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EkaHOW? Ekahau 102: Creating a Predictive Survey

Predictive surveys are an essential part of any enterprise wireless deployment. By creating a predictive survey, engineers are able to predict crucial components of the build out process, such as total number of access points needed, any special installation construction requirements, and ensure a thoughtful design that will in turn create a satisfying end user experience.

We’ll start where we left off in Ekahau 101- with a completed, aligned floorplan:

My house, in the middle of my street.

From here, there are several key factors to contemplate while creating your design. First, is “can and should I put an access point here?” For example- keep your APs out of bathrooms for maintenance and device protection reasons. Showers will create condensation, which could negatively impact the longevity of your AP. It’s also good to keep them out of hallways, and place them in the areas they’ll be used. While that might seem counter intuitive, APs in hallways will have a tendency to saturate a hallway with signal since there is very little to attenuate the it, creating the possibility for interference. There’s an extremely well written article on the subject already, so if you’re curious, feel free to read more on it here. Also, try to keep access points out of mechanical spaces or areas that might not be maintenance friendly if possible. The best rule of thumb is “place the APs where the people are.”

So, let’s see what that looks like! For my design, I’ll be using EnGenius EWS357 access points, as they are the closest to the Ubiquiti UniFi 6 Lite APs that I will be implementing. From a hardware standpoint, both have 2×2 802.11ax radios capable of OFDMA and MU-MIMO, as well as similar max transmit power, so they should model fairly similarly. Not that we’ll be leaving the transmit power at max, but more on that later. To add an AP, select the Simulated Access Point button on the button bar, and pick the AP you’d like to model with using the drop down menu. Then place the AP in the desired location to begin your predictive survey.

Ok! So, now we have locations for our APs, and coverage is looking pretty good. However, you’ll notice that the APs are all on the same channels, which is bound to cause some headache. Feel free to check out this post if you skipped it to find out why. So let’s adjust the APs and create a channel plan to ensure we have minimal signal overlap. Ekahau has an auto-planner function, but that’s not exactly the best way to learn.

To adjust the AP Radio settings, select Access Points in the left pane, select the three dot icon on the AP you wish to edit, and click “Edit Access Point.”

Radio, Radio, Come in Radio

In this window, you can see that I’ve changed the channel for the 2nd radio to a 40Mhz wide channel on channel 40. I’ve also lowered the transmit power from 23dB to 20dB. It might not sound like a lot, but every 3dB indicates a *doubling* or *halving* of transmission power, so it’s actually a fairly substantial cut. I’ll dive into why TX (transmission) power is important in another post. There are other important fields here to note as well; from this menu, you can change the mounting style (vertical vs horizontal), add and modify external antennas, adjust the number of spatial streams and guard interval, and ceiling height. All of these adjustments combined can have a substantial impact on your design, so keep that in mind as you create them!

And here we have the design with a completed channel plan:

1000 channels and no overlap to watch…

The end result of the channel plan is no overlapping channels, and adequate signal in all areas. You’ll note that the selected AP has two radios transmitting on the 5GHz spectrum- this is because when viewing primary coverage on 2.4GHz, the coverage in the area is within our parameters, and we’ve run out of non-overlapping channels on the 2.4 band. It would be possible to put radio 1 on the selected access point to channel 6, since the nearest radio transmitting on that frequency is up one floor and through a stairwell, but given the coverage, it would be more beneficial to keep it on a non-interfering 5GHz channel.

To validate there is adequate 2.4GHz coverage in the basement, we’ll change our view to 2.4 only by clicking the 2.4 button on the view button bar:

The leftmost button changes your view to simulate a mobile device. This can be extremely handy, as not every device will have a wireless module with an antenna as powerful as one simulated in the default view. The arrow indicates whether you’re viewing the 2.4GHz or 5GHz spectrum, or both.

Using this view, we can successfully verify that we have adequate coverage for our design on the 2.4GHz spectrum.

No areas where users will be present are projected to have a 2.4GHz signal less than -65dB, which is a commonly accepted lowest acceptable signal strength for most designs.

While we’re verifying things, let’s take a look at some of the other more common views used to validate a design. Now, we know that there is no co-channel or adjacent channel interference, because we designed the channel plan ourselves, but let’s change the view to Channel Interference just for good measure.

I love it when a plan comes to fruition!

Great! No interference inherent in the design. This doesn’t mean that when we go to implement it, that we won’t run into the neighbors networks transmitting at full blast, but there are only so many variables we can account for without an active survey.

Next, let’s check for secondary coverage. This is coverage from other access points that will assist users when roaming from AP to AP, and ensure that the area remains covered in the event of an AP failure. Select “Secondary Signal Strength” from the view drop down menu, and you should see something similar to this:

Interesting- take a look at the green dot in the garage. Wonder what that could be from?
Answer: the upstairs APs! To see which APs can be heard in a given area, hover over the point you’d like info on, and an information box like the one above will tell you which APs are visible, and how strong the signal is. It looks like we might have to go back and lower the transmit power on an access point or two, but we’ll leave that for another post.

Another important view is noise. If your radios are transmitting with too much power or are placed too closely to one another, or you happen to have a cafeteria full of microwaves running simultaneously, you could end up with a crowded spectrum. The post I referenced earlier is also relevant here, so just in case you’ve missed it, here it is again. So what does our noise look like?

Green with envy… or low noise floor levels. Both maybe, depending on your career. Under -90dBm is considered to be near-ideal noise levels. Granted, this measurement will very likely be different in the real world, but this shows us that our design isn’t creating excessive noise inherently.

And one last view- let’s see how coverage would look to a mobile device like a cell phone. Click on the icon shaped like a phone in the view menu area, and take a look at how that changes things:

Even mobile devices have adequate coverage, unless you’re in time out in the corner of the garage.
(Note to self: maybe I *do* need to put the garage back in scope…)

In summary- we’ve placed our APs, created a channel plan, modified the AP transmit power, verified our interference and noise floor levels, and validated primary, secondary, and mobile device coverage. With all these things considered, you now have a great starting point for a predictive survey!

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