Method for estimating optimal viewable position of display device

PURPOSE: An available watching range measurement method for a display device is provided to offer service mobility in an optimal position through a service available range measuring method considering display characteristics. CONSTITUTION: An available watching distance and a view angle are determined in a manufacturing process of a display device. A home gateway (320) stores the available watching range information of the display device. The home network system confirms the location of the portable terminal by using a wireless signal transmitted and received from a portable terminal. The home network system confirms whether the portable terminal is moved to an available watching range based on the available watching range information of the display device in the home gateway. [Reference numerals] (310) Display device; (320) Home gateway; (330) Terminal; (AA,EE) Allowable range; (BB) Signal range; (CC) Signal; (DD) Viewing angle