The most common cause for this issue is the signal levels being out of range or close to being out of range. Check out the link below for more info on signal levels. 

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Cable-Signal-Levels

If the LEDs stay solid when you lose connection, then this means wireless interference issue. This is usually caused by the Wi-Fi channel being too congested by other networks. A simple reboot can help with this as your gateway will search for the least congested channel after the reboot.

Post the reboot if the issue persists, you could change the Wi-Fi channels manually. Check the link below for the steps:

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Changing-the-Wi-Fi-Channel

 Other things that can help are:

• Placing your gateway at the center of the house
• Don’t place it behind any electronics or appliances
• Don’t place it too close to cordless phones (landline not cell), baby monitors, or the microwave
• Ensure it’s not behind a metal or concrete wall as the signal has a hard time getting through them

If none of the above apply, ensure that co-axial cable is connected properly, if not you could reach out to your ISP tech for further assistance.