Combined Source and Channel Strategies for Optimized Video Communications

ISBN 978-953-7619-70-

Characterisation of a non-pathogenic and non-protective infectious rabbit lagovirus related to RHDV

The existence of non-pathogenic RHDV strains was established when a non-lethal virus named rabbit calicivirus (RCV) was characterised in 1996 in Italy. Since then, different RNA sequences related to RHDV have been detected in apparently healthy domestic and wild rabbits, and recently a new lagovirus was identified in Australia. We have characterised from seropositive healthy domestic rabbits a non-lethal lagovirus that differs from RHDV in terms of pathogenicity, tissue tropism and capsid protein sequence. Phylogenetic analyses have revealed that it is close to the Ashington strain and to the RCV, but distinct. We proved experimentally that it is infectious but non-pathogenic and demonstrated that, contrary to the other described non-pathogenic lagoviruses, it induces antibodies that do not protect against RHDV. Our results indicate the existence of a gradient of cross-protection between circulating strains, from non-protective, partially protective to protective strains, and highlight the extent of diversity within the genus Lagovirus

Souvent peu connue, la cuniculture des pays de l'Europe du Nord (3. partie et fin)

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Physical layer reliability vs ARQ in MIMO block-fading channels

International audienceIn today's wireless communication systems, automatic repeat request (ARQ) is implemented at the MAC layer in order to retransmit packets that have been erroneously transmitted at the physical (PHY) layer. Following a joint PHY-MAC design, information provided by the ARQ scheme can be exploited at the PHY layer in order to improve the system's performance. This paper extends the work presented in [1] in the context of SISO channels to the context of MIMO block-fading channels. Based on statistical channel knowledge at the transmitter, it provides an analysis of the natural tradeoff that exists between the PHY layer transmission rate and the number of ARQ retransmissions. We derive a very accurate analytical formulation of the optimum transmission rate (and, equivalently, the optimum PHY packet error-rate) that maximizes the goodput, as a function of the system parameters, namely the SNR, the number of antennas and the diversity order of the channel. Interestingly, we find that the PHY layer has to be made more reliable for MIMO channels than for SISO channels, and also that the MIMO ARQ system is less sensitive to a wrong choice of the rate of transmission than the SISO ARQ system

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Random Matrix Theory Based Resource Allocation in Correlated MIMO Systems with ARQ Feedback

International audienceWe consider resource allocation under partial feed-back in a spatially correlated MIMO link, when the ARQ protocol is implemented at the MAC layer. We propose a design framework, which makes use of results from random matrix theory (RMT), to find the rate as well as the input covariance matrix that maximize the long term goodput. We consider partial feedback in terms of positive/negative acknowledgment bits (ACK/NAK), which comes essentially for free since they are always present in the signaling of the upper layers. We provide explicit expressions of the long term goodput, which, in association with a RMT based approximation of the mu-tual information enable us to optimize the resource allocation problem. Interestingly, the simulations show that the asymptotic optimization analysis is still valid for MIMO sizes as small as 2x2. Index Terms—MIMO, resource allocation, random matrix theory, ARQ, partial feedback. I. BACKGROUND AND MOTIVATION R ESOURCE allocation is a widely studied subject (e.g. [1] and references therein) for which the assumptions may be of two kinds: perfect channel state information at the transmitter (CSI-T), and partial CSI-T, also known as partial feedback. Only the latest is acceptable from a practical point of view as soon as the number of degrees of freedom in the system gets large (MIMO, wideband or/and multi-user systems for example). The objective of this paper is to present a design framework to optimize the long term goodput by using the ACK/NAK bits provided by ARQ. This can be viewed as a cross-layer design in the sense that physical layer parameters are optimized based on (ARQ) information provided at the MAC layer [2]. We apply results from Random Matrix Theory (RMT) to estimate the average received SNR and determine the rate and the input covariance matrix to maximize the goodput. To the best of the authors' knowledge, RMT results have never been applied to the resource allocation problem for MIMO-ARQ systems. Importantly, general considerations about the optimal transmission scheme without perfect CSI-T (training-based methods, blind methods, error-rate based methods. . .) are out of the scope of this paper. The proposed framework can be seen as a proof of concept that acknowledgment bits can be used for the resource allocation problem in a MIMO-ARQ setup, although it is probable that optimal solutions would be, e.g., mixed training-ARQ based

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Synergies entre insecticides et fongicides appliques a des doses subletales chez l'abeille

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