Laboratoire des Signaux & Systèmes

In the past as well as present wireless communication systems, the wireless propagation environment is regarded as an uncontrollable black box that impairs the received signal quality, and its negative impacts are compensated for by relying on the design of various sophisticated transmission/reception schemes. However, the improvements through applying such schemes operating only at two endpoints (i.e., transmitter and receiver) are limited even after five generations of wireless systems. Reconfigurable intelligent surface (RIS) or intelligent reflecting surface (IRS) have emerged as a new and promising technology that can configure the wireless environment in a favorable manner by properly tuning the phase shifts of a large number of quasi passive and low-cost reflecting elements, thus standing out as a promising candidate technology for the next/sixth-generation (6G) wireless system. However, to reap the performance benefits promised by RIS/IRS, efficient signal processing techniques are crucial, for a variety of purposes such as channel estimation, transmission design, radio localization, and so on. In this paper, we provide a comprehensive overview of recent advances on RIS/IRS-aided wireless systems from the signal processing perspective.We also highlight promising research directions that are worthy of investigation in the future.

Producing truly realistic and immersive digital imaging is widely seen as the ultimate goal towards further improving Quality of Experience (QoE) for end users of multimedia services. The human visual system is able to perceive a wide range of colors, luminous intensities, and depth, as present in a real scene. However, current traditional imaging technologies cannot capture nor reproduce such a rich visual information. Recent research innovations have made it possible to address these bottlenecks in multimedia systems. As a result, new multimedia signal processing areas have emerged such as ultra-high definition, high frame rate, high dynamic range imaging, light fields, and point cloud. These technologies have the potential to bring a leap forward for upcoming multimedia systems. However, the effective deployment of hyper-realistic video technologies entails many technical and scientific challenges. In this talk, I will discuss recent research activities covering several aspects of hyper-realistic imaging, including point cloud compression, light field compression, and semantic-aware tone mapping for high dynamic range imaging.

Several heuristic procedures to estimate the rotor position of interior permanent magnet synchronous motors (IPMSM) via signal injection have been reported in the application literature, and are widely used in practice. These methods, based on the use of linear time‐invariant (LTI) high‐pass/low‐pass filtering, are instrumental for the development of sensorless controllers. To the best of authors’ knowledge, no theoretical analysis of these methods has been carried out. The objectives of this note are (i) to invoke some recent work on the application of averaging techniques for injection‐based observer design to develop a theoretical framework to analyse the LTI filtering used in sensorless methods and (ii) to propose a new method that on the one hand ensures improved accuracy and on the other hand can be related to the current filtering technique. An additional advantage of the new method is that it relies on the use of linear operators, implementable with simple computations. The effectiveness of the proposed scheme is assessed by experiments on an IPMSM platform driven by a 521 V DC bus with a 5‐kHz pulse‐width modulation.

SummaryOver‐The‐Top broadcasts a huge number of medias that mobile network operators have to manage efficiently before to deliver it to their subscribers. We propose an economic pricing approach to address caching resource management issues in the 5G wireless networks and to overcome limitations in terms of throughput, latency, and reliability. Moreover, we consider this approach based on an oligopolistic multi‐market deducted from Cournot, Stackelberg, and Bertrand models. For simulation purpose, we consider the routing protocol (Ad‐hoc On‐Demand Distance Vector [AODV]) commonly used for the wireless network. We use the NS‐2 package, and we analyze results in terms of End‐to‐End delay representing latency, throughput, packet delivery ratio, and normalized network load.

Cyclostationary signals can be met in various domains, such as telecomunications and vibration analysis. Cyclostationarity allows to model repetitive signals and hidden periodicities such as those induced by modulation for communications and by rotating machines for vibrations. In some cases, the fundamental frequency of these repetitive phenomena can be known. The algorithm that we propose aims at extracting one cyclostationary source, whose cyclic frequency is a priori known, from a set of observations. We propose a new criterion based on second order statistics of the measures which is easy to estimate and leads to extraction with very good accuracy.

The present work is an account of an ongoing work on biogas production from animal wastes at LEREA (Laboratoire d’enseignement et de recherche en énergétique appliquée) in Mamou, Guinea. The work consists of biogas production from anaerobic digestion and co-digestion of cow dung and droppings. We focus in this report on the determination of the physico-chemical characteristics of the experimental setup. We have carried out three experiments of anaerobic digestion each one lasting 45 days at mesophilic temperature (temperature was maintained in the range 27°C - 28°C). Biogas - 28.4 liters have been obtained from droppings, 22.6 liters from cow dung and 38.7 liters from co-digestion of the previous two wastes. The following physico-chemical characteristcs were observed for cow dung: humidity 43%, dry matter 20.83%, organic matter 57%, density 625kg/m3, carbon content 31%, nitrogen content 1.46%, nitrogen-carbon ratio 21/30. For droppings we measured: humidity 35%, dry matter 65%, organic matter 62%, density 250 kg/m3, carbon content 36%, nitrogen level 1.83%. This characterization was carried out on a sample of 3 g of each type of substrate. These results agree with those of the literature that we were able to compare with. Keywords: anaerobic digestion; anaerobic co-digestion; physico-chimical characterization; cow dung weste; droppings weste; methanation; animal waste

In this article, we present a framework for taking into account user preferences in multi-objective Bayesian optimization in the case where the objectives are expensive-to-evaluate black-box functions. A novel expected improvement criterion to be used within Bayesian optimization algorithms is introduced. This criterion, which we call the expected weighted hypervolume improvement (EWHI) criterion, is a generalization of the popular expected hypervolume improvement to the case where the hypervolume of the dominated region is defined using an absolutely continuous measure instead of the Lebesgue measure. The EWHI criterion takes the form of an integral for which no closed form expression exists in the general case. To deal with its computation, we propose an importance sampling approximation method. A sampling density that is optimal for the computation of the EWHI for a predefined set of points is crafted and a sequential Monte-Carlo (SMC) approach is used to obtain a sample approximately distributed from this density. The ability of the criterion to produce optimization strategies oriented by user preferences is demonstrated on a simple bi-objective test problem in the cases of a preference for one objective and of a preference for certain regions of the Pareto front.

Abstract One of the most challenging problems in AC drives applications is the design of a simple plug‐in adaptation scheme to estimate the unknown rotor resistance and load torque for the industry‐standard indirect field oriented control. In this paper we give the first globally convergent solution to this problem for torque control of current‐fed induction motors that does not rely on any excitation assumption. Some results on speed regulation are also presented.

Abstract This paper addresses the problem of regulating the output voltage of a DC‐DC buck‐boost converter feeding a constant power load, which is a problem of current practical interest. Designing a stabilising controller is theoretically challenging because its average model is a bilinear second order system that, due to the presence of the constant power load, is non‐minimum phase with respect to both states. Moreover, to design a high‐performance controller, the knowledge of the extracted load power, which is difficult to measure in industrial applications, is required. In this paper, an adaptive interconnection and damping assignment passivity‐based control—that incorporates the immersion and invariance parameter estimator for the load power—is proposed to solve the problem. Some detailed simulations are provided to validate the transient behaviour of the proposed controller and compare it with the performance of a classical PD scheme.