The present invention discloses a user equipment and a communication system. The user equipment configured in a first communication system comprises: a receiver for receiving pre-configured information for co-existence working mode from a base station in the first communication system; a processor for generating a mode establishing request for indicating a co-existence problem experienced by the user equipment and providing assistance information for co-existence working mode in which the user equipment performs a first communication with the base station of the first communication system and performs a second communication with an apparatus in a second communication system which is different from the first communication system; and a transmitter for transmitting the mode establishing request to the base station in the first communication system.