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.
翻译:智能反射表面(IRS)已成为通过被动信号反射提高无线通信性能的一个具有成本效益的被动解决方案。IRS的现有工作主要侧重于调查IRS的被动波形成形/反射设计,以提高用户的通信率,假设其频道状态信息(CSI)已经完全或部分为人知;然而,如何利用IRS提高无线传输可靠性,而没有任何CSI,这在高流动性/耐久敏感通信情景中是典型的,但在很大程度上仍然是被动的。在本文中,我们研究与IRS整合到其辅助访问点(AP)的新的IRS辅助通信系统,以同时实现传输多样性和被动成形的功能。具体地说,我们首先展示一个令人感兴趣的结果,即IRS在任何反映要素的通用阶段性变换式中,因此,我们设计IRS元素的通用阶段变换式,以便在APS方面实现传输多样性,而不需要任何 CSI的用户。此外,我们提出一个实用的方法,即CRSAS系统化的用户在常规化中显示其变换式,我们在SIS格式上显示其变换成其他信息。