Community Forum
Some tips for improving WiFi performance;
http://corporate.comcast.com/comcast-voices/10-ways-you-might-be-killing-your-home-wi-fi-signal
https://www.xfinity.com/support/articles/improve-your-wireless-home-network
There are other options. Google for WiFi repeaters / range extenders, WiFi mesh systems / pods, powerline ethernet adapters, MoCA adapters. Good luck !