wireless 2.0: smart radio environments empowered by ... · acm hotnets 2017. how does an ris look...

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Wireless 2.0: Smart Radio Environments Empowered by Reconfigurable Intelligent Surfaces(How it Works, State of Research, and the Road Ahead)

Marco Di Renzo Paris-Saclay University

Laboratory of Signals and Systems (L2S) CNRS and CentraleSupelec

Paris, [email protected]

VDL IEEE COMSOCAtlanta Chapter, USANovember 19th, 2020

Smart Radio Environments & Reconf. Metasurfaces

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Current Wireless Networks

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Current Wireless Networks: No Control of Radio Waves

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“Dumb” Wireless


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In conventional networks:


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In conventional networks: We usually perceive the environment as an

“unintentional adversary” to communication


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We usually optimize only the end-points of thecommunication network


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We have no control of the environment, which isviewed as a passive spectator


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We have no control of the environment, which isviewed as a passive spectator: we just adapt to it


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We have no control of the environment, which isviewed as a passive spectator: we just adapt to it

… WHAT IF …

Smart Radio Environments

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Smart Wireless


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Smart Wireless

From Radio Environments…

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From Radio Environments…

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From Reflections …

… to Smart Radio Environments

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… to Smart Radio Environments

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… to Smart Reflections

Radio Environments

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Adaptation: End-Points Optimization

Radio Environments

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Adaptation: End-Points Optimization


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Control & Programmability: Joint Optimization


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Control & Programmability: Joint Optimization


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Smart Wireless

… from adaptation to …

Control & Programmability


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Smart Wireless


Control & Programmability↓

Technology↓

RISs (metasurface)

↓Algorithms

↓AI


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Smart Wireless



Technology↓

RIS (metasurface)

↓Algorithms

↓AI


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Smart Wireless



Technology↓

RIS (metasurface)

↓Algorithms

↓AI


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Smart Wireless



Technology↓

RIS (metasurface)

↓Algorithms

↓ML/AI


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Smart Wireless



Technology↓

RIS (metasurface)

↓Algorithms

↓ML/AI

How Can We Realize Smart Radio Environments ?

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How Can We Realize Smart Radio Environments ?

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Reconfigurable Intelligent Surfaces (RISs)

What is an RIS ?

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What is an RIS ? …A New Antenna Technology for 6G

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July 14, 2020

What is an RIS ? …A New Antenna Technology for 6G

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July 14, 2020

Ei,HiEs,Hs

= f(Ei,Hi)

What Wave Transformations Can an RIS Apply ?

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What Wave Transformations Can an RIS Apply ?

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RIS-Assisted Wireless: What Wave Transformations ?

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Reflection/Transmission“Surfaces”


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Transmit “Antennas”

How Does an RIS Look Like ?

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How Does an RIS Look Like (“surfaces”) ?

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Univ. CaliforniaSan Diego

MobiCom 2020

Aalto UniversityPhysics Appl. 2017

MITUSENIX 2020

Docomo 2020Transparent Metasurface

Southeast UniversityTWC 2020

Tsinghua UniversityAccess 2020

PRESS-LAIAACM HotNets 2017

How Does an RIS Look Like (“antennas”) ?

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How Does an RIS Look Like (“antennas”) ?

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What is an RIS Useful For ?

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What is an RIS Useful For ? …RIS-Empowered Wireless

“Smart Radio Environments Empowered by RISs”, arXiv:2007.03435

What is an RIS Useful For ? …Smart Glasses

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What is an RIS Useful For ? …Large Smart Walls

52“SREs: An Idea Whose Time Has Come”, arXiv:1903.08925

Enhancing Coverage, Rate, Security Through RISs

53“RISs: Principles & Opportunities”, arXiv:2007.03435

Examples…

54“RISs vs. Relays”, arXiv:1908.08747

Reconfigurable Intelligent Surfaces

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Conceptual Structure


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Conceptual Structure


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Conceptual Structure and Operation

How To Construct an RIS ?

