Taking into account that the 802.11ac channels are in the range of 2.4–2.5 GHz, and the active/passive scanning feature supported by the standard, seems that the WiFi spectrum scanning can be done using home routers and a modified firmware.
Yes. Wifi hardware tunes to a potential channel, senses it for a while, and hops on.
But: that hardware is only designed to detect two kinds of signal:
- Wifi signals: These are pretty wideband signals, and you won't be able to detect narrowband signals with that
- specific types of radar signals (I think, mostly weather radar) to avoid interfering with that radar's operation. These are typically detected as chirps by observing the post-DFT data (at least in some wireless chipset's firmware) as appears within the OFDM receiver chain; the signals as such are broadband enough to be relatively similar to Wifi channels.
So, yes, to a very limited amount, you can hypothetically do spectrum sensing with a wifi card. You'd have to find one, however, where you have a very well-documented and most importantly accessible baseband processor firmware. Good luck with that! Also, the analog properties of the receiver chain will very likely not allow you to even detect the presence of narrowband signals, and you won't be able to tune the card to arbitrary frequencies, but only within the channel raster.
Furthermore, don't forget that this is hardware specifically designed as receiver for digital transmissions – there's absolutely no reason to assume you can use what you'd see in digital baseband as being similar to the PSD of the channel. You'll have to deal with an always-on AGC, quite possibly some hardware that might or might not try to correct the sample rates to make sync easier, and very limited processing power for tasks that are not supported by dedicated hardware components within the baseband processor.
whether a home router or a base station equipment, which is capable to perform such task.
I can only guess as to what you need:
- if it is a WiFi device for which a spectrum sensing firmware exists: No. There's no such device that I'd know of, but I'm sure there's some firmwares that can give you something like a "Wifi occupancy" graph. But I'd argue that would only be a very restricted aspect of spectrum sensing – you wouldn't necessarily (or even, likely) detect non-WiFi usage with that, as it works on a much, much higher level.
- if we're talking about finding a device that you can modify yourself: Again, the much more time- and probably cost-effective alternative would be getting proper general-purpose SDR hardware.
Alternatively, there's a lot of different vendors that offer WiFi chipsets. Those are generally SoCs, with a user-programmable CPU core, and a CPU core dedicated to handling WiFi (as that gets quite timing-sensitive). You can usually program the first and must live with the firmware hidden away in some usually inaccessible memory somewhere. You'd have to do a proper market analysis to find a chip where you can do what you need from the user CPU, or you'd need to become a hardware reverse-engineering expert. And that before you could even write a single line of firmware that would allow you to do spectrum sensing.
So, I think it would be very worth writing down a detailed requirement of what you want to sense, and decide whether WiFi hardware has the analog capabilities to do that, at all. If it does, I'd basically go out and buy every single Wifi adapter to which I have access to a firmware blob – that includes the common and cheap atheros9k_htc USB dongles and so on. Then, I'd figure out what part (and if it's the device driver, maybe, even) does the legally required spectrum sensing to avoid interference with primary users (radar). And that's where I'd try to "shim in" my sensing. Again, I do not believe Wifi hardware is what you're aiming for when you're actually after spectrum sensing, since AGCs really don't allow you to compare measurements.