  Several challenging optimization problems arise while considering the
deployment of the space-air-ground integrated networks (SAGINs), among which
the optimal satellite gateway deployment problem is of significant importance.
Moreover, with the increasing interest in the software-defined integration of
5G networks and satellites, the existence of an effective scheme for optimal
placement of SDN controllers is essential. In this paper, we discuss the
interrelation between the two problems above and propose suitable methods to
solve them under various network design criteria. We first provide a MILP model
for solving the joint problem, and then motivate the decomposition of the model
into two disjoint MILPs. We then show that the resulting problems can be
modeled as the optimization of submodular set functions and can be solved
efficiently with provable optimality gaps.
