Radio channel modeling and localization

Team: J.C. Cousin, B Huyart, C. Roblin, A. Sibille

Fundings: European FP7 projects (SELECT, LEXNET, PHYLAWS), FUI projects (URC, RECOSS)

Joint antennas and channels statistical modelling Wireless networks need channel models in order to be able to test competing physical/link layer schemes and perform network level simulations. However there is an increasing complexity in the current and future communications standards, which are multi-antennas, multi-frequency and where the behaviour of terminals in a use context is highly variable. The group has initiated and developed since a few years a statistical approach of this behaviour, taking into account the variability of the terminals characteristics in their close environment. The method combines full antenna performance data to local propagation characteristics in order to arrive an effective gain concept, seen as a stochastic quantity. It has been applied to the efficiency and effective gains of handsets in proximity to a user head and hand and to multiple antenna systems. In body area networks, the influence of the human body on the behaviour of antennas is often of prime importance; the properties of the on-body propagation channel are very specific, and are notably sensitive to the subject movement for most scenarios. Both aspects, which are intricately related, have been studied with a statistical approach. Joint space and frequency correlated path loss data have also been modelled through a simple semi-Kronecker approximation. The latest works address the statistical analysis and modelling of UWB tag antennas employed in a backscattering based RFID system. A related topic newly launched is focusing on physical based security. The project intends to address the improvement of the protection and confidentiality of information exchanged at physical interface through public wireless media by developing security techniques operating at the physical layer level or exploiting the characteristics of signals transmitted at the physical layer, accounting for realistic propagation channels characteristics.

Parametric models for ultra wide band antennas The full characterisation of the radiation of UWB antennas requires a significant amount of data arising from either measurement or electromagnetic simulations. It is therefore desirable to use "data compression" methods to handle them more easily. A complete (parametric) modelling of both frequency and time domain far field antenna responses (for any direction of radiation) with extremely high order reduction ("ultra compression") has been developed. It is based on both the singularity expansion and the spherical mode expansion methods. Theoretical properties of the model parameters and relationships with global indicators of performance of UWB antennas have been derived. The modelling has been applied to full 3D measurements of omni-directionnal or moderately directive UWB antennas with a good accuracy and high data compression rates of more than 97 percents (and up to more than 99.9 percents for some cases). These models can be efficiently used in simulations of the physical or radio link layers, or in deterministic propagation simulators based on asymptotic methods (UTD/GTD "ray tracing", etc.).

Localization Localization of human beings or objects is a current subject. This one becomes major as well to improve wireless communications systems by allowing a better management of the power as telemonitoring for the supervision of patients. In this way, the group develops a localization system for indoor environments based on a multistatic radar technique using FMCW (Frequency Modulation Continuous Wave) signals covering the European UWB frequency bandwidth. This system allows to give the localization of active tags in range and angles of arrival. Compared to the others known systems, the main advantages are that it doesn’t need an accurate synchronization clock, and the multipath effects are reduced by using jointly FMCW signals and circular polarization antennas. Initial efforts led to the design of 2 circular polarization antennas, covering the [6-8.5 GHz] frequency bandwidth, and of different sizes fitted to the tag and base station.

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