Why do WiFi routers do such a bad job of channel selection


Wi-Fi congestion, especially in the 2.4GHz range, is a serious problem in some areas. It is widespread enough that there are many guides to choosing a less congested channel. E.g. https://www.howtogeek.com/197268/how-to-find-the-best-wi-fi-channel-for-your-router-on-any-operating-system/

Given that most routers default to automatically choosing their channel and the hardware seems capable of detecting conflicting networks, why don't they do a better job of channel selection?

Best Answer

The failure of Wi-Fi APs to pick 2.4GHz channels well comes down to a small handful of issues:

  • Most only pick a channel at boot time, but a channel that was good when the AP was last rebooted may have become a poor choice days, weeks, or months later.
  • Most do not want to delay booting by spending long enough to truly evaluate every channel, so they use poor heuristics like "just pick the channel where we see the fewest APs", which doesn't necessarily correlate to which channel will provide the best throughput and reliability. Even worse, these oversimplified heuristics can cause problems like choosing a channel that partially overlaps with channels other APs are on, which will cause APs to interfere with each other without being able to cooperate with each other like they would if they were on the exact same channel.
  • Most don't even have the spectrum analyzer hardware necessary to truly evaluate the RF interference on each channel; they have Wi-Fi radios and focus on interference from other Wi-Fi devices, and are fairly ignorant of interference caused by non-Wi-Fi devices such as Bluetooth, microwave ovens, cordless phones, wireless subwoofers, baby monitors, wireless cameras, and more.
  • Creating an AP that has the hardware and the algorithms to choose channels well not just at boot, but to keep re-evaluating the channel choices later, and change channels when there would be benefit to do so, is both expensive and fraught with potential interop problems. Not all clients are great at honoring channel switch announcements from the AP, so an AP that changes channels on the fly risks having clients fall off the network every time it does so.