Abstract
In this paper, we propose a hybrid relay-reflecting intelligent surface (HR-RIS)-assisted cell-free (CF) massive multiple-input multiple-output (mMIMO) network to achieve consistent spectral efficiency (SE). The HR-RIS technique manipulates the propagation environment by reflecting and enhancing radio signals in desired locations, providing a symbiotic integration with CF mMIMO for future wireless communication systems. We first model uplink and downlink channels, obtaining minimum-mean-square-error estimations for efficient transmission paths. We then analyze the SE performance of the proposed system. To enhance sum spectral efficiency in downlink multi-antenna, multi-user, and millimeter-wave massive MIMO networks, we introduce a low-complexity hybrid precoding approach. The optimal analog equalizer is determined by converting the analog precoding matrix dimensions into square matrices and selecting a few discrete Fourier transforms to maximize the amplitude of corresponding wideband channel matrices. We employ the equal gain transmission technique to combine channel gains efficiently and ensure spectral efficiency. To mitigate inter-user interference, we propose an enhanced block diagonalization method for designing the digital precoder and combiner. Our study demonstrates that the proposed HR-RIS-assisted CF mMIMO system offers significant improvements in SE performance, paving the way for advanced wireless communication systems.
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Victoria, A.H., Devarajan, N.M., Saravanakumar, R. et al. Spectral efficiency enhancement by hybrid pre-coding technique for reconfigurable intelligent surfaces-based massive MIMO systems under variable CSI. Soft Comput (2023). https://doi.org/10.1007/s00500-023-08464-7
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DOI: https://doi.org/10.1007/s00500-023-08464-7