June 09, 2020 | InBrief

Impact of FCC’s unlicensed 6 GHz ruling

While many applauded the FCC’s ruling on the 6 GHz spectrum, utilities face obstacles that require action to avoid interference with wireless communication

The FCC unanimously approved a ruling on April 23 that opens the 6 GHz spectrum for unlicensed devices. Although many applauded the decision as an opportunity to expand consumer products with the new WiFi 6 spectrum, utilities and other critical infrastructure industries (CII) are concerned about the possible interference this might cause to their existing wireless communication links. 

Utility communications

Utilities and other CII rely on wireless and wireline communications systems to provide monitoring and protection of critical utility assets, including substations, transmission and distribution power lines, and generation stations. Utilities depend on wireless communications to support the continued operations and monitoring of their assets in remote areas where traditional wireline communications systems (copper, fiber) aren’t feasible.  

Utilities frequently use 6 GHz licensed fixed wireless communications for critical communications with remote facilities. 6 GHz spectrum provides superior RF propagation, throughput, rain fade, and overall link distance when compared to the other licensed frequencies available. It is estimated that there are approximately 97,0001 fixed wireless links in operation across all users of the U-NII-5 and U-NII-76 GHz sub-bands.

Unlicensed usage in the 6 GHz spectrum 

Before the ruling opened all 1,200 MHz of the 6 GHz spectrum for unlicensed use of low power indoor WiFi, the FCC limited WiFi users to operate in only the 2.4 GHz and 5 GHz bands, with only about 580 MHz of spectrum available. Opening the 6 GHz spectrum to unlicensed frequencies allows new WiFi devices to operate with lower latency and increased bandwidth when compared with previous WiFi technologies.   

In addition to allowing low-power indoor unlicensed devices across the entire 6 GHz band, the FCC ruling allows standard-power unlicensed devices to use 850 MHz of the 6 GHz spectrum (U-NII-5 and U-NII-7) under the control of an AFC. The AFC is intended to protect incumbent licensed users by using the license data in FCC’s Universal Licensing System (ULS) to calculate exclusion zones in which unlicensed standard-power devices are not permitted to operate.  

Challenges to utilities 

Utilities have deployed licensed fixed wireless links in the 6 GHz band with the expectation that they will not encounter interference in their licensed band and the ruling requires the use of an AFC. Similar to the Spectrum Allocation System (SAS) in the CBRS bands, an AFC appears to be an appropriate mechanism to prevent interference if designed and implemented properly. That said, there are significant challenges with the current AFC specifications. To understand these challenges, consider what an AFC system must do:

  1. Know the geolocations of all devices in the band 
  2. Know the transmit and receive frequencies of the devices 
  3. Know the power, height, and possibly direction of the antennas 
  4. Calculate the interference for a given receiver based on these parameters 
  5. Inform the potential transmitter(s) with clearance to transmit at a given frequency  
  6. Contact an AFC system every 24 hours for frequency confirmation/adjustments to avoid interference with licensed devices

There are several challenges with the currently defined AFC:

  1. While there is a limit on the amount of interference allowed for a given receiver by a given transmitter, there is no clear definition on what constitutes “harmful interference”  
  2. There is no consensus on how to calculate the amount of expected interference because of the various propagation models used; these prevent a clear way to determine how much is too much for a given receiver 
  3. Multiple AFC system operators are allowed and though each uses the ULS as the single source for license holder information, there are no requirements for synchronization between AFC operators other than they must update their database every 24 hours 
  4. A given AFC system need not determine the total potential interference on that same licensed receiver by multiple sources across its own list of unlicensed transmitters 
  5. There is no clearly defined method of remediation should a utility or other CII incumbent encounter interference from unlicensed standard power device
  6. Low power indoor devices are exempt from AFC control and could create interference especially in more urban/dense environments

Next Steps 

With the new rules set to take effect July 27, utilities and other CII incumbents have several immediate actions they can take to help identify and protect their links from unlicensed interference: 

  • Validate the information on their current licensed link information in the ULS. Verifying that licenses are accurate (geolocation, antenna height, power, azimuth) and valid in the ULS is a fundamental step to avoid interference.  
  • Start planning now for any new licensed 6 GHz links and apply for the licenses as soon as possible. The AFC is required to consider new license applications when allocating unlicensed spectrum to the standard power access points, even if the license is not fully approved.  
  • Begin developing performance baselines for each of their existing 6 GHz links as a way to identify interference caused by other 6 GHz devices.

The ruling also presents utilities with an opportunity to evaluate alternate communication technologies to connect critical assets. Moving to another microwave band or transitioning toward fiber communications are also options, but each has capital and operational impacts that must be fully evaluated via a cost-benefit analysis.

Summary 

While the FCC’s ruling can be seen as an obvious boon for the unlicensed indoor low power consumer market ecosystem and end consumer, there are still several questions and challenges to address before the unlicensed standard power devices can be released into full production. Utilities can act now to prepare to address the challenges within their control and begin to plan both short- and long-term strategies. Ultimately, the successful integration of unlicensed standard power 6 GHz devices and the existing licensed 6 GHz environment will depend the correct and appropriate implementation of an AFC. 

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