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Uplink transmission design for crowded correlated cell-free massive MIMO-OFDM systems
Science China Information Sciences ( IF 7.3 ) Pub Date : 2021-06-02 , DOI: 10.1007/s11432-020-3103-3
Junyuan Gao , Yongpeng Wu , Yongjian Wang , Wenjun Zhang , Fan Wei

In cell-free massive multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, user equipments (UEs) are served by many distributed access points (APs), where channels are correlated owing to finite angle-delay spread in realistic outdoor wireless propagation environments. Meanwhile, the number of UEs is growing rapidly for future fully networked society. In this paper, we focus on the uplink transmission design in crowded correlated cell-free massive MIMO-OFDM systems with a limited number of orthogonal pilots. For the pilot transmission phase, we identify active UEs based on non-orthogonal pilot phase shift hopping patterns and non-orthogonal adjustable phase shift pilots (APSP). We derive a closed-form expression of mean square error of channel estimation (MSE-CE) and obtain an optimal condition for minimizing MSE-CE. According to this condition, the APSP set allocation scheme is proposed. Furthermore, for the data transmission, the max-min power control algorithm is devised to maximize the minimum spectral efficiency (SE) lower bound among active UEs. Simulation results indicate significant performance gains in terms of MSE-CE for the proposed APSP set allocation scheme. The proposed power control scheme can further improve the minimum SE among active UEs. Hence, they are crucial for crowded correlated cell-free massive MIMO-OFDM systems.



中文翻译:

拥挤相关无蜂窝大规模MIMO-OFDM系统的上行传输设计

在无小区大规模多输入多输出 (MIMO) 正交频分复用 (OFDM) 系统中,用户设备 (UE) 由许多分布式接入点 (AP) 提供服务,其中信道由于有限的角度延迟扩展而相关在真实的室外无线传播环境中。同时,对于未来完全网络化的社会,UE 的数量正在快速增长。在本文中,我们专注于具有有限数量正交导频的拥挤相关无小区大规模 MIMO-OFDM 系统中的上行链路传输设计。对于导频传输阶段,我们根据非正交导频相移跳频模式和非正交可调相移导频 (APSP) 识别活动 UE。我们推导出信道估计均方误差 (MSE-CE) 的闭式表达式,并获得最小化 MSE-CE 的最佳条件。针对这种情况,提出了APSP集分配方案。此外,对于数据传输,设计了最大-最小功率控制算法以最大化活动UE之间的最小频谱效率(SE)下限。仿真结果表明,对于提议的 APSP 集分配方案,MSE-CE 方面的性能显着提高。所提出的功率控制方案可以进一步提高活动 UE 之间的最小 SE。因此,它们对于拥挤的相关无蜂窝大规模 MIMO-OFDM 系统至关重要。设计最大最小功率控制算法以最大化活动 UE 之间的最小频谱效率 (SE) 下限。仿真结果表明,对于提议的 APSP 集分配方案,MSE-CE 方面的性能显着提高。所提出的功率控制方案可以进一步提高活动 UE 之间的最小 SE。因此,它们对于拥挤的相关无蜂窝大规模 MIMO-OFDM 系统至关重要。设计最大最小功率控制算法以最大化活动 UE 之间的最小频谱效率 (SE) 下限。仿真结果表明,对于提议的 APSP 集分配方案,MSE-CE 方面的性能显着提高。所提出的功率控制方案可以进一步提高活动 UE 之间的最小 SE。因此,它们对于拥挤的相关无蜂窝大规模 MIMO-OFDM 系统至关重要。

更新日期:2021-06-18
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