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Dumb RIS-Assisted Random Beamforming for Energy Efficiency Enhancement of Wireless Communications

Yixin Zhang, Wenchi Cheng, Wei Zhang

TL;DR

This work tackles EE optimization in RIS-assisted wireless networks where obtaining full CSI is impractical. It introduces a single-active-antenna RIS transmitter and a dumb RIS with random beamforming (Darb) to avoid full CSI, coupled with a joint design of RIS element count and transmit power via alternating optimization (Darb-based-Jeta). A threshold feedback strategy further reduces signaling overhead while preserving rate performance. The approach yields substantial EE gains over conventional multi-antenna setups and offers a scalable, hardware-efficient route for RIS-enabled 6G deployments. Overall, the paper provides a practical framework for EE enhancement that leverages random phase shifts, limited feedback, and AO-driven resource design.

Abstract

Energy efficiency (EE) is one of the most important metrics for the beyond fifth generation (B5G) and the future sixth generation (6G) wireless networks. Reconfigurable intelligent surface (RIS) has been widely focused on EE enhancement for wireless networks because it is power-saving, programmable, and easy to be deployed. However, RIS is generally passive and thus difficult to obtain corresponding full channel state information (CSI), which severely impacts the EE enhancement of RIS-assisted wireless communications. To solve this problem, in this paper we propose the new single-active-antenna combined RIS transmitter structure, which can replace traditional multiple antennas to reduce hardware cost and power consumption. Based on the single-active-antenna combined RIS structure, we develop the Dumb RIS-Assisted Random Beamforming (Darb)-based Joint RIS-Elements and Transmit-power optimizAtion (Jeta) scheme, where dumb RIS randomly changes its phase shift according to isotropic distribution only depending on the CSI feedback from users to RIS-assisted transmitter. Then, we jointly design the number of RIS elements and optimize the transmit power to maximize the EE of RIS-assisted wireless communications. Simulation results show that compared with the traditional multi-antenna system, our developed Darb-based-Jeta scheme can significantly increase the EE without the full CSI.

Dumb RIS-Assisted Random Beamforming for Energy Efficiency Enhancement of Wireless Communications

TL;DR

This work tackles EE optimization in RIS-assisted wireless networks where obtaining full CSI is impractical. It introduces a single-active-antenna RIS transmitter and a dumb RIS with random beamforming (Darb) to avoid full CSI, coupled with a joint design of RIS element count and transmit power via alternating optimization (Darb-based-Jeta). A threshold feedback strategy further reduces signaling overhead while preserving rate performance. The approach yields substantial EE gains over conventional multi-antenna setups and offers a scalable, hardware-efficient route for RIS-enabled 6G deployments. Overall, the paper provides a practical framework for EE enhancement that leverages random phase shifts, limited feedback, and AO-driven resource design.

Abstract

Energy efficiency (EE) is one of the most important metrics for the beyond fifth generation (B5G) and the future sixth generation (6G) wireless networks. Reconfigurable intelligent surface (RIS) has been widely focused on EE enhancement for wireless networks because it is power-saving, programmable, and easy to be deployed. However, RIS is generally passive and thus difficult to obtain corresponding full channel state information (CSI), which severely impacts the EE enhancement of RIS-assisted wireless communications. To solve this problem, in this paper we propose the new single-active-antenna combined RIS transmitter structure, which can replace traditional multiple antennas to reduce hardware cost and power consumption. Based on the single-active-antenna combined RIS structure, we develop the Dumb RIS-Assisted Random Beamforming (Darb)-based Joint RIS-Elements and Transmit-power optimizAtion (Jeta) scheme, where dumb RIS randomly changes its phase shift according to isotropic distribution only depending on the CSI feedback from users to RIS-assisted transmitter. Then, we jointly design the number of RIS elements and optimize the transmit power to maximize the EE of RIS-assisted wireless communications. Simulation results show that compared with the traditional multi-antenna system, our developed Darb-based-Jeta scheme can significantly increase the EE without the full CSI.
Paper Structure (13 sections, 24 equations, 4 figures, 1 table, 1 algorithm)

This paper contains 13 sections, 24 equations, 4 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model
  3. RIS-Assisted Transmitter Structure
  4. Signal Model
  5. Problem Formulation
  6. Total Power Consumption and Energy Efficiency Model
  7. Energy Efficiency Optimization Problem Formulation
  8. Darb-based Energy Efficiency Optimization
  9. Random Beamforming Using Dumb RIS
  10. Darb-based Joint RIS-elements and Transmit-power Optimization Scheme
  11. Darb-based-Jeta Scheme and Its Convergence
  12. Performance Evaluations
  13. Conclusions

Figures (4)

  • Figure 1: The RIS-assisted wireless communications system.
  • Figure 2: The energy efficiency comparison of RIS-assisted and multi-antenna wireless communication system with different numbers of RIS elements and antennas.
  • Figure 3: The energy efficiency comparison of RIS-assisted with Darb scheme, Darb-based-Jeta scheme and multi-antenna wireless communication system.
  • Figure 4: The average rate and feedback overhead comparison of the selective-threshold feedback strategy.