a method for setting transmit power of a small base station by using a signal to interference and noise ratio received by the small base station while the small base station is providing service and a mobile telecommunication system using the same . in one embodiment , a mobile telecommunication system includes a network base station configured to variably set a transmit power so that a signal to interference and noise ratio received from a user equipment may fall between an upper limit and a lower limit of a predetermined target signal to interference and noise ratio .