Narrow spotbeam scheduling and interbeam interference management can make the advanced multibeam satellite equipped with phased array antenna more effective to serve a large number of users over its coverage area. Further, if the satellite has an option of making use of ground stations to forward packets to end user terminals, path diversity can improve the overall system throughput. However, onboard resource management has been only analyzed without terrestrial resources into account. In this paper, we develop a power allocation scheme for a multibeam satellite and ground relay stations into joint consideration. We attempt to minimize the power consumption of a heterogeneous network by differently weighting power usage of the satellite and ground stations. The analytical solution is given in terms of channel conditions, quality of service (QoS) requirements, po- tential interbeam interference that is primarily determined by geographical distribution of users and relay locations, and the penalty cost for relaying. The optimum power allocation indicates that path selection between via relay station and directly to users, beamforming of multiple spotbeams, and user scheduling over a small number of beams should be de- cided in a cross-layer approach. Simulation results show that the proposed method seeks for a trade-off between the use of satellite and terrestrial resources. The formulation and analysis developed in this paper may hint at the direction of the cross-layer solutions in heterogeneous networks in general.