Robust Scheduling for IRS-assisted mm-Wave Train-Ground Communications

At present, in order to make use of sufficient spectrum resources to provide even better quality of service and with the development of millimeter wave (mm-wave) communications technology, high speed railway (HSR) communication systems have also taken mm-wave frequency band into consideration. However, since the train runs with high speed as well as the operating environment is complex and dynamic, which may cause the communication link blockage issue for a while. To solve the problem, we adopt the emerging innovative intelligent reflecting surface (IRS) technology to enhance the robustness of mm-wave HSR communication system by introducing a reflection link. Therefore, when the direct communication link is blocked in some case, the reflection link can ensure that the communication is not interrupted. In this paper, we focus on maximizing the number of flows meeting their QoS requirements. A robust IRS-assisted scheduling scheme is proposed under the constraints of half duplex transmission, transmit power, IRS phase shift and limited time slots. As the formulated problem is non-convex, it is difficult to solve directly. Therefore, we divide it into four subproblems, and utilize alternative optimization method to get a sub-optimal solution. The simulation results show that compared with the other three baseline schemes, the IRS-assisted transmission scheduling algorithm proposed in this paper can improve the system performance effectively.