Wireless Access Point problem?

Hi! I just bought a wireless access point TP-link TL-WA801ND and I have set it up as a repeater of my router up stairs. I'm using it to give my old xbox a wireless connection when directly connected to the AP. It works but only when I disable my routers password leaving it open to anyone. I tried to lock it to a particular mac address but it doesnt work. I want to still have internet access downstairs through my AP but with the password on the router. Does anyone have any advice?