92 research outputs found
Ausleseelektronik fĂŒr magnetische Mikrokalorimeter im Frequenzmultiplexverfahren
Magnetische Mikrokalorimeter (MMC) sind Tieftemperatur-Kalorimeter mit exzellenter Auflösung und hoher LinearitĂ€t. Dadurch sind sie als SchlĂŒsseltechnologie fĂŒr eine Vielzahl an Experimenten und Instrumenten in der Grundlagenforschung prĂ€destiniert. Das Sensorprinzip erfordert Betriebstemperaturen weit unter 100mK. Bei einer groĂen Anzahl von mehreren hundert Detektoren mit paralleler Anbindung wird die Auslese zu einer hochgradig komplexen Aufgabe. Frequenzmultiplex-Verfahren wie der Mikrowellen-SQUID-Multiplexer sind in der Lage, die Auslese all dieser Detektoren mit wenigen Leitungen zu realisieren, und sind fĂŒr MMCs geeignet. Die Auslese des Mikrowellen-SQUID-Multiplexers erfordert jedoch hohe Bandbreiten im Gigahertzbereich, leistungsfĂ€hige Hardware und mehrstufige Signalverarbeitung zur Datenreduktion. In der vorliegenden Arbeit wird erstmals ein optimiertes Raumtemperatur-Auslesesystem fĂŒr 400 Multiplexer-KanĂ€le mit 4GHz Bandbreite fĂŒr MMCs vorgestellt. Ausgehend vom konzeptionierten Auslesesystem werden zwei Prototyp-Elektroniken realisiert und evaluiert. Mit dem Auslesesystem wurden in einem Testaufbau Energieauflösungen von 6,2eV mit 16 und 10,7eV mit 80 KanĂ€len im Bereich von 3,3keV erreicht. Mit MMCs im Kryostaten und Achtkanalauslese wurden Auflösungen von 8,8eV bei 5,9keV erreicht. Die entwickelten Methoden und Prototypen werden darĂŒber hinaus auf eine neuartige Multiplexer-Variante mit dc-SQUIDs ĂŒbertragen und ferner wird eine Vierkanal-Auslese mit Tieftemperaturaufbau demonstriert. Mit den Ergebnissen der vorliegenden Arbeit steht nun ein hochoptimiertes Auslesesystem in einer ersten Version zur VerfĂŒgung
Améliorations des transmissions VLC (Visible Light Communication) sous contrainte d'éclairage : études théoriques et expérimentations
Abstract : Indoor visible light communication (VLC) networks based on light-emitting diodes (LEDs)
currently enjoy growing interest thanks in part to their robustness against interference,
wide license-free available bandwidth, low cost, good energy efficiency and compatibility
with existing lighting infrastructure. In this thesis, we investigate spectral-efficient modulation
techniques for the physical layer of VLC to increase throughput while considering
the quality of illumination as well as implementation costs. Numerical and experimental
studies are performed employing pulse amplitude modulation (PAM) and carrierless amplitude
and phase (CAP) modulation under illumination constraints and for high modulation
orders. Furthermore, the impact of LED nonlinearity is investigated and a postdistortion
technique is evaluated to compensate these nonlinear effects. Within this framework,
transmission rates in the order of a few hundred Mb/s are achieved using a test bench made
of low-cost components. In addition, an imaging multiple input multiple-output (MIMO)
system is developed and the impact on performance of imaging lens misalignment is theoretically
and numerically assessed. Finally, a polynomial matrix decomposition technique
based on the classical LU factorization method is studied and applied for the first time to
MIMO VLC systems in large space indoor environments.Les rĂ©seaux de communication en lumiĂšre visible (VLC) sâappuyant sur lâutilisation de diodes Ă©lectroluminescentes (LED) bĂ©nĂ©ficient actuellement dâun intĂ©rĂȘt grandissant, en partie grĂące Ă leur robustesse face aux interfĂ©rences Ă©lectromagnĂ©tiques, leur large bande disponible non-rĂ©gulĂ©e, leur faible coĂ»t, leur bonne efficacitĂ© Ă©nergĂ©tique, ainsi que leur compatibilitĂ© avec les infrastructures dâĂ©clairage dĂ©jĂ existantes. Dans cette thĂšse, nous Ă©tudions des techniques de modulation Ă haute efficacitĂ© spectrale pour la couche physique des VLC pour augmenter les dĂ©bits tout en considĂ©rant la qualitĂ© de lâĂ©clairage ainsi que les coĂ»ts dâimplĂ©mentation. Des Ă©tudes numĂ©riques et expĂ©rimentales sont rĂ©alisĂ©es sur la modulation dâimpulsion dâamplitude (PAM) et sur la modulation dâamplitude et de phase sans porteuse (CAP) sous des contraintes dâĂ©clairage et pour des grands ordres de modulation. De plus, lâimpact des non-linĂ©aritĂ©s de la LED est Ă©tudiĂ© et une technique de post-distorsion est Ă©valuĂ©e pour corriger ces effets non-linĂ©aires. Dans ce cadre, des dĂ©bits de plusieurs centaines de Mb/s sont atteints en utilisant un banc de test rĂ©alisĂ© Ă partir de composants Ă bas coĂ»ts. Par ailleurs, un systĂšme multi-entrĂ©es multi-sorties (MIMO) imageant est Ă©galement dĂ©veloppĂ© et lâimpact du dĂ©saxage de lâimageur sur les performances est Ă©tudiĂ©. Finalement, une technique de dĂ©composition polynomiale basĂ©e sur la mĂ©thode de factorisation classique LU est Ă©tudiĂ©e et appliquĂ©e aux systĂšmes MIMO VLC dans des grands espaces intĂ©rieurs
Photovoltaics as high-speed optical wireless communication receiver
