In this paper, we investigate multi-user modular extremely large-scale multiple-input multiple-output (XL-MIMO) communication systems, where modular extremely large-scale uniform linear array (XL-ULA) is deployed at the base station (BS) to serve multiple single-antenna users. By exploiting the unique modular array architecture and considering the potential near-field propagation, we develop sub-array based uniform spherical wave (USW) models for distinct versus common angles of arrival/departure (AoAs/AoDs) with respect to different sub-arrays/modules, respectively. Under such USW models, we analyze the beam focusing patterns at the near-field observation location by using near-field beamforming. The analysis reveals that compared to the conventional XL-MIMO with collocated antenna elements, modular XL-MIMO can provide better spatial resolution by benefiting from its larger array aperture. However, it also incurs undesired grating lobes due to the large inter-module separation. Moreover, it is found that for multi-user modular XL-MIMO communications, the achievable signal-to-interference-plus-noise ratio (SINR) for users may be degraded by the grating lobes of the beam focusing pattern. To address this issue, an efficient user grouping method is proposed for multi-user transmission scheduling, so that users located within the grating lobes of each other are not allocated to the same time-frequency resource block (RB) for their communications. Numerical results are presented to verify the effectiveness of the proposed user grouping method, as well as the superior performance of modular XL-MIMO over its collocated counterpart with densely distributed users.

翻译：本文研究了多用户模块化极大规模多输入多输出（XL-MIMO）通信系统，其中基站的模块化极大规模均匀线性阵列（XL-ULA）服务于多个单天线用户。通过利用独特的模块化阵列架构并考虑潜在的近场传播，我们针对不同子阵列/模块间不同与公共的到达角/离开角，分别建立了基于子阵列的均匀球面波模型。在此类均匀球面波模型下，我们利用近场波束赋形分析了近场观测位置的波束聚焦模式。分析表明，相较于传统共址天线单元的XL-MIMO，模块化XL-MIMO凭借更大的阵列孔径可提供更优的空间分辨率，但模块间大间距也会引发不必要的栅瓣。此外，研究发现对于多用户模块化XL-MIMO通信，用户可达的信干噪比可能因波束聚焦模式的栅瓣而恶化。针对该问题，本文提出了一种高效的用户分组方法用于多用户传输调度，使得位于彼此栅瓣内的用户不被分配至相同时频资源块进行通信。数值结果验证了所提用户分组方法的有效性，以及模块化XL-MIMO在用户密集分布场景下相较于传统共址结构的性能优势。