February 2008 — News

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The 2 Mistakes Schools Make in Deploying Wireless Networks

by Dian Schaffhauser

One of the biggest problems in putting a big omni-directional antenna on top of a building outdoors is not only is it sending its signal in all directions, but it's also receiving noise from all directions. Noise is typically one of the big factors in limiting distance of the network. You may put up this great network all over, but [you also need to expect to do] some work to isolate the interference. Everybody else is out there--the next door neighbors, the building next door, they may all have access points on the same frequency.

If you're using something directional, you can also choose what's called polarization, and an antenna can be vertically or horizontally polarized. That can give you some isolation from noise. Of course, you maybe limited to what you can use based on the equipment--if it's on laptops or PDAs. They may all be vertical.

What could also often happen indoors is if a microwave oven is old or if it's not very good, it will actually interfere with WiFi. WiFi and microwave ovens use the same frequency.

I've seen situations where a company had a few hundred employees and several access points spread out across the floor of their office space. Then during lunchtime and breaks, people would heat stuff up in the microwave. All the people around the lunch area would just get knocked off their networks. That was because the microwave oven had leaks.

There are many video transmitters that use the same frequency range. Many cordless phones that hook to the phone system share the same frequencies, and if they do, they have the potential of causing interference and then degrading the wireless networks.

So typically the best installers will go out there with what's called the spectrum analyzer, an instrument that will measure the noise level on a given frequency. So they can choose the right frequency to use in a given location.

Part of installing the network is managing the wireless spectrum. It's knowing what's actually out there using it. Then once your network is in, it's preventing other equipment that you have control over from interfering with the network.

Schaffhauser: Any advice about finding the right vendor to help with the deployment?

Keeney: You need to get somebody that has experience in both the security and the wireless aspects of the installations. It's not just plug and play. When you start doing outdoor devices, it can get quite a bit more expensive because then you're dealing with installing poles on the roof, which means you may need to either bolt into the concrete or bolt through the roof. And now you've got to waterproof that.

Indoor networks are fairly simple. Many schools are already wired. Setting up another device inside of a building is usually not complicated--running another cat5 cable, plugging in the device and mounting the antenna, and it's fairly simple. The outdoor stuff, it's all the waterproofing and making it ruggedized.