Explore automatic frequency coordination (AFC) technology for Wi-Fi 6GHz field

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Explore automatic frequency coordination (AFC) technology for Wi-Fi 6GHz field

Posted Date: 2024-01-25

Wi-Fi 6E/7 tri-band technology will provide an additional 1200MHz of bandwidth, opening the door to gateways achieving gigabit speeds. However, this additional bandwidth also requires some additional coexistence techniques to operate in certain environments. In the 6GHz band, licensed fixed-line networks, public operators, as well as local television transmission, broadcast auxiliary and cable television retransmission services are also within the same bandwidth, so some higher-level spectrum coexistence measures need to be taken.

Below, we’ll explore the impact of this situation and how the FCC can pass resolutions to help ensure that Wi-Fi can coexist fairly and consistently with other licensed and unlicensed radios.

Existing licensed operators in the 6GHz band

As shown in the figure below, several "players" currently in the 6GHz band include fixed wireless, fixed satellite and mobile operators. To operate in this band, these existing users have paid license fees. Therefore, the FCC must take steps to protect their investments. Wi-Fi 6E and Wi-Fi 7 cover the entire UNII-5 to UNII-8 spectrum; therefore, there are requirements that need to be met to ensure coexistence in areas where existing radio signals are present; this is where Automatic Frequency Coordination (AFC) comes into play field.

To protect existing network operators in the 6GHz band, unlicensed devices and any outdoor devices exceeding the power levels specified in Low Power Indoor (LPI) can only access the spectrum under the control of the AFC system. This will help reduce interference to existing services and increase needed spectrum for unlicensed innovative applications.

FCC and 6GHz band regulations

In April 2020, the FCC unanimously voted to adopt new rules for wireless operation in the 6GHz band, opening the 1200MHz spectrum to unlicensed devices such as Wi-Fi access points (APs). This decision triples the available bandwidth of Wi-Fi, bringing more spectrum for backhaul, gaming, and for scenarios such as higher data capacity, outdoor mesh networks, and dense outdoor deployments.

The opening of the 6GHz band means that indoor and outdoor Wi-Fi access points (APs) can enjoy high data rate video streaming at home and in places such as open-air stadiums, parking lots, and outdoor cafes.

LPI mode APs intended for indoor operation will take into account the certain attenuation of the device signal caused by building walls during operation to ensure that there is no interference with existing licensed equipment. In addition, the FCC has defined a standard power AFC control mode that can be authorized for indoor and outdoor operation. For unlicensed indoor low-power access points, this provision provides the opportunity to expand capacity and performance for channels up to 320MHz.

The FCC's regulations authorize two categories of unlicensed operation in the 6GHz band, as shown in the table below. The first category of devices will be standard power access points using automatic frequency coordination (AFC) in the UNII-5 and UNII-7 bands; this will allow the use of unlicensed broadband in the 5GHz and 6GHz bands. The AFC will mitigate potential disruption to existing fixed and mobile licensed service providers. Standard power APs must interact with the AFC system before they can start operating in the 6GHz band. We will discuss this in detail later in this article.

The power level used by client devices depends on the type of access point - either standard power or LPI AP-specified power. Its maximum power level depends on the location of use. When the client device is controlled by a standard power AP, it will be very close to the access point; and when transmitting, it can only use the AFC system to determine the frequency that will not cause interference to the fixed microwave link.

Both provisions will optimize unlicensed Wi-Fi access to the 6GHz spectrum while protecting existing services.

Detailed explanation of automatic frequency coordination (AFC) process system

The FCC regulates interstate and international communications across the United States through radio, television, cable and satellite, and is responsible for enforcing and enforcing all communications laws and regulations. Fixed microwave systems are already required to register with the FCC - noting their location and antenna height. This information can be obtained through the AFC system.

