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A Survey of NOMA for VLC Systems: Research Challenges and Future Trends
No full textInternational audienceVisible light communication (VLC) has become a promising technology for high data rate communications and an attractive complementary to conventional radio frequency (RF) communication. VLC is a secure, energy efficient and cost-effective technology that exploits the existing infrastructure, particularly in indoor environments, for wireless data transmission. Nevertheless, the main limitation of developing high data rate VLC links is the narrow modulation bandwidth of light-emitting diodes (LEDs), which is in the megahertz range. The power domain nonorthogonal multiple access (PD-NOMA) scheme is envisioned to address several challenges in VLC systems. In this paper, we present a detailed overview of PD-NOMA based VLC systems. Moreover, we introduce insights on some PD-NOMA VLC system constraints and challenges such as power allocation, clipping effect, MIMO and security. Finally, we provide open research problems as well as possible directions for future research to pave the way for the implementation of PD-NOMA VLC systems
Optimistic Planning Algorithms For State-Constrained Optimal Control Problems
No full textInternational audienceIn this work, we study optimistic planning methods to solve some state-constrained optimal control problems in finite horizon. While classical methods for calculating the value function are generally based on a discretization in the state space, optimistic planning algorithms have the advantage of using adaptive discretization in the control space. These approaches are therefore very suitable for control problems where the dimension of the control variable is low and allow to deal with problems where the dimension of the state space can be very high. Our algorithms also have the advantage of providing, for given computing resources, the best control strategy whose performance is as close as possible to optimality while its corresponding trajectory comply with the state constraints up to a given accuracy
Energy harvesting efficiency of unimorph piezoelectric acoustic black hole cantilever shunted by resistive and inductive circuits
No full textInternational audienceA unimorph piezoelectric cantilever equipped with an Acoustic Black Hole (ABH) termination is designed for broadband energy harvesting. The ABH termination, with its tapered region, induces a focusing of the flexural vibrations which can be used to increase the efficiency of an energy harvesting device. A modal-based analytical model is presented, providing an explicit form of the electro-mechanical coupling for each beam eigenmode. Closed-form expressions for the coupled mechanical response and electrical outputs are obtained, allowing one to draw out a complete parametric study to optimize the device. The optimization procedure is conducted following two steps: first, optimal location and dimensions of a single piezoelectric patch are achieved by maximizing the modal electro-mechanical coupling factor (MEMCF) for each structural mode. Thanks to the proposed analytical approach, it is clearly shown that by putting the piezoelectric patch at the maximum of the strain field in the tapered termination, and by adjusting its length in accordance with the focalization created by the ABH effect, the ABH cantilever produces much higher MEMCFs over a wide frequency range and thus outperforms those of a uniform beam. Second, optimization of the shunted circuit is comprehensively performed for a circuit with only resistance, or both resistance and inductance, in series or in parallel. Analytical results show that the key design rule resides in matching the time scale of the circuit with that of the forcing frequency. Addition of the inductance allows enhancing the performance, but on a narrow frequency band. Finally, broadband advantages can be further obtained by considering multiple piezoelectric patches, in which the optimum is obtained when the shunted circuit in each patch is tuned targeting an eigenmode of the ABH beam
Learning-Based vs Model-Free Adaptive Control of a MAV Under Wind Gust
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Learning equilibria with personalized incentives in a class of nonmonotone games
No full textInternational audienceWe consider quadratic, nonmonotone generalized Nash equilibrium problems with symmetric interactions among the agents, which are known to be potential. As may happen in practical cases, we envision a scenario in which an explicit expression of the underlying potential function is not available, and we design a two-layer Nash equilibrium seeking algorithm. In the proposed scheme, a coordinator iteratively integrates the noisy agents' feedback to learn the pseudo-gradients of the agents, and then design personalized incentives for them. On their side, the agents receive those personalized incentives, compute a solution to an extended game, and then return feedback measures to the coordinator. We show that our algorithm returns an equilibrium in case the coordinator is endowed with standard learning policies, and corroborate our results on a numerical instance of a hypomonotone game
Time-resolved structural dynamics of the out-of-equilibrium charge density wave phase transition in GdTe 3
No full textInternational audienceWe use ultrafast electron diffraction (UED) to study the out-of-equilibrium dynamics of the charge density wave (CDW) phase transition in GdTe3, a quasi-two-dimensional compound displaying a unidirectional CDW state. Experiments were conducted at different incident fluences and different initial sample temperatures below Tc. We find that following photo-excitation, the system undergoes a non-thermal ultrafast phase transition that occurs in out-of-equilibrium conditions. The intrinsic crystal temperature was estimated at each time delay from the atomic thermal motion which affects each Bragg peak intensity via the Debye Waller factor. Assuming an isotropic harmonic potential, we estimate the out-of-equilibrium temperature Tqe as a function of the laser fluence. We then relate the recovery time constants and correlation lengths as a function of Tqe. The charge density wave is suppressed in less than a picosecond and recovers the long range order with increasing recovery times with increasing fluences and increasing initial temperatures. The measured relaxation times are discussed in terms of the Rothwarf-Taylor model. If indeed, the recovery time increasesfor initial temperatures closer to Tc in agreement with the model, this one cannot however explain the slowness of the system to return to its ground state. In addition, the transient CDW phase recently observed along the transverse direction in LaTe3 and CeTe3 is not observed in GdTe3
Une recherche sur les formations d’ingénieurs au Maghreb face aux enjeux environnementaux
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Genre féminin et ingénierie, une équation impossible à résoudre? Un éclairage sous l'angle des tabous
No full textInternational audienceLa présence minoritaire des femmes dans les formations d’ingénieurs (28.7% en moyenne en 2021) est souvent mise en regard de leurs très bonnes performances scolaires : comment expliquer un tel paradoxe ? C’est à l’appui du concept de tabou que nous proposons de comprendre cet état de fait. Entre imaginaire collectif et système de prohibitions et d’interdits, le concept de tabou peut nourrir une lecture plus distanciée des discriminations entre les femmes et les hommes en écoles d’ingénieurs et ainsi d’en saisir les ressorts profonds
Stackelberg and MAB Models for Decision-Making Process
No full textInternational audienceThis paper considers the Stackelberg and the Multi-Armed Bandit (MAB) models in the context of Cognitive Radio (CR) in order to enhance the spectrum learning of the secondary users (SU s), In such context, a SU tries to maximize selfishly its utility function which generally depends on the throughput, transmit power level, and the interference from other users. Recently, MAB model is widely suggested in the literature to learn the availability of channels for a single SU. While, in this work, beside the MAB, we focus on the Stackelberg model to consider more developed scenarios, such as: Learn channels' availability, enhance the Quality of Service, adjust transmit power level and decrease the interference among SUs. We also focus on the priority access, where a leader reacts first and then the followers make their decisions and actions by taking into consideration the action of the leader. We show that the Stackelberg model can represent an optimal solution in a real radio environment to help a SU make a good decision
Estimating the Coverage Measure and the Area Explored by a Side-Scan Sonar
No full textInternational audienceFull coverage of an area of interest is a common task for a robot in the underwater environment. Estimating the area explored by the robot is indeed essential for determining if path-planning algorithms lead to complete coverage. In this work, we propose a method for estimating the area explored by a Side-Scan Sonar. The proposed method is able to determine how many times each portion of the space has been sensed by the sonar using a novel approach based on the topological properties of the environment that has been scanned, and more precisely on an estimation of certain winding numbers. This property is useful for localization inside homogeneous environments, e.g. the underwater environment, and assessment for potential revisiting missions