QoS-Aware Scheduling of Airship-Assisted Train-to-Ground Millimeter-Wave Communication for HSR Scenario

Millimeter-wave (mmWave) communication is one of the key technologies to enhance the mobile networks for high-speed railway (HSR) scenarios. However, the cost of using mmWave base stations (BSs) to completely cover the HSR lines is unaffordable in practice. In this paper, we introduc the airship-assisted train-to-ground communications in space-air-ground integrated network (SAGIN), aiming to maximize the number of scheduling flows that satisfy quality of service (QoS) requirements. Then we formulate an optimization problem by configuring the number of networks, QoS requirements of flows, and the number of time slots (TSs) in each frame for transmission schedule. To address the problem, we first propose a network selection algorithm to help the airship and BSs select the right MRs, and determine whether the number of TSs occupied by flows can satisfy the QoS requirements. Furthermore, to enhance the number of scheduling flows, we propose a flow scheduling algorithm to optimizing the scheduling order of flows in different networks, and we also consider the flow scheduling when there is no network switching in certain frames. Finally, simulation results show that the proposed algorithm can effectively improve the number of scheduling flows and transmitted bits. We also verify that the proposed algorithm can further improve the system performance with different periods of network switching compared to other algorithms.