Research Topics
Recruited in September 2003 at the CITI laboratory , I came to strengthen activities in the field of radio communications , particularly that of what, from a network point of view, is called the physical layer. These activities were previously carried by a single permanent (JM Gorce ) and a PhD student. To be consistent and complementary , I had to make a change in my thematic interest in aspects of signal processing and system-level modeling, further upstream of my closest electromagnetism previous activities (even if the antennas are aspects still at the heart of the issues). My role then evolved by establishing a measurement platform for better consideration and comprehensive validation of transmission chains. This move towards a more holistic view of communications systems has now allowed me to develop my own line of research on aspects flexible RF systems in the laboratory while pursuing multiple transverse collaborations with my colleagues on aspects of software radio or modeling of the radio channel .
SIMULATION OF
RADIOWAVE PROPAGATION
My first activity in the CITI Lab was to develop
a technique of radiation pattern synthesis. Indeed the indoor radio propagation
tool previously developed in the laboratory was already recognized for its the
speed and accuracy of prediction. But this software was then limited to the
taking into account of omnidirectional radiation sources. We have therefore
included a technique inspired by the classic array synthesis of radiation
patterns, based on a more precise matrix approach, to recreate the influence of
complex sources by association of elementary sources weighted in amplitude and
phase. We have subsequently improved methods of calibration and validation of
the software through the use of the laboratory (see below) radio platform.
In the context of the European project IPLAN,
we then sought to further improve this simulator mainly in two axes: study the
possible extensions and optimizations of the method of calculation of the
electromagnetic field and enrich the exploitation of fields predicted to
extract new significant parameters of the radio link. The first axis was the
subject of Dmitry Umansky post-doctoral, the second of the thesis of Meiling
Luo. D. Umansky worked on the possible extension in three dimensions of the
principle of calculation and Mrs. Luo on the extraction of statistical
parameters of the radio channel for the performance evaluation of wireless
systems. Also, Luis Gonçalvez completed a postdoc on the experimental
validation of this work. In this project I more had the opportunity of a
research stay for 2 months in Luton, and a week in Sheffield among our British
partners. In parallel, under the ADT Inria Mobsim project, Tao Wang worked on
this Wiplan software with a network simulator (NS3) interfacing.
DIGITAL
PROCESSING AND MULTI-ANTENNA TECHNIQUES
A fundamental theme in my work is the study
of the performance of signal processing techniques based on the multiplication
of antennas (SIMO, MISO, MIMO). This area is already an important subject of
research for a long time in the world of telecoms, but it is only since little
time possible to use this kind of techniques at the level of compact terminals,
for obvious reasons of integration and calculation capacity. A thorough knowledge
of the compact antennas is precious to improve the estimation of the expected
performance of such systems and evaluation in difficult contexts of ad hoc
networks and sensor networks. Preliminary work in this area gave rise to a
major contract with France Telecom - Orange Labs on multi-mode multi-antenna terminals
based on software radio. Two thesis were conducted in this theme, that of
Philippe Mary, defended in February 2008, the algorithmic aspects and
analytical estimation of performance, as well as that of Pierre-François
Morlat, defended in December 2008, on the overall architecture, simulation and
the development of a demonstrator of these techniques.
RADIO
TESTBED AND SOFTWARE RADIO
End of 2004, with exceptional funding from
Inria and INSA-Lyon, we have put in place a platform of testing particularly
radio system performance and interface with system simulation tools we use. The
potential for studies by confrontation simulations/measures with this tool
makes an argument of weight with our industrial partners (notably at the origin
of the contract with France Telecom). The use of this platform is also
perfectly suited to the development of approaches like software-defined radio
that we explore. This fundamental tool allowed us to carry out validation
measurements of the propagation engine Wiplan, characterizations of the wireless
channel (in different environments and at different frequencies) with including
the extension to two branches of measurement offering a detailed analysis of
the MIMO communications. Interfacing of this material with simulations software
also allowed us to directly validate complex structures simulated in a realistic
propagation channel, allowing more refine simulated models. This platform was
finally also made profit in the development of prototypes of sensor networks.
We have more in collaboration with France Telecom carried out the design and
implementation of a demonstrator of a multi-antenna, multi-mode and
multi-channel receiver based on software-defined radio. This single
demonstrator in its kind is based on a 4-branches with wide band front-end RF
and digitizers, combined with multi-FPGA/DSP cards hosted on a quad-processor
server.
In a more general approach, the thesis of
Cédric Lévy-Bencheton, co-directed with Tanguy Risset, helped to implement a
more general study framework, by simulation, the potential of software-defined
radio terminals for the multi-mode relay in radio networks. This work must find
a framework of experimental validation with the CorteXlab testbed that we are currently
deploying following an Equipex grant. This platform whose premises are to be
completed, will allow the study of principles of cognitive radio on a large
scale.
GLOBAL
RADIO SYSTEM DESIGN
Always around the themes of multi-antenna,
multi-mode, and software-defined radio, we initiated collaboration with the INL
Lab on aspects of overall design around the radio platform and common
simulation tools. This approach was intended to jointly optimize the RF parts
and digital system by analyzing the potentials of compensation of part and
other. The great return of the community on this work allowed us to start a
thesis with France Telecom on this approach (Ioan Burciu). The work of this
thesis have allowed to propose a new architecture of analog-digital mixed
receiver allowing the receipt of two standards (UMTS and 802.11) with a reduced
complexity (covered by an international patent) and an extension to 4G and beyond
(LTE-Advanced) terminals. We have simultaneously developed with Matthieu
Gautier (France Telecom) a new approach to multi-antenna receivers at reduced
cost based on multiplexing codes of receptions, basis of another contract of
research. Following these works geared towards the reduction of the complexity
of terminals, we look at the aspect of reducing the consumption of such
systems, particularly in the context of the FUI project EconHome. Also, the
thesis funded by the CSC of Z. Zhan allows us to study the potential of
full-duplex architectures to increase the capacity of local area networks.
Doctoral activities
This thesis took place in short
range wireless communication systems. In such a field, the major challenge for
antennas is to combine size reduction and good matching and radiating
characteristics to satisfy the required specifications.
Thanks to numerical (FDTD) and experimental tools, the
study of strip antennas based on quarter wavelength resonators folded in three
dimensions and fed via a coupling gap has been performed. This study was
particularly dedicated to achieve spherical or hemispherical radiation patterns
offering a flawless coverage of the entire space. Several developments are
exposed, some of them allowing a wider bandwidth.
Two main applications are detailed : a coplanar
antenna integrated in a compact module
for wireless metering of energy resources, and a multiband antenna used in a
cellular phones localization system for isolated people rescue.
Postdoc activities
My postdoc position was dedicated to the development, optimization, realization and test of a multi-sensor receiver for hidden mobile phones localization. A multiband hybrid antenna array was proposed, simulated and experimentally validated.
Contact
CITI LaboratoryINSA de Lyon
Bat. Claude Chappe - 6 av. des Arts
69621 Villeurbanne Cedex - FRANCE
VOICE: +33 472 436 067
FAX: +33 472 436 227
EMAIL: guillaume.villemaud@insa-lyon.fr