Intelligent reflecting surface (IRS) has emerged as a promising technique to control wireless propagation environment for enhancing the communication performance cost-effectively. However, the rapidly time-varying channel in high-mobility communication scenarios such as vehicular communication renders it challenging to obtain the instantaneous channel state information (CSI) efficiently for IRS with a large number of reflecting elements. In this paper, we propose a new roadside IRS-aided vehicular communication system to tackle this challenge. Specifically, by exploiting the symmetrical deployment of IRSs with inter-laced equal intervals on both sides of the road and the cooperation among nearby IRS controllers, we propose a new two-stage channel estimation scheme with off-line and online training, respectively, to obtain the static/time-varying CSI required by the proposed low-complexity passive beamforming scheme efficiently. The proposed IRS beamforming and online channel estimation designs leverage the existing uplink pilots in wireless networks and do not require any change of the existing transmission protocol. Moreover, they can be implemented by each of IRS controllers independently, without the need of any real-time feedback from the user's serving BS. Simulation results show that the proposed designs can efficiently achieve the high IRS passive beamforming gain and thus significantly enhance the achievable communication throughput for high-speed vehicular communications.

翻译：智能反射面（IRS）作为一种有前景的技术，能够经济高效地控制无线传播环境以提升通信性能。然而，在车载通信等高移动性场景中，信道快速时变特性使得为具有大量反射单元的IRS高效获取瞬时信道状态信息（CSI）面临挑战。本文提出一种新的道路IRS辅助车载通信系统来应对这一挑战。具体而言，通过利用道路两侧等间距交错部署的IRS对称布局以及邻近IRS控制器间的协作，我们提出一种包含离线训练与在线训练的两阶段信道估计方案，以高效获取所提出的低复杂度无源波束赋形方案所需的静态/时变CSI。所提出的IRS波束赋形与在线信道估计设计利用无线网络中现有的上行导频，无需改变现有传输协议。此外，各IRS控制器可独立实现这些设计，无需用户服务基站的任何实时反馈。仿真结果表明，所提设计能高效实现高IRS无源波束赋形增益，从而显著提升高速车载通信的可达通信吞吐量。