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Tiny Antenna Elements vs. (Homogenized) Metasurfaces

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“Terahertz Massive MIMO with Holographic RIS”, arXiv:2009.10963


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RISs can be built in different ways, which include:



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Implementations based on large arrays of inexpensiveantennas that are usually spaced half of the wavelengthapart



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Implementations based on large arrays of inexpensiveantennas that are usually spaced half of the wavelengthapart

Metamaterial-based planar or conformal large surfaceswhose scattering elements have sizes and inter-distancesmuch smaller than the wavelength


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What Does Make an RIS Different ?

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What Does Make an RIS (surfaces) Different ?

Nearly-Passive Design / Implementation


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Normal OperationPhase

Control & ConfigurationPhase


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An RIS is nearly-passive if the following three conditions arefulfilled simultaneously: No power amplification is used after configuration (during the

normal operation phase)

Minimal digital signal processing capabilities are needed only toconfigure the surface (during the control and programming phase)

Minimal power is used only to configure the surface (during thecontrol and programming phase)

Normal OperationPhase Passive

Control & ConfigurationPhase

Nearly-Passive RISs: Advantages and Limitations

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Example: RIS vs. (FD) Relay


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Reduced hardware complexity

No additive noise

No power amplifiers

Interference-free full-duplex

…


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RIS (1.5m = 140𝜆, reflector)vs. FD Relay (1-antenna)

arXiv:1908.08747


No additive noise

No power amplifiers


…

Nearly-Passive RISs: Advantages and Limitations (?)

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3,720 inexpensive antennas on a 6 square-meter surface

MITUSENIX 2020


No additive noise

No power amplifiers


…

Nearly-Passive RISs: Long-Term Vision

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For these reasons, RISs may constitute an emerging andpromising software-defined architecture that can be realizedat reduced cost, size, weight, and power (C-SWaP design)

C-SWaP

Nearly-Passive RISs: Long-Term Vision

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Sustainable wireless design (e.g., low EMF exposure) without generating new waves and possibly made of physically &

aesthetically unobtrusive and recyclable material

C-SWaP

NTT Docomo, MetaWave, AGCTransparent Metasurface

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What Does Make an RIS Different ?

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What Does Make an RIS (antennas) Different ?

Low Complexity / Low Power / Single-RF Design

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What Does Make an RIS (antennas) Different ?

Low Complexity / Low Power / Single-RF Design

RIS-Based Antennas: Advantages and Limitations

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RIS


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RIS


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RIS


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RIS


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Example: Power Consumption


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RIS


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RIS


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RIS


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Compared with other transmission technologies, e.g.,phased arrays, multi-antenna transmitters, and relays, RISsrequire the largest number of scattering elements, but eachof them needs to be backed by the fewest and least costlycomponents. Also, no power amplifiers are usually needed.

RIS


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… no free lunch rule …

Compared with other transmission technologies, e.g.,phased arrays, multi-antenna transmitters, and relays, RISsrequire the largest number of scattering elements, but eachof them needs to be backed by the fewest and least costlycomponents. Also, no power amplifiers are usually needed.

RIS

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Communication-Theoretic View

Communication-Theoretic View

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Conventional IT/COM Wireless

… encoder and decoder are optimized given the environment …

Communication-Theoretic View (“surfaces”)

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RIS-Empowered: “Optimizing the Environment”

… encoder and decoder are optimized jointly with the environment …

Communication-Theoretic View (“surfaces & antennas”)

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RIS-Empowered: “Modulating the Environment”

… encoder and decoder are optimized jointly with the environment …… and information data is modulated into environment-dependent states …

Example: Modulating the Environment (“antennas”)

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Spatial Modulation

modulation symbol: s1

RIS phases: R1, …, R12

Spatial ModulationIEEE Proc. 2014

Metasurface ModulationarXiv:2009.00789


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Spatial Modulation

modulation symbol: s2

RIS phases: R1, …, R12

Spatial ModulationIEEE Proc. 2014


Example: Modulating the Environment (“surfaces”)

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Spatial Modulation


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Spatial Modulation


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Spatial Modulation

Joint Active & Passive Wireless Networks Design

“Holographic MIMO Surfaces for 6G”, arXiv:1911.12296

“RISs can fundamentallytransform today’s wirelessnetworks with active nodessolely into a new hybridnetwork comprising active andpassive components co-working in an intelligent way,in order to achieve asustainable capacity growthwith low and affordable costand power consumption”

Joint Active & Passive Wireless Networks Design

“Holographic MIMO Surfaces for 6G”, arXiv:1911.12296

What Do We Do @ CNRS & Paris-Saclay Univ. ?

