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Analog-Only Beamforming for Near-Field Multiuser MIMO Communications

Ying Wang, Chenhao Qi

TL;DR

This paper tackles the pilot-overhead and CSI challenges of near-field multiuser MIMO by proposing analog-only beamforming (AoBF) as a low-complexity alternative to hybrid beamforming. It develops two majorization-minimization–based AoBF schemes: one assuming perfect CSI using SLNR decoupling, and another handling imperfect CSI via near-field codebook beam sweeping and auxiliary-point channel approximations. Simulation results show AoBF can closely match the sum-rate of HBF under perfect CSI and provide energy-efficiency advantages, with meaningful gains even under imperfect CSI, thanks to beam focusing and nulling in the distance-augmented near-field domain. The work suggests AoBF as a practical route to high EE and simpler reconfiguration in next-generation near-field wireless systems, with future work on PCM-based AoBF designs.

Abstract

For the existing near-field multiuser communications based on hybrid beamforming (HBF) architectures, high-quality effective channel estimation is required to obtain the channel state information (CSI) for the design of the digital beamformer. To simplify the system reconfiguration and eliminate the pilot overhead required by the effective channel estimation, we considered an analog-only beamforming (AoBF) architecture in this study. The AoBF is designed with the aim of maximizing the sum rate, which is then transformed into a problem, maximizing the power transmitted to the target user equipment (UE) and meanwhile minimizing the power leaked to the other UEs. To solve this problem, we used beam focusing and beam nulling and proposed two AoBF schemes based on the majorization-minimization (MM) algorithm. First, the AoBF scheme based on perfect CSI is proposed, with the focus on the beamforming performance and regardless of the CSI acquisition. Then, the AoBF scheme based on imperfect CSI is proposed, where the low-dimensional imperfect CSI is obtained by beam sweeping based on a near-field codebook. Simulation results demonstrate that the two AoBF schemes can approach the sum rate of the HBF schemes but outperform HBF schemes in terms of energy efficiency (EE).

Analog-Only Beamforming for Near-Field Multiuser MIMO Communications

TL;DR

This paper tackles the pilot-overhead and CSI challenges of near-field multiuser MIMO by proposing analog-only beamforming (AoBF) as a low-complexity alternative to hybrid beamforming. It develops two majorization-minimization–based AoBF schemes: one assuming perfect CSI using SLNR decoupling, and another handling imperfect CSI via near-field codebook beam sweeping and auxiliary-point channel approximations. Simulation results show AoBF can closely match the sum-rate of HBF under perfect CSI and provide energy-efficiency advantages, with meaningful gains even under imperfect CSI, thanks to beam focusing and nulling in the distance-augmented near-field domain. The work suggests AoBF as a practical route to high EE and simpler reconfiguration in next-generation near-field wireless systems, with future work on PCM-based AoBF designs.

Abstract

For the existing near-field multiuser communications based on hybrid beamforming (HBF) architectures, high-quality effective channel estimation is required to obtain the channel state information (CSI) for the design of the digital beamformer. To simplify the system reconfiguration and eliminate the pilot overhead required by the effective channel estimation, we considered an analog-only beamforming (AoBF) architecture in this study. The AoBF is designed with the aim of maximizing the sum rate, which is then transformed into a problem, maximizing the power transmitted to the target user equipment (UE) and meanwhile minimizing the power leaked to the other UEs. To solve this problem, we used beam focusing and beam nulling and proposed two AoBF schemes based on the majorization-minimization (MM) algorithm. First, the AoBF scheme based on perfect CSI is proposed, with the focus on the beamforming performance and regardless of the CSI acquisition. Then, the AoBF scheme based on imperfect CSI is proposed, where the low-dimensional imperfect CSI is obtained by beam sweeping based on a near-field codebook. Simulation results demonstrate that the two AoBF schemes can approach the sum rate of the HBF schemes but outperform HBF schemes in terms of energy efficiency (EE).

Paper Structure

This paper contains 10 sections, 30 equations, 11 figures, 1 table, 2 algorithms.

Table of Contents

  1. Introduction
  2. System Model
  3. AoBF for Near-Field Multiuser MIMO
  4. AoBF Based on Perfect CSI
  5. AoBF Based on Imperfect CSI
  6. Simulation Results
  7. Beam Pattern Comparison
  8. Sum Rate Evaluation
  9. EE Evaluation
  10. Conclusion

Figures (11)

  • Figure 1: Beamforming architecture comparison: (a) the HBF architecture; (b) the AoBF architecture.
  • Figure 2: The channel models: (a) in the far field; (b) in the near field.
  • Figure 3: Illustration of beam sweeping code words and auxiliary points.
  • Figure 4: The performance of AoBF based on imperfect CSI with different $R$ and $S$.
  • Figure 5: Beam pattern comparison: (a) the beam pattern generated by analog-only beam steering based on perfect CSI; (b) the beam pattern generated by analog-only beam steering based on imperfect CSI; (c) the beam pattern generated by HBF with WMMSE based on perfect CSI; (d) the beam pattern generated by HBF with WMMSE based on imperfect CSI; (e) the beam pattern generated by AoBF based on perfect CSI; (f) the beam pattern generated by AoBF based on imperfect CSI.
  • ...and 6 more figures