The present disclosure relates, in part, to non-terrestrial communication systems, and in some embodiments to the integration of terrestrial and non-terrestrial communication systems. Non-terrestrial communication systems can provide a more flexible communication system with extended wireless coverage range and enhanced service quality compared to conventional communication systems. A method representative of aspects of the present application includes receiving, by an apparatus connected in a first sub-system, from a radio access network, configuration information for performing a channel condition measurement on a second sub-system, reporting, by the apparatus to the radio access network, channel condition measurement of a downlink reference signal received from the second sub-system, transmitting, by the apparatus, a wireless transmission to the second sub-system responsive to the channel condition measurement meeting a predefined condition.