Wifi deployment considerations

First, I've got to get an old movie reference out of my system because it will be relevant to an incorrect line of thinking in deploying WAPs (wireless access points).

Anyone who has seen the movie "Spinal Tap" should be familiar with the term "Up to eleven".  If not, I highly recommend the movie and question your geek-ness.

Anyway, when deploying WAPs you might think to yourself, "If this WAP goes up to 5 mW why wouldn't I want to set it to the maximum power?".  Anyone who ever watched Home Improvement knows that you always want "More Power!", right?  WRONG!

In order to communicate you've got two objects be they people, WiFi devices, fish, or whatever.  SO... in our example we'll say that we've got two people standing on either part of a football field.  Bob represents a WAP that is turned to 5mW and he'll be yelling at the top of his lungs.  Chad represents a smartphone or some other relatively low powered device and he'll be whispering to represent that.  Now Chad has no problem hearing Bob... in terms of signal strength he'd show full bars for connectivity because the signal strength is so strong.  However, when Chad tries to communicate back to Bob via whispering, Bob can't even see Chad's lips moving let alone hear what he is saying.  Both sides have to be able to hear and respond to each other to equal "Communication" and that just isn't happening.

SO... in this case Less truly is More.  In a vendor class the instructor used the phrase "Use only the power you need and not a milliwatt more" and that is absolutely accurate.  It is actually better to dial down the WAP to use power roughly equivalent to what the wireless devices can respond with.

The next point I bring up is whether to use 2.4GHz or 5Ghz.  In layman terms I'll explain it simply that the lower the GHz the further the signal goes which again kinda goes against the whole "MORE IS BETTER" theme.  However, that is really the ONLY advantage to 2.4GHz.  Now I'll list a couple of disadvantages.

  1. Three Channels in 2.4GHz - Yep, despite what you may have heard about hybrid channels there really are only 3 channels and each channel can only handle a certain load.  Every device on that channel adds to the channel's duty cycle.  Guess what, pretty much every Internet Service Provider gives their customers a 2.4GHz router.  If you are in a crowded environment with a lot of independent 2.4GHz WAPs you are looking at severe interference.  5Ghz has 23 non-overlapping channels so it is MUCH easier to find a channel that nobody else in range of interference is using.

  2. Microwaves - If you turn on a spectrum analyzer and then pop on a microwave you'll see that a good old microwave oven basically takes over the 2.4GHz spectrum.  If you are lucky you'll just see a severe slowdown of your WiFi network.  Microwaves don't even touch the 5Ghz spectrum.  Notice that most cordless phones now use 5Ghz?  Now you know why.

So, the two take aways from this blog are:

  1. Only the power you need and not a milliwatt more.

  2. 5Ghz is much better than 2.4GHz.