With an ever-growing network of billions of interconnected smart
devices in the era of the Internet of Things, high-speed communication has
inspired research into the use of low energy and high-speed free-space optical
(FSO) communication systems. In FSO communication, light-emitting diodes
(LEDs) and lasers are used for wireless data transmission in indoor and
outdoor environments and photodiodes are used as data receivers. But these
receivers have two main disadvantages â they require an external power
source to operate, and their small active area makes alignment challenging. A
promising solution to these problems is the use of solar panels as data
receivers. As photovoltaic (PV) panels have a larger active area compared to
that of conventional photodiodes, they relax the strict alignment requirements
and can also simultaneously harvest energy from sunlight.
The current work investigates the use of Si-based off-the-shelf PV
panels as FSO receivers to build an energy-neutral and high-speed FSO
system. As solar panels were never built as optical data communication
receivers, they have a very small communication bandwidth compared to
photodiodes. In this work, a theoretical model of the solar panel is provided
and, using analogue equalization, the usable communication bandwidth of a
solar panel is extended. PV panels were primarily designed to harvest energy
from sunlight. Using the analytical model, simultaneous energy harvesting,
and data communication performances are evaluated. Moreover, the trade-off
between the energy harvesting and data communication capability of the solar
panel is shown. Furthermore, the use of different spectrally efficient
modulation techniques such as direct current optical orthogonal frequency
division multiplexing (DCO-OFDM) and discrete multitone pulse-amplitude
modulation (DMT-PAM) are compared when used with a solar panel as an
optical receiver. It has been found that each modulation scheme is usable
under different applications.
Using the simulated results from the analytical model an FSO prototype
was designed and developed, demonstrating the use of solar panels as the
receivers. A receiver circuit to interface the solar panel with the FSO system
was designed and developed to demonstrate the data communication and
energy harvesting performance. Data rates as high as 75 Mb/s is
demonstrated using DCO-OFDM and offline processing using an off-the-shelf
Si-based solar panel. The PV panel-based FSO system was used to provide
internet access to two residential properties on a remote island in the northern
part of Scotland. The performance of the prototype was carefully studied
under various weather conditions. Furthermore, the maximum user throughput
achieved by the prototype is 28.3 Mb/s with the simultaneous energy
harvesting capability of up to 4.5 W. Lastly, the design of a custom-built solar
panel is proposed which doubles the data rates shown in this work and can be
implemented alongside a small-scale to large-scale solar energy harvesting
infrastructure
Filtered Multicarrier Transmission
Orthogonal frequencyâdivision multiplexing (OFDM) has been adopted as the waveform of choice in the existing and emerging broadband wireless communication systems for a number of advantages it can offer. Nevertheless, investigations of more advanced multicarrier transmission schemes have continued with the aim of eliminating or mitigating its essential limitations. This article discusses multicarrier schemes with enhanced spectrum localization, which manage to reduce the spectral sidelobes of plain OFDM that are problematic in various advanced communication scenarios. These include schemes for enhancing the OFDM waveform characteristics through additional signal processing as well as filterâbank multicarrier (FBMC) waveforms utilizing frequencyâselective filter banks instead of plain (inverse) discrete Fourier transform processing for waveform generation and demodulation.acceptedVersionPeer reviewe
Discrete Wavelet Transforms
The discrete wavelet transform (DWT) algorithms have a firm position in processing of signals in several areas of research and industry. As DWT provides both octave-scale frequency and spatial timing of the analyzed signal, it is constantly used to solve and treat more and more advanced problems. The present book: Discrete Wavelet Transforms: Algorithms and Applications reviews the recent progress in discrete wavelet transform algorithms and applications. The book covers a wide range of methods (e.g. lifting, shift invariance, multi-scale analysis) for constructing DWTs. The book chapters are organized into four major parts. Part I describes the progress in hardware implementations of the DWT algorithms. Applications include multitone modulation for ADSL and equalization techniques, a scalable architecture for FPGA-implementation, lifting based algorithm for VLSI implementation, comparison between DWT and FFT based OFDM and modified SPIHT codec. Part II addresses image processing algorithms such as multiresolution approach for edge detection, low bit rate image compression, low complexity implementation of CQF wavelets and compression of multi-component images. Part III focuses watermaking DWT algorithms. Finally, Part IV describes shift invariant DWTs, DC lossless property, DWT based analysis and estimation of colored noise and an application of the wavelet Galerkin method. The chapters of the present book consist of both tutorial and highly advanced material. Therefore, the book is intended to be a reference text for graduate students and researchers to obtain state-of-the-art knowledge on specific applications
