双IRS辅助大规模MIMO系统中基于双时间尺度的信道估计方案

Two-Timescale Channel Estimation Scheme for Double-IRS-Assisted Massive MIMO System

在双智能反射面(IRS)辅助的大规模多入多出(MIMO)通信系统中,为获取信道状态信息(CSI)而进行的信道估计需要较大的导频开销。考虑到基站(BS)-IRS信道与IRS-IRS信道具有高维且准静态的特性,而IRS-用户(UE)信道具有低维且时变的特性,本文提出一种基于双时间尺度的信道估计方案。首先,对于准静态信道,由BS发送导频并基于坐标下降算法和最小二乘法分别估计BS-IRS信道和IRS-IRS信道。然后根据准静态信道的估计结果进一步基于最小二乘法估计IRS-UE信道。仿真结果表明,本文所提出的方案可以采用低于对比方案50%的导频开销来获取低于对比方案近10 dB的估计归一化均方误差(NMSE),实现用更少的导频开销获取更高的信道估计精度。

In a massive multiple-input multiple-output(MIMO)communication system assisted by double intelligent reflecting surfaces(IRSs),the channel estimation to obtain channel state information(CSI)requires significant pilot overhead.Considering that the base station(BS)-IRS and IRS-IRS channels have high-dimensional and quasi-static characteristics,while the IRS-user equipment(UE)channel has low-dimensional and time-varying characteristics,this study investigated a channel-estimation scheme based on two timescales.First,for the quasi-static channel,the base station sends pilots and estimates the BS-IRS and IRS-IRS channels using the coordinate descent algorithm and least square method.Then,based on the quasi-static channel-estimation results,the least square method is used to estimate the IRS-UE channel.Simulation results showed that the scheme proposed in this paper could obtain an estimated normalized mean square error that was nearly 10 dB lower than that of the comparison scheme,with only half of the pilot overhead of the comparison scheme.Thus,a higher channel-estimation accuracy was achieved with less pilot overhead.