RF Interference and Attenuation
One of the biggest challenges when working with wireless networks is the RF interference and attenuation. It takes practice to develop the skills necessary to predict the coverage and performance of wireless networks to aid in a proper installation. Keep in mind that 802.11 wireless devices share the airwaves with other wireless technologies that might cause significant interference with your wireless network or hotspot. The most common of these devices are as follows:
Using these devices in or around your wireless coverage area will likely degrade the performance of your network, or hotspot. In some cases, you might not even be able to keep a connection with the wireless network such as when using a wireless client next to an operating microwave oven. You can take some simple steps to help prevent these issues. Try to use cordless phones and other wireless devices in other frequency bands, such as 900 MHz or 5 GHz. Try not to use microwave ovens around APs or wireless clients. You might also avoid RF interference from microwave ovens by avoiding channel 11, because the top one-third of a band is typically affected the worst. You can also refrain from installing APs close to microwave ovens.
Attenuation, as discussed in this book, means the loss of radio signal strength. Free space loss is a type of attenuation that is the natural loss of the radio signal when propagating through the air without obstructions. As Figure A-11 illustrates, the signal gets weaker and weaker when traveling away from the AP.
If buildings did not have walls, desks, filing cabinets, or elevators, it would be much easier to install wireless networks. This is because pretty much all you would have to think about would be free space loss when determining how many APs a facility needs, where to put them, and what antennas to use. However, this is not the case; buildings are usually filled with things that cause significant attenuation to your Wi-Fi signals. For instance, Figure A-12 shows how a wall might block RF signals.
Suppose that you need good coverage on the other side of the brick wall, as shown in Figure A-12. You could replace the standard antennas on the AP with high-gain antennas. Then you would likely increase the signal quality enough to better penetrate the brick wall, and wireless clients on the other side would have a good connection. Alternatively, you could move the AP closer to the wall.
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