I've installed my Ralink card (rt2800usb) on Comtrend AR-5315u and it works fine. However, when I reboot the router I need to delete the wifi (Client) on my router and reconnect it again because the wireless is not associated. Is there any way to fix this problem? I want the wifi to connect itself even if I reboot the router or shut it down for a while.
Are you saying that you have to delete an upstream WAN (client) connection - in order to connect to the local LAN access point?
My main router is on the first floor and the signal is quite weak on the third one. So, I've installed OpenWrt on another router to use it as a hotspot, capturing wifi and sharing it again. But, I'm doing this using an external wifi card (rt2800usb), not the router's. When I connect the OpenWrt router to the main one through wifi, everything works just fine. However, if I happen to reboot the router, the wifi doesn't connect itself automatically, so I have to redo the exact same process again and again, removing the wifi and adding it again.
Even in the best of all cases (which rt2800usb is far from), USB WLAN cards in 24/7 operation and/or AP mode are problematic. The only winning move is not to play and to switch to a good PCI(e) WLAN card (respectively a different device) instead. Even paying the repeater penalty is cheap, compared to the hassles of USB WLAN.