The AFC system will establish restricted areas to prohibit the operation of non-permitted equipment. For example, before the AP starts transmission, a standard power AP needs to obtain a list of frequencies that are allowed or prohibited from transmission from the AFC system. As a result, the AFC system will bring protection to fixed service microwave links. (See below)

The AFC system will help manage and eliminate any possible interference between APs and fixed and mobile microwave infrastructure systems; it will also protect frequencies used by certain radio astronomy observatories. AFC's understanding of microwave links is based on the Universal Licensing System (ULS) database shown above. It serves as an existing database for licensed microwave links in the UNII-5 and UNII-7 bands and is the official licensing database for microwave links in these bands. It contains extensive technical data based on site licenses, such as transmitter and receiver locations, frequencies, bandwidths , polarization, transmitter EIRP, antenna height, and make and model of antennas and equipment used.

AFC synchronizes with the ULS database daily. According to FCC regulations, APs need to log in to the AFC system every day to confirm that there are no fixed microwave clients - thereby eliminating any wireless signal interference.

After connecting to the AFC system, the AP device will determine the Wi-Fi channel suitable for the AP based on the interference model that may be generated by the AP. It will then calculate the no-go zones where an AP can interfere with existing fixed microwave systems; this calculation requires the AP's location and antenna height.

Impact of FCC regulations on engineers

To fully utilize the 6GHz spectrum, engineers must adopt some best practices to ensure a pleasant user experience while meeting FCC requirements.

First, devices intended for indoor use should ideally operate in standard and low-power modes. Ideally, the device would default to LPI mode when interference issues arise.

For outdoor equipment, engineers must be aware that their AP products will be subject to FCC rules - requiring AFC system functionality and compliance. Therefore, development engineers designing products for outdoor APs must consider the system requirements, thermal considerations, and environmental conditions of the AFC while meeting standard power regulations.

For example, a high-power standard power AP device will generate more heat than a device operating in low transmission level LPI mode. Therefore, when designing devices that support standard power AFC, more power efficient AP components are required.

To this end, engineers would be wise to adopt components used in standard power AP units based on more efficient semiconductor processes, as well as high-performance filters that can increase power while controlling heat and generate more efficient RF signals. This will help improve the performance of the AP, thereby reducing heat generation.

Looking ahead to new opportunities

It is true that moving up to the 6GHz frequency range brings greater data flow capacity and a better user experience, but this bandwidth space is already used by others. The FCC is aware of this and is working with users, system developers and standards organizations to ensure compliance for all wireless users. Their solution is to leverage the AFC system to ensure licensed service providers in the space maintain their service levels, while allowing other unlicensed providers to gain access to spectrum capacity.

Although AFC currently applies strictly to the FCC's regulatory region, which is the United States, it may be expanded to other regions; especially those with similar frequency license ranges. One of the limiting factors is that countries must maintain lists of mature licensed technologies and their corresponding power levels and locations - currently still a limiting factor outside the United States.

Currently, engineers focused on taking advantage of the 6GHz spectrum can use the AFC system established by the FCC in device design to create a new experience for American consumers. Therefore, by adopting AFC, engineers can expand the scope of their Wi-Fi products in the UNII-5 and UNII-7 6GHz bands in regulated areas, ultimately avoiding interference to existing users of this band. This system will enable wireless engineers in licensed and unlicensed services to work closely together to develop new applications of the future.

About the author

David Schnauzer
Technical Marketing Communications Manager
David serves as the voice of Qorvo Applications Engineers, providing technical insights on RF trends and tips to help RF engineers solve complex design problems.

Jeremy Foland
Senior Product Marketing Manager, Wireless Connectivity
Jeremy focuses on Wi-Fi; he has been working in the field of wired and wireless networks since 2007 and has witnessed the development and prosperity of the industry. Today, he has a direct impact on the development of Wi-Fi technology, both through his achievements in expanding Qorvo's product portfolio and in his role as the company's liaison to the Wi-Fi Alliance.

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