“Exploration Japon 2024” Program

Optical Wireless Communications Research at LISVAn Overview
Dr. Bastien Béchadergue
Université de Versailles Saint-Quentin
Laboratoire d’Ingénierie des Systèmes de Versailles
bastien.bechadergue@uvsq.fr

April 19, 2024, Nagoya University

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1. UVSQ and Université Paris-Saclay

2. Overview of the LISV
3. Vehicular communication activities

4. Beamsteering activities
5. Other activities (SPAD, FSO…)

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1. UVSQ and Université Paris-Saclay

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University of Versailles Saint-Quentin (UVSQ): Where Is It?
Near Paris and Versailles Castle

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LISV: Laboratory of Engineering Systems

LISV laboratory is on
the Vélizy campus

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Key Figures of UVSQ
• Around 20,000 students• 215 academic programs (including 100 Masters
programs)• 3,750 students enrolled in life-long learningprograms• 2,669 foreign students from 120 different countries• 708 PhD students• 155 research contracts• 1,110 faculty members• 744 administrative staff• 310 students enrolled in exchange programs

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UVSQ Is Now Part of Université Paris-Saclay
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71Aprojetcommon projectto buildpour
thecommun
university
construire
uneof the 21st century
Université duAround 60,000ème
21 students
siècleShort Course on VLC - Nagoya University

17 Graduate Schools in Université Paris-Saclay

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2. Overview of the LISV

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History and Structure of the LISV
• The LISV exists since 2006:• About 30 professors/associate professors and technical staff,• About 40 PhD students from more than 18 nationalities.
• Building located in Vélizy (mid-distance from Paris and Versailles), around 2700 m2• Structured in three teams: ISA, RI and SyMRIC.
• Two structures are nearly associated with the Lab:• OLEDCOMM, a startup about LiFi technology• CEREMH, an association about healthcare and help for disabled persons

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Scientific Aims of the LISVStudy, realization and performances evaluation of systems that include optomechanical-electronical-instrumentation parts
Modelling

Innovating
designSensors

Interactive robotics
Instrumentation and modelling for
Systems (ISA)

Multi-physics
modelsEmbeddedsystems

Instrumentation

Control andcommand

Performances
evaluation

Help andassistance forservices

11Metrology

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Research About Help and Assistance for Disabled Persons

Gyrolift
Seagway withverticalization

Help for driving

Brain interfaces

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Research About Mechatronic Robotised Systems
Humanoïd control

Prosthesis
and orthosis

Drones controlµrobotics

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PhD Students
Thesis (average figures over 5 years period)
Sources of funding
Government
Funding with large collaboration with industry
CIFRE (direct link with industry)
Foreign funding with co-tutelle agreements
OthersTOTAL

14Number5221325
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%
7%
30%
17%
34%
12%
100 %

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Partnership Between LISV and OLEDCOMM• About OLEDCOMM:• OWC and LiFi products design and industrialization company.
• Created in 2012 by two Professors of LISV.
• Now among the world leaders on this market with pureLiFi (UK) and Signify (NED).
• Collaboration with MaxLinear and STMicroelectronics for on-chip embedded system.
• Since 2012, scientific collaboration agreement
between LISV/UVSQ and OLEDCOMM forresearch related to various use cases and markets.

• Main markets:• Indoor LiFi with high privacy/security/healthrequirements (army, education…).
• In-satellite cable replacement (firstLiFi-embedded satellite lauched in 2023).
• High speed and low costs satellite-to-satellitelinks.
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3. Vehicular communication activities

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Integrated V2V Sensing and Communication (2014 – 2017)• 2009–2014: Work on V2V and I2V/V2I communication started at LISV in 2009 (thesis of A. M Cailean)→ Demonstration of 100 m low bit rate (< 100 kbps) I2V links and 50 m V2V links.

• 2014–2017: Thesis of B. Béchadergue to study joint V2V communication and distance measurement :• Simulations validation of the proposed system.
• Experimental validation using COTS car lights: distance measurement from 5 m to 25 m with ameasurement error < 3%.

FPGA for distancemeasurement

LED17Analog processing
board

Photodetector

B. Béchadergue, “Visible Light Range-Finding and Communication Using the Automotive LED
Lighting,” PhD Thesis, Université Paris-Saclay, 2017.

