wifi access point
This is where wireless access points come into play.
Wireless access points unlike your ISP supplied 'all-in-one' device do just one job, they transmit and receive wireless data. The access points are hardwired back to your router or switch, the WiFi on your 'all-in-one' is turned off and the access point takes over the job of supplying WiFi.
If have a large premises or live in a large house then multiple access points are deployed to cover 'dead spots' and to provide a reliable signal. The access points are setup correctly to prevent channel overlapping and once setup correctly client devices will 'roam' from one device to another.
There are many manufacturers of Access points Ubiquiti, EnGenius, Netgear, Draytek, TP-Link, Cisco etc. We normally supply and install either Ubiquiti or EnGenius as they provide a nice middle point for price vs performance.