Make a wall in Ekahau Site Survey

If you consider your self a WLAN designer, you're going to have to use a Site Survey tool and knowing how to construct walls in it will be the key to success. In this post I'll explain how to make a wall in Ekahau Site Survey software tool which as of this writing is on software version 7.6.2.

Ekahau Site Survey (ESS for short) comes predefined with a couple of walls but I'm yet to use any of them for a simple reason that no 2 walls are alike. This is due to the fact that walls in ESS are 3D modelled and any difference in thickens and/or attenuation value per meter will impact the result when modelling RF signal penetration through it.

To fully understand why this is important you can imagine an AP in front of a 10cm thick wall with some kind of attenuation level, for ex. 50dB/m. When a narrow beam of RF signal from the AP penetrates the wall perpendicularly i.e. hits the wall head on, it will loose a certain amount of energy while passing through those 10cm of wall material. But when another narrow beam of RF signal from the same AP hits the same wall at an angle, that distance traveled through the wall will be greater. If we take an example of 45° angle the distance traveled through the wall would be just over 14cm or 40% more than when the beam would hit it straight on.

So to compare the attenuation of the two beams:
- the head on beam would attenuate by 5dB
- the 45° beam would attenuate by 7dB.

Now if we were to use a predefined wall from ESS that would be for example 15cm instead of our 10cm with 50dB/m the following would be true:
- the head on beam would attenuate by 7,5dB (Δ of 2,5dB to the example above)
- the 45° beam would attenuate by 10,5dB (Δ of 3dB to the example above)

So it is important to get your measurements right in order to construct a proper wall in ESS and be able to make the right WLAN design for the building.


NOTE!
This post is only relevant if you are still using a version of ESS before v8. As of ESSv8 constructing a wall is made so much easier in the GUI. Ekahau indubitably made this change in response to this post. A fact which they will surely deny in public, but one that is true. OK, that last sentence is probably a fiction of my imagination, but that won't stop me from putting it in my CV.

Where to start?

To construct a wall you'll need to edit 2 files in your ESS installation directory. In the "/conf" directory you'll find various object types and properties files. That's where you'll also find the 2 files that you'll need to edit. These are "wallTypes.xml" that holds the actual data properties of a wall and the "wallTypes.properties" which is the key-to-name mapping file. The name in this file is the name that you'll see in ESS when selecting the wall button to draw the wall.

The "wallTypes.xml" file

The wallTypes.xml file consits of an xml schema. Each wall type is defined inside the <type> elements that house 4 other elements and a comment at the beginning. The comment here is especially useful in clearly explaining the properties of your wall and I suggest you use it too. The whole wall schema looks like the one below

<type id="wall_id">
        <!-- wall Xm YdB = Z dB/m -->
        <key>wall_key_mapping</key>
        <width>some width in meters</width>
        <absorption>attenuation per meter</absorption>
        <color>color HEX</color>
</type>

So you can just copy/paste one of the schemas and edit it. The elements inside the type element are pretty self explanatory but I'll go through them here:

• key is the element used to map the wall property to the name of your property in the "wallTypes.properties" file
• width is the actual width of the wall you are creating
• absorption is the amount of attenuation the wall presents
• color is the color you want it to appear in your ESS

I'm yet to understand what the id value in the type element is used for but you can make it the same as your key element just in case. 

The "wallTypes.properties" file

The key-to-name mappings file is pretty straight forward with lines of "key = name" mappings for each wall type that you make. Note here that ESS will add a dB attenuation value next to the name in brackets but not the width so I would suggest you name your wall with the width parameter, just so you'll know it. For example

my_key = My wall 10cm

and the wall will be visible like so

Don't forget to merge

There is one caveat of this feature. A new wall type will appear only for new projects you start after you have edited and saved both "wallTypes" files. For existing projects you have made before you edited those files you will need to use the File > Merge feature in order to be able to see the new wall in the drop down list of the wall. Then you can overwrite your previous project.

 

Final thoughts

Hopefully wall construction will become easier in the future as editing files is just not practical, plus there is a bug that appears whenever you make a change in an existing wall type ESS will show a duplicate of that wall in the GUI, but for now you know how to make a wall to fit the needs of the building you are planing the WLAN network for.