A radio resource allocation method in a communication node is disclosed. The method comprises determining (424) that a first time reference or a first communication using a first component carrier has a time shift compared to a second time reference of a second communication using a second component carrier. The method further comprises determining (426) a duration of a communication sub-frame based on the time shift, and scheduling (428) the determined communication sub-frame on a first component carrier to a first communication device. The determined frame duration is equal to the time shift or equal to the normal sub-frame length minus the time shift so as to avoid any overlap or interference. Corresponding computer program product, arrangement, communication node and first communication device are also disclosed.