Does your WiFi suck for video calls? Use 20MHz channels!

After years of trials and tribulations in San Francisco apartments, the single best thing I did for my home network was to switch most devices to the 5GHz band and limit it to 20MHz channel width. Once I did that pretty much all of my WiFi woes went away. But why?

Very recently, as many of the more blessed among us have shifted to working from home to reduce the spread of the SARS-CoV-2 virus, it has become apparent that many of the home WiFi setups that were perfectly fine for flipping through Instagram or streaming movies are an absolute disaster for video calls.

(continuing the great tradition of corny stock art)

You may have great equipment and impressive multi-hundred-megabit speed test results, but still experience drop outs that seriously hinder your experience communicating with friends and colleagues over video calls. What the frick is happening?

Video calls are a surprisingly demanding application. While bandwidth requirements are modest relative to the available broadband connectivity in much of the world, it is quite intolerant of any interruption. Web browsing or movie streaming can tolerate an unstable connection without noticeable interruption, but it is disastrous for video calls.

Video calls need a consistently stable connection. And the radio waves are, unfortunately, a very unstable environment. In particular, data transmission over air waves is extremely sensitive to interference. Even with a very powerful signal, a noisy environment results in instability. The single best thing you can do to improve your video call experience over WiFi is to reduce interference.

The most common radio band for WiFi is 2.4GHz, a very noisy one. Microwave ovens, Bluetooth devices, car alarms, and home automation all share this band. It also travels further and through more objects than the other WiFi band — 5GHz. Generally speaking, 5GHz is the preferred band for indoor home WiFi networks, particularly for people with smaller homes in dense environments like apartments or more crowded cities.

Wild swings in quality (signal-to-noise ratio) on 2.4GHz. Noise floor levels vary by around 30X over tens of seconds. On a Mac this data can be accessed using the built-in Wireless Diagnostics tool (use search to find) under Window > Performance.

The lesser-known problem is that the default configuration for the 5GHz band on most WiFi routers and access points optimizes for peak speeds in ideal conditions over stability at range.

Modern WiFi equipment will combine or “bond” adjacent standard 20MHz channels to provide higher throughput. 40MHz provides roughly twice as much throughput, and 80MHz provides roughly 4X the throughput. However, wider channels are subject to more interference, roughly proportional to their width. 80MHz channels, typically the default for the 5GHz band on modern WiFi gear, are vulnerable to 4X the interference.

And it doesn’t matter how fancy your gear is, or what the manufacturer claims, this is a physical limitation of radio waves. Beamforming and impressive-looking MIMO antenna arrays can’t reduce interference.

While many devices will indeed switch to a narrower channel width in the presence of interference, there will always be some amount of connection instability before the switch occurs. Once the interference passes, it will switch back to the wider channel… until the interference returns, and it swaps back to the narrower channel. Each time interference rears its ugly head, it will destabilize your connectivity.

A speedtest.net run through my home WiFi. The peak throughput is much lower than the equipment is capable of (~75% less), but the connection is rock solid. Equipment is 2018 MacBook Pro, Ubiquiti UniFi UAP-AC-Pro. Uses the 5GHz band with 20MHz channel width only. During the run, RSSI was steady at -66dBm with SNR between 30 and 32. Internet connectivity is gigabit fiber from Sonic.

The good news is that a 20MHz channel width on high-quality, modern equipment provides more enough throughput for most households. So read the documentation for your router or access point and switch the 5GHz channel bandwidth to only use 20MHz. Give that a test drive for a few days and see if it makes things better for you. 🤞

I do Software Engineering on High-Impact, Large-Scale Internet Services.