Eric recently upgraded his internet for GB access. But he's having issues with where the network terminal is located. He has his own wifi router but the problem is the wall separating the optical router. So he had to buy a long ethernet cable in order to move the router to where he can get a good connection. But it slows him down. Leo says that powerline networking is an option, but the speed will drop about the same. It's also dependent on the quality of wiring. MOCA is possible, or wireless over cable. It's essentially Ethernet over coax. And it's pretty fast. It can definitely handle gigabit speeds. Here's how to set up MOCA. There's also this Lifehacker article. And the chatroom recommends the Motorola MM10000 router.
Another option is to put the router as high up as he can get it. And maybe investing in a mesh router system would also help.