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Repeater-Assisted MIMO Can Also Boost Frequency Diversity: A Semi-Analytic Study

Hiroki Iimori, Yuto Hama

Abstract

Massive multiple-input multiple-output (MIMO) has enabled substantial spatial multiplexing and array gains in real-world systems, while distributed MIMO (D-MIMO) improves macro-diversity over wide areas at the cost of deployment complexity. Repeater-assisted massive MIMO (RA-MIMO) is a lower-cost alternative that can recover key distributed-MIMO advantages. This paper asks whether repeater assistance can also enhance frequency diversity. We study an uncoded discrete Fourier transform-spread orthogonal frequency-division multiplexing (DFT-s-OFDM) uplink with one-tap single-carrier frequency-domain equalization (SC-FDE) based on minimum mean-square error (MMSE) and derive a receiver-matched semi-analytic bit-error rate (BER) expression by averaging over channel and interference realizations, without Gaussian approximation of residual despreading interference. The analysis clarifies how repeater delay reshapes frequency correlation, and waveform simulations confirm tight agreement with the derived expression together with improved high-signal-to-noise ratio (SNR) BER decay, highlighting delay as a practical tuning knob.

Repeater-Assisted MIMO Can Also Boost Frequency Diversity: A Semi-Analytic Study

Abstract

Massive multiple-input multiple-output (MIMO) has enabled substantial spatial multiplexing and array gains in real-world systems, while distributed MIMO (D-MIMO) improves macro-diversity over wide areas at the cost of deployment complexity. Repeater-assisted massive MIMO (RA-MIMO) is a lower-cost alternative that can recover key distributed-MIMO advantages. This paper asks whether repeater assistance can also enhance frequency diversity. We study an uncoded discrete Fourier transform-spread orthogonal frequency-division multiplexing (DFT-s-OFDM) uplink with one-tap single-carrier frequency-domain equalization (SC-FDE) based on minimum mean-square error (MMSE) and derive a receiver-matched semi-analytic bit-error rate (BER) expression by averaging over channel and interference realizations, without Gaussian approximation of residual despreading interference. The analysis clarifies how repeater delay reshapes frequency correlation, and waveform simulations confirm tight agreement with the derived expression together with improved high-signal-to-noise ratio (SNR) BER decay, highlighting delay as a practical tuning knob.

Paper Structure

This paper contains 16 sections, 36 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Notation
  3. System Model
  4. Input-Output Signal Model
  5. Repeater-Assisted Equivalent Channel
  6. Semi-Analytic BER Expression
  7. Delay-Domain PDP and Subcarrier Correlation
  8. MMSE Equalization and Despreading
  9. Gain Normalization and Symbol-Domain Decomposition
  10. Post-Despread Noise Statistics and Modulation-General BER Form
  11. QPSK Example
  12. Final Semi-Analytic and Practical Estimator
  13. Simulation Results
  14. Semi-Analytic and Waveform Consistency
  15. Numerical Diversity Comparison
  16. ...and 1 more sections

Figures (2)

  • Figure 1: comparison between the proposed semi-analytic evaluation and full-stack waveform Monte Carlo simulation.
  • Figure 2: Numerical comparison of frequency-diversity behavior for the direct-only and repeater-assisted cases.