1,212 research outputs found
Signal Processing using Chromatic Derivatives and Chromatic Approximation
Modern Digital Signal Processing (DSP) is based upon the fundamental Whittaker–Kotel’nikov–Nyquist–Shannon Sampling Theorem,
which, as we will argue, is complementary to the Taylor Theorem. Whilst the sampling theorem provides global signal
representation, its truncations fail to provide an accurate, localised view of the original signal. The Taylor series, on the other
hand, provides satisfactory local representation of the signal, but is deficient in providing a global signal representation because
its truncations rapidly diverge for values of the input that are far away from the point of expansion. Taylor series is also very
sensitive to noise when high order derivatives are numerically evaluated from samples of the input signal.
Chromatic derivatives operators were developed to overcome the inaccuracy and instability issues in numerically evaluating higher
order derivatives. The corresponding chromatic expansions combine the benefits of both the sampling theorem and Taylor expansion;
its truncations, named chromatic approximations, are globally uniformly converging approximations based on a numerically
robust set of differential operators. Chromatic Approximations are capable of not only recovering signals in the global sense, but
also provide excellent accurate local approximations. Experimental results, detailed in this body of work, involving the use of
chromatic derivatives and chromatic approximations to recover band limited signals under various unfavourable conditions, provide
an insight into the potential use of these operators as an alternative or enhancement to the current, state-of-the-art digital signal
processing methods. Specifically, we explore and present successful experimentation results for the following:
• Two point chromatic approximation and signal reconstruction from an analog filterbank (Chapter 2)
• Signal resampling algorithm using a chromatic approximation that can operate with rational and non rational resampling
rates (Chapter 2)
• Signal recovery from non uniform samples and recovery of distorted signals (missing samples) from partial content using a
novel, iterative algorithm (Chapter 3)
• A novel, adaptive denoising algorithm that significantly enhances the performance of common frequency estimation methods
such as ESPRIT and MUSIC (Chapter 4
Transmissores-recetores de baixa complexidade para redes óticas
Traditional coherent (COH) transceivers allow encoding of information in
both quadratures and the two orthogonal polarizations of the electric field.
Nevertheless, such transceivers used today are based on the intradyne
scheme, which requires two 90o optical hybrids and four pairs of balanced
photodetectors for dual-polarization transmission systems, making its overall
cost unattractive for short-reach applications. Therefore, SSB methods
with DD reception, commonly referred to as self-coherent (SCOH)
transceivers, can be employed as a cost-effective alternative to the traditional
COH transceivers. Nevertheless, the performance of SSB systems
is severely degraded. This work provides a novel SCOH transceiver architecture
with improved performance for short-reach applications. In particular,
the development of phase reconstruction digital signal processing (DSP)
techniques, the development of other DSP subsystems that relax the hardware
requirement, and their performance optimization are the main highlights
of this research.
The fundamental principle of the proposed transceiver is based on the reception
of the signal that satisfies the minimum phase condition upon DD.
To reconstruct the missing phase information imposed by DD, a novel DCValue
method exploring the SSB and the DC-Value properties of the minimum
phase signal is developed in this Ph.D. study. The DC-Value method
facilitates the phase reconstruction process at the Nyquist sampling rate
and requires a low intensity pilot signal. Also, the experimental validation
of the DC-Value method was successfully carried out for short-reach optical
networks. Additionally, an extensive study was performed on the DC-Value
method to optimize the system performance. In the optimization process,
it was found that the estimation of the CCF is an important parameter to
exploit all advantages of the DC-Value method. A novel CCF estimation
technique was proposed. Further, the performance of the DC-Value method
is optimized employing the rate-adaptive probabilistic constellation shaping.Os sistemas de transcetores coerentes tradicionais permitem a codificação
de informação em ambas quadraturas e em duas polarizações ortogonais
do campo elétrico. Contudo, estes transcetores utilizados atualmente são
baseados num esquema intradino, que requer dois híbridos óticos de 90o
e quatro pares de foto detetores para sistemas de transmissão com polarização dupla, fazendo com que o custo destes sistemas seja pouco atrativo
para aplicações de curto alcance. Por isso, métodos de banda lateral única com deteção direta, também referidos como transcetores coerentes simplificados,
podem ser implementados como uma alternativa de baixo custo
aos sistemas coerentes tradicionais. Contudo, o desempenho de sistemas
de banda lateral única tradicionais é gravemente degradado pelo batimento
sinal-sinal. Nesta tese foi desenvolvida uma nova arquitetura de transcetor
coerente simplificada com um melhor desempenho para aplicações de curto
alcance. Em particular, o desenvolvimento de técnicas de processamento
digital de sinal para a reconstrução de fase, bem como de outros subsistemas
de processamento digital de sinal que minimizem os requerimentos
de hardware e a sua otimização de desempenho são o foco principal desta
tese.
