By now everyone should have heard the news on 6 GHz and Wi-Fi 6E that was announced initially back in April of 2020. Customers have been deploying and turning up these networks on Wi-Fi 6E AP’s operating under LPI (Low Power Indoor) rules for many months now. LPI operating rules limit operations to Indoor only, and no external antenna’s, no weatherproof enclosures, and a limit on the power of 5 dBm /MHz PSD (Power Spectral Density). Like any new technology, there were many concerns about the new technology and its frequencies. Would it even be useful with the restricted power limits, or how will the propagation differ from 5 GHz (how far the signal goes). Would the power mismatch produce un-even 5 and 6 GHz cell sizes? In spite of all the initial concerns it turns out it is all quite useful– in an indoor carpeted office space it is very easy to deploy co-located 5/6 GHz cells and maintain even coverage for both. Indoor densification (capacity increases) of Wi-Fi requires relatively small (lower power) cells and for this – LPI has been perfect.
What is the SP operating Class in Wi-Fi 6E in the US?
The other operating class that the FCC had announced at the same time was Standard Power (SP) which came with a requirement that its operations be coordinated through an AFC or Automated Frequency Coordination service. This was required to prevent interference with incumbent users (legal license holders still using these frequencies) and protect their existing deployments. The AFC provides coordination so that Wi-Fi and other users can both operate without worry of interference. Wi-Fi 6E operating under Standard Power opens up several of the use cases that LPI cannot address. The SP operating class rules:
Indoor and Outdoor operations
Allows the use of external antenna’s
Allows more power with 23 dBm/MHz PSD and max AP EIRP of 36 dBm and Client max *EIRP of 30 dBm
Operations are limited to UNii-5 and UNii-7, with UNii 6 and 8 being protected for Incumbents
*EIRP = Equivalent Isotropic Radiated Power or radio geek for what comes out of the antennas.
For a deep dive and all the details please see FCC KDB 987594
Figure 1 Wi-Fi 6E FCC Operating spectrum by Class
Fast forward to 2024 – We now have all the pieces in place to finally operate Wi-Fi under the SP operating class rules including FCC approval. That’s a really good thing because the limitations of LPI are just fine for the majority of carpeted office space, it is lacking in some key corner cases that we will be covering here. Much has been written regarding AFC’s describing the what and how. This blog is focused on the why. For an excellent brief on what an AFC provides and how it does it see Automated Frequency Coordination (AFC) System, Connecting You to the Future by Federated Wireless, Cisco’s service partner.
Do I need Wi-Fi 6E SP and AFC?
Why would I, as a network architect, need or want to add this to my network infrastructure? It’s a good question. Do you “Need” SP Power and AFC? It’s an easy answer for outdoor plans, if you need to go outdoors you will need to operate equipment under the SP operating rules. The same can be said for Stadiums and large public venues where the distances to the users can be quite long and directional antennas are a must to direct the energy. But what about indoor SP? Is Higher Power or antennas something that is needed indoors, probably not in most modern carpeted enterprise spaces, but in each deployment, there are corner cases that matter, and Wi-Fi 6E SP brings some important tools you should consider and likely be happy to have in your toolkit. In all use cases, an AFC is absolutely required to operate Wi-Fi 6E in SP mode.
FCC SP operations allows higher power limits is the big tag, and this is important for many indoor scenarios. Think about a high ceiling indoors like atriums, warehouse spaces, auditoriums/theaters, stairwells and all those little one-off situations many organizations have somewhere. In today’s connected world users can’t afford to drop a video conference because they took the stairs to their next meeting. If the solution is for retail or logistics operations, then high ceiling and usually lower client density is part of most use cases. Deploying APs with 5&6 GHz combined coverage cells means tri-band radios and the 5&6 GHz cell coverage edges need to match for a good user experience (especially with Wi-Fi 7 and MLO on the way). Today with LPI rules deployed in indoor carpeted offices this is easily managed by increasing the power on 6 GHz 2-3 dB over the 5 GHz power to align the cell edges for 5&6GHz. Indoor office space typically deploys in higher density to provide capacity for a denser population of users. The average power levels at 5 GHz range between 8-12 dBm (or lower) on a network with an average AP density of 2K f2/185m2 or less and ceilings between 10 and 12 feet (2.5-3 meters).
With a high ceiling the clients will be further from the AP and higher power is needed to reach them at the floor. In 5 GHz, this is no problem with up to 27 dBm available. But 6 GHz beacons under Wi-Fi 6E LPI rules will always be limited to a max EIRP of 18 dBm. LPI rules state 5 dBm/MHz so at 40 MHz that’s 21 dBm and 80 MHz it will be 24 dBm and so on, in all cases though, 20 MHz is limited to 18 dBm in FCC LPI rules. The power increases we see for additional channels – apply to data only and are there to preserve the SNR that otherwise reduces by 3dB with every doubling. Management traffic i.e., beacons probe responses etc. and other broadcast traffic is always transmitted at 20 MHz. The edge of a 6 GHz LPI cell is 18 dBm and possibly won’t cover the same area as a 5 GHz cell if it’s operating at a higher power because of distance or height. In other words – to match the cell size of a 5 GHz cell at even 18 dBm would require 20-21 dBm in 6 GHz and that cannot be done with LPI US rules.
