Announces Approval of Seven 6 GHz Band AFC Systems, the FCC approved 7 companies, Qualcomm, Federated Wireless, Sony, Comsearch, Wi-Fi Alliance, the Wireless Broadband Alliance, and Broadcom, to begin operating Automated Frequency Coordination systems in the U-NII-5 (5925–6425 MHz) and U-NII-7 (6525–6875 MHz) bands.
How does it work?
In August 2023, the Wi-Fi Alliance established a subsidiary, Wi-Fi Alliance Services, to provide AFC system access. Specific details on implementation are accessible via the Wi-Fi Alliance’s AFC Specification and Test Plans page but from the FCC AFC approval public notice we can infer the general operation. From DA-24–166, OET Announces Approval of Seven 6 GHz Band AFC Systems:
“The Internet-based test portal must permit the user to specify test locations anywhere within the United States and return a list of the frequency ranges on which a standard-power device at that location would be able to transmit and the corresponding maximum power level for each frequency range”
At a high-level, the access point needs to have access to an AFC system. Given the abundance of options with the initial 7 AFC system operators, this shouldn’t be an issue. With access to an AFC system the access point will need to know its location. While Wi-Fi location systems and services have been around for some time now, it seems that some access points will be using their own embedded global navigation satellite system (GNSS) receivers to get their location. For example, one commercial grade access point, the Gemtek Technology Co., Ltd. Wi-Fi 7 Router/AP W1701K (FCC ID MXF-W1700K), uses what (based on documentation (Internal Photos-1) submitted to the FCC) appears to be a Taoglas GPVSF.25.8.A.08 GNSS+IRNSS Stacked Patch Antenna.
With location available the access point will send a request to the AFC system for a response of acceptable frequencies and corresponding power levels for its location. The AFC system, having knowledge of other users of the spectrum, can factor in other variables such propagation based on location terrain.
To learn more about the Wi-Fi Alliance’s plans, visit their 6 GHz Wi-Fi Information Center.
References
[1] “FCC ADOPTS NEW RULES FOR THE 6 GHz BAND, UNLEASHING 1,200 MEGAHERTZ OF SPECTRUM FOR UNLICENSED USE Commission Provides a Boost to Wi-Fi and Other Unlicensed Uses While Protecting Incumbent Services in the Band.” https://docs.fcc.gov/public/attachments/DOC-363945A1.pdf.
[2] United States. Federal Communications Commission. FCC Record, Volume 35, №5, Pages 3492 to 4344, April 13 — April 24, 2020, book, April 2020; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc1754005/m1/374/?q=%226%20GHz%20Report%20and%20Order%22: accessed March 31, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.
[3] D. Wright, “The Global Race to Authorize Wi-Fi 6E Standard Power and AFC | Aruba Blogs,” blogs.arubanetworks.com, Sep. 08, 2022. https://blogs.arubanetworks.com/solutions/the-global-race-to-authorize-wi-fi-6e-standard-power-and-afc/.
