Multi-User Communications Systems, Cognitive Radio and Radio over Fiber

This research theme concerns intelligent, multi-user, cooperative and opportunistic communication systems.

Theme: Multi-user Communications Systems, Cognitive Radio and Radio over Fiber

This research theme is concerned with intelligent, multi-user, cooperative and opportunistic communication systems. We are interested in  the development of transmission, multiple access and reception technologies for radio frequency communication systems as well as for mixed radio optical networks. Intelligent transportation systems are one of the targeted applications. The work addressed is mainly :

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Cognitive Radio : We have seen an explosion of new radio standards as the terminal evolves in an increasingly heterogeneous and complex radio landscape. This raises issues of system cohabitation, interoperability between systems and frequency availability.

These systems must guarantee availability, service continuity, traffic heterogeneity, robustness and quality of service requirements for the targeted applications, sometimes in a context of high mobility and regardless of the environments traversed.

These requirements of dynamic reconfigurability are common with the world of telecommunications and solutions are sought through the development of "intelligent" radio allowing to realize, via software functions, the functions currently provided by hardware components in radio modems.

In this context, we are interested in the problems of blind identification and classification of waveforms of 2nd, 3rd and 4th generation telecommunication systems as well as the adaptive estimation of the radio channel especially at high mobility (i.e. railway, TGV).

In the context of multi-cell networks, we are interested in the problem of low spectral efficiency at the cell edge, due to the high level of interference between cells in this area.

Three topics addressed:

The search for a cooperative strategy between the base stations of the network (downlink), with a distributed scheme constraint (decisions are made at each base station, not centrally). This corresponds to a virtual MIMO approach.

We have proposed a cooperation scheme taking advantage of the spatial diversity, but also the frequency diversity of the network. This is implemented through an adaptation of the optimal space-time coding: the golden code.

The golden code is the most efficient way to implement the network.

The search for a statistical model of the inter-cell interference power experienced by a network user. The interest of such a model is to facilitate the analysis and simulation of the network, especially in the search for solutions to limit these interferences.

We implemented a semi-analytical method that allowed us to obtain a reliable model, including path-loss, shadowing and multipath propagation phenomena, for the downstream channel, and in a distributed environment where the resource allocation is opportunistic (optimal from a sum flow point of view).

The proposed statistical model is derived from a Burr's law, and is parameterized by the magnitude parameter of the mask effect σdB. Resource allocation with ARQ feedback (Xlayer approach).

Mixed Radio-Optical Networks

Due to their unbeatable throughput, single-mode (SMF) or multi-mode (MMF) fiber links represent an ever-growing infrastructure today. Thus, the need for a mixed radio-fiber technology is becoming apparent to satisfy requirements (i.e., high-speed services) and take advantage of the complementarity of the two technologies.

Two themes developed:

CDMA Optical and multiple access interference handling: the direct radio transmission model over fiber limits the use of it for the radio application only. In this context, we are interested in the optical CDMA multiple access technique (i.e. more specifically in the multiple access interference treatment) over SMF fiber.

The main objective of this paper is to develop a new approach to the treatment of multiple access interference over SMF.

Thus, we develop optical multi-user detectors (O-MUD) based on  parallel (SPIC) and serial (SIC) cancellation of multiple access interference associated with 1 and 2 Dimensions optical codes (i.e. OOC, PC).

Optical MMO: With its enormous bandwidth, the MMF fibre appears to be the only media capable of providing a high-speed multi-service system in enterprise and "in-door" networks. An MMF network can be the network backbone that feeds fixe-filaire services (such as GbE data services), as well as wireless services (e.g., IEEE 802.x) throughout the building using a multiplexing technique.

In this context, we have performed a complete analytical development of an optical MIMO system using the principle of mode group diversity multiplexing (MGDM). We are also interested in the optimization of these systems, namely: optical power and frequency allocation per service, modeling and decompositions of the optical MIMO channel, cross-layer (PHY-MAC) for better capacity and/or quality.

Support

This work is supported by several projects and contacts: CPER program "CISIT", Europe/INTERREG "ROSETTE", Europe/INTERREG "EXTRACTT", ANR/CORRIDOR, IRT/RAILENIUM,...

Academic collaborations

  • National: IFSTTAR, UBO-LabSTICC, TELECOM Bretagne, Supelec, EURECOM, XLIM, INSA de Rouen (LITIS),
  • International: Univ. Concordia (Canada), Kent (UK), Detroit (USA), EPT and ENIT (Tunis), Univ. Damascus, ENSAT (Tangiers).
  • Industry: THALES, SNCF, RFF, Micromodule, Bombardier