So it seems that the camera is at the most distant point from the main host router? If so, you'll need to either get a more powerful main host router, install a wireless access point near the camera while using the power line units to connect the access point to the main host router, or just use a wireless extender to help extend or get more signal from the main host router into the cameras area.
Wireless AP is just that, a stand alone wireless device that broadcasts just a wireless signal. It needs a physical LAN cable connection to a main host router to connect to internet services.
Extender or repeater is similar to the AP however doesn't need a physical LAN cable connected to the main host router, it connects wirelessly to the main host routers wifi radios using the SSID name and PW.