论文标题
同时发射多样性和被动横梁，并具有大规模智能反射表面：远场还是近场？
Simultaneous Transmit Diversity and Passive Beamforming with Large-Scale Intelligent Reflecting Surface: Far-Field or Near-Field?
论文作者
论文摘要
智能反射表面（IRS）已成为一种具有成本效益的解决方案，可以通过被动信号反射提高无线通信性能。现有有关IRS的作品主要集中于研究IRS的被动横梁形成/反思设计，以提高用户的通信率，假设其频道状态信息（CSI）是完全或部分知道的。但是，如何利用IRS在没有任何CSI的情况下提高无线传输可靠性，这在高运动/延迟敏感的通信方案中是典型的。在本文中，我们研究了一个新的IRS辅助通信系统与IRS集成到其辅助访问点（AP），以同时实现传输多样性和被动束缚的两种功能。具体而言，我们首先显示出一个有趣的结果，即IRS在任何方向上的被动横梁形成增益均与应用于其所有反射元件的常见相移相变。因此，我们设计了IRS元素的常见相移，以在不需要任何用户的CSI的情况下在AP方面实现多样性。此外，我们为用户提出了一种实用方法，以估算接收器端的CSI以进行信息解码。同时，我们表明，以AP已知的CSI为其他用户，可以保留IRS的常规无源束成绩增益。此外，我们通过考虑具有无数元素数量的大型IRS来得出IRS辅助传输多样性和被动式封闭形式的无源光束形成的渐近性能。数值结果验证了我们的分析，并显示了与其他基准方案相比，提出的IRS辅助同时发射多样性和被动光束成型方案的性能提高。
Intelligent reflecting surface (IRS) has emerged as a cost-effective solution to enhance wireless communication performance via passive signal reflection. Existing works on IRS have mainly focused on investigating IRS's passive beamforming/reflection design to boost the communication rate for users assuming that their channel state information (CSI) is fully or partially known. However, how to exploit IRS to improve the wireless transmission reliability without any CSI, which is typical in high-mobility/delay-sensitive communication scenarios, remains largely open. In this paper, we study a new IRS-aided communication system with the IRS integrated to its aided access point (AP) to achieve both functions of transmit diversity and passive beamforming simultaneously. Specifically, we first show an interesting result that the IRS's passive beamforming gain in any direction is invariant to the common phase-shift applied to all of its reflecting elements. Accordingly, we design the common phase-shift of IRS elements to achieve transmit diversity at the AP side without the need of any CSI of the users. In addition, we propose a practical method for the users to estimate the CSI at the receiver side for information decoding. Meanwhile, we show that the conventional passive beamforming gain of IRS can be retained for the other users with their CSI known at the AP. Furthermore, we derive the asymptotic performance of both IRS-aided transmit diversity and passive beamforming in closed-form, by considering the large-scale IRS with an infinite number of elements. Numerical results validate our analysis and show the performance gains of the proposed IRS-aided simultaneous transmit diversity and passive beamforming scheme over other benchmark schemes.
