Index modulation (IM) significantly enhances the spectral efficiency of fluid antennas (FAs) enabled multiple-input multiple-output (MIMO) systems, which is named FA-IM. However, due to the dense distribution of ports on fluid antennas, the wireless channel exhibits a high spatial correlation, resulting in severe performance degradation in the existing FA-IM scheme. This paper proposes a novel fluid antenna grouping index modulation (FA-GIM) scheme to mitigate the spatial correlation of the FA-IM channel, further enhancing system performance. Based on the spatial correlation model of two-dimensional (2D) fluid antenna surfaces, this paper specifically adopts a block grouping method where adjacent ports are allocated to the same group. The numerical results demonstrate that the proposed scheme exhibits superior bit error rate (BER) performance compared to the state-of-the-art scheme, enhancing the robustness of FA-assisted MIMO systems.

翻译：索引调制（IM）显著提升了流体天线（FA）支持的多输入多输出（MIMO）系统的频谱效率，该系统被称为FA-IM。然而，由于流体天线上端口分布密集，无线信道表现出高度的空间相关性，导致现有FA-IM方案性能严重下降。本文提出了一种新颖的流体天线分组索引调制（FA-GIM）方案，以减轻FA-IM信道的空间相关性，进一步提升系统性能。基于二维流体天线表面的空间相关性模型，本文特别采用了一种块分组方法，将相邻端口分配到同一组。数值结果表明，所提方案相比现有先进方案展现出更优越的误码率（BER）性能，增强了FA辅助MIMO系统的鲁棒性。