How do I improve my Xbox wifi signal?

Solution 1:

Have you looked into PowerLine networking? Assuming your router and XBox are on the same mains circuit in your house, then that should be able to get a wired connection between your rooms without having to mess about laying new wiring. It's also generally better bandwidth and latency than a wireless solution (though not quite up with proper wired ethernet kit).

lots of companies do it these days, a quick Amazon listing for Powerline networking kit has a whole list of them.

Solution 2:

Most of the WiFi AP manufacturers also sell repeaters. Plug one into an outlet halfway between your AP and your XBox, and, voila!

See this. Yes, to answer a comment, config is required to tell it which SSID to repeat.