O princípio fundamental do transcetor proposto é baseado na receção de
um sinal que satisfaz a condição mínima de fase na deteção direta. Para
reconstruir a informação de fase em falta causada pela deteção direta,
um novo método de valor DC que explora sinais de banda lateral única
e as propriedades DC da condição de fase mínima é desenvolvido nesta
tese. O método de valor DC facilita a reconstrução da fase à frequência
de amostragem de Nyquist e requer um sinal piloto de baixa intensidade.
Além disso, a validação experimental do método de valor DC foi executada
com sucesso em ligações óticas de curto alcance. Adicionalmente,
foi realizado um estudo intensivo do método de valor DC para otimizar o
desempenho do sistema. Neste processo de otimização, verificou-se que o
fator de contribuição da portadora é um parâmetro importante para explorar
todas as vantagens do método de valor DC. Neste contexto, é proposto
um novo método para a sua estimativa. Por último, o desempenho do
método de valor DC é otimizado recorrendo a mapeamento probabilístico
de constelação com taxa adaptativa.Programa Doutoral em Engenharia Eletrotécnic
Digital Signal Processing Techniques For Coherent Optical Communication
Coherent detection with subsequent digital signal processing (DSP) is developed, analyzed theoretically and numerically and experimentally demonstrated in various fiber-optic transmission scenarios. The use of DSP in conjunction with coherent detection unleashes the benefits of coherent detection which rely on the preservation of full information of the incoming field. These benefits include high receiver sensitivity, the ability to achieve high spectral-efficiency and the use of advanced modulation formats. With the immense advancements in DSP speeds, many of the problems hindering the use of coherent detection in optical transmission systems have been eliminated. Most notably, DSP alleviates the need for hardware phase-locking and polarization tracking, which can now be achieved in the digital domain. The complexity previously associated with coherent detection is hence significantly diminished and coherent detection is once again considered a feasible detection alternative. In this thesis, several aspects of coherent detection (with or without subsequent DSP) are addressed. Coherent detection is presented as a means to extend the dispersion limit of a duobinary signal using an analog decision-directed phase-lock loop. Analytical bit-error ratio estimation for quadrature phase-shift keying signals is derived. To validate the promise for high spectral efficiency, the orthogonal-wavelength-division multiplexing scheme is suggested. In this scheme the WDM channels are spaced at the symbol rate, thus achieving the spectral efficiency limit. Theory, simulation and experimental results demonstrate the feasibility of this approach. Infinite impulse response filtering is shown to be an efficient alternative to finite impulse response filtering for chromatic dispersion compensation. Theory, design considerations, simulation and experimental results relating to this topic are presented. Interaction between fiber dispersion and nonlinearity remains the last major challenge deterministic effects pose for long-haul optical data transmission. Experimental results which demonstrate the possibility to digitally mitigate both dispersion and nonlinearity are presented. Impairment compensation is achieved using backward propagation by implementing the split-step method. Efficient realizations of the dispersion compensation operator used in this implementation are considered. Infinite-impulse response and wavelet-based filtering are both investigated as a means to reduce the required computational load associated with signal backward-propagation. Possible future research directions conclude this dissertation
Polarization Drift Channel Model for Coherent Fibre-Optic Systems
A theoretical framework is introduced to model the dynamical changes of the
state of polarization during transmission in coherent fibre-optic systems. The
model generalizes the one-dimensional phase noise random walk to higher
dimensions, accounting for random polarization drifts, emulating a random walk
on the Poincar\'e sphere, which has been successfully verified using
experimental data. The model is described in the Jones, Stokes and real
four-dimensional formalisms, and the mapping between them is derived. Such a
model will be increasingly important in simulating and optimizing future
systems, where polarization-multiplexed transmission and sophisticated digital
signal processing will be natural parts. The proposed polarization drift model
is the first of its kind as prior work either models polarization drift as a
deterministic process or focuses on polarization-mode dispersion in systems
where the state of polarization does not affect the receiver performance. We
expect the model to be useful in a wide-range of photonics applications where
stochastic polarization fluctuation is an issue.Comment: 15 pages, 4 figure
Design of communication systems based on broadband sources for fiber and free space optical links
[ES] Las comunicaciones ópticas inalámbricas (OWC) constituyen una tecnología muy prometedora para el desarrollo de futuras comunicaciones inalámbricas. De hecho, ha despertado un interés creciente entre los investigadores y varias empresas de todo el mundo trabajan actualmente en el desarrollo de redes inalámbricas de muy alta velocidad. Las comunidades científica e industrial consideran la OWC como una tecnología complementaria en sus diversas formas: comunicaciones ópticas en el espacio libre (FSO), comunicaciones de luz visible (VLC) o fidelidad de la luz (Li-Fi). El espectro óptico ha sido considerado durante muchos años como una gran oportunidad para las comunicaciones inalámbricas, especialmente debido a la saturación del espectro de radiofrecuencia (RF).