Unified Framework for Multicarrier and Multiple Access based on Generalized Frequency Division Multiplexing
The advancements in wireless communications are the key-enablers of new applications with stringent requirements in low-latency, ultra-reliability, high data rate, high mobility, and massive connectivity. Diverse types of devices, ranging from tiny sensors to vehicles, with different capabilities need to be connected under various channel conditions. Thus, modern connectivity and network techniques at all layers are essential to overcome these challenges. In particular, the physical layer (PHY) transmission is required to achieve certain link reliability, data rate, and latency. In modern digital communications systems, the transmission is performed by means of a digital signal processing module that derives analog hardware. The performance of the analog part is influenced by the quality of the hardware and the baseband signal denoted as waveform. In most of the modern systems such as fifth generation (5G) and WiFi, orthogonal frequency division multiplexing (OFDM) is adopted as a favorite waveform due to its low-complexity advantages in terms of signal processing. However, OFDM requires strict requirements on hardware quality.
Many devices are equipped with simplified analog hardware to reduce the cost. In this case, OFDM does not work properly as a result of its high peak-to-average power ratio (PAPR) and sensitivity to synchronization errors. To tackle these problems, many waveforms design have been recently proposed in the literature. Some of these designs are modified versions of OFDM or based on conventional single subcarrier. Moreover, multicarrier frameworks, such as generalized frequency division multiplexing (GFDM), have been proposed to realize varieties of conventional waveforms. Furthermore, recent studies show the potential of using non-conventional waveforms for increasing the link reliability with affordable complexity. Based on that, flexible waveforms and transmission techniques are necessary to adapt the system for different hardware and channel constraints in order to fulfill the applications requirements while optimizing the resources.
The objective of this thesis is to provide a holistic view of waveforms and the related multiple access (MA) techniques to enable efficient study and evaluation of different approaches. First, the wireless communications system is reviewed with specific focus on the impact of hardware impairments and the wireless channel on the waveform design. Then, generalized model of waveforms and MA are presented highlighting various special cases. Finally, this work introduces low-complexity architectures for hardware implementation of flexible waveforms. Integrating such designs with software-defined radio (SDR) contributes to the development of practical real-time flexible PHY.:1 Introduction
1.1 Baseband transmission model
1.2 History of multicarrier systems
1.3 The state-of-the-art waveforms
1.4 Prior works related to GFDM
1.5 Objective and contributions
2 Fundamentals of Wireless Communications
2.1 Wireless communications system
2.2 RF transceiver
2.2.1 Digital-analogue conversion
2.2.2 QAM modulation
2.2.3 Effective channel
2.2.4 Hardware impairments
2.3 Waveform aspects
2.3.1 Single-carrier waveform
2.3.2 Multicarrier waveform
2.3.3 MIMO-Waveforms
2.3.4 Waveform performance metrics
2.4 Wireless Channel
2.4.1 Line-of-sight propagation
2.4.2 Multi path and fading process
2.4.3 General baseband statistical channel model
2.4.4 MIMO channel
2.5 Summary
3 Generic Block-based Waveforms
3.1 Block-based waveform formulation
3.1.1 Variable-rate multicarrier
3.1.2 General block-based multicarrier model
3.2 Waveform processing techniques
3.2.1 Linear and circular filtering
3.2.2 Windowing
3.3 Structured representation
3.3.1 Modulator
3.3.2 Demodulator
3.3.3 MIMO Waveform processing
3.4 Detection
3.4.1 Maximum-likelihood detection
3.4.2 Linear detection
3.4.3 Iterative Detection
3.4.4 Numerical example and insights
3.5 Summary
4 Generic Multiple Access Schemes 57
4.1 Basic multiple access and multiplexing schemes
4.1.1 Infrastructure network system model
4.1.2 Duplex schemes
4.1.3 Common multiplexing and multiple access schemes
4.2 General multicarrier-based multiple access
