Like here at home the WiFi won't start at some points, thought about buying a router these models with three antennas, to better distribute the signal. This is one of the cheapest. Has a large number of resources, as Repeater, ...

This is a tutorial of how to put a WiFi IP camera on the internet, where I used a modem/router ZTE W300 and the camera WansCam JW004. If you have another camera or another router some information may be slightly different, but ...