Building Wireless Community Networks

Repeaters

Unfortunately, long distance line of sight isn’t always possible. Sometimes, you will encounter an obstacle that you simply can’t go over (or through). Or you might need to stretch a link to go farther than your available radios and antennas permit. Maybe you are just on the edge of range of a good AP but need to provide access to a room full of people (and they don’t all have high-gain antennas). A repeater may help in your application.

A radio repeater is a piece of equipment with two complete radios in it. Any traffic heard on the first radio is repeated to the second, and vice versa. If directional antennas are used, a weak signal reaching one of the transmitters is then rebroadcast over the other channel, as if it had originated from that point. Figure 7-4 shows the use of this technique to extend range or get around obstacles.

Figure 7-4. A repeater does just that: repeat everything it hears to someone else down the line

While a classic radio repeater might work fine with 802.11b, I unfortunately don’t have access to radio gear capable of broadcasting a 25MHz wide signal at 2.4GHz. But I do have the next best thing: a couple of 802.11b PCMCIA cards.

The following sections describe two repeater-like configurations that I’ve used successfully.

Two Cards in One PC

If you have a PC with two PCMCIA slots, you can configure Linux to use both interfaces, and pass packets between ...