Wi-Fi in all its forms relies on good signal propagation. Signals are attenuated by various objects - it's not that well known, but trees are a particularly attenuating object - let's take a look!
External Wi-Fi need design, just as all Wi-Fi installations do. Trees and foliage are often overlooked though - and in this blog we'll investigate the effect they have on Wi-Fi signal propagation.
The Problem with Foliage and Wi-Fi
The problem is probably pretty obvious - we have a tree in the way.
This isn’t uncommon of course - many external areas have trees and foliage around them, and apart from cutting them back, there’s not a lot we can do to mitigate the issue.
You can (and should) include a caveat in any report and Wi-Fi Markup, where you think this could be an issue, so we’re covered.
As a side note, if you have a point-point wireless link, you need the bottom of the Fresnel zone (look it up, if you’re not sure what this is), to be clear of the highest obstruction - which is higher than you’d think.
The Effect on RF
We’ve got a closer view here of the side of the building:
As you can see there’s space in front of the building, but the tree and foliage is covering a fair bit.
The Wi-Fi signals will definitely propagate through the gaps, but you've also got to take into account how the foliage here will change over time - and the effect that future growth will have on the RF signals.
Let's take a look at some results..
Wi-Fi Predictive Design
First up, let's see how we expected the area to be covered. Ignore that other AP shown on the LHS - we're only looking at the one in the middle with the highlight around it.
The image below shows the predictive survey:
We can see we have a nice wide coverage pattern.
This is of course ignoring the foliage, but gives you an ideas that without an attenuation zone, you appear to have great coverage.
If you relied on this and failed to tell the customer there could be an issue, we could have a problem down the track.
The issue with all foliage is that it contains a lot of water - which is pretty good at attenuating RF signals.
When we survey the area though, we find out the actual results.
The image below shows the actual survey results:
We’re getting coverage right in front of the building now and a little to the right hand side.
The coverage is no longer omni-directional and is now pretty poor each side of the AP.
This is consistent with what you’d expect to see anywhere there is a lot of foliage.
Not all trees are evergreen
You arrive and do your survey - there’s no leaves on the tree and it all looks good. Few months later all the leaves have grown back and we have a major problem.
Keep your eyes open for how the environment could change over time!
Effect of Trees on Wi-Fi: Summary
When surveying external areas, you always have to take into account any obstructions.
The foliage and trees in particular are often overlooked, particularly if its autumn and they've dropped their leaves. It's a different story in the spring when the leaves re-emerge though!
There's no great answer to this problem though - we all like to see trees and foliage, so cutting it down it not the option. You can install APs in various locations to provide better coverage (or higher up to provide top-down coverage), but in the end might need to accept that external coverage sometimes has to be best effort.