Active RISs: Modeling and Optimization
🤖 AI Summary
Conventional reconfigurable intelligent surfaces (RISs) suffer from severe signal attenuation due to double-path loss, fundamentally limiting their performance. Method: This paper investigates active RISs and proposes two novel hardware architectures: a dual-RIS structure driven by a single power amplifier and a reflective amplifying unit based on tunnel diodes. We systematically characterize their phase–amplitude coupling behavior and energy-efficiency trade-offs via power amplifier modeling, analysis of the tunnel diode’s negative differential resistance, and compact linear-algebraic modeling. A joint phase–gain optimization algorithm is then designed. Contribution/Results: Theoretical analysis and simulations demonstrate that active RISs effectively overcome the double-path loss bottleneck, significantly enhancing spectral efficiency and energy efficiency under power constraints. Crucially, performance gains are non-monotonic with respect to the number of active elements, underscoring the necessity of co-optimizing hardware architecture and signal processing algorithms.
Application Category
📝 Abstract
Reconfigurable Intelligent Surfaces (RIS)-empowered communication has emerged as a transformative technology for next generation wireless networks, enabling the programmable shaping of the propagation environment. However, conventional RISs are fundamentally limited by the double path loss effect, which severely attenuates the reflected signals. To overcome this, active RIS architectures, capable of amplifying impinging signals, have been proposed. This chapter investigates the modeling, performance analysis, and optimization of active RISs, focusing on two hardware designs: a dual-RIS structure with a single Power Amplifier (PA), and a reflection amplification structure at the unit cell level using tunnel diodes. For the PA-based design, a comprehensive mathematical model is developed, and closed-form expressions for the received signal-to-noise ratio, bit error probability, and Energy Efficiency (EE) are derived. An optimization framework for configuring the phase shifts and amplifier gain is proposed to maximize system capacity under power constraints. Regarding the second design, the integration of a tunnel diode into the unit cell is carefully studied by analyzing its I-V characteristic, enabling the derivation of the negative resistance range and the power consumption model. Furthermore, the intrinsic phase-amplitude coupling of the reflection coefficient is characterized through compact linear algebra formulations, enabling practical optimization of active RISs. Extensive numerical simulations validate the theoretical analyses, demonstrating that active RISs can effectively overcome the double path loss limitation and achieve favorable EE trade-offs compared to passive RISs. Finally, the trade-off between the available power budget and the number of active elements is examined, revealing that a higher number of active elements does not always lead to optimal performance.
Problem
Research questions and friction points this paper is trying to address.
Overcoming double path loss in RIS with active amplification
Modeling and optimizing dual-RIS and tunnel diode designs
Balancing power budget and active elements for efficiency
Innovation
Methods, ideas, or system contributions that make the work stand out.
Active RIS amplifies signals to overcome path loss
Dual-RIS with single PA optimizes phase and gain
Tunnel diode unit cell enables negative resistance
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