U-NII band - how to use

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  • Updated 2 years ago
Hello experts

I want to discuss the use of U-NII bands in de 5Ghz spectrum. Every body knows that using the 5Ghz bands are less crowded then the 2.4Ghz ISM spectrum and that there are more channels on this spectrum. However, I see a lot of configs only using U-NII 1 band in an indoor environment. Doesn't this mean that there are only 4 available channels? And what if this is configured in combination with 40 Mhz channels?
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Hans Matthé

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Posted 2 years ago

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Roberto Casula, Champ

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The benefits of 5GHz over 2GHz, even when just limited to the four U-NII-1 channels are more than just being "less crowded".

First of all, the channels do not overlap, so you do not have the situation where neighbouring wireless networks may select a partially overlapping channel, causing nasty cross-channel interference. Plus you have four channels available rather than three, which is an immediate benefit (a four-channel model on 2.4GHz in countries where channels 12 and 13 are available is not a good idea generally except in very specific situations in a green-field site with no neighbouring wireless systems).

In addition, there are far fewer sources of non-WiFi interference in the 5GHz spectrum so we typically get lower error rates.

In many environments, you can even run 40MHz channels successfully even with just the four U-NII-1 channels.

As for the reasons why we often limit ourselves to the U-NNI-1 channels in an indoor environment, this can be for a few reasons:

1. In many environments, we get DFS triggering channel changes. Over the years, the regulatory requirements for the DFS trigger sensitivity have increased to the point where now many environments see dozens of channel changes every day across many channels. Because the AP has to switch to a random channel, it is very common to end up with multiple adjacent APs on the same channel at the end of the day.
2. Certain devices, especially VoWLAN handsets, may take longer to roam when the whole 5GHz band is used, as they have to scan so many channels. Roaming time can be improved in many environments by limiting the number of channels in use and configuring the handset only to scan those channels. Again, due to DFS, this can be a problem if anything other than U-NNI-1 channels are used (though if you have external APs as part of the environment, then there is no choice).