Why does my wifi disconnect whenever my roommate's phone or computer connects?

The modem is a Cox Panoramic Gateway. The PC is hardwired, but even if it weren't, a single device connecting to the network shouldn't cause all other devices to drop their connection.  Not for the amount I'm paying for Gigablast internet with "the best available modem."

A single device could drop a wireless connection.  For example, a microwave oven could congest your ether with data-less radio waves.  Wireless NICs read everything on your frequency so if your network gets overly bombarded, it could drop connections.

Every time your roommate boots a wired PC, your wireless connection drops?  This sounds sneaky.  Does your roommate's PC have a wireless card?  It may be still enabled...and...have a higher priority than your devices.

A higher priority would be a QoS setting in the router.  If your roommate configured your router to give the PC a higher priority than you, your router may have to renegotiate your share of the network.  Log in and verify.

I checked and he was not wired. I confirmed that the issue happened again when an additional laptop was started up (connected to wifi), as my work computer (with cisco anyconnect) fully lost connection and had to reestablish the secure connection, but not until 2-3 minutes later when it reconnected to the network.

I've looked in the router settings and have not found any way to change QoS, is this something that can be modified at all? Or does Cox not allow for changing these settings within their products?

Thanks for your replies, I very much appreciate it.

The modem is a Cox Panoramic Gateway.

roommate is drawing a lot of bandwidth.