  Inter-satellite links (ISLs) are adopted in global navigation satellite
systems (GNSSs) for high-precision orbit determination and space-based
end-to-end telemetry telecommand control and communications. Due to limited
onboard ISL terminals, the polling time division duplex (PTDD) mechanism is
usually proposed for space link layer networking. By extending the polling
mechanism to ground-satellite links (GSLs), a unified management system of the
space segment and the ground segment can be realized. However, under the
polling system how to jointly design the topology of ISLs and GSLs during every
slot to improve data interaction has not been studied. In this paper, we
formulate the topology design problem as an integer linear programming, aiming
at minimizing the average delay of data delivery from satellites to ground
stations while satisfying the ranging requirement for the orbit determination.
To tackle the computational complexity problem, we first present a novel
modeling method of delay to reduce the number of decision variables. Further,
we propose a more efficient heuristic based on maximum weight matching
algorithms. Simulation results demonstrate the feasibility of the proposed
methods for practical operation in GNSSs. Comparing the two methods, the
heuristic can achieve similar performance with respect to average delay but
with significantly less complexity.
