Relais électromécanique | EPFL Graph Search

Un relais électromécanique est un organe électrique permettant de distribuer la puissance à partir d'un ordre émis par la partie commande. Ainsi, un relais permet l'ouverture et la fermeture d'un circuit électrique de puissance à partir d'une information logique. Les deux circuits, puissance et information, sont complètement isolés (isolation galvanique) et peuvent avoir des caractéristiques d'alimentation électrique différentes. Description

Un relais est composé principalement d'un électroaimant qui, lorsqu'il est alimenté, soumet à une force une palette qui agit mécaniquement sur le système de commutation électrique : les contacts.
L'électroaimant peut être, suivant les spécifications et les besoins, alimenté en TBT (Très Basse Tension) (moins de , , ) continu ou alternatif ou en BT (Basse Tension) (, , ).
Le système de commutation peut être composé d'un ou plusieurs interrupteurs simple effet appelés contacts normalement ouverts (NO) ou normalement ferm

Control of velocity for a linear actuator

Silas Kull

This project was done in the laboratory of integrated actuators (LAI) during the first master semester. It is part of a PhD-work with linear actuators, also called relays, where these actuators are optimized in design and equipped with a speed control during closure and aperture. The aim of this semester project was to find an optimal control algorithm for the closure of a relay. The relay has to follow a specific speed profile in function of position, so that a certain speed can be guaranteed near the contact closure position. To follow this speed profile, which has been developed by the corresponding company, will decrease electrical and mechanical wearout during closure. In this report, different approaches of control are shown and compared. It is also a report that should help as a guide to develop an optimal control for a specific relay. A final conclusion will give some advices on how to design an optimal control.

2010

Physical Layer Cooperation

Ayan Sengupta

Information theory has long pointed to the promise of physical layer cooperation in boosting the spectral efficiency of wireless networks. Yet, the optimum relaying strategy to achieve the network capacity has till date remained elusive. Recently however, a relaying strategy termed Quantize-Map-and-Forward (QMF) was proved to achieve the capacity of arbitrary wireless networks within a bounded additive gap. This thesis contributes to the design, analysis and implementation of QMF relaying by optimizing its performance for small relay networks, proposing low-complexity iteratively decodable codes, and carrying out over-the-air experiments using software-radio testbeds to assess real-world potential and competitiveness. The original QMF scheme has each relay performing the same operation, agnostic to the network topology and the channel state information (CSI); this facilitates the analysis for arbitrary networks, yet comes at a performance penalty for small networks and medium SNR regimes. In this thesis, we demonstrate the benefits one can gain for QMF if we optimize its performance by leveraging topological and channel state information. We show that for the N-relay diamond network, by taking into account topological information, we can exponentially reduce the QMF additive approximation gap from

\Theta(N)

bits/s/Hz to

\Theta(\log N)

bits/s/Hz, while for the one-relay and two-relay networks, use of topological information and CSI can help to gain as much as

6

dB. Moreover, we explore what benefits we can realize if we jointly optimize QMF and half-duplex scheduling, as well as if we employ hybrid schemes that combine QMF and Decode-and-Forward (DF) relay operations. To take QMF from being a purely information-theoretic idea to an implementable strategy, we derive a structure employing Low-Density-Parity-Check (LDPC) ensembles for the relay node operations and message-passing algorithms for decoding. We demonstrate through extensive simulation results over the full-duplex diamond network, that our designs offer a robust performance over fading channels and achieves the full diversity order of our network at moderate SNRs. Next, we explore the potential real-world impact of QMF and present the design and experimental evaluation of a wireless system that exploits relaying in the context of WiFi. We deploy three main competing strategies that have been proposed for relaying, Amplify-and-Forward (AF), DF and QMF, on the WarpLab software radio platform. We present experimental results--to the best of our knowledge, the first ones--that compare QMF, AF and DF in a realistic indoor setting. We find that QMF is a competitive scheme to the other two, offering in some cases up to 12% throughput benefits and up to 60% improvement in frame error-rates over the next best scheme. We then present a more advanced architecture for physical layer cooperation (termed QUILT), that seamlessly adapts to the underlying network configuration to achieve competitive or better performance than the best current approaches. It combines on-demand, opportunistic use of DF or QMF followed by interleaving at the relay, with hybrid decoding at the destination that extracts information from even potentially undecodable received frames. We theoretically quantify how our design choices affect the system performance. We also deploy QUILT on WarpLab and show through over-the-air experiments up to

5

times FER improvement over the next best cooperative protocol.

EPFL2015

Schemes and architectures for wireless ad hoc networks and cooperative communication

Tarik Tabet

The focus of this thesis is on the study of decentralized wireless multi-hop networks. We are particularly interested in establishing bounds on the traffic-carrying capabilities of wireless ad hoc networks and conditions on the scalability of such networks with node mobility. This theoretical investigation brings forward challenges on the design of such networks. This leads to a second part of this thesis that considers the feasibility and the design of physical layer architectures and schemes for decentralized wireless multi-hop networks. In the first part of this thesis, bounds on the capacity of wireless ad hoc networks with two types of non-uniform traffic patterns are established. We focus on the impact of traffic patterns where local communications predominate and show the improvement in terms of per user-capacity over ad hoc networks with unbounded average communication distances. We then study the capacity of hybrid wireless networks, where long-distance relaying is performed by a fixed overlay network of base-stations. We investigate the scaling of capacity versus the number of nodes and the density of base-stations in the area of the network. It is shown that the gain in performance is mainly due to the reduction in the mean number of hops from source to destination. Then, we investigate the impact of mobility on the ad hoc network capacity. We propose a set of necessary and sufficient conditions under which the long-term averaged throughput in an ad hoc network can remain constant as the number of nodes increases. The main idea is to use a connectivity graph that does not represent the actual physical network, but rather the available communication resources. This graph also allows to translate the problem of maximizing the throughput in ad hoc networks to the multi-commodity flow problem and directly apply related results. In contrast to these macroscopic studies, in the second part we focus on a microscopic analysis of ad hoc wireless networks. We are interested in characterizing the performance of decentralized multiple-access and retransmission schemes for multi-hop wireless networks with the goal of drawing conclusions on cross-layer design. We investigate different transmission strategies in order to assess the tradeoff between spatial density of communications and the range of each transmission. We present tools for characterizing the spatial throughput as a function of topological parameters (e.g node population density) and system parameters (propagation, bandwith etc). The results of this work also show that coding and retransmissions provide means of reliable communication coupled with a completely decentralized multiple-access strategy. Finally, an efficient protocol for the delay-limited fading Automatic Retransmission reQuest (ARQ) single relay channel is considered for cooperative communications. The proposed protocol exploits two kinds of diversity: (i) space diversity available through the cooperative (relay) terminal, which retransmits the source's signals, (ii) ARQ diversity obtained by leveraging the retransmission delay to enhance the reliability. The performance characterization is in terms of the achievable diversity, multiplexing gain and delay tradeoff for a high signal-to-noise ratio (SNR) regime. Then, by letting the source's power level vary over the retransmission rounds, we show the benefits of power control on the diversity.

EPFL2007