The present invention discloses a signaling method, an apparatus and a computer program for controlled transmission signal deferring utilizing both licensed and unlicensed frequency bands for carrier aggregation. In the method, a connection is established between a User Equipment and a base station. For example, based on a sensed interference level, a transmission deferring indication is generated regarding a secondary component carrier locating on an unlicensed band, in case the secondary component carrier is occupied. This indication may be generated and sent either by the base station or by the User Equipment. Finally, the secondary component carrier is deactivated for data transmission, for deferring data transmission for a certain time period. After the deferring time has passed, the data transmission can be re-performed on the same secondary component carrier, or through switching to another secondary component carrier in unlicensed spectrum.