PhD Adaptative Modulations for Visible Light Communications
09/2021 - 09/2024
Laboratory : Gipsa-lab, Grenoble, France
11 rue des Mathématiques, Grenoble, FRANCE, Campus BP46, F-38402 SAINT MARTIN D'HERES
Yannis LE GUENNEC, Associate Professor, Grenoble INP
e-mail : firstname.lastname@example.org
Candidates with very good academic results and very good skillsin digital communications & signal processing techniques, very good background in programming (Matlab, Python,…), knowledge in radiofrequency and optics.
Excellent writing and communication in English.
CV, motivation letter and references must be sent to email@example.com
Gipsa-lab is a French CNRS (National Committee of Scientific Research) unit joint with Grenoble-INP (Grenoble Institute of Technology), Université Grenoble Alpes and Université Stendhal. Located in the heart of French Alps, in one of the most dynamic high-tech environment in Europe, Gipsa-labbrings together more than 350 people, including about 150 doctoral students. Gipsa-lab is a research unit developing both basic and applied researches on complex signals and systems. Gipsa-lab is internationally recognized for the research achieved in Automatic Control, Signal and Images processing, Speech and Cognition, developing ambitious projects in the strategic areas of energy, environment, communications, artificial intelligence, Life and Health and language engineering. Gipsa-lab maintains a constant link with the economic environment through a strong partnership with industry. Gipsa-lab staff is involved in teaching and training in various universities and engineering schools of the Grenoble academic area (Université Grenoble Alpes).
Context and objectives of the PhD
With the advent of Internet-of-Everything (IoE), there is a growing demand for wireless connectivity leading to radio-frequency (RF) spectrum saturation. With IoE, RF transceivers will be integrated into billions of devices causing a significant increase in the overall power consumption of communication networks. In this scenario, Visible Light Communications (VLC)  are of considerable interest because they provide a large unlicensed spectrum for wireless connectivity and they rely on the massive deployment of light emitting diodes (LEDs) to operate low power communications (Fig. 1).
Fig. 1 VLC communications in the context of self-driving cars 
To design an energy-efficient VLC system, the choice of the digital modulation is of fundamental importance. Due the constraint from light intensity modulation, the modulated signal driving the LED must be unipolar and real-valued. Among available modulation schemes, 2 groups are specially identified : (i) linear modulations; and (ii) orthogonal modulations. On one hand, linear modulation and their multicarrier extensions including optical-orthogonal frequency-division multiplexing (O-OFDM)  reach high spectral efficiency by increasing modulation order M at the expense of low energy efficiency. On the other hand, orthogonal modulations, such as pulse position modulation (PPM) or frequency-shift keying (FSK), are known in RF domain to show higher energy efficiency than linear modulations, at the expense of degraded spectral efficiencies .
In this PhD work, we will investigate versatile modulation techniques to provide flexibility in the spectral resource allocation to address both high data rate and low data rate VLC communications, targeting the best energy efficiency vs spectral efficiency trade-off, and reducing the modulator/demodulator complexities -. Side benefits of this research project goes beyond the context of visible light communications, since they concern also innovative concepts for laser-based free space optics (FSO) communications or even radiofrequency communication techniques.
An analytical approach will be conducted to explore new concepts for adaptative VLC. Simulations will be carried on to predict the performance of these new techniques into a variety of visible light channel models. Finally, based on an already existing experimental VLC platform available in Gipsa-lab, the proposed VLC communication techniques will be tested in practical scenario.
PhD progress and achievements
i) State of the Art for VLC technologies and related hardware constraints. Getting familiar with already developed VLC algorithms - in Gipsa-lab.
ii) Theory on adaptative VLC modulation techniques.
iii) Simulation model, prediction of performance, comparison with State-of-The-Art.
iv) Implementation of the proposed concept on a VLC experiment platform.
We expect that the development of an analytical approach together with numerical simulation models and experimental data will provide State-of-The Art achievements to be published in top level scientific journals and conferences.
IDEX project funding or Ministry of Higher Education and Research grant depending on candidate academic background.
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(c) GdR 720 ISIS - CNRS - 2011-2020.