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 the FA, the wireless channel exhibits a high spatial correlation, leading to severe performance degradation in the existing FA-IM-assisted MIMO systems. To tackle this issue, this paper proposes a novel fluid antenna grouping index modulation (FA-GIM) scheme to mitigate the high correlation between the activated ports. Specifically, considering the characteristics of the FA two-dimensional (2D) surface structure and the spatially correlated channel model in FA-assisted MIMO systems, a block grouping method is adopted, where adjacent ports are assigned to the same group. Subsequently, different groups independently perform port index selection and constellation symbol mapping, with only one port being activated within each group during each transmission interval. Numerical results show that, compared to state-of-the-art schemes, the proposed FA-GIM scheme consistently achieves significant bit error rate (BER) performance gains under various conditions. It has also been confirmed that the proposed scheme is both efficient and robust, enhancing the performance 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FA上端口的密集分布，无线信道呈现出高度的空间相关性，导致现有FA-IM辅助的MIMO系统性能严重下降。为解决这一问题，本文提出了一种新颖的流体天线分组索引调制（FA-GIM）方案，以减轻激活端口之间的高相关性。具体而言，考虑到FA二维表面结构的特性以及FA辅助MIMO系统中的空间相关信道模型，采用了一种块分组方法，其中相邻端口被分配到同一组。随后，不同组独立执行端口索引选择和星座符号映射，在每个传输间隔内每组仅激活一个端口。数值结果表明，与现有先进方案相比，所提出的FA-GIM方案在各种条件下均能持续实现显著的误码率（BER）性能增益。研究也证实，该方案既高效又稳健，有效提升了FA辅助MIMO系统的性能。