Reconfigurable Intelligent Surface (RIS) can create favorable multipath to establish strong links that are useful in millimeter wave (mmWave) communications. While previous works assumed Rayleigh or Rician fading, we use the fluctuating two-ray (FTR) distribution to model the small-scale fading in mmWave frequency. First, we obtain the statistical characterizations of the product of independent FTR random variables (RVs) and the sum of product of FTR RVs. For the RIS-aided and amplify-and-forward (AF) relay systems, we derive exact end-to-end signal-to-noise ratio (SNR) expressions. To maximize the end-to-end SNR, we propose a novel and simple way to obtain the optimal phase shifts at the RIS elements. The optimal power allocation scheme for the AF relay system is also proposed. Furthermore, we evaluate important performance metrics including the outage probability and the average bit-error probability. To validate the accuracy of our analytical results, Monte-Carlo simulations are subsequently conducted to provide interesting insights. It is found that the RIS-aided system can attain the same performance as the AF relay system with low transmit power. More interestingly, as the channel conditions improve, the RIS-aided system can outperform the AF relay system using a smaller number of reflecting elements.

中文翻译：

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具有可重新配置的智能表面的毫米波通信：性能分析和优化

可重新配置的智能曲面（RIS）可以创建有利的多路径，以建立在毫米波（mmWave）通信中有用的牢固链接。尽管先前的工作假设是瑞利衰落或Rician衰落，但我们使用波动的两射线（FTR）分布来模拟毫米波频率下的小尺度衰落。首先，我们获得独立FTR随机变量（RVs）乘积与FTR RVs乘积之和的统计特征。对于RIS辅助和放大转发（AF）中继系统，我们得出了精确的端到端信噪比（SNR）表达式。为了最大化端到端SNR，我们提出了一种新颖而简单的方法来获得RIS元件的最佳相移。还提出了AF中继系统的最佳功率分配方案。此外，我们评估重要的性能指标，包括中断概率和平均误码率。为了验证我们分析结果的准确性，随后进行了蒙特卡洛模拟，以提供有趣的见解。发现RIS辅助系统可以以低发射功率获得与AF中继系统相同的性能。更有趣的是，随着通道条件的改善，使用少量反射元件的RIS辅助系统可以胜过AF中继系统。