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What Do We Do @ CNRS & Paris-Saclay Univ. ?

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… from theory to simulations and experiments…

Mainly, we do theory and simulations (physics-basedmodeling, analysis, and optimization in small-scale andlarge-scale wireless networks)

But, we validate our models in collaboration with partnerswhose research activity focuses on hardware development,experimental measurements, and ray tracing simulations

IEEE Trans. Wireless Commun.world’s first (arXiv:1911.05326)

Partner University (China)

Path-Loss: What is the Power Scattered by an RIS ?

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TxRx

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Path-Loss Modeling (Theory)

106“On the Path-Loss of RISs”, arXiv2007.13158

Path-Loss Modeling (Experiments)

107IEEE Trans. Wireless Communications – arXiv:1911.05326

Path-Loss Modeling (Experiments)

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Some Recent Results

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Path-Loss Modeling – Physics-Based Foundation (submitted) M. Di Renzo et al., On the Path-Loss of Reconfigurable Intelligent Surfaces: An

Approach Based on Green’s Theorem Applied to Vector Fields (arXiv:2007.13158)

E2E Commun. Model – Mutual-Coupling/Unit-Cell Aware (submitted) M. Di Renzo et al., End-to-End Mutual-Coupling-Aware Communication Model for

Reconfigurable Intelligent Surfaces: An Electromagnetic-Compliant Approach Basedon Mutual Impedances (arXiv:2009.02694)

SNR Distribution – Improving Signal Reliability (WCL 2020) M. Di Renzo et al., Beamforming Through Reconfigurable Intelligent Surfaces in

Single-User MIMO Systems: SNR Distribution and Scaling Laws in the Presence ofChannel Fading and Phase Noise (arXiv:2005.07472)

Rate Optimization – RIS-Aided MIMO (submitted) M. Di Renzo et al., Achievable Rate Optimization for MIMO Systems with

Reconfigurable Intelligent Surfaces (arXiv:2008.09563)

Overhead-Aware Design – SE & EE (TWC 2020) M. Di Renzo et al., Overhead-Aware Design of Reconfigurable Intelligent Surfaces in

Smart Radio Environments (arXiv:2003.02538)

Joint Encoding – Capacity-Optimal Design (ISIT 2020) M. Di Renzo et al., Beyond max-SNR: Joint Encoding for Reconfigurable Intelligent

Surfaces (arXiv:1911.09443)

Single-RF MIMO – Metasurface-Based Modulation (submitted) Miaowen Wen, M. Di Renzo et al., Single-RF MIMO: From Spatial Modulation to

Metasurface-Based Modulation (arXiv:2009.00789)

Recurrent Questions (addressed in part)

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Ei, Hi Es, Hs = f(Ei, Hi)


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Ei, Hi Es, Hs = f(Ei, Hi)

2 2

1 1

S R exN pN N

n n n nn nn

nn

h g h jg


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Power scaling law vs. size of the RIS (~N2)

Power scaling law vs. transmission distancearXiv:1911.05326(measurements)

arXiv:2007.13158(theory)


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Sub-wavelength inter-distance

arXiv:2007.13158 arXiv:2009.10963

(left) d= 0.25 λ, (right) d = 0.5 λ

d = λ/2 d < λ/2 d 0 (<< λ/2)


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Robustness to fading (Amount of Fading ~ 1/N)

arXiv:2005.07472


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Channel estimation/feedback overhead

arXiv:2003.02538


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Hardware limitations (e.g., quantization bits)

arXiv:2008.05317


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Network deployment and optimization

arXiv:2008.09563


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Network deployment and optimization

arXiv:2008.09563


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Physics-aware communication model

(i) E2E Model(ii) EM-Compliant(iii) Mutual Coupling Aware(iv) Unit Cell Aware

arXiv:2009.02694

Physics-Aware Model – SNR vs. Impedance Modeling

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ris

ris

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ST SR1

2optimization

ST SR1

SNR : ,

,

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Rn

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n n n n

Γ h g

Γ h g


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ris

ris

22no coupling no coupling ST SR

VLOS1

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RIS SS

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ST SRoptimization

1 SS Sopt

R

... lots to optimize :)

