802.11ac – 160 MHz Is Coming To My Home – At Least In Theory

Image: 160 MHz ChannelsAbout two years ago I bought my current VDSL + Wifi Access Point router, a Fritzbox 7590. It is still AVM’s flagship model to this date with 802.11ac Wifi-5 support and it is good to see that the manufacturer continues to develop the software to this day. Especially the Wifi functionality around Mesh and 5 GHz operation keeps getting better and better.

160 MHz Channels!

In particular I have noticed two new functions: One function that has already made it into the release version is support of 160 MHz bandwidth in the 5 GHz range. Previously, operation was ‘limited’ to 80 MHz bandwidth. This suited me just fine so far for two reasons. The problem in Germany and in many other parts of the world is that only the first 80 MHz of the 5 GHz range can be used without a 10 minute Dynamic Frequency Sharing (DFS) backoff. Selecting channel 52 or higher always meant that for 10 minutes after booting or after a config change, the 5 GHz band is not available while the router listens for weather radar signals and other higher priority users of the band. That means that I wouldn’t even have considered a 160 MHz channel because that would implicitly have meant a 10 minute wait time.

Intelligent DFS Handling

The DFS backoff time is the second thing AVM has worked on for the next feature release. If channel 52 or higher is selected, the router will use channel 36-48 for the first 10 minutes after booting or reconfiguration and offer service over an 80 MHz channel there. At the same time, the router observes the rest of the band for weather radar and other signals. If not found, the router then moves the channel to the desired target location in the band. Very cool! Whether this only works for 80 MHz channels or also for 160 MHz channels is not quite clear. I found one page that says that the dynamic-DFS feature is limited to 80 MHz channels and deactivated for 160 MHz operation, while another page says it works with 160 MHz channels as well. Time will tell.

160 MHz Won’t Help Much At The Moment

Two slight problems though: The notebooks in the household are limited to 802.11ac 80 MHz operation at best. And 160 MHz operation would be particularly useful with my notebooks, e.g. for large file transfers to my local cloud or between notebooks, which I do quite often. This is not going to change anytime soon as even the Lenovo X270 models only support 80 MHz operation. Only the latest X390 model supports 802.11ax (Wifi-6) and 160 MHz operation.

And the second problem: Already today, I can ‘only’ get around 300 Mbit/s out of the channel at my desk compared to the 600 Mbit/s when I move closer to the router. So I’m not sure 160 MHz channels would help me any. Perhaps switching the AC into 160 MHz mode would even been counter productive as the transmit power and hence reception level at my desk would drop to half the current value, as the available power has to cover twice as much bandwidth. Hm, perhaps a Mesh setup with a repeater would help, if the repeater could use the full 160 MHz bandwidth? That’s an interesting though for another post.