4.2.1 Design with fixed set of pulses
4.2.2 Computational model
4.2.3 Asynchronous multiple access
4.3 Summary
5 Time-Frequency Analyses of Multicarrier
5.1 General time-frequency representation
5.1.1 Block representation
5.1.2 Relation to Zak transform
5.2 Time-frequency spreading
5.3 Time-frequency block in LTV channel
5.3.1 Subcarrier and subsymbol numerology
5.3.2 Processing based on the time-domain signal
5.3.3 Processing based on the frequency-domain signal
5.3.4 Unified signal model
5.4 summary
6 Generalized waveforms based on time-frequency shifts
6.1 General time-frequency shift
6.1.1 Time-frequency shift design
6.1.2 Relation between the shifted pulses
6.2 Time-frequency shift in Gabor frame
6.2.1 Conventional GFDM
6.3 GFDM modulation
6.3.1 Filter bank representation
6.3.2 Block representation
6.3.3 GFDM matrix structure
6.3.4 GFDM demodulator
6.3.5 Alternative interpretation of GFDM
6.3.6 Orthogonal modulation and GFDM spreading
6.4 Summary
7 Modulation Framework: Architectures and Applications
7.1 Modem architectures
7.1.1 General modulation matrix structure
7.1.2 Run-time flexibility
7.1.3 Generic GFDM-based architecture
7.1.4 Flexible parallel multiplications architecture
7.1.5 MIMO waveform architecture
7.2 Extended GFDM framework
7.2.1 Architectures complexity and flexibility analysis
7.2.2 Number of multiplications
7.2.3 Hardware analysis
7.3 Applications of the extended GFDM framework
7.3.1 Generalized FDMA
7.3.2 Enchantment of OFDM system
7.4 Summary
7 Conclusions and Future work
Discrete Time Systems
Discrete-Time Systems comprehend an important and broad research field. The consolidation of digital-based computational means in the present, pushes a technological tool into the field with a tremendous impact in areas like Control, Signal Processing, Communications, System Modelling and related Applications. This book attempts to give a scope in the wide area of Discrete-Time Systems. Their contents are grouped conveniently in sections according to significant areas, namely Filtering, Fixed and Adaptive Control Systems, Stability Problems and Miscellaneous Applications. We think that the contribution of the book enlarges the field of the Discrete-Time Systems with signification in the present state-of-the-art. Despite the vertiginous advance in the field, we also believe that the topics described here allow us also to look through some main tendencies in the next years in the research area
Cost-Effective Network Planning and Operation for Rural Communities.
PhD Theses.Broadband Internet access is central to the regeneration of remote communities and reducing the digital divide between rural and urban regions. This thesis focuses on rural communities with limited financial resources, environmental issues including long reach from conurbations, and mountainous or otherwise adverse terrain, typically with limited access to a wired power supply. As such, regular access technologies based on cable or fibre optics are not financially viable. To overcome this challenge, we consider the deployment of a Free-Space Optical (FSO) based relay network as the primary technology, using diversity to provide resilience to atmospheric effects. The aim of this research is to design and evaluate a rural network planning and traffic engineering framework employing FSO communication using light emitting diodes/lasers to construct backhaul rural network infrastructures.
FSO systems are relatively cheap and easy to implement [1]. Various proof-of-concept technologies already exist [2] [3] [4]. However, the focus of this work is on the design of a flexible network-planning tool together with a robust management framework that is designed to operate over such an infrastructure to ensure it functions efficiently despite changes in load or communication channel outages. Although the work concentrates on an FSO based infrastructure, this could be extended to support heterogeneous networks employing a combination of technologies.
More precisely, this research first describes a novel network planning tool with an intelligent resource management system based on a Multi-Objective Evolutionary Algorithm (MOEA) that determines the suitable location of FSO relay nodes, taking into account end-to-end link speed which is bitrate of user data and the degree of path diversity coupling with battery power. This MOEA approach can account for Line-of-Sight occlusions and allows various compromises to be selected from a Pareto front to suit individual needs. We provide suitable results to show the satisfactory operation of the tool and outline avenues for future development. Following on from this, we design and evaluate an intelligent traffic-engineering framework to make the best use of the deployed infrastructure that can adapt to environmental changes. This aims to ensure a good service is maintained at all times by suitable reconfiguration
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