  With the increasing attention to the integrated satellite-terrestrial
networks (ISTNs), the satellite gateway placement problem becomes of paramount
importance. The resulting network performance may vary depending on the
different design strategies. In this paper, a joint satellite gateway placement
and routing strategy for the terrestrial network is proposed to minimize the
overall cost of gateway deployment and traffic routing, while adhering to the
average delay requirement for traffic demands. Although traffic routing and
gateway placement can be solved independently, the dependence between the
routing decisions for different demands makes it more realistic to solve an
aggregated model instead. We develop a mixed-integer linear program (MILP)
formulation for the problem. We relax the integrality constraints to achieve a
linear program (LP) which reduces time-complexity at the expense of a
sub-optimal solution. We further propose a variant of the proposed model to
balance the load between the selected gateways.
