iPhone 5 wireless problems

I've been having problems with my iPhone not connecting to my wifi when further than 10 ft away from the router. I've sent my phone in to Apple and they said nothing was wrong with it, yet, it still doesn't work. I have a Belkin N300 router that I got a few months ago and I've tried setting I could think of. There is no security settings enabled either. Anyone have suggestions or similar problems?