Complementary service apparatus and method in communication system

PURPOSE: A complementary service device and a method of a communication system are provided to use a resource efficiently, and to improve a reliability of a system and a channel capacity by using a complementary channel in a CDMA mobile communication system. CONSTITUTION: In order to supply a complementary service, Plow and Phigh are compared. When P of a total transmission power is smaller than the Plow, namely the total transmission power is smaller than a reference power, this means that there is a spare channel capacity for the complementary service. A complementary data capacity capable of being transmitted maximally is calculated according to a difference of the P and the Plow calculated by a base station processor(724). After this, the decider(728) supplies the complementary service pertinent to the complementary data capacity through a complementary channel. In the result of a comparison of the second comparator(730), when the P is bigger than a Phigh, this means that a transmitted power is bigger than the total transmission power of a base station. In this case, the total transmission power of the base station is decreased by stopping the complementary service. At this time, the total transmission power of the base station is decreased until the P is same and smaller than the Phigh.