Mind you not that I am an expert in this kind of setup, but bear with me.
Your "rover" for all it matters is (should be) a "client" to an existing wireless network, not much different from (say) your phone or tablet.
The mechanism is loosely the following:
- the client detects the wireless network
- then, it sends to the found SSID the credentials (WPAx password)
- the nearest/better signal (hopefully) AP that receives these credentials connects and sends back:
a) a valid network address (through its DHCP server)
b) some other needed information, namely gateway address and route, and DNS
- at this point the client is joined to the wireless network and can access its resources
BUT you have THREE of these clients on the rover, each one "covering" around 120°.
Calling them C1, C2, C3 you will have these possible situations, the first three are the "easy" ones
- C1 connected, C2 and C3 NOT connected
- C2 connected, C1 and C3 NOT connected
- C3 connected, C1 and C2 NOT connected
then you have the more complex ones:
- C1 AND C2 connected, C3 NOT connected
- C2 AND C3 connected, C1 NOT connected
- C1 AND C3 connected, C2 NOT connected
and the "final":
- C1, C2 and C3 ALL connected
- C1, C2 and C3 ALL NOT connected
The three clients will have three distinct IP addresses, for the sake of the example, let's say 192.168.1.10, 192.168.1.20, 192.168.1.30.
BUT the rover is not "static", it moves, so a packet originated from 192.168.1.10 will be acknowledged/replied to that same 192.168.1.10, if the "previous" condition is #1 and the rover moves and goes into condition #2, the address 192.168.1.10 simply does not exist anymore.
If you want to "detect" which antenna has:
- connection
- in case of more of one connection, which one is the best one
you need somehow to check all three connections and switch between them according to the "current" situation.
But this - no matter the exact mechanism used - will take some time, and some more time will be needed to switch from one connection to the other.
And in any case the choice needs to be done on the device to which all three "antennas" are connected, i.e. the "switch" in your scheme.
Maybe it is possible to use a "bonding" interface on that device, thus "merging" the three wireless devices, or maybe load balancing could be (mis-) used, but really cannot say.