Fixed Wireless Business

ISPCON: Determining Whether Interference is Malicious or Not

There's plenty of work to do before you bring in the lawyers.

by Alex Goldman ISP-Planet Managing Editor [May 27, 2008]

Jack Unger, wi-fi educator and principal of Chatsworth, Calif.-based Ask-Wi.com, spoke at ISPCON in several sessions. He is a Wi-Fi consultant and, when not otherwise employed, does a roadshow in which he teaches the basics of Wi-Fi all around the country.

I think of him as a professor without a college.

In the ISPCON session called Defeat Malicious Interference (Legally), he talked about your first step when you run into interference: how do you know whether or not it's malicious interference.

In fact, there's a step before that: determine whether or not it's your own fault.

"When I trip or stumble," Unger said, pretending to trip on the carpet as he said this, "I immediately blame anyone but myself. That's natural."

But often it's your own fault.

So, when the interference began, had you modified your own network in any way? Did you add a new tower? If so, look there first. Perhaps your network was recently reconfigured by outside forces, like mother nature? Check you network data. If the signal to noise ratio is up, then you've got interference. If not, it might be something else (a router issue, perhaps).

Step two is to find the source of the interference. Is the interference network-wide or on one AP? "Inteference comes from a fixed physical location," Unger said.

Use your spectrum analyzer. Unger said that almost everyone in the fixed wireless ISP business has one, but many people don't take the time to learn how to use it. He pointed out that it's easier to take time to get to know this tool before you need to use it, preferably when you buy it.

Once you identify the source of interference, gather your data showing that it is in fact the source of the interference. Use photographs, maps, spectrum analyzer images.

"Interference works two ways. You need to cooperate to share frequencies. You can point antennas away from each other. This is what reasonable people do. How many business people are reasonable? I would guess that 85 percent of us are reasonable."

Sometimes you can eliminate interference simply by aiming your antennas slightly downward. This will decrease their coverage range and lessen the background noise level.

If they are willing to work with you, that's great. If they say they'll work with you but don't change anything, that's a problem.

If, after some time, there's no cooperation, you'll need legal help, which may be the subject of a future article but is also the subject of a discussion between you and your lawyer. Just like the spectrum analyzer, identify the lawyer you would use if this situation arose—before it happens.

—End