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Harnessing The Power Of 5GHz

By Albert Colas in · Technology · July 13, 2017
This is the first of many posts explaining dual 5GHz access points and software defined radios - how this technology works and what the capacity and performance benefits are.

Wireless LAN design has evolved drastically over the years. In the early years of 802.11 technology, WLAN design was strictly for coverage.

But as we all know, times have changed due to the big increase in the WLAN client population of mobile devices, IoT and BYOD devices. This explosion of Wi-Fi client devices, combined with new features and enhanced 802.11 technologies, has forced us to rethink about how we design WLANs. Video: Dual 5GHz Wi-Fi Designs Explained

The challenge with spectrum

Designing for client-device capacity or airtime consumption has now become the norm.

We know that proper channel reuse design, lower power settings, disabling lower data rates, short guard interval, and other settings is just the beginning when planning for a high-density or very-high-density WLAN design.

Due to this design change, access points are getting closer and closer to each other, therefore co-channel interference in 2.4GHz is much worse than before when we used to plan for coverage-oriented wireless networks.

Also, when designing wireless networks in metropolitan areas and high-rise buildings - especially in cities like San Francisco, New York, and Chicago -  2.4GHz can become quite challenging or virtually unusable. 

These two uses cases are some of the best examples for dual 5GHz access points (which I will discuss in great detail later in this post and in subsequent posts).

Additionally, nowadays most of the client devices, and especially all the new ones are 5GHz-capable and smart enough to prefer the 5GHz band. When they see an SSID that is being broadcasted in both 2.4GHz and 5GHz, they prefer the 5GHz and therefore connect to 5GHz.

Solving the spectrum challenge

  • Let’s say that we have multiple access points in your network, and they experiencing performance issues on 2.4GHz. 
  • What if we could switch that 2.4GHz radio to a 5GHz radio?

A 2.4GHz signal travels farther than a 5GHz signal, and the number of non-overlapping channels is much higher in 5GHz. Wi-Fi engineers and architects know that a good wireless design will still provide some 2.4GHz coverage for IoT and legacy devices, but most of the time, especially with high-density and very high-density deployments, the majority of 2.4GHz radios need to be disabled since the APs get closer and closer to each other in order to support those density requirements and we still need to reduce CCI, channel utilization, and medium contention.

With that in mind, when we are designing a wireless network for a customer, we want to have the most optimal use of the radios, mixing the right number of dual band (2.4GHz/5GHz) and dual 5GHz (5GHz/5GHz) APs, with a goal of providing the best of coverage and also capacity.

At the same time, we want to avoid unused radios.

Addressing this issue, Aerohive AP250 and AP550 access points offer dual 5GHz capabilities. One radio (WiFi0) is fixed at 5GHz and the other one (WiFi1) is software defined or configurable either in 2.4GHz or 5GHz.

This allows you to combine the right mix of radios in order to find the best experience.

Please note that the AP250 is a 3x3:3 802.11ac wave 2 access point with the WiFi1 radio being wave 2 and WiFi0 radio wave 1. The AP550 is a 4x4:4 802.11ac wave 2 with both radios WiFi0 and WiFi1 being wave 2.

Accordingly, here is how to configure these access points.

First of all, we need to log in to our Hivemanager NG account and go to the Monitor page. Then click on the AP hostname:

Secondly, we will click on “Interface Settings” and will select if we want to have the WiFi0 radio on that AP operate in 2.4GHz or in 5GHz:

Once that has been defined, we can associate the proper radio profile and click “Save” at the bottom of the page. We can use the default radio profile “radio_ng_ac0” but if we want to have a different one applied, it can be configured in the Configuration menu, under “Common Objects” and “Radio Profiles” as seen below:

In case a custom radio profile is required, this should be configured before changing the Radio Operating Mode to be able to select it from the drop-down menu. Click “Add” to configure the custom radio profile and define all the required settings:

Please keep in mind that radio WiFi1 will be fixed at 5GHz.

Finally, we just need to upload the configuration to the access point(s). To do so, we need to checkbox the modified AP, and click on Update Devices. It is recommended to push a complete configuration update if possible:


The flexibility of Software Define Radios

Another option: What if you do not want to manually configure and set the radio in one band (either in 2.4GHz or 5GHz)? Use Software Defined Radio (SDR) option! If the radio is manually defined, it will always function in the same band. But if we use SDR, this will allow the access points that support this feature to automatically and dynamically choose the best frequency band.

