The Ubiquiti access points and I assume some other brands use the following method to implement roaming:
All of the access points broadcast a certain SSID. When a client tries to connect, they coordinate with each other to choose which one will reply to that particular client. That is, the client things it is connected to one AP and doesn't know anything special is happening.
If the system wants to move your client to another AP it just disconnects you from the first AP and when you try to reconnect the second AP will reply to you.
In a case like that, assignment is driven as much as "having a clear channel" as "having a better connection on the channel". If you had a choice between two channels, once of which was shared and slightly "better" and another you can have to yourself, you are better off having one to
yourself. (That way you aren't having to wait for other clients to stop sending or receiving, dealing with interference, etc.)
A corollary to that is that if you have both 5GHz and 2.4GHz support on an access point you do best distributing clients between both sides, even if people think 5GHz is better or that 2.4GHz performs better in real life.
I am amazed that instead of all the silly gimmicks that APs have been marketed with, nobody has come out with one that has a lot of radios working on different channels and just behaves like a large number of APs. Practically I think this would work way better than channel aggregation.
Xirrus sells multi-radio access points to do as you described. The only installs I know of, though, are replacing them with more APs spread around because the Xirrus units just cost too much to cover real world buildings, comparatively.
It's a description of Zero-Handoff in Ubiquiti's 1st-gen APs. Fast Roaming is 802.11r.
Getting good roaming is theoretically not that difficult. Lower transmit power so that the device's RSSI in the locations where it's expected to transition to another AP (or off WiFi) are lower than the device's roam scanning threshold (-70 for iOS). Set the minRSSI on APs to something sensible and enable strict mode so that more troublesome devices aren't able to cling to an AP @ -85.
In practice, tweaking those knobs and figuring out placement and channel planning start to get tough beyond 3 APs.
That type of roaming actually ends up breaking a lot of WiFi implementations — it’s really only super useful for WiFi VoIP phones. I worked with a vendor (Bandspeed) doing that kind of WiFi roaming back in 2005, so it’s not remotely a new concept.
Most other devices will jump to another AP broadcasting on the same SSID if the signal is a lot stronger. It’s not nearly as much of an issue as it used to be, but people expect WiFi to Just Work (tm) so it’s better to let the OS’ network stack manage it.
My understanding is that "fast roaming" and many of the proprietary tricks are just ways to speed up the cryptographic pairing process when you switch AP's. I think the same thing happens, but some steps are streamlined.
All of the access points broadcast a certain SSID. When a client tries to connect, they coordinate with each other to choose which one will reply to that particular client. That is, the client things it is connected to one AP and doesn't know anything special is happening.
If the system wants to move your client to another AP it just disconnects you from the first AP and when you try to reconnect the second AP will reply to you.
In a case like that, assignment is driven as much as "having a clear channel" as "having a better connection on the channel". If you had a choice between two channels, once of which was shared and slightly "better" and another you can have to yourself, you are better off having one to yourself. (That way you aren't having to wait for other clients to stop sending or receiving, dealing with interference, etc.)
A corollary to that is that if you have both 5GHz and 2.4GHz support on an access point you do best distributing clients between both sides, even if people think 5GHz is better or that 2.4GHz performs better in real life.
I am amazed that instead of all the silly gimmicks that APs have been marketed with, nobody has come out with one that has a lot of radios working on different channels and just behaves like a large number of APs. Practically I think this would work way better than channel aggregation.