Building Wireless Community Networks, Second Edition

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 7-6 shows the use of this technique to extend range or get around obstacles.

Figure 7-6. 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 three repeater-like configurations that are useful in many circumstances.

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 ...