WAN Failover to Cell phone hotspot -- do I need two radios?

Hi, with my current Cradlepoint MBR1200 router, I can connect the router as a WiFi client to my cell phone with wifi hotspot (internet sharing) turned on. This makes a nice failover mechanism for when the main Internet service is down.

It looks like OpenWRT can be configured to do this:

If I also want to use the device as a WiFI AP at the same time during WiFI as WAN failover, would I need two WiFI radios, or can one radio function as both the client and AP at the same time?


Ideally, yes.

Many drivers (and the corresponding hardware) can do that (check iw list for the details), however there are usually severe limitations on the concurrent interface combinations. In (almost) all cases, there can only be one STA (client) interface on a given radio, which becomes the master interface and decides over the used channel - only once this connection is up and established, an AP interface can be added as well (no STA connection --> no AP connection either, which isn't quite ideal for failover, nor for performance).