Electromagnetic interference is unwanted electromagnetic energy or overlapping wireless channel use that disrupts or degrades communication. Wireless signals travel through an unbounded medium, so nearby devices and other equipment can affect the same transmission space. section 18.1.1 section 18.5
Interference appears in several operational forms:
- Neighboring wireless LANs compete for airtime, especially when access points use overlapping or identical channels. section 18.1.1 section 18.2.2
- The 2.4 GHz band is particularly vulnerable because Bluetooth, microwave ovens, cordless telephones, and other technologies use it. section 18.2.2 section 18.5
- Interference can force devices to contend for airtime; simultaneous transmissions collide, while CSMA/CA listens for a free channel before transmitting. section 18.1.1
- Channel planning reduces interference: 2.4 GHz deployments commonly use non-overlapping channels 1, 6, and 11, or 1, 5, 9, and 13 where permitted. section 18.2.2 section 18.2.3
Exam-style channel selection
When asked which standards require careful channel selection to avoid interference among neighboring access points, choose 802.11b and 802.11g because both use the overlapping 2.4 GHz band. 802.11a and 802.11ac use 5 GHz in the stated comparison. section 18.2.3
