My First Design Part 3 – ADDENDUM

I received some feedback on this post that I’d like to share. The idea behind this series of posts was to share my admittedly novice design process so that others could learn with me; and so, rather than edit the original post to fix errors, I’d like to call them out so others can see what I’m learning.

Here’s a quick recap of the coverage requirements set for this project:

CV-Reqs

Note that the channel overlap is set to a max of two APs at -86 dBm before the requirement is flagged as not being met. We’ll look at this later.

My signal strength heatmap settings were called into question:

SigStrLeg

Specifically, the fact that the grey edge ends at -73 dBm. What I had done was used the signal strength visualization to represent two metrics:

  1. Coverage I want – where the requirement is met, or anything above -67 dBm
  2. Coverage I don’t care about – where the requirement isn’t met, or anything below -67 dBm

Then I arbitrarily set -73 dBm as a threshold to indicate where the requirement wasn’t quite met, but wasn’t terrible overall. This was a poor choice on my part!

I had forgotten about something useful that I had learned in the ECSE course. The signal strength visualization can show us three useful metrics:

    1. Coverage I want – where the requirement is met, or anything above -67 dBm
    2. Coverage I DON’T WANT – where the requirement isn’t met, but the AP is still causing CCI on that channel, or -67 dBm to -86 dBm (-86 dBm to match the channel overlap requirement)
    3. Coverage I don’t care about – where the requirement isn’t met, and the AP signal should be low enough to not cause noticeable CCI; anything below -86 dBm

There’s an important distinction there!

Now this doesn’t change my design much. Let’s take a look with the heatmap coloring rules set to the appropriate “want/don’t want/don’t care” levels. Here again is the signal strength for the main floor showing the where the requirement is measured against the two strongest APs:

SS2-CCI86

and here is what it looked like before:

Main Floor - Signal Strength (2 Strongest APs)

Minor changes showing where CCI flows into the areas I had stopped caring about before hand. For reference, here is the signal heat map for the strongest one AP, with the “don’t want” levels set to go to -86 dBm:

SS1-CCI86.PNG

The real benefit of this though comes when we look at one AP at a time. Here I’m only looking at the coverage for a single AP. The green areas again indicate where our requirement is met, but look at all of that grey! These are areas where this AP is still heard above -86 dBm, meaning we can’t reuse that channel without causing CCI!

SS-OneAPCCI.PNG

Ok, so has there been any effect on my CCI metrics? Let’s take a look. In this heatmap, the “don’t want” signal strength level has been left at -67 to -86 dBm, but we’ve moved to the channel overlap visualization:

Main Floor - Channel Overlap

Looks the same! Phew! Let’s see what it’s telling us:

We’re still using the -86 dBm threshold as the point where we stop counting overlap as CCI, so here we have two APs on the 40 MHz channel covering channels 108 and 112, both heard above -86 dBm (-63 and -74 in this case).

Hopefully this helps to clear up some of the last post! Let me know if anyone has more questions or comments!

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