Esta disertación trata del uso de fuentes de banda ancha en sistemas de transmisión de luz visible (VLC), así como en sistemas de transmisión en el espectro infrarrojo por fibra óptica. En el trabajo de investigación realizado se pueden distinguir tres partes:
En la primera parte, se considera el estudio y la simulación de componentes de Diodos Emisores de Luz (LED) con el software WIEN2k centrándose en las propiedades ópticas y eléctricas de los elementos II-VI.
La segunda parte trata del diseño, la implementación y las pruebas de diferentes prototipos de comunicación VLC para la transmisión analógica y digital en modo simplex y semidúplex. Hemos demostrado un sistema OWC empleando una fuente de banda ancha (LED) para la transmisión no sólo de datos, sino también para la transmisión inalámbrica de energía. Además, se aborda el problema de la sincronización y la detección del nivel "1" o "0" de un bit en los sistemas de comunicación inalámbrica óptica implementados que surge como consecuencia de la atenuación de la luz a lo largo de la distancia y al problema de la pérdida de línea de visión (NLOS) entre el emisor y el receptor. Para hacer frente a este problema, se ha proporcionado un protocolo de comunicación que garantiza la transmisión fiable de datos digitales con un algoritmo de detección de nivel de bits adaptativo y se ha demostrado su eficacia mediante la transmisión de textos e imágenes.
Además, esta tesis aporta una solución para la implementación de transmisores multiplexados en redes con división de longitud de onda (WDM) para formatos de modulación con multiplexación por división de frecuencia ortogonal (OFDM) basados en el uso de fuentes de banda ancha en el espectro infrarrojo para redes de fibra bidireccionales centralizadas. A pesar de las limitaciones impuestas por la dispersión cromática en el uso de este tipo de fuentes ópticas, la inclusión de ciertas estructuras antes de la detección permite la transmisión de señales OFDM en enlaces ópticos. En este trabajo se ha demostrado experimentalmente la reutilización de portadoras, la asignación dinámica de ancho de banda y la transmisión de señales OFDM multibanda mediante el uso de fuentes ópticas de banda ancha en redes WDM.
Los principales resultados obtenidos en cada parte de esta tesis doctoral muestran los procedimientos de estudio, la eficacia de las soluciones propuestas y las limitaciones encontradas.[CA] Les comunicacions òptiques sense fils (OWC) constitueixen una tecnologia molt prometedora per al desenvolupament de futures comunicacions sense fils. De fet, ha despertat un interés creixent entre els investigadors i diverses empreses de tot el món treballen actualment en el desenvolupament de xarxes sense fils de molt alta velocitat. Les comunitats científica i industrial consideren la OWC com una tecnologia complementària en les seues diverses formes: comunicacions òptiques en l'espai lliure (FSO), comunicacions de llum visible (VLC) o fidelitat de la llum (Li-Fi).
L'espectre òptic ha sigut considerat durant molts anys com una gran oportunitat per a les comunicacions sense fils, especialment a causa de la saturació de l'espectre de radiofreqüència (RF).
Aquesta dissertació tracta de l'ús de fonts de banda ampla en sistemes de transmissió de llum visible (VLC), així com en sistemes de transmissió en l'espectre infraroig per fibra òptica. En el treball de recerca realitzat es poden distingir tres parts:
¿ En la primera part, es considera l'estudi i la simulació de components de Díodes Emissors de Llum (LED) amb el software WIEN2k centrant-se en les propietats òptiques i elèctriques dels elements II-VI.
¿ La segona part tracta del disseny, la implementació i les proves de diferents prototips de comunicació VLC per a la transmissió analògica i digital de manera simplex i semidúplex. Hem demostrat un sistema OWC emprant una font de banda ampla (LED) per a la transmissió no sols de dades, sinó també per a la transmissió sense fil d'energia. A més, s'aborda el problema de la sincronització i la detecció del nivell "1" o "0" d'un bit en els sistemes de comunicació sense fil òptica implementats, que sorgeix a conseqüència de l'atenuació de la llum al llarg de la distància i al problema de la pèrdua de línia de visió (NLOS) entre l'emissor i el receptor. Per a fer front a aquest problema, s'ha proporcionat un protocol de comunicació que garanteix la transmissió fiable de dades digitals amb un algorisme de detecció de nivell de bits adaptatiu i s'ha demostrat la seua eficàcia mitjançant la transmissió de textos i imatges.
