100mW Access Point Coverage Boundary

We now consider the "edge" of the coverage area inside which the signal from the Access Point is sufficiently strong for acceptable Client use. Notice that our example supposes that the Access Point (A) is unable to reach the Client notebook computer on the conference table (B).

The problem would manifest itself by the fact that a few people at one side of the conference room might have connectivity but, if you're sitting up front near the projection screen (B) you just don't have a strong enough signal from the Access Point - you can't connect to the Wi-Fi wireless LAN.

100mW Client Card Coverage Boundary

We assume, for the purpose of this example, that the Client and the Access Point both use an antenna with essentially the same characteristics. In this case it should be obvious that if the 100mW Access Point can't reach the Client then a 100mW Client can't reach the Access Point.

The RF signal transmitted by the Client notebook computer is not sufficiently powerful to overcome the attenuation caused by the walls of the building in exactly the same way that the 100mW signal from the Access Point couldn't reach the Client.

200mW Access Point Coverage Boundary

The network administrator in our example has not read this page or they would know that simply increasing the Access Point's power will not fix the problem.

On the left you see the Access Point (A) with the same antenna and in the same location, but now we're using a 200mW input power level. Notice that the signal coverage boundary for the Access Point (A) has now extended beyond the notebook computer in the conference room (B).

The problem is actually worse now than it was before. You see, now the Client (B) sees that an Access Point (a WLAN) appears to be available (whereas before the WLAN didn't even appear.) The Client, however, still can't send a signal back to the Access Point.

100mW Access Point with 3dB Gain Antenna

The solution to the problem is to use a high-gain antenna with the 100mW Access Point. The rule is: "An Access Point should never have a higher input power than the lowest power Client Adapter being supported."

The picture shows that a high-gain antenna works because it's construction causes transmitted RF to be focused (notice that the boundary is beyond the Client at 'B') but the same construction acts to "reach out" and acquire RF energy from the air in reverse, as if a much larger antenna existed for reception (as shown by the blue lines at "C" - these are not antenna elements; they simply represent the way the antenna works. Hence: "To allow more Clients to "hear" and Access Point, use a high-gain antenna, don't increase the power! "