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Blog Post

Mar 02

WiFi and the Cinema Story


WiFi and the Cinema Story

I've touched on the subject of power caps in previous blogs. The issue is a reasonably simple one about not having an AP blasting at maximum power, while you have a low powered device broadcasting back. 

In explaining the principle of exactly why this doesn't work, I've come up with a little story to help. Let's translate WiFi in to audio. So here's the scenario.

Properly Designed WiFi

Imagine you're in a cinema. There's cracking Dolby surround sound, making the movie come alive with sound hitting you from all angles. The sound is crystal clear and has that great effect of having sound effects hit you from all sides.

This is just like a properly designed wireless network - you have equitable access to the sound from wherever you sit. If you walk around the Cinema (if you could without annoying everyone), you'd find the sound is just as good no matter where you sat.

 

 

The Minimalists Approach to WiFi Design

Back to WiFi for a minute - if you went for the 'minimalists' approach and decided to use as few APs as you couldd, you'd find that you would have to turn them all the way up. Let's explore in our Cinema setting what that would do.

You're sat in your seat enjoying the movie, thinking it would be nice if the sound were a little louder. Going for that walk around the cinema, you discover there's places that the sound is ok and places its really hard to hear. Speaking with the Cinema manager, he realises that the volume knob has been way down. Great! Let's just turn it up and that will solve the issue!

You return to your seat and the sound it just right now! The problem has been solved - how easy was that! No additional speakers, just turning them up has fixed it.

Walking around though you notice that there are areas of the cinema no one is sitting in. Going to those spots, you realise that you're right under a speaker and its ridiculously loud - no wonder no one wants to sit there.

What you've discovered is that to get a nice smooth sound experience you can't just turn the power right up on a few of the speakers, you need to add some more, so none of the speakers are too loud, but the sound is nice and even.

Think about your minimal number of APs running at full power - not only are they blasting out right under them, but clients will not roam easily, sticking to the AP they think is so good, even though they should have roamed.

The Poor WiFi Design Approach

So, the Cinema manager decided he was going to employ someone who knows nothing about speakers and sound to install his audio system. He figured that he can always fix it up later on.

When they arrived to do it, they figured that the shortest cable runs would be to install all the speakers on one wall. They're pretty directional, and with a bit of extra volume all good!

The people in the cinema didn't agree. The sound was terrible now with interference from all those speakers and the audio sounding like it was all over the place. The Dolby didn't work any more either - everything was coming from the left hand side, which didn't make sense when you look at the screen.

This is just the same in WiFi. If you're presented an Access Point layout where someone has placed them on a grid pattern (likely only up and down the corridors) they clearly haven't designed it with any modelling software to make the coverage even. Any location tracking isn't going to work and you will get dropout when clients are roaming.

 

The Conclusion: What you Should ask for when requesting a WLAN Survey

The conclusion is that if you want WiFi to work properly, you need to get a proper WLAN site survey. If you don't get asked these sort of questions, think twice about the people doing your designs:

  • What do you want to support on the network? Voice? Video? Biomedical? BYOD?
  • What devices do you want to support? What is the weakest transmitting device?
  • Have you got up to date floor plans we can use?
  • A site survey is used to confirm actual wall thickness - when can we attend site to do that?

If you've got phones dropping out and people complaining of poor coverage, you have probably already had the design done incorrectly.

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