Low Complexity Scalable Iterative Algorithms for IEEE 802.11p Receivers

In this paper, we investigate receivers for Vehicular to Vehicular (V2V) and Vehicular to Infrastructure (V2I) communications. Vehicular channels are characterized by multiple paths and time variations, which introduces challenges in the design of receivers. We propose an algorithm for IEEE 802.11p compliant receivers, based on Orthogonal Frequency Division Multiplexing (OFDM). We employ iterative structures in the receiver as a way to estimate the channel despite variations within a frame. The channel estimator is based on factor graphs, which allow the design of soft iterative receivers while keeping an acceptable computational complexity. Throughout this work, we focus on designing a receiver offering a good complexity performance trade-off. Moreover, we propose a scalable algorithm in order to be able to tune the trade-off depending on the channel conditions. Our algorithm allows reliable communications while offering a considerable decrease in computational complexity. In particular, numerical results show the trade-off between complexity and performance measured in computational time and BER as well as FER achieved by various interpolation lengths used by the estimator which both outperform by decades the standard least square solution. Furthermore our adaptive algorithm shows a considerable improvement in terms of computational time and complexity against state of the art and classical receptors whilst showing acceptable BER and FER performance

Le paradoxe français

C’est l’historien belge Maxime Steinberg qui a parlé d’un « paradoxe français » au regard du bilan de la Shoah en Europe occidentale. Dans un article de 1993, il se demande pourquoi la France, pays ayant eu un gouvernement antisémite et collaborateur, connaît un taux d’extermination des juifs plus faible (25 %) que les Pays-Bas (80 %) et la Belgique (45 %) alors que ces pays n’ont pas eu de tel gouvernement. Cette comparaison est plus pertinente qu’avec l’Italie (16 %) dans la mesure où ces trois pays ont été occupés dans la même période (mai-juin 1940) et la « solution finale » décidée au même moment (juin 1942). Cette forte proportion de survie des juifs en France – l’une des plus élevées d’Europe – n’exonère en rien les crimes de Vichy. Tout sentiment de satisfaction serait indécent au regard des 80 000 morts de la Shoah. Mais qui travaille sur le génocide ne peut que s’interroger sur cette singularité du cas français. [Premier paragraphe de l'article

Matérialisation, dématérialisation et circulations des musiques du monde arabe (XXe-XXIe siècle)

International audienc

On the transmit beamforming for MIMO wiretap channels : Large-system analysis

With the growth of wireless networks, security has become a fundamental issue in wireless communications due to the broadcast nature of these networks. In this work, we consider MIMO wiretap channels in a fast fading environment, for which the overall performance is characterized by the ergodic MIMO secrecy rate. Unfortunately, the direct solution to finding ergodic secrecy rates is prohibitive due to the expectations in the rates expressions in this setting. To overcome this difficulty, we invoke the large-system assumption, which allows a deterministic approximation to the ergodic mutual information. Leveraging results from random matrix theory, we are able to characterize the achievable ergodic secrecy rates. Based on this characterization, we address the problem of covariance optimization at the transmitter. Our numerical results demonstrate a good match between the large-system approximation and the actual simulated secrecy rates, as well as some interesting features of the precoder optimization.QC 20140613</p