Zeng Jie, Song Yuxin, Wu Teng, Lv Tiejun, Zhou Shidong
School of Communication and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing 400065, China.
Beijing National Research Center for Information Science and Technology, Tsinghua University, Beijing 100084, China.
Sensors (Basel). 2022 Jul 14;22(14):5279. doi: 10.3390/s22145279.
Sixth-generation (6G) wireless communication scenarios are complex and diverse. Small-scale fading is a key part of wireless channels and its impact on performance in scenarios with time sensitivity and 6G ultrareliable and low latency communications (URLLC) quality-of-service requirements cannot be ignored. Therefore, it is necessary to accurately characterize small-scale fading when designing wireless communication systems. In this paper, we derive approximate closed form expressions for the probability density function, cumulative distribution function and moment-generating function of the postprocessing signal-to-noise ratio following the zero-forcing detector in a cell-free massive multiple-input multiple-output (CF mMIMO) system. CF mMIMO system is a nonorthogonal multiple access (NOMA) system that enables users to share all channel uses and can ensure the fairness of the communication quality experienced by different users. Our key contributions include the extension of the κ-μ shadowed fading model to a CF mMIMO system and the proposal of theoretical tools (the derived closed-form expression) to improve its mathematical tractability. By exploiting the statistical characterizations of the arrival and service processes, another important contribution is the exploitation of the upper bound of the queuing delay violation probability (UB-QDVP) over the Mellin transforms of the arrival and service processes in the proposed CF mMIMO system under the κ-μ shadowed fading model. Corroborated by extensive simulations, our analyses validate that the CF mMIMO system outperforms the orthogonal multiple access and power-domain NOMA systems and reveal the relationships among different small-scale fading types, energy efficiency, delay and the UB-QDVP, as well as the accuracy and effectiveness of the proposed theoretical tools based on the κ-μ shadowed fading model.
第六代（6G）无线通信场景复杂多样。小尺度衰落是无线信道的关键部分，其对具有时间敏感性的场景以及6G超可靠低延迟通信（URLLC）服务质量要求下的性能影响不可忽视。因此，在设计无线通信系统时，准确表征小尺度衰落很有必要。在本文中，我们推导了在无小区大规模多输入多输出（CF mMIMO）系统中，迫零检测器之后的后处理信噪比的概率密度函数、累积分布函数和矩生成函数的近似闭式表达式。CF mMIMO系统是一种非正交多址（NOMA）系统，它能让用户共享所有信道资源，并能确保不同用户所体验到的通信质量的公平性。我们的主要贡献包括将κ-μ阴影衰落模型扩展到CF mMIMO系统，以及提出理论工具（推导的闭式表达式）以提高其数学易处理性。通过利用到达和服务过程的统计特征，另一个重要贡献是在所提出的CF mMIMO系统中，在κ-μ阴影衰落模型下，利用到达和服务过程的梅林变换来研究排队延迟违反概率的上界（UB-QDVP）。大量仿真验证了我们的分析，即CF mMIMO系统优于正交多址和功率域NOMA系统，并揭示了不同小尺度衰落类型、能量效率、延迟和UB-QDVP之间的关系，以及基于κ-μ阴影衰落模型所提出的理论工具的准确性和有效性。
