What causes co-channel interference in a WLAN?

• A. Interference from other devices on different channels.
• B. An overlap in the signal ranges of APs or different WLANs operating on the same channels.
• C. High background noise on 5 GHz channels.
• D. Too many STAs contending for a single AP.

Answer: (B)

Co-channel interference happens when multiple transmitters share the same wireless channel within overlapping coverage areas. Because the medium is shared, those APs or WLANs contend for the same space, and their transmissions can collide. In CSMA/CA, devices listen before transmitting, but if two APs in each other’s range start sending at roughly the same time, their signals interfere, causing reduced performance. That overlap of coverage on the same channel is what causes the interference.

In practice, this is why we try to place APs on different, non-overlapping channels (especially in the 2.4 GHz band) to avoid this contention. Adjacent-channel interference or noise on other bands aren’t the same-channel co-channel interference described here, and having many stations contending for one AP is a throughput issue stemming from access methods rather than interference between APs on the same channel.