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Outdoor V2V Communication Tests (2017)• In 2017, research visit at National Taiwan University, withHsin-Mu Tsai.
• V2V communication demonstrator assembled and tested onopen roads.
• Results: > 90% of packets transmitted without errors over 30
m at 100 kbps (35 m à 10 kbps).

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Multiple Access Protocols for V2V Communication (2019-2022)• 2019–2022: Thesis of E. Plascencia on inter-vehicle interferences in multi-lanes scenarios.
• Study of the performance/complexity tradeoff of various CDMA codes (ROC, PN, OOC, etc.).
• Implementation of an integrated and real time 100 kbps V2V link and tests on a circuit.

19L. E. Plascencia Cruz, “Visible light communication control in a platoon vehicle environment”, PhD Thesis,Université Paris-Saclay, 2022.

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4. Beamsteering activities

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Since 2016, an Interest for Indoor Applications• 2016–2019: Thesis of M. Merah to initiate works on indoor applications (e.g. LiFi).
• Experimental work on modulations and multiples access schemes (m-CAP, OFDMA, NOMA, etc.)• Demonstration of 300 Mbps capacity cells shared between up to 20 users using commercial whiteLEDs.

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M. Mohammedi Merah, “Conception and realization of an indoor multi-user Light-Fidelity link”, PhD Thesis,
Université Paris-Saclay, 2019.

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Since 2020, a Strong Focus on Beamsteering• Motivations for using beamsteering:• In any OWC system, the larger SNR, the better.
Tx• The main goal of the OWC receiver is to optimize the SNR, and thus
the received signal power 𝑆, defined as:
𝜙𝑆=

Light sourceparameters:• 𝑚 → directivity

𝑚 + 1 𝑃𝑡𝑚cos
𝜙 cos 𝜓 𝛾𝐴𝑟 𝑔(𝜓)22𝜋𝑑Link geometry:• 𝜙, 𝜓 → Alignment Tx/Rx

2𝑑Receiver parameters:• 𝛾 → Photosensitivity• 𝐴𝑟 → Sensitive area
• 𝑔(𝜓) → Optical gain

Use beamsteering
Use sensitive Rx, e.g. SPAD
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𝜓RxInterest of Beamsteering for Indoor Applications

Cell-based architecture:• Each AP generates a cell
• If UE in the cell, communication possible• Continuous coverage is ensured by celloverlapping (i.e. interference, handover…)

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Proposed cell-free architecture:• Each AP can target 1+ UEs using beamsteering• Real-time tracking of UEs necessary• Real-time optical beam orientation necessary• Focused beam = secured and high SNR link

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Interest of Beamsteering for Outdoor Applications

Strong interest for free-space optics (FSO) applications:• Acquisition, tracking and pointing (ATP) mechanisms are critical to fight misalignement and maintainhigh performance.
• Use cases explored:• Buiding-to-building communication (Al-Furat Al-Awsat Technical University, Irak)• Satellite-to-satellite communications (OLEDCOMM & Thales)
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Implement Beamsteering: Open Issues• Issue 1: Is beamsteering really effective toenhance OWC performance?
• Issue 2: How to localize the target?
• Issue 3: How to ensure actual beam orientation?

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Performance Enhancement With Beamsteering: Approach• 3 scenarios studied to determine the OWC system coverage (i.e. area where BER < 3,8x10-3).
• With beamsteeering → Tx and Rx perfectly aligned,• Without beamsteering → Tx pointing toward the floor, Rx toward the ceiling,• AP = IR-LED source of optical power depending of the source directivity (= maximum optical power
allowed by photobiological safety standard with this directivity).

• In beamsteering configuration, addition of misalignement between the AP and UE in a second step.
With beamsteering

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Without beamsteering

H. AL Satai, B. Béchadergue, L. Chassagne and W. M. Ridha Shakir, “Coverage Optimization With
Beamsteering-Based Indoor Optical Wireless Communications,” 2023 IEEE ICC, 2023, pp. 1149-1154.

Performance Enhancement With Beamsteering: Results• Conclusions:• Whathever the directivity, beamsteering enables a large increase in the communication coverage.
• But, the more directive the source, the more sensitive the link to misalignement.
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How to Localize the Target? Integrated Sensing and Communication•28

Objectives: Model, build and evaluate asystem for joint :•Lighting (except if IR source),•Communication (VLC),•
Positioning (VLP).

•Methodology: We considered:•The use of m-CAP modulation and RSS
positioning technique,•First through simulations and thenexperimentally.

