511 research outputs found
Next-generation optical access networks based on Orthogonal Frequency Division Multiplexing
Orthogonal Frequency Division Multiplexing (OFDM) is a robust modulation and multiplexing format which is at the base of many present communication standards.
The interest of the OFDM application in optical fiber deployments is quite recent. As the next generation of Passive Optical Networks (NG-PONs) is envisioned, targeting greater capacity and user counts, the limitations of TDMA (Time Division Multiplexing Access) approaches to meet the expected increase in requirements becomes evident and therefore new technologies are being explored. Optical OFDMA is an emerging technology which can be a promising candidate.
The main goal of this Master Thesis is to study the problem of users multiplexing in access networks, using OFDM as a technology to transmit the user information data. This work has focused in the uplink study of the network, because it is the most challenging part of the network to design.
The studies have been conducted both in a theoretical way and also by simulating the targeted environments by means of a fiber optics transmission simulation tool. Virtual Photonics Integrated (VPI) is the software selected for the simulations. This tool is specially designed to simulate optical transmission system environments.
The analysis of the Optical Beat Interference, which is a critical impairment in optical carrier multiplexing schemes, is the most important part of the user
multiplexing study
Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications
The rapid proliferation of the Internet has been driving communication networks closer and closer to their limits, while available bandwidth is disappearing due to an ever-increasing network load. Over the past decade, optical fiber communication technology has increased per fiber data rate from 10 Tb/s to exceeding 10 Pb/s. The major explosion came after the maturity of coherent detection and advanced digital signal processing (DSP). DSP has played a critical role in accommodating channel impairments mitigation, enabling advanced modulation formats for spectral efficiency transmission and realizing flexible bandwidth. This book aims to explore novel, advanced DSP techniques to enable multi-Tb/s/channel optical transmission to address pressing bandwidth and power-efficiency demands. It provides state-of-the-art advances and future perspectives of DSP as well
Modelação comportamental da camada física de NB-IoT em downlink
Mestrado em Engenharia Eletrónica e TelecomunicaçõesThe Internet of Things (IoT) paradigm de nes a fully connected network of
devices enabling new forms of interaction between users and devices. The
constant growth of these networks, as well as an increasing demand for
more reliable, low bit rate and massive communication data
ows lead to
the emergence of new technologies and set of standards, such as, the Low
Power Wide Area Networks (LPWAN).
In June 2016, 3GPP, the consortium responsible for LTE development and
standardization, released a new licensed band based standard, named Narrow
Band (NB) IoT. NB-IoT was designed based on the same principles
of other LPWAN standards, providing better coverage and additionally an
easier integration on existing cellular systems.
In this dissertation a study on the NB-IoT Physical Layer is presented along
with an open source behavioral implementation in MATLAB of the downlink
transmission and reception chains.
The system generates and recovers one radio frame successfully performings
procedures such as MIB and SIB1-N extracting along with scheduling
and recovering data scheduled through control channels by higher layer
paramenters. The project models and executes the downlink transmission
(eNodeB) and reception (terminal) PHYs either in a pure simulation environment
using di erent channel models, as well as integrated with an USRP
software de ned radio device for co-simulation.
The simulation and co-simulation results are presented evaluating the transmission's
quality and performance of the implemented Zero Forcing equalizer.O paradigma da Internet of Things (IoT) define uma rede interligada de
dispositivos que permite o surgimento de novas formas de interacção entre
utilizadores e dispositivos. O constante crescimento destas redes assim
como a crescente demanda por uma fiabilidade maior, bit rates mais baixos
e circulação massiva de informação insurgiu o aparecimento de novas tecnologias
tais como as Low Power Wide Area Networks (LPWAN).
Em Junho de 2016 a 3GPP, o órgão responsável pelo LTE, lançou um novo
standard para bandas licenciadas o Narrowband (NB) -IoT. O NB-IoT foi
desenhado com base nos mesmos princípios que as outras LPWAN com o
acréscimo de uma maior cobertura assim como uma mais fácil integração
em sistemas celulares existentes.
Nesta dissertação aborda-se um estudo da sua camada física (PHY Layer)
juntamente com uma implementação comportamental open source em Matlab
das cadeias de transmissão e recepção em downlink. O projecto modela
e executa transmissões em downlink (eNodeB) e sua recepcção (terminal)
tanto em ambiente simulado como integrado com um dispositivo de software
defined radio, USRP, para validação laboratorial.
