A method of registering, by a multi radio access technology, RAT, device (800, 61, 62, 63, 64, 65) supporting a plurality of RATs, an entity of a secondary RAT system in a management device of a primary RAT system in a wireless communication system, the method comprising: receiving (S110, S210) a request for registration of an entity of a secondary RAT system from the entity of the secondary RAT system; if the request for registration is authorized, determining (S120, S220, S520) whether the entity of the secondary RAT system is included in a list of entities of the secondary RAT system registered in a management device of a primary RAT system; if it is determined that the entity of the secondary RAT system is not included in the list, transmitting (S130, S230, S530) a registration request message including information on the entity of the secondary RAT system to the management device of the primary RAT system; receiving (S131, S231, S531) a registration response message including a result of the request for registration of the entity of the secondary RAT system from the management device of the primary RAT system; and transmitting (S140, S240) a registration result parameter including the result of the registration of the entity of the secondary RAT system to the entity of the secondary RAT system, wherein the primary RAT system is a cellular system, and the management device of the primary RAT system is one of an eNodeB, eNB or a mobility management entity, MME,, wherein the secondary RAT system is a Wi-FiTM system, and the entity of the secondary RAT system is an access point, AP, (900, 81, 82, 83), and wherein the information on the entity of the secondary RAT system includes at least one of a media access control, MAC, address of the entity of the secondary RAT system, a service set identifier, SSID, of the entity of the secondary RAT system, a position of the entity of the secondary RAT system, an homogeneous extended service set ID, HESSID, of the entity of the secondary RAT system, whether of the entity of the secondary RAT system can be used by a limited user, or information on a frequency channel used by the entity of the secondary RAT system. receiving (S110, S210) a request for registration of an entity of a secondary RAT system from the entity of the secondary RAT system; if the request for registration is authorized, determining (S120, S220, S520) whether the entity of the secondary RAT system is included in a list of entities of the secondary RAT system registered in a management device of a primary RAT system; if it is determined that the entity of the secondary RAT system is not included in the list, transmitting (S130, S230, S530) a registration request message including information on the entity of the secondary RAT system to the management device of the primary RAT system; receiving (S131, S231, S531) a registration response message including a result of the request for registration of the entity of the secondary RAT system from the management device of the primary RAT system; and transmitting (S140, S240) a registration result parameter including the result of the registration of the entity of the secondary RAT system to the entity of the secondary RAT system, wherein the primary RAT system is a cellular system, and the management device of the primary RAT system is one of an eNodeB, eNB or a mobility management entity, MME,, wherein the secondary RAT system is a Wi-FiTM system, and the entity of the secondary RAT system is an access point, AP, (900, 81, 82, 83), and wherein the information on the entity of the secondary RAT system includes at least one of a media access control, MAC, address of the entity of the secondary RAT system, a service set identifier, SSID, of the entity of the secondary RAT system, a position of the entity of the secondary RAT system, an homogeneous extended service set ID, HESSID, of the entity of the secondary RAT system, whether of the entity of the secondary RAT system can be used by a limited user, or information on a frequency channel used by the entity of the secondary RAT system.