Top 5 actions a Licensed Microwave Operator should take in response to the new 6 GHz RLAN initiative (Wi-Fi 6E)
RLAN (Radio Local Area Network), a regulator’s technical term for Wi-Fi, got a new update in 2020, with FCC opening a 1,200 MHz of channel bandwidth between 5.925 GHz and 7.125 GHz. This operation of unlicensed devices across the current 6 GHz band enables the next generation of wireless broadband called Wi-Fi 6E.
The 6 GHz band consists of a lower 6 Ghz sub-band (5.925-6.425 GHz) and an upper sub-band (6.525-6.875 GHz), which are utilized by North American Public Safety and Utility entities because of the higher reliability properties in rainy conditions. Both L6 and U6 bands are strictly regulated by a licensing process which involves a thorough interference analysis, before issuing a frequency to a new link. The interference study uses specialized interference tools, to ensure new links do not interfere with existing links in the region. The analysis considers all existing links at a site, the individual and cumulative components or spectral energy from these sites and then recommends the optimal frequency configuration. This can include variables like the operational frequency, the power of the radio and also sometimes recommends narrow-band antennas, that limit leaked emitted power outside the intended antenna direction. This process is crucial to the utilization of 6 GHz and left uncontrolled, it would degrade receive threshold of the existing licensed links, which in turn, will degrade the fade margin of the path and result in poor performance of the link. Poor performance for mission critical links which carry the nation’s most important traffic, can be disastrous. The fade margin is the difference between receive level in a normal day and the receive threshold level of the radio, and fade margin is a key parameter in determining the reliability of the path ( i.e., 99.999% or 99.9999% reliability). All public safety and utility microwave paths are designed for very high reliability to ensure communication, control and data traffic between first responders or substations site can be relayed and delivered without any issues.
6 GHz RLAN differentiates between Wi-Fi 6E outdoor and indoor uses. For the latter, users have access to the whole 1,200 MHz, via four new UNII bands (UNII5 – UNII8) and are limited to 30 dBm EIRP power. For outdoor, users are limited to the U-NII-5 (L6 sub-band) and U-NII-7(part of the U6 sub-band) bands. These new UNII bands traverse the same frequencies used by licensed Public safety and Utility links and for the outdoor device category, RLAN devices can operate up to 36 dBm of EIRP for the access point, and up to 30 dBm for a client. In terms of actual output power of the device, this translates to 30 dBm per RLAN AP, which is the equivalent of a high power microwave radio. These power levels will not only increase the noise floor in a region but also have a strong potential to cause interference to licensed microwave links.
Outdoor access points are required to connect to an AFC (Automated Frequency Control) system, which will create exclusion zones around MW paths and manage the frequency assignments and power levels of the RLAN AP based on incumbent licensed 6 GHz entities in the exclusion zone. AFC decision will be based on the licensed path coordinates, antenna type, height, direction, etc. and the coordinates of the unlicensed access point and is written to mimic the current interference analysis used in the licensed 6 GHz band.
This approach, however, is flawed and incomplete for the following reasons:
- The most popular deployment configuration for outdoor access points are point-to-multi-point (PtMP), which radiates at full power in all directions. In environments where the deployments are adjacent to licensed microwave, interference from the PtMP radios has been picked up by the licensed radio antenna’s side-lobes. This is true interference that degrades the link’s fade margin.
- Outdoor clients that connect to an outdoor access point, are not required to connect to an AFC system, which can lead to undetected client devices roaming in the exclusion zone, and therefore diminishing the value of the AFC exclusion zone creation process.
- Additionally, the FCC did not take into consideration the aggregated effect of interference coming from different unlicensed users. Currently, AFC can allow multiple unlicensed access points to use the same channel, outside the exclusion zones because it does not measure the impact of the sum of these devices nor any associated client devices. The aggregated and cumulative power will cause an increased amount of interference seen by the licensed antenna.
- Indoor unlicensed radios are not required to register with an AFC service, which is problematic since these radios can exist in the exclusion zone of the licensed path without detection. Also, similar to how your home Wi-Fi signal can often be picked up outside of your house, energy from the indoor radio can leak outside causing interference.
- The FCC has not yet described the remediation process (to fix issues if and when they are discovered) – so we need to wait for more information.
Given the concerns around the deployment of Wi-Fi 6E and the issues surrounding the AFC and remediation processes, here are the top 5 actions a Licensed Microwave Operator should take to protect their links:
- Correct site coordinates and information as much as possible: The ULS database will be the basis of the AFC process for determining exclusion zones and RLAN configurations, but the ULS is also highly inaccurate and outdated. This means the FCC may allow Wi-Fi 6E APs to be coordinated near actual tower locations. Licensees will have zero protection from interference if their FCC data is incorrect, and that should be particularly troubling to critical infrastructure licensees.
- Use an automated path monitoring system: Using an automated path monitoring system would monitor the link 24×7, using the same methodologies used by an expert Microwave engineer. Aviat’s Frequency Assurance Software (FAS) was developed with this approach in mind and to automate the analysis process to flag cases of interference, and alarm the user to take steps towards identifying the interferer and stop it as quickly as possible. FAS will provide predictive and real-time status of the path relative to interference.
- Baseline the microwave path performance: Baselining RSL, SNR, SES, BER, Availability data, over an extended period of time, ahead of unlicensed access points deployment, will help with future remediation once those processes are defined. This baselining process should start right now to enable adequate data trending ahead of interference level trends.
- Use Paperless Chart recorder (PCR): Tracking the performance of the path, down to second-by-second performance, is essential to differentiate between an outage caused by interference vs. normal phenomenon experienced regularly by a microwave link. Utilizing just a 15 minute window of performance data can be subject to doubt when building a case against interference.
- Executive reporting: When facing an interference case, a formal report showing the link baseline level, and the interference trend will be needed to ensure awareness of the system reliability and to use for remediation. Executive reporting and dashboards are integrated tools within the Aviat FAS Expert System.
Bonus item: If you’re using an IRU 600v4, or an ODU 600v2 radio, you can use the spectrum analyzer to check for interference prior to link deployment or doing scheduled maintenance downtimes, without any external tools or devices.