Abstract: This study addresses the challenges of near-field interference suppression and resource allocation in extremely large-scale multiple-input multiple-output (XL-MIMO) communication systems, particularly under dense-user scenarios. We propose a quality-of-service (QoS)-aware joint user scheduling and power control scheme. Leveraging the spherical wave (SW) characteristics of near field channels, a dual-domain interference suppression strategy is developed by analyzing the spatial correlation of beam focusing vectors in terms of both angular separation and distance constraints. Based on this, a spatial correlation-based scheduling (SCS) algorithm is designed. By integrating this user selection strategy with a dynamic power allocation mechanism, the proposed approach optimizes the sum spectral efficiency while ensuring the user QoS. This framework is further extended to modular XL-MIMO systems. We show how modular deployment can enhance spatial resolution and develop an adapted QoS-aware user scheduling algorithm, called modular SCS (SCS-mod), for this architecture. Simulation results validate that the proposed algorithms significantly outperform existing schemes in terms of sum spectral efficiency and the number of scheduled users, especially under high user density and high transmission power conditions.

面向模块化XL-MIMO通信的QoS感知多用户调度和功率控制

[1]Björnson E, Sanguinetti L, Wymeersch H, et al., 2019. Massive MIMO is a reality—what is next?: five promising research directions for antenna arrays. Digit Signal Process, 94:3-20.

[2]Chen YH, Dai LL, 2024. Non-stationary channel estimation for extremely large-scale MIMO. IEEE Trans Wirel Commun, 23(7):7683-7697.

[3]Cui MY, Dai LL, 2022. Channel estimation for extremely large-scale MIMO: far-field or near-field? IEEE Trans Commun, 70(4):2663-2677.

[4]De Carvalho E, Ali A, Amiri A, et al., 2020. Non-stationarities in extra-large-scale massive MIMO. IEEE Wirel Commun, 27(4):74-80.

[5]De Souza JHI, Filho JCM, Amiri A, et al., 2023. QoS-aware user scheduling in crowded XL-MIMO systems under non-stationary multi-state LoS/NLoS channels. IEEE Trans Veh Technol, 72(6):7639-7652.

[6]Dong ZJ, Zeng Y, 2022. Near-field spatial correlation for extremely large-scale array communications. IEEE Commun Lett, 26(7):1534-1538.

[7]Dong ZJ, Li XR, Zeng Y, 2024. Characterizing and utilizing near-field spatial correlation for XL-MIMO communication. IEEE Trans Commun, 72(12):7922-7937.

[8]Du HY, Kang JW, Niyato D, et al., 2022. Reconfigurable intelligent surface-aided joint radar and covert communications: fundamentals, optimization, and challenges. IEEE Veh Technol Mag, 17(3):54-64.

[9]González-Coma JP, Lopez-Martinez FJ, Castedo L, 2021. Low-complexity distance-based scheduling for multi-user XL-MIMO systems. IEEE Wirel Commun Lett, 10(11):2407-2411.

[10]González-Coma JP, Lopez-Martinez FJ, Castedo L, 2023. Joint user scheduling and precoding for XL-MIMO systems with imperfect CSI. IEEE Wirel Commun Lett, 12(10):1657-1661.

[11]Jeon J, Lee G, Ibrahim AAI, et al., 2021. MIMO evolution toward 6G: modular massive MIMO in low-frequency bands. IEEE Commun Mag, 59(11):52-58.

[12]Lee J, Chung H, Cho Y, et al., 2025. Near-field channel estimation for XL-RIS assisted multi-user XL-MIMO systems: hybrid beamforming architectures. IEEE Trans Commun, 73(3):1560-1574.

[13]Li XR, Lu HQ, Zeng Y, et al., 2022. Near-field modeling and performance analysis of modular extremely large-scale array communications. IEEE Commun Lett, 26(7):1529-1533.

[14]Li XR, Dong ZJ, Zeng Y, et al., 2023. Near-field beam focusing pattern and grating lobe characterization for modular XL-array. Proc IEEE Global Communications Conf, p.4068-4073.

[15]Li XR, Dong ZJ, Zeng Y, et al., 2024. Multi-user modular XL-MIMO communications: near-field beam focusing pattern and user grouping. IEEE Trans Wirel Commun, 23(10):13766-13781.

[16]Liu ZL, Zhang JY, Liu ZH, et al., 2024. Cell-free XL-MIMO meets multi-agent reinforcement learning: architectures, challenges, and future directions. IEEE Wirel Commun, 31(4):155-162.

[17]Lu HQ, Zeng Y, 2021. How does performance scale with antenna number for extremely large-scale MIMO? Proc IEEE Int Conf on Communications, p.1-6.

[18]Lu HQ, Zeng Y, 2022. Communicating with extremely large-scale array/surface: unified modeling and performance analysis. IEEE Trans Wirel Commun, 21(6):4039-4053.

[19]Lu HQ, Zeng Y, You CS, et al., 2024. A tutorial on near-field XL-MIMO communications toward 6G. IEEE Commun Surv Tutor, 26(4):2213-2257.

[20]Palomar DP, Fonollosa JR, 2005. Practical algorithms for a family of waterfilling solutions. IEEE Trans Signal Process, 53(2):686-695.

[21]Qu N, Li BB, Shafin R, et al., 2022. Angle-based downlink beam selection and user scheduling for massive MIMO systems. IEEE Trans Wirel Commun, 21(10):8077-8089.

[22]Sherman J, 1962. Properties of focused apertures in the Fresnel region. IRE Trans Antenn Propag, 10(4):399-408.

[23]Tang AZ, Wang JB, Pan YJ, et al., 2024. Line-of-sight extra-large MIMO systems with angular-domain processing: channel representation and transceiver architecture. IEEE Trans Commun, 72(1):570-584.

[24]Wang HZ, Zeng Y, 2023. Can sparse arrays outperform collocated arrays for future wireless communications? Proc IEEE Globecom Workshops, p.667-672.

[25]Wu ZD, Dai LL, 2023. Multiple access for near-field communications: SDMA or LDMA? IEEE J Sel Areas Commun, 41(6):1918-1935.

[26]Yang JY, Zhang JY, Xu BK, et al., 2024. Precoding and power control design for cell-free XL-MIMO: from far-field to near-field. Proc Int Conf on Ubiquitous Communication, p.63-67.

[27]Zhang YZ, Yang ZA, Yue SH, et al., 2024. Hybrid near-field and far-field XL-MIMO: how many users can be supported? IEEE Commun Lett, 28(10):2402-2406.

[28]Zheng Y, Wang CX, Huang J, et al., 2024. A novel ultra-massive MIMO BDCM for 6G wireless communication systems. IEEE Trans Wirel Commun, 23(4):3221-3237.