Z : H, ,

, ,

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Rn

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n n n

n nP

n n n n

n nn n

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Z ZZ Z

Z ZZ


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ris

ris

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ST SR1

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ST SR1

SNR : ,

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Rn

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P n n n n

n n n n

Γ h g

Γ h g

ris

ris

22no coupling no coupling ST SR

VLOS1

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RIS SS

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ST SRoptimization

1 SS Sopt

R

... lots to optimize :)

Z : H, ,

, ,

N

Rn

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n n n

n nP

n n n n

n nn n

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Z ZZ Z

Z ZZ


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Channel capacity limitJoint EncodingarXiv:1911.09443



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What gains without instantaneous CSI (in writing) ?

RIS 4

RIS 3

RIS 2

RIS 1

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Closing Remarks

Programming the Environment: Towards Wireless 2.0

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Enhancing Coverage, EE, Rate Through Space Waves

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Reconfigurable Intelligent Metasurfaces

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Where Are We ?

Reconfigurable Intelligent Metasurfaces

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Where Are We ?

Professor Stefano Maci, Huawei Antenna Summit 2019

Hundreds of Papers on arXiv… What’s Left ?

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Hundreds of Papers on arXiv… What’s Left ?

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EM-based circuital models

Path-loss and channel modeling

Fundamental performance limits

Robust optimization and resource allocation

Constrained system design and optimization

EM-based communications: “Layer-0” networking

Large-scale networks: Deployment, analysis, optimization

Ray tracing and system-level simulators

Beyond far-field communications

Beyond communications

Advantages and limitations… do RISs bring any (substantial) gains as compared with other

well-established technologies in wireless networks ?

On Electromagnetic Information Theory (EIT)

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Opportunity – EIT: Reconciling COM, SP, IT, EM, …

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G. Green, “An Essay on the Application of Mathematical Analysis to theTheories of Electricity and Magnetism”, 1828.

J. C. Maxwell, “A Dynamical Theory of the Electromagnetic Field”, 1865.

C. E. Shannon, “A (The) Mathematical Theory of Communication”, 1948.

Further Information: JSAC SI on “RIS-Assisted SREs”

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RIS-Assisted SREs in IEEE-COMSOC

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WTC & SPCC-TC

RIS-Assisted SREs in Europe (European Commission)

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H2020-ICT ARIADNE (grant 871464, 6 million EUR) – Nov. 2019 - Oct. 2022

H2020-MSCA-EiD 5GSmartFact (grant 956670, 3.7 million EUR) – Mar. 2021 - Feb. 2025

H2020-MSCA-IF PathFinder (grant 891030, 185k EUR) – May 2021 – Apr. 2023

H2020-MSCA-ETN MetaWireless (grant 956256, 4.0 million EUR) – Dec. 2020 - Nov. 2024

H2020-ICT RISE-6G (grant 101017011, 6.5 million EUR) – Jan. 2021 – Dec. 2023

Thank You For Having Me… Appreciated… ICT-ARIADNE (H2020, 5G-PPP, grant 871464)

November 1st, 2019 – October 31st, 2022

A collaborative research project on RISs & AIFrom 2021: PathFinder (IF), 5GSmartFact (EiD), MetaWireless (ETN), RISE-6G (ICT-52)

Marco Di Renzo, Ph.D., H.D.R.Directeur de Recherche CNRS (CNRS Professor)Highly Cited Researcher, Web of Science (2019)IEEE Fellow, IEEE Communications Society (USA)IET Fellow, Institution of Engineering and Technology (UK)Editor-in-Chief, IEEE Communications LettersDistinguished Lecturer, IEEE Communications SocietyDistinguished Lecturer, IEEE Vehicular Technol. SocietyNokia Foundation Visiting Professor, Aalto Univ., Finland

Paris-Saclay UniversityLaboratory of Signals and Systems (L2S)CNRS and CentraleSupelec

E-Mail: [email protected]

wireless 2.0: smart radio environments empowered by ... · acm hotnets 2017. how does an ris look...

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