Future wireless communication systems will increasingly rely on the integration of millimeter wave (mmWave) and sub-6 GHz bands to meet heterogeneous demands on high-speed data transmission and extensive coverage. To fully exploit the benefits of mmWave bands in massive multiple-input multiple-output (MIMO) systems, highly accurate channel state information (CSI) is required. However, directly estimating the mmWave channel demands substantial pilot overhead due to the large CSI dimension and low signal-to-noise ratio (SNR) led by severe path loss and blockage attenuation. In this paper, we propose an efficient \textbf{M}ulti-\textbf{D}omain \textbf{F}usion \textbf{C}hannel \textbf{E}xtrapolator (MDFCE) to extrapolate sub-6 GHz band CSI to mmWave band CSI, so as to reduce the pilot overhead for mmWave CSI acquisition in dual band massive MIMO systems. Unlike traditional channel extrapolation methods based on mathematical modeling, the proposed MDFCE combines the mixture-of-experts framework and the multi-head self-attention mechanism to fuse multi-domain features of sub-6 GHz CSI, aiming to characterize the mapping from sub-6 GHz CSI to mmWave CSI effectively and efficiently. The simulation results demonstrate that MDFCE can achieve superior performance with less training pilots compared with existing methods across various antenna array scales and signal-to-noise ratio levels while showing a much higher computational efficiency.

翻译：未来无线通信系统将日益依赖毫米波（mmWave）与6GHz以下频段的融合，以满足高速数据传输与广域覆盖的异构需求。为充分发挥毫米波频段在大规模多输入多输出（MIMO）系统中的优势，需要获取高精度的信道状态信息（CSI）。然而，由于CSI维度巨大以及严重路径损耗与遮挡衰减导致的低信噪比（SNR），直接估计毫米波信道需要大量导频开销。本文提出一种高效的**多域融合信道外推器**（MDFCE），通过将6GHz以下频段CSI外推至毫米波频段CSI，以降低双频段大规模MIMO系统中获取毫米波CSI所需的导频开销。与传统基于数学建模的信道外推方法不同，所提出的MDFCE融合专家混合框架与多头自注意力机制，以整合6GHz以下CSI的多域特征，从而高效地表征从6GHz以下CSI到毫米波CSI的映射关系。仿真结果表明，在不同天线阵列规模与信噪比水平下，MDFCE相比现有方法能以更少的训练导频实现更优性能，同时展现出显著更高的计算效率。