WiFi at Conferences Done Right

Posted: October 10th, 2009 | Author: | Filed under: Insight, Wireless | Tags: , , , | No Comments »

I hate, HATE, when I go into a conference, large meeting, campus, whatever and get a WiFi signal but my requests seem to go into the the database in the sky. Conferences are notorious for this. They pack a large group of people, into a small space with a single wireless access point for them all to share. Or worse, they place multiple access points in the conference hall, all with the same SSID, on the same channel and relatively close to each other. WiFi can support an extremely large amount of clients if setup properly. However you will need to take into account that as more and more people come into your network, they each create a signal with their laptop or phone and thus interference to other people around them.

First, cell phones, I do not mean WiFi enabled phones, no. I mean just standard cell phones that operate on either side of the WiFi 2.4GHz band. All those cell phones are creating interference at the beginning and end of the WiFi spectrum. With that in mind we first want to setup an access point in the middle of the spectrum, around channel 6. Most access points have a channel setting feature. However, as more clients join the network more noise will be placed into that little channel. Most people think that the WiFi access point is just overloaded and so they add another access point to the network. This will only ever make the problem worse. The problem is not bandwidth. Say it with me now: The problem is NOT bandwidth! The problem is the ‘signal to noise ratio.’

When Signal met Noise

The definition of signal to noise ratio is the ratio of noise power that is corrupting the signal power. A ratio higher than 1:1 indicates more signal than noise. You will notice that higher data rates like 54Mbps will drop off quickly the further you move away from the access point, a lot of people then try increasing the transmission power to allow the signal to travel further, but this just introduces more noise and thus the same SNR. The SNR dictates which data rates can be used in a wireless network. As data rates get higher, more complex methods are used for transmission and that requires much higher SNR to properly decode the signal back to the data stream on the receiving side.

Introducing Multiple Access Points

As I previously mentioned, you want to try and setup your access point around channel 6, for the sake of specificity let’s say channel 6. But once there are 25 people or so using this one channel it will be saturated and the SNR is going to go way down, thus reducing the data rates for you clients. Therefore adding another access point on this same channel is not answer, instead you want to add an access point on 2 channels away from 6, one at 4 and perhaps another at 8. Give them different SSID’s so clients can pick and choose which one to use, and name them based on the geography in which they lie. Name’s such “Access Point 1” are not a good idea, however a name like “South Wall AP” or “Stage Left AP” is. That way the user can figure out which AP is closest to them, thus ensuring maximum data rates.

Location, Location, Location

As previously mentioned, you’ll want to name your access points after where they physically lie. Also though, is to think about electric and magnetic interference. For example, placing an access point in ceiling directly beside a 3x20A conduit is probably not a good idea. Neither is putting it on top of a microwave or fridge. Give the access points ample space between them and finally try to get some better antenna’s than the stock ones.

With these tips you’ll be able to support a large amount of people in same location with ease and without frustrating the hell out of the conference attendees.