In this article, we want to show you some of the best practices we have collected over the Years when deploying a Wireless Network.
We will look at the channel deployment, roaming, smart steering, DFS, and DCS.
Considering 2.4GHz, the most common non-overlapping three-channel selection is 1, 6, and 11.
If we need four channels, we choose 1, 4, 7, 11, or 1, 5, 8, and 13 for the smallest overlapping range in frequency.
(Ch 12~13 is only available in some countries).
By default, 2.4GHz uses 20MHz Bandwidth.
If we have a low-density deployment, we can also consider a channel Bandwidth of 40MHz.
Why would we need to consider this?
If we enhance the channel Width, we cut down our non-overlapping channels.
For 2.4GHz, we are now sending in the space of 2 channels, for example, channels 1 and 2.
Here we need to remember that every other Channel interferes with its Neighboring channel, which can impact performance.
But sometimes, it is still better to go for the overlapping (20MHz) channels than using the default non-overlap channels since if multiple APs in the vicinity are using the same channel, we need to wait for the other APs to finish sending and receiving traffic before we can emit or receive a Signal.
As for 5GHz, we have way more non-overlapping channels.
This band has significantly more spectrum available, with each channel occupying its own 20 MHz non-overlapping slices.
This is where the topic of channel width gets interesting.
In general, 5GHz Bands are way less crowded anyways, whereas, in 2.4GHz, even the Microwave can create interference; the 5GHz Bands are mostly only susceptible to Radar (The so-called DFS Channels).
But still, we have to be wary about non-overlapping channels and interference!
Our colleagues over at Ekahau explain it very good:
Let’s say we have decided to use 80MHz channels for our deployment.
We just went from 25 non-overlapping channels down to 6.
This is not a problem for APs at opposite ends of the facility that cannot hear each other too loudly. Where problems begin is APs that are close to each other (hearing each other with at least 4dB above the noise floor, typically around -85 dBm or higher).
These APs and any STAs associated with them become part of the same cell, slowing everything down due to increased contention.
All STAs need to wait their turn to access the medium.
The other item to consider here is that every time you widen the channel (20MHz – 40MHz & 40MHz – 80MHz, etc.), you introduce an extra 3dB of noise to the channel.
That is effectively doubling the noise.
Simplifying this, you now have more noise and no gain in the signal.
This equates to a lower SNR (Signal-to-Noise Ratio), which will, in turn, force a lower MCS rate, shrinking your data rate and throughput and possibly negating the benefits of using channel aggregation entirely or even resulting in lower capacity vs. 20 MHz channels.
Coming back to the DFS channels:
Just because they are used by Radar (be it Weather or flight) doesn't mean we cannot use them.
Before deployment, we must ensure that there is no Radar in the vicinity.
If there is a Radar, we should avoid those.
If there was no information found on Radar in the proximity, we still could go for the DFS channels, but we must(!) use the DCS and DFS features.
What does this mean?
This means that the AP is constantly on the lookout for Radar Signals.
Once a Radar Signal is detected, it will shut off the 5GHz Radio and switch to a non-DFS channel before turning it back on again.
Please note that the AP will not go back to the DFS Frequency on its own afterward.
What is DFS?
If you like a more autonomous approach, you could use the DCS (Dynamic Channel Selection) feature on our Access Points.
Dynamic Channel Selection (DCS) allows a Wireless AP to monitor traffic and noise levels on the channel the AP is currently operating.
When DCS is enabled in active mode and traffic or noise levels exceed the configured DCS thresholds, an alarm is triggered, and an information log is generated. In addition, the AP ceases operating on the current channel, and ACS is employed to select an alternate channel for the AP to work on. DCS does not trigger channel changes on neighboring APs.
Now that we have taken care of the channel deployment, let's look at other options.
One thing, in particular, might be overlap with our own APs.
Especially if we want to use roaming, we need to check that we do not have too much overlap or the roaming won't work correctly.
This is done by adjusting the output power and the signal threshold.
Roaming Issues on professional wireless devices and how to get rid of them
For Nebula Access Points, we have a feature called Smart Steering:
Improving WiFi roaming on my Nebula Access Points?
If you still are experiencing issues with stability and performance, you might want to look at the Multicast Rate (if the AP has enough wireless coverage and signal).
Essentially, the multicast rate is the minimum speed that a wireless device must be able to communicate to connect to the AP.
So, the lower the multicast rate, the further away, or more accurately, the weaker the wireless signal is allowed to connect.
Therefore, turning up your multicast rate will decrease the range of your wireless network.
If you are experiencing your wireless devices constantly losing their wireless connections and restoring those connections automatically seconds later, check this setting.
It’s probably too high.
Go to Configuration > Object > AP profile > Radio. Edit the radio profile of 2.4 GHz in Show Advanced Settings: Multicast Settings.
In any case, it is highly recommended to do a Site Survey before any deployment:
WiFi Site Survey - WiFi coverage study on plan and audit on site
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