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Randomized Control of Wireless Temporal Coherence via Reconfigurable Intelligent Surface

João Henrique Inacio de Souza, Victor Croisfelt, Fabio Saggese, Taufik Abrão, Petar Popovski

TL;DR

The paper addresses how a reconfigurable intelligent surface can actively shape the temporal statistics of a wireless channel, notably its coherence time. It develops a generalized discrete-time-varying channel model for RIS-aided links by combining time-invariant and time-variant components within a time-variant Rician framework, and derives the autocorrelation of the equivalent channel. A randomized framework is proposed to control temporal correlation by selecting the RIS element count N and the distribution of reflection phases (characterized by theta), enabling on-demand manipulation of coherence time. Simulations validate that the framework can realize target correlation and support a flexible block-fading model, with practical implications for adaptive resource allocation and service-aware communications.

Abstract

A reconfigurable intelligent surface (RIS) can shape the wireless propagation channel by inducing controlled phase shift variations to the impinging signals. Multiple works have considered the use of RIS by time-varying configurations of reflection coefficients. In this work we use the RIS to control the channel coherence time and introduce a generalized discrete-time-varying channel model for RIS-aided systems. We characterize the temporal variation of channel correlation by assuming that a configuration of RIS' elements changes at every time step. The analysis converges to a randomized framework to control the channel coherence time by setting the number of RIS' elements and their phase shifts. The main result is a framework for a flexible block-fading model, where the number of samples within a coherence block can be dynamically adapted.

Randomized Control of Wireless Temporal Coherence via Reconfigurable Intelligent Surface

TL;DR

The paper addresses how a reconfigurable intelligent surface can actively shape the temporal statistics of a wireless channel, notably its coherence time. It develops a generalized discrete-time-varying channel model for RIS-aided links by combining time-invariant and time-variant components within a time-variant Rician framework, and derives the autocorrelation of the equivalent channel. A randomized framework is proposed to control temporal correlation by selecting the RIS element count N and the distribution of reflection phases (characterized by theta), enabling on-demand manipulation of coherence time. Simulations validate that the framework can realize target correlation and support a flexible block-fading model, with practical implications for adaptive resource allocation and service-aware communications.

Abstract

A reconfigurable intelligent surface (RIS) can shape the wireless propagation channel by inducing controlled phase shift variations to the impinging signals. Multiple works have considered the use of RIS by time-varying configurations of reflection coefficients. In this work we use the RIS to control the channel coherence time and introduce a generalized discrete-time-varying channel model for RIS-aided systems. We characterize the temporal variation of channel correlation by assuming that a configuration of RIS' elements changes at every time step. The analysis converges to a randomized framework to control the channel coherence time by setting the number of RIS' elements and their phase shifts. The main result is a framework for a flexible block-fading model, where the number of samples within a coherence block can be dynamically adapted.
Paper Structure (12 sections, 1 theorem, 30 equations, 4 figures)

This paper contains 12 sections, 1 theorem, 30 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Discrete-Time-Varying Channel Model
  4. The Model
  5. Temporal Correlation of the Equivalent Channel
  6. A Randomized Framework for Controlling the Temporal Correlation
  7. Temporal Correlation under Random Phase Shifts
  8. Controlling the Temporal Correlation
  9. Simulation Results
  10. Towards a Flexible Block-Fading Model
  11. Conclusion
  12. Proof of the ACF of the Equivalent Channel

Key Result

Lemma 1

Consider that the channel coefficients $h_{\mathrm{D}}[k]$, $g_n[k]$, and $h_n[k]$, $\forall n$, follow the time-variant Rician model in eq. eq:rician-model. Then, the $R_{h_{\mathrm{eq}}h_{\mathrm{eq}}} : \mathbb{Z} \rightarrow \mathbb{R}$ of the equivalent channel is given by eq. eq:acf-equivalent

Figures (4)

  • Figure 1: RIS-aided communication system, where the ' elements imposing time-variant reflection configurations can alter the channel response.
  • Figure 2: Orthogonality between the components as a function of $N$.
  • Figure 3: Channel temporal correlation. The markers indicate the points where the correlation should reach $0.9$ according to the project requirements $p$.
  • Figure 4: Channel temporal correlation as a function of (a) $\alpha$ and (b) $\kappa$.

Theorems & Definitions (7)

  • Definition 1
  • Lemma 1
  • proof : Proof
  • Remark 1
  • Remark 2
  • Definition 2
  • Remark 3