A door assembly comprises an interior panel and an exterior panel. A quality monitoring apparatus includes a terminal information collection unit that collects the terminal information from at least one mobile terminal, and a terminal information classification unit and a quality analyzing unit that monitor communication quality in a predetermined target area for each moving speed range of the mobile terminal based on the collected terminal information. The first electrode is connected with the thin film transistor so that an electric potential of the video signal is supplied thereto, and a standard electric potential is supplied to the second electrode.