Abstract
Cell-free multiple-input multiple-output (MIMO) and reconfigurable intelligent surface (RIS) have been envisioned as two promising techniques to enhance the data transmission rate of high-speed railway (HSR) networks. This paper considers the HSR cell-free MIMO system empowered by RIS with finite discrete phase shifters to pursue performance improvement. Particularly, the RIS phase shift optimization problem is formulated, aiming at maximizing the achievable rate. To deal with the complicated control problem, a deep reinforcement learning (DRL)-based scheme is proposed, where double deep Q-network (DDQN) method is invoked for designing phase shifts. Simulation results demonstrate that compared with the existing optimization-based baseline scheme, the proposed scheme can obtain the comparable achievable rate with much shorter time consumption.
Funding Information
  • High-level Talents Research Start-up Project of Hebei University (521100222061)
  • National key research and development program (2021YFB2900301)
  • National key research and development program (2020YFB1806604)
  • National key research and development program (2021YFB3901302)
  • National Natural Science Foundation of China (62221001)
  • Royal Society Newton Advanced Fellowship (NA191006)
  • Royal Society Newton Advanced Fellowship (61961130391)
  • Natural Science Foundation of Jiangsu Province Major Project (BK20212002)
  • Open Research Fund from the Shenzhen Research Institute of Big Data (2019ORF01006)

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