Reconfigurable intelligent surface (RIS) has attracted extensive attention in recent years. However, most research focuses on the scenario of the narrowband and/or instantaneous channel state information (CSI), while wide bandwidth with the use of millimeter-wave (mmWave) (including sub-Terahertz) spectrum is a major trend in next-generation wireless communications, and statistical CSI is more practical to obtain in realistic systems. Thus, we {consider} the ergodic achievable rate of RIS-assisted mmWave multiple-input multiple-output orthogonal frequency division multiplexing communication systems. The widely used Saleh-Valenzuela channel model is adopted to characterize the mmWave channels and only the statistical CSI is available. We first derive the approximations of the ergodic achievable rate by means of the majorization theory and Jensen's inequality. Then, an alternating optimization based algorithm is proposed to maximize the ergodic achievable rate by jointly designing the transmit covariance matrix at the base station and the reflection coefficients at the RIS. Specifically, the design of the transmit covariance matrix is transformed into a power allocation problem and solved by spatial-frequency water-filling. The reflection coefficients are optimized by the Riemannian conjugate gradient algorithm. Simulation results corroborate the effectiveness of the proposed algorithms.
翻译:近些年来,大多数研究都侧重于窄带和/或即时频道状态信息(CSI)的情景,而使用毫米波(mmWave)的宽带宽(包括亚特拉赫茨)频谱是下一代无线通信的主要趋势,而统计CSI在现实系统中更切合实际。因此,我们考虑,通过联合设计基站的传输变异性矩阵和RIS的反射系数,使RIS辅助毫米Wave的可实现率最大化。具体地说,应用广泛使用的Saleh-Valenzuela频道模型来描述毫米电波频道的特点,只有统计CSI可用。我们首先通过主要理论和Jensen的不平等性来得出可实现率的近似值。然后,我们提出基于交替优化的算法,通过联合设计基站的传输变异性矩阵和RIS的反射系数,从而最大限度地实现ERgod可实现率。具体地说,拟议的变异性传输共振度矩阵的设计,通过空间变异性矩阵配置,通过Simalgalalalalalalalalalalalation 将Slation 递解后,Simstalviglationalationalationalationalgal dalblation 。