We will talk more about SDR in a future blog.

In the meantime, here are some recommendations when designing for 5GHz only and dual 5GHz APs:

1) Keep the channel width to 20MHz, or maximum 40MHz if using DFS for adequate channel reuse. Also, when bonding channels results in an increase of approximately 3 dB of noise floor, therefore data rates could be lower, CCI increased and performance affected.

2) With low maximum transmit power (never using max power – 20 dBm), in this case we could start with maximum transmit power set between 9-12 dBm (depending on the deployment) so Aerohive Channel Selection Protocol (ACSP) could be used to lower transmit power down if needed. The goal behind that is that we do not want power mismatch and asymmetric communication between APs and clients, reduce co-channel interface (CCI), avoid capacity problems, hidden node and very important: sticky clients.

3) Enable Dynamic Frequency Selection (DFS) channels to take advantage of the available spectrum and knowing that almost all client devices support it. The strategy would be to have every AP with one radio on a non-DFS channel and the other on a DFS channel.

4) Transmit Power Control (TPC) could be enabled and tested first in defined areas since clients could then adjust their power to match the AP’s Tx Power and help reduce interference caused by clients. Then, after confirming it, this could be deployed campus-wide. I have seen a big number of clients having issues when TPC is enabled because of legacy clients.

5) In case it is required to deploy some 2.4GHz radios for guest access and legacy devices, completely disable 802.11b data rates, with a basic data rate in 2.4GHz of 12Mbps to be conservative first, then we could be more aggressive after deployment. For 5GHz, disable the OFDM rates for 6Mbps and 9 Mbps conservatively first, and would consider disabling 12Mbps and 18Mbps after evaluating the environment and performance. That would help with airtime and channel utilization and take advantage of high data rates.

6) A high percentage of the APs should be configured with dual 5GHz radio, with a small percentage of them dual band 2.4GHz/5GHz if needed throughout the building(s) in order to still let legacy and guest devices connect.

7) We want to maximize the user experience so we want to configure radio load balance between both 5GHz radios, enable short guard interval, and several other radio settings.

It is always recommended from my perspective to do a predictive-site survey, then an AP on a stick to verify the environment and confirm the validity of the predictive site survey. And finally, do a post-deployment site survey. Then we can fine tune all the settings.

Below we can see a quick example for K-12 when an AP per classroom is required using predictive site survey design where best-effort is provided outside the classrooms and best-experience in the classrooms:

In the United States, 2.4GHz has 3 non-overlapping channels whereas 5GHz has 25 if we take DFS into consideration (9 without DFS) and 20MHz channels. Also, in 5GHz we can take advantage of 802.11ac, with denser modulation schemes, wider channels, more spatial streams and higher data rates. 

The ROI on Dual 5GHz APs

SDR access points such as the Aerohive AP250 and AP550 have a better ROI than fixed-radio access points since there is no need to turn off radios. Also, for high density and very high density deployments, 5GHz is the frequency we want to use specially since access points are closer to each other, as well as clients.

2.4GHz is becoming a best-effort frequency band, and when renewing client infrastructure - especially devices such as laptops, smartphones, and tablets - we should guide organizations and make sure they support the 5GHz band where we can provide the required capacity. 

2.4GHz has proven to be very problematic all the time. So spectrum analysis is key to information such as amplitude, channel utilization, and duty cycle, and helps us locate possible interferences. Even today, most APs are fixed-band, where one radio is locked at 2.4GHz and the other one at 5GHz. However, Aerohive has already taken steps to innovate with SDR Access Points

The future is SDR, and with software defined radios we can have the flexibility to create a design that fits the needs of each environment while reducing congestion challenges.

Albert Colas Prunera is a Systems Engineer for US and LATAM. He has been working in the Tech industry for over 9 years, starting his career in Barcelona, Spain and moving to the United States in May 2012. His knowledge includes Networking (Routing and Switching), Wireless, Security (including endpoint protection), Servers and Systems, Unified Communications (VoIP, Video and Mobility) and Virtualization. In his spare time Albert enjoys spending time with friends and family, being outdoors, biking, hiking and travelling all over the world.