This is where SP operations comes to the rescue. SP allows a max EIRP of 36 dBm – in all channel configurations from 20 MHz to 160 MHz channel widths. This ability to use higher power in 20 MHz allows for a larger cell boundary and the possibility of continuing to provide even multiband coverage as the power level requirement goes up in 5 GHz. That same limitation of power on 20 MHz also gets relieved on the client side. A client device operating within a 20 MHz RSU also gets more power under SP rules it goes from 12 dBm max to 30 dBm. So indoor SP benefits both the Uplink and Downlink operations in a positive way that increases throughput and opens up design options not possible with LPI.
Regions with no SP operations like ETSI don’t have the same restrictions as the FCC does. The majority of the countries that have access limited to Unii-5 only also have a different PSD value which allows for a max EIRP of 23 dBm for all channel widths from 20-160 MHz in LPI. You still can’t use external antennas or operate outdoors though but those talks persist in ETSI.
What’s required to operate in SP mode?
Ok, so maybe you do need some Wi-Fi 6E SP mode to meet your design goals, what’s needed to get started? Two things that are required for AFC are
- An accurate location from a GNSS receiver permanently attached to the system – Note: you can enter geolocation coordinates manually – but these will not be considered for AFC request.
- access to the AFC which requires internet access to coordinate the channel plans.
The good news is that all Cisco Wireless indoor and outdoor Wi-Fi 6E capable APs including the C9136 and the MR57 are certified for SP operations already. The outdoor CW9163E, an outdoor AP with external antennas, can only be operated at 6 GHz under SP rules with an AFC connection. The CW9163E has an inbuilt GNSS radio to support this and can rely on the internal antenna, or us an external antenna if mounting restrictions require it. For the indoor AP’s, a USB connected GNSS module can be added. A GNSS signal can be difficult to get indoors, and the Cisco Wireless GNSS module supports an external antenna connection with a 10-meter cable length to help make finding a decent signal manageable. A good GNSS signal should be available from just inside of most window types with a decent view of the horizon.
At minimum at least one AP per switch stack must have a GNSS provided location. The remaining APs can calculate a derived geolocation based on the GNSS enabled APs measured location. A derived location can be established by either an AP Neighbor relationship (preferred, provides more accuracy and a lower area oof uncertainty in the results) or through CDP/LLDP on a switch/stack. Note that locations derived through connections on a switch stack automatically incur a 200-meter area of uncertainty.
Figure 2 Cisco GNSS Module for CW Wi-Fi 6E AP models
In addition to the geolocation requirements, enabling the AFC service is required to prepare the system to operate in SP mode. Cisco Wireless makes this transparent to the user by providing the service to your network. The AFC Service requires a connection to the internet to operate with the AFC provider.
At the time an AP is configured for SP operations it must meet the geolocation requirements using either measured (GNSS) or derived CDP or AP neighbor. Latitude and Longitude will be entered automatically, the antenna height above ground and cable length must be entered manually. Other details are already on file with the AFC and include model number, and details about the antenna type and gain characteristics. That’s it - after that the MR Dashboard or the C9800 wireless Lan controller sends a request to the AFC on behalf of the connecting device. AFC communications is managed automatically for the device as long as it is connected. Authorization from the AFC is required once every 24 hours. If the connection is lost, there is a 24-hour grace period from the last authorization time before operations would be impacted and an SP device would be suspended or return to LPI mode if possible.
Figure 3 Cisco C9800-l AFC Service Monitor
It is the job of the AFC to determine per geolocation the list of allowed channels, channel widths and maximum power limits allowed and ensure that the operation of Wi-Fi does not interfere with licensed incumbent operators. The AFC has no part in coordinating Wi-Fi 6E APs and prevent them from interfering with themselves. That remains the job of the systems radio resource management, and the allowed channels and maximums are directly consumed by them to be used in an interference-free assignment on your Wi-Fi network. Both RRM and AutoRF are fully compatible with AFC today.
Figure 4 AP's and their individual AFC Statuses
Although you may be tempted to turn on SP mode for a group of indoor APs because you can, keep in mind that it comes with a reduced spectrum set. Access will be lost to any channel or portion of a channel that crosses into Unii-6 or UNii-8.
Figure 5 Showing the response that the AP receives from the AFC
If SP Mode is enabled in the “normal” carpeted office defined above it probably won’t change things a whole lot. Nor would you want it to, if just one AP in the room raises its power higher than the rest of the APs, clients will start to join the loudest radio and the higher the power the more cells it will cover. The remaining AP’s will see little business and the really loud one will be getting a serious workout.
Summary
The introduction of SP mode and a working AFC to the Wi-Fi design tool set adds some very needed options for architects to maintain consistent client experience across their entire deployments with 6 GHz.
Today with just the LPI rules, it is not possible to operate in most stadiums and Large Public Venues because of either being outdoors, or due to very high ceiling heights (average 40 feet / 15 meters). In these environments dedicated directional antennas are generally required to maintain cell isolation and help the clients perform at distance.
The SP rules coming to market will ensure that these use cases get the benefits of this amazing new spectrum, today and well beyond the gains we will establish in Wi-Fi 7.
