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RIS-aided Wireless Communication with Movable Elements Geometry Impact on Performance

Yan Zhang, Indrakshi Dey, Nicola Marchetti

TL;DR

The study addresses how movable MA elements integrated into a RIS (MA-RIS) alter outage probability and SNR in downlink wireless links, by explicitly modeling the illuminated area and the resulting effective number of active elements $N_{eff}$ for 1D and 2D configurations. It develops a LoS-focused channel model using FRVs, derives the instantaneous SNR as a function of the illuminated MA elements, and formulates outage probability via $F_{\gamma_{max}}$ that incorporates blockage-aware effective counts. Key findings show MA-RIS can yield about a 24% outage improvement and a ~2 dB SNR gain over conventional FPA-RIS, with 2D MA-RIS offering the largest gains due to improved geometric utilization and beam control; MA-RIS can achieve comparable performance with fewer elements. The results underscore the practical potential of movable reflectors in dynamic or large-scale settings (e.g., V2X) and highlight the need to account for illumination geometry in RIS design, while recognizing limitations such as single-user and single-path assumptions that future work should address.

Abstract

Reconfigurable Intelligent Surfaces (RIS) are known as a promising technology to improve the performance of wireless communication networks, and have been extensively studied. Movable Antennas (MA) are a novel technology that fully exploits the antenna placement for enhancing the system performance. This article aims at evaluating the impact of transmit power and number of antenna elements on the outage probability performance of an MA-enabled RIS structure (MA-RIS), compared to existing Fixed-Position Antenna RIS (FPA-RIS). The change in geometry caused by the movement of antennas and its implications for the effective number of illuminated elements, are studied for 1D and 2D array structures. Our numerical results confirm the performance advantage provided by MA-RIS, achieving 24\% improvement in outage probability, and 2 dB gain in Signal-to-Noise Ratio (SNR), as compared to FPA-RIS.

RIS-aided Wireless Communication with Movable Elements Geometry Impact on Performance

TL;DR

The study addresses how movable MA elements integrated into a RIS (MA-RIS) alter outage probability and SNR in downlink wireless links, by explicitly modeling the illuminated area and the resulting effective number of active elements for 1D and 2D configurations. It develops a LoS-focused channel model using FRVs, derives the instantaneous SNR as a function of the illuminated MA elements, and formulates outage probability via that incorporates blockage-aware effective counts. Key findings show MA-RIS can yield about a 24% outage improvement and a ~2 dB SNR gain over conventional FPA-RIS, with 2D MA-RIS offering the largest gains due to improved geometric utilization and beam control; MA-RIS can achieve comparable performance with fewer elements. The results underscore the practical potential of movable reflectors in dynamic or large-scale settings (e.g., V2X) and highlight the need to account for illumination geometry in RIS design, while recognizing limitations such as single-user and single-path assumptions that future work should address.

Abstract

Reconfigurable Intelligent Surfaces (RIS) are known as a promising technology to improve the performance of wireless communication networks, and have been extensively studied. Movable Antennas (MA) are a novel technology that fully exploits the antenna placement for enhancing the system performance. This article aims at evaluating the impact of transmit power and number of antenna elements on the outage probability performance of an MA-enabled RIS structure (MA-RIS), compared to existing Fixed-Position Antenna RIS (FPA-RIS). The change in geometry caused by the movement of antennas and its implications for the effective number of illuminated elements, are studied for 1D and 2D array structures. Our numerical results confirm the performance advantage provided by MA-RIS, achieving 24\% improvement in outage probability, and 2 dB gain in Signal-to-Noise Ratio (SNR), as compared to FPA-RIS.
Paper Structure (10 sections, 15 equations, 4 figures)

This paper contains 10 sections, 15 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System model
  3. Channel model
  4. Topology of MA-RIS illumination area
  5. Outage Probability
  6. Performance Analysis
  7. Transmit Power and Number of Elements : Effect on Outage probability
  8. Effective Number of MA-RIS
  9. Instantaneous SNR
  10. Conclusion

Figures (4)

  • Figure 1: Illustration of the system model. In the MA-RIS panel, yellow blocks depict all the $N$ MA units moving with speed $v$, while the green blocks signify the effective antennas. The solid blue ellipse is an enlarged representation of the hollow ellipse which represents the illumination area labeled as $S_m$, with semi-major axis $a$ and semi-minor axis $b$, and represents the illumination area, showing the HPBW $\phi_0$ from the BS. The terms $\varphi_n^r$ and $\varphi_n^t$ denote the AoA and AoD associated with each antenna element, respectively.
  • Figure 2: Outage probability performance comparison. (a) $P_{out}$ versus $P_t$. (b) $P_{out}$ versus elements number.
  • Figure 3: Comparisons of effective numbers in MA-RIS and FPA-RIS versus $y_s$
  • Figure 4: Instantaneous SNR $\gamma$ versus transmit power $P_t$