Simon Hubert

Vehicle-to-Vehicle Radio Channel Characterization in Crossroad Scenarios

Vehicle-to-vehicle (V2V)-communication-based collision avoidance systems detect if two vehicles are on a collision course (e.g., in crossroads, intersections, and highway merging), and they are particularly useful in the absence of line of sight (LOS) owing to buildings, roadside infrastructures, and road bending. Relying on radio measurements using a 4 × 30 multiple-input-multiple-output (MIMO) system at 5.3 GHz, this paper presents the results of an empirical study of V2V propagation channels in two suburban crossroad scenarios, where vehicles are either moving in the same direction and separate from each other along different roads or pass each other in opposite directions at the crossing. The quasi-stationarity interval is first characterized using correlation matrix distance (CMD). Small-scale fading follows a Nakagami distribution based on the Akaike information criteria (AIC). Delay and angular dispersions are found to be significantly affected by the type of crossroad and the presence of an LOS. Cross-correlation coefficients between delay dispersion, angular dispersion, and small-scale fading behavior are also evaluated. By comparing the results of the different crossroads, it is found that the delay and angular dispersions are large in the first type of crossroad. By contrast, in the second type of crossroad, small delay and angular dispersions are observed due to road bending and obstruction by roadside trees.

Error analysis for the contour-FFT based Green's function evaluation

A novel approach based on the Method of Moments has been recently presented to analyse very large irregular arrays printed on layered substrates. However, that method requires some tuning to minimize the error in the layered medium Greens functions while presenting a low computation time. In this work, an analysis of the influence of every parameter on these two figures of merit is presented for 2D free-space, and a simple algorithm is provided to automatize the tuning procedure. The procedure is then validated for 3D layered structures.

Modeling of impedance-loaded sub-wavelength metasurfaces

In the context of the optimization of a versatile type of metasurface consisting of intertwined spirals printed on a dielectric substrate and loaded with discrete impedances, we propose a simple development of the method of moments interaction matrix that allows obtaining the scattered field almost instantly for any distribution of discrete loads. Simulation results for a sample design are presented to illustrate the effectiveness and validity of the method.

Error model for Contour-FFT evaluation of the free-space on-plane Green's function

Closed-form analytical expressions are derived for the numerical integration of the spectral Greens function with Contour-FFT. Results indicates that a proper uniform grid of spatial points enhances the convergence rate of the truncation error, that the Nyquist-Shannon theorem can be generalized to inverse Laplace transforms on linear path and that the relative error specific to Contour-FFT is a regularized gamma function. Two examples illustrate the modularity of the approach.

Compact circular boxed slot antenna array devoted to polarimetric direction finding

We present a boxed slotline array devoted to portable direction finding. The structure is presented and the tight links between figures of merit such as radiation efficiency, input reflection coefficient, phase center of the radiation patterns and unit cell area are explicited. We then optimize the design and propose a simulated direction finding scenario for maximum radiation efficiency, which shows reasonably good resolution for the target application.

SVD post-compression combined with shielded-block preconditioner

We present a post-compression method based on the Singular Value Decomposition that can be used to retrieve the low-rank representation of the Method of Moments interaction matrix after using the shielded-block preconditioner. A compression ratio of more than 17 has be achieved without significant loss of accuracy. The time needed to compress the preconditioned matrix is negligible with respect to the preconditioning time. We also show that the compression can decrease the solution complexity using iterative solvers or multiple-scattering MBFs, thereby significantly decreasing the total computation time.

Compact mathematical description of sectorially symmetrical arrays

The proposed approach is being developed in the framework of compact direction-finding systems that include polarization estimation. This work concentrates on sectorially symmetrical arrays, and combines the classical Array Scanning Method (ASM) with a Spherical Waves Decomposition (SWD) in order to directly compute the SWD coefficients based on the ASM current distributions. This approach offers the advantages of a fast computation based on the current distribution on only one antenna, as well as a reduced set of parameters needed to evaluate the embedded element patterns.