low-power Wifi

Several years ago I did something similar to that. I was suspecting my neighbor was accessing my local network, so I remived the antennas from my WRT54G router. I was still able to access it with my laptop wirelessly, but only from within the same room. I eventually instituted WAP protection, so I no longer need the antenna-less protection.

Some third party firmware, dd-wrt comes to mind, allows you to specify the transmit power. You'd probably dial it down until you're satisfied.

Sure. Some of the devices that have wi-fi built in have a very limited range. For example, the SD card for cameras:

I've been doing that at coffee shops for years. Just use a terminator for an antenna and you'll get some limited range. It really depends on the unit. Most AP's have two antennas. However, the one's with a single antenna usually also have a 2nd antenna inside the box. Usually that's a PIFA PCB antenna or chip antenna. Don't try to just unplug the outside antenna, as there's a huge difference between the MAIN and AUX antennas. The AP sits on the MAIN antenna all the time, unless the error rate gets high enough to justify trying to use the AUX antenna. If you just use the AUX antenna, you'll have really lousy association time and erratic disconnects as the AP keeps trying to use the MAIN. Fortunately, you can disable diversity in firmware such as DD-WRT.

A few years ago, I worked on a project that was designed to restrict the USABLE range of a coffee shop wireless to only the floor area. I'm required to keep my big mouth shut on how it works, but I can assure that I can measure range and block users outside the usable range. However, it was expensive and somewhat messy.

A half-posterior approach that almost works is to use two access points. One is just a monitor, while the other actually does the connecting. By comparing the relative signal strengths for a given MAC address, you can calculate a tolerable guess as to the location. If the numbers are outside the acceptable limits, they get blocked until it either recovers to acceptable limits, or disconnected if it stays outside the limits.

Even if you dial down the power, you have the issue of wifi going into the low speed fallback modes. That is, you dial down the power so 54mbps just works, and you might find a long distance 1mbps user.

Now if you can dial down the power and force the wifi to only be at one speed, then maybe you have a plan.

I find that not placing the wifi router too high helps in keeping it local. Don't put it on a shelf.

Good points, thanks.

Good idea. For coffee shops, I previously set the wireless router for

54Mbits/sec fixed speed to limit the range. As a bonus, overall performance improved since less air time was needed. However, retransmission increased dramatically.

I stopped doing it that way because some laptops and devices did not respond gracefully to a loss of signal at 54Mbit/sec associations. Instead of going into standby when the signal disappeared, they would disconnect, scan for other SSID's, and take forever to reconnect. Users were complaining to the baristas that they "couldn't stay connected". My iPhone 3G was one of the devices with a problem.

There was also a problem with people arriving with 802.11b only hardware. I had thought all those were dead and being recycled, until I realized that several of my ancient IBM Thinkpads (A30, A31, X30, X31) come stock with 802.11b. Also, lots of game pads are 802.11b only.

I gave up and went back to auto speed at the coffee shops.

I was setting mine to 1 milliwatt from 15 foot away, no much change from 70 .

Greg

All of our "big Cisco" APs support turning down the power - e.g. the AIR-AP1131AG-A-K9 supports setting the power down as as low as -1 dBm (1 mW.) Also you can pick and choose which data rates are mandatory/ supported/disabled. (See e.g.

What's the point, though, may I ask?

Aaron

Nit pick:

-1dBm is about 0.8mw. 0dBm is 1mw.