  This paper aims to develop satellite-user association and resource allocation
mechanisms to minimize the total transmit power for integrated terrestrial and
non-terrestrial networks wherein a constellation of LEO satellites provides the
radio access services to both terrestrial base stations (BSs) and the
satellite-enabled users (SUEs). In this work, beside maintaining the
traditional SatCom connection for SUEs, the LEO satellites provide backhaul
links to the BSs to upload the data received from their ground customers.
Taking the individual SUE traffic demands and the aggregated BS demands, we
formulate a mixed integer programming which consists of the binary variables
due to satellite association selection, power control and bandwidth allocation
related variables. To cope with this challenging problem, an iterative
optimization-based algorithm is proposed by relaxing the binary components and
alternating updating all variables. A greedy mechanism is also presented for
comparison purpose. Then, numerical results are presented to confirm the
effectiveness of our proposed algorithms.
