Bad internet coection though WiFi has high link quality

At my house, when I check the Link Quality in the room where the router is, the Link Quality is 70/70 (-39 dBm) and there is high-speed inteet access. In the next room behind a wall, the Link Quality is 57/70 (-52 dBm), however there is no inteet access at all (Might coect twice in a minute for brief seconds).

What seems to be the problem? Is there some kind of configuration for this? The Router is a TP Link TL-Wr740n.