How to control station to associate special AP?

[张 yf]

hi, would anyone pls give me some suggestion about realization the function 
below:

     AP1(hostap) &              & AP2(hostap)
                 \              /
                  \            /
                   \         /
                    \      /
                      & STA1(hostap as the driver)

AP1 and AP2 use the same ESSID, and works in different channels, such as 
AP1 with channel 1 and ap2 with channel6. In this case, Can I program to 
control STA1 (also driven with hostap driver) to associate with the special 
AP?  and when STA1 is associated with AP1, can I program to make STA1 
handover to AP2? if it is possible, should it be realized in user daemon or 
hostap driver? 

Thands and regards, and I will appreciate your any suggestion.

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