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Positioning Performance (Experimental Results)
••

•

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Experimental testbed
developed.
90% of the positioning
error < 5.9 cm
Communication
performance: BER <3.8x10-3 over thewhole 1.2 x 1.2 mzone.

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How to Actually Steer the Optical Beam?
Technique30

Operates by varying the…

…mainly with…

Motorized gimbal

Orientation of thesource/receiver

All types of sources andreceivers.

Array of optical sources

Active optical source

Arrays of VCSEL/LED

Mobile mirrors (e.g.
MEMS)

Mirrors position

Laser source or LED (oflow divergence)

Delay lines with silicon
photonics

Time/phase delays between
Laser source
copies of the same signal

Lens with variable focallength

The focal length of a lensLaser source or LED (oflow divergence)

…

…

…

Reconfigurable intelligent
surfaces (RIS)

Multiple working principles

Various types of sources
and receivers.

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Liquid Lenses for Cells of Variable Size

• By varying the liquid lens drive voltage, the focal distance changes.
⇒ So are the beam spot size and therefore the coverage area at a given distance.
• Cells of areas ranging from 6 mm² to 528 cm² over distances from 4 à 26 m demonstrated.
• Great interest for tracking before beamsteering and to fight misalignement.

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Liquid Lenses for Beamsteering• If the liquid lens is shifted from the source optical axis
⇒ Beam deflection is possible by varying the lensvoltage.
• Deflection angle up to 13° demontrated.
• Angles > 70° possible with more complex setup(multiple lenses for abberation correction etc.).
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335. Other activities (SPAD, FSO…)

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The Sensitivity/Size Tradeoff
Access point by Oledcomm

User equipment by pureLiFi

Several photodides (PD) arecommonly used to increase
the collected optical power…

… but current off-the-shelfreceivers too bulky for mass
market applications

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ASIC optical antenna by Oledcomm

Which solution to this issue?
Single-photon avalanche
diodes (SPADs)

Working Principles of a SPAD
• A SPAD transforms a detected
photon into a current pulse.
Photon• The number of pulses over aduration 𝑇𝑠 is proportional to thereceived photon flux.

APD en modeGeiger• Problem : After a photon detection,
the SPAD cannot detect anotherphoton over a certain dead time.

𝑖(𝑡)

𝑝(𝑡)

Résistance dequenching• Solution : Use instead a SPAD array, or silicon photomultiplier (SiPM) ⟹ Increase the probabilityof having at least one active SPAD at a given time instant.
• In practice, SiPM = 10000+ SPAD, spread over < 1 mm² ⟹ very small and sensitive sensor!

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Short Course on VLC - Nagoya University𝑁OWC Performance Optimization: SPAD vs PD
Question: Does a SiPM enable to enhance the OWC
communication performance?
• Principle : Simulations, in similar conditions, of thecommunication coverage (i.e. zone where BER < 3.8 ×10−3 ) with state-of-the-art SiPM and PDs.
• Results (in a 4x4 m room):•••

0% of the room covered with a single PD of 26.4 mm².
Similar coverage (~50%) with a 0.625 mm² SiPM and a 105.8mm² PD de surface 105.8 mm² (i.e. 66 time larfer!).
Room entirely covered with a SiPM smaller than 1.5 mm².

Conclusion: SiPMs ensure a significant increase incoverage area with a very small footprint.

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Top view of the coverage areas ensured by variouskinds of SiPMs and arrays of PDs.

B. Béchadergue, T. Cazimajou, F. Mandorlo, and F. Calmon, “Indoor Optical Wireless Communication
Coverage Optimisation Using a SiPM Photoreceiver,” 2023 IEEE WCNC, 2023, pp. 1-6.

Energy Harvesting With Photovoltaic Modules• Question: Is beamsteering interesting to enhance energy
harvesting performance despite its own power cost?
• Ongoing work: Implementation of a simple simulation
platform to estimate the energy harvested and BER of anOWC system with PV module as receiver and with(out)beamsteering.

• First results obtained without beamsteering. Moreresults to come next.

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O. Cissoko, B. Béchadergue, and I. Tavakkolnia, “Performance of a Photovoltaic Module for Energy
Harvesting and Optical Wireless Communications,” 2023 JWOC, 2023, pp. 1-2.

Thanks For Your Attention
bastien.bechadergue@uvsq.fr

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