Cell-free (CF) massive multiple-input multiple-output (MIMO) systems show great potentials in low-mobility scenarios, due to cell boundary disappearance and strong macro diversity. However, the great Doppler frequency offset (DFO) leads to serious inter-carrier interference in orthogonal frequency division multiplexing (OFDM) technology, which makes it difficult to provide high-quality transmissions for both high-speed train (HST) operation control systems and passengers. In this paper, we focus on the performance of CF massive MIMO-OFDM systems with both fully centralized and local minimum mean square error (MMSE) combining in HST communications. Considering the local maximum ratio (MR) combining, the large-scale fading decoding (LSFD) cooperation and the practical effect of DFO on system performance, exact closed-form expressions for uplink spectral efficiency (SE) expressions are derived. We observe that cooperative MMSE combining achieves better SE performance than uncooperative MR combining. In addition, HST communications with small cell and cellular massive MIMO-OFDM systems are compared in terms of SE. Numerical results reveal that the CF massive MIMO-OFDM system achieves a larger and more uniform SE than the other systems. Finally, the train antenna centric (TA-centric) CF massive MIMO-OFDM system is designed for practical implementation in HST communications, and three power control schemes are adopted to optimize the propagation of TAs for reducing the impact of the DFO.
翻译:由于细胞边界消失和宏观多样性强,无细胞(CFD)大规模多输出多输出(MIMO)系统在低移动性假设情景中显示出巨大的潜力,但是,由于细胞边界消失和宏观多样性的强强,巨大的多普勒频率抵消(DFO)导致对正心频率分多氧化(OFDM)技术的严重跨载干扰,这使得很难为高速列车(HST)操作控制系统和乘客提供高质量的传输。在本文件中,我们侧重于具有完全集中和地方最小平均正方差的CFMIM-OFDM系统(MMSE)的性能。考虑到当地最大比率(MMR)的结合、大规模反向解码(LSFD)合作以及DFO对系统性能的实际影响,因此很难为高光谱效率(SEVT)提供精确的封闭式表达方式。我们观察到,将SEME(HST)小型和移动电话(MODMDM)系统与大型直径(SO)系统(SO-CFA)的大规模直径直径直径(MFO)系统的执行(MFO-CMFO-CMDMDMA)系统,最后显示的机械(MDMDMFO-CFDMDR)进行较大规模平级)系统进行较大型平坦(SDMDM)的三等的机械操作系统进行对比。