Intelligent reflecting surface (IRS) is a promising new paradigm to achieve high spectral and energy efficiency for future wireless networks by reconfiguring the wireless signal propagation via passive reflection. To reap the promising gains of IRS, channel state information (CSI) is essential, whereas channel estimation errors are inevitable in practice due to limited channel training resources. In this paper, in order to optimize the performance of IRS-aided multiuser communications with imperfect CSI, we propose to jointly design the active transmit precoding at the access point (AP) and passive reflection coefficients of the IRS, each consisting of not only the conventional phase shift and also the newly exploited amplitude variation. First, the achievable rate of each user is derived assuming a practical IRS channel estimation method, which shows that the interference due to CSI errors is intricately related to the AP transmit precoders, the channel training power and the IRS reflection coefficients during both channel training and data transmission. Next, for the single-user case, by combining the benefits of the penalty method, Dinkelbach method and block successive upper-bound minimization (BSUM) method, a new penalized Dinkelbach-BSUM algorithm is proposed to optimize the IRS reflection coefficients for maximizing the achievable data transmission rate subjected to CSI errors; while for the multiuser case, a new penalty dual decomposition (PDD)-based algorithm is proposed to maximize the users’ weighted sum-rate. Finally, simulation results are presented to validate the effectiveness of our proposed algorithms as compared to benchmark schemes. In particular, useful insights are drawn to characterize the effect of IRS reflection amplitude control (with/without the conventional phase-shift control) on the system performance under imperfect CSI.

中文翻译：

---

在CSI不完善的智能反射面辅助无线通信中利用幅度控制

智能反射面 (IRS) 是一种很有前途的新范式，通过被动反射重新配置无线信号传播，为未来的无线网络实现高频谱和能源效率。为了获得 IRS 的有希望的收益，信道状态信息 (CSI) 是必不可少的，而由于信道训练资源有限，信道估计错误在实践中是不可避免的。在本文中，为了优化具有不完善 CSI 的 IRS 辅助多用户通信的性能，我们建议联合设计接入点 (AP) 的主动发射预编码和 IRS 的被动反射系数，每个参数不仅包括传统的相移以及新开发的幅度变化。首先，假设一个实用的 IRS 信道估计方法，推导出每个用户的可实现速率，这表明 CSI 错误造成的干扰与 AP 传输预编码器、信道训练功率和信道训练和数据传输期间的 IRS 反射系数有着错综复杂的关系。接下来，对于单用户情况，结合惩罚法、丁克尔巴赫方法和块连续上限最小化（BSUM）方法的优点，提出了一种新的惩罚丁克尔巴赫-BSUM算法来优化IRS反射系数，以最大化受CSI错误影响的可达到的数据传输速率；而对于多用户情况，提出了一种新的基于惩罚对偶分解（PDD）的算法来最大化用户的加权和率。最后，提供了仿真结果以验证我们提出的算法与基准方案相比的有效性。特别是，