부산대학교 도서관

A radio communication system (100) provides a radio air interface at a master node (102) for subscriber units associated with the master node. Among the subscriber units are several slave nodes (104, 106). The communication system has the ability to operate as a secondary user in unused spectrum portions of a frequency band otherwise reserved for primary operators. The master node accesses an authorization server (108) to obtain a list of unused channels in the region of the master node. Each slave node also contacts the authorization server to obtain a list of unused channels in the region where each respective slave node is located, via another network (118, 121). The unused channels common to the slave nodes and the master node are used to create a backup radio operating parameter list which is used by the master node if a fault occurs between the master node the authorization server.