Help me for making redundant link

Dear All,
I had a link running from site A (AP mode) to site B (Client mode). I want to add another radio at site A, so that when one radio gets down the link will shift to another radio without breaking the ping. Can you send me settings? Should I have to use any router for that?

Few pings will be lost 100% for the time of switchover from one AP to another.
Second AP should have the same SSID, you can use connect-list to set priority for AP1 and AP2.
Station should connect to AP1, when it is not reachable to AP2.
You have to give more information about IP addressing, that is planned on AP1 and AP2.