I don't have a PS3, but when my Wii's online bits were acting up, I found that changing the channel that my router was using completely fixed the problem. For some reason, my Wii hates channel 6 but loves channel 1. Maybe the PS3 works the same way?

I have a similar router model, so if you don't know how to change the channel, give this a try: type your router's IP address into the URL bar of your browser, go to Wireless -> Basic Wireless Settings and play around with different Wireless Channels.

I hope this helps.