Os resultados obtidos tanto de simulação como co-simulação são apresentados
avaliando a qualidade de transmissão assim como o comportamento
do equalizador Zero Forcing implementado
Automatic modulation classification of communication signals
The automatic modulation recognition (AMR) plays an important role in various civilian and military applications. Most of the existing AMR algorithms assume that the input signal is only of analog modulation or is only of digital modulation. In blind environments, however, it is impossible to know in advance if the received communication signal is analogue modulated or digitally modulated. Furthermore, it is noted that the applications of the currently existing AMR algorithms designed for handling both analog and digital communication signals are rather restricted in practice. Motivated by this, an AMR algorithm that is able to discriminate between analog communication signals and digital communication signals is developed in this dissertation. The proposed algorithm is able to recognize the concrete modulation type if the input is an analog communication signal and to estimate the number of modulation levels and the frequency deviation if the input is an exponentially modulated digital communication signal. For linearly modulated digital communication signals, the proposed classifier will classify them into one of several nonoverlapping sets of modulation types. In addition, in M-ary FSK (MFSK) signal classification, two classifiers have also been developed. These two classifiers are also capable of providing good estimate of the frequency deviation of a received MFSK signal.
For further classification of linearly modulated digital communication signals, it is often necessary to blindly equalize the received signal before performing modulation recognition. This doing generally requires knowing the carrier frequency and symbol rate of the input signal. For this purpose, a blind carrier frequency estimation algorithm and a blind symbol rate estimation algorithm have been developed. The carrier frequency estimator is based on the phases of the autocorrelation functions of the received signal. Unlike the cyclic correlation based estimators, it does not require the transmitted symbols being non-circularly distributed. The symbol rate estimator is based on digital communication signals\u27 cyclostationarity related to the symbol rate. In order to adapt to the unknown symbol rate as well as the unknown excess bandwidth, the received signal is first filtered by using a bank of filters. Symbol rate candidates and their associated confident measurements are extracted from the fourth order cyclic moments of the filtered outputs, and the final estimate of symbol rate is made based on weighted majority voting.
A thorough evaluation of some well-known feature based AMR algorithms is also presented in this dissertation
Range-resolved optical interferometric signal processing
The ability to identify the range of an interferometric signal is very useful in interferometry,
allowing the suppression of parasitic signal components or permitting
several signal sources to be multiplexed. Two novel range-resolved optical interferometric
signal processing techniques, employing very different working principles,
are theoretically described and experimentally demonstrated in this thesis. The first
technique is based on code-division multiplexing (CDM), which is combined with
single-sideband signal processing, resulting in a technique that, unlike prior work,
only uses a single, regular electro-optic phase modulator to perform both range-based
signal identification and interferometric phase evaluation. The second approach
uses sinusoidal optical frequency modulation (SFM), induced by injection current
modulation of a diode laser, to introduce range-dependent carriers to determine phase
signals in interferometers of non-zero optical path difference. Here, a key innovation
is the application of a smooth window function, which, when used together with
a time-variant demodulation approach, allows optical path lengths of constituent
interferometers to be continuously and independently variable, subject to a minimum
separation, greatly increasing the practicality of the approach.
Both techniques are applied to fibre segment interferometry, where fibre segments
that act as long-gauge length interferometric sensors are formed between pairs of
partial in-fibre reflectors. Using a regular single-mode laser diode, six fibre segments
of length 12.5 cm are multiplexed with a quadrature bandwidth of 43 kHz and a phase
noise floor of 0.19 mrad
·
Hz
-0.5
using the SFM technique. In contrast, the 16.5 m
spatial resolution achieved with the CDM technique points towards its applicability
in medium-to-long range sensing. The SFM technique also allows high linearity,
with cyclic errors as low as 1 mrad demonstrated, and with modelling indicating
further room for improvement. Additionally, in an industrial measurement, the SFM
technique is applied to single-beam, multi-surface vibrometry, allowing simultaneous
differential measurements between two vibrating surfaces
Ultra-Wideband Secure Communications and Direct RF Sampling Transceivers
Larger wireless device bandwidth results in new capabilities in terms of higher data rates and security. The 5G evolution is focus on exploiting larger bandwidths for higher though-puts. Interference and co-existence issues can also be addressed by the larger bandwidth in the 5G and 6G evolution. This dissertation introduces of a novel Ultra-wideband (UWB) Code Division Multiple Access (CDMA) technique to exploit the largest bandwidth available in the upcoming wireless connectivity scenarios. The dissertation addresses interference immunity, secure communication at the physical layer and longer distance communication due to increased receiver sensitivity. The dissertation presents the design, workflow, simulations, hardware prototypes and experimental measurements to demonstrate the benefits of wideband Code-Division-Multiple-Access. Specifically, a description of each of the hardware and software stages is presented along with simulations of different scenarios using a test-bench and open-field measurements. The measurements provided experimental validation carried out to demonstrate the interference mitigation capabilities. In addition, Direct RF sampling techniques are employed to handle the larger bandwidth and avoid analog components. Additionally, a transmit and receive chain is designed and implemented at 28 GHz to provide a proof-of-concept for future 5G applications. The proposed wideband transceiver is also used to demonstrate higher accuracy direction finding, as much as 10 times improvement
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
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