¿ A més, aquesta tesi aporta una solució per a la implementació de transmissors multiplexats en xarxes amb divisió de longitud d'ona (WDM) per a formats de modulació amb multiplexació per divisió de freqüència ortogonal (OFDM) basats en l'ús de fonts de banda ampla en l'espectre infraroig per a xarxes de fibra bidireccionals centralitzades. Malgrat les limitacions imposades per la dispersió cromàtica en l'ús d'aquest tipus de fonts òptiques, la inclusió d'unes certes estructures abans de la detecció permet la transmissió de senyals OFDM en enllaços òptics. En aquest treball s'ha demostrat experimentalment la reutilització de portadores, l'assignació dinàmica d'amplada de banda i la transmissió de senyals OFDM multibanda mitjançant l'ús de fonts òptiques de banda ampla en xarxes WDM.
Els principals resultats obtinguts en cada part d'aquesta tesi doctoral mostren els procediments d'estudi, l'eficàcia de les solucions proposades i les limitacions trobades.[EN] Optical wireless communication (OWC) is a very promising technology for future wireless communications developments. It has attracted increasing interest from researchers and several companies around the world are currently working on the development of very high-speed wireless networks. The scientific and industrial communities believe that OWC will be a complementary technology in its various forms: Free Space Optical communications (FSO), Visible Light Communications (VLC), Light Fidelity (Li-Fi).
In fact, the optical spectrum has been considered for many years as a great opportunity for wireless communications especially due to the saturation of the radio frequency (RF) spectrum.
This dissertation deals with the use of broadband sources in visible light transmission systems (VLC) as well as fiber optic systems. To carry out the research, three parts can be distinguished:
In the first part, we consider the study and simulation of Light Emitting Diode (LED) components with the WIEN2k software by focusing on the optical and electrical properties of elements II-VI.
The second part deals with the design, implementation and testing of different VLC communication prototypes for analog and digital transmission in simplex and half-duplex mode. We have demonstrated that an OWC system using a broadband source (i.e. an LED) can be used not only for data transmission, but also for wireless power transmission. Moreover, the synchronization problem and the detection of level "1" or "0" of a bit often arise in the optical wireless communication systems. This is a result of the attenuation nature of the light over the distance and the problem of Non Line-Of-Sight (NLOS) between the emitter and the receiver. To deal with this problem, a communication protocol ensuring reliable digital data transmission with an adaptive bit level detection algorithm has been provided and its effectiveness has been demonstrated by the transmission of texts and images.
In addition, this thesis provides a solution for the implementation of wavelength division multiplexed - orthogonal frequency division multiplexed (WDM-OFDM) transmitters based on the use of broadband sources in the infrared spectrum for centralized bidirectional fiber networks. Despite the chromatic dispersion that avoids the use of this type of optical sources, the inclusion of certain structures before detection allows the transmission of OFDM signals in optical links. Carrier reuse, dynamic bandwidth allocation and multiband OFDM signals transmission will be experimentally demonstrated by using optical broadband sources in WDM networks.
The main results obtained during this thesis work demonstrate the study procedures, for each part, the effectiveness of the proposed solutions as well as the constraints encountered.Sekkiou, I. (2021). Design of communication systems based on broadband sources for fiber and free space optical links [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172542TESI
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Optical fibre communication over a noisy partially coherent channel
As global IP traffic grows unceasingly, optical networks demand for technology upgrades in order to keep the feared “capacity crunch” away. The most celebrated technologies of coherent detection and wavelength-division multiplexing (WDM), widely deployed in long-haul links, are gaining ground in access networks, which is particularly challenging due to the shared-cost requirements, leading to denser channel spacings and the use of cheaper devices that tend to be noisier. In order to make the most of this technology combination, it is crucial to have a model of the channel that accurately describes all the present sources of noise. Traditionally, the most used model has been the additive white Gaussian noise (AWGN) channel, which, although only accounting for a linear contribution of complex noise and being insensitive to rotational phenomena, has shown its validity in numerous studies, as well as in commercial equipment. In this thesis, however, it is observed that the adoption of coherent detection and WDM, with lower-grade semiconductor lasers showing a moderate linewidth, yields scenarios where a phase-sensitive model becomes a must. The partially coherent AWGN (PCAWGN) channel is a popular choice that fulfils this need, but its high complexity due to non-trivial functions involved, deprives it from being suitable in high-speed digital circuits. The main goal of this thesis is to describe a reduced-complexity approximation in polar coordinates, accurate enough to find its applicability in modern systems. Furthermore, this works explores some possible end-to-end applications, like channel capacity estimation or symbol detection, assessing its performance by means of extensive simulations. Lastly, the emerging field of complex modulation of directly modulated lasers is revisited, with a special interest in how the proposed approximation can help to improve the performance of previously reported techniques, as well as proposing a new way to design spiral-shaped constellations aimed to maximise the channel capacity
Advanced Digital Signal Processing Techniques for High-Speed Optical Links
L'abstract è presente nell'allegato / the abstract is in the attachmen
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