203 research outputs found
A Numerical Assessment of an Effective Envelope-Tracking Semiconductor Optical Amplifier Design for Coherent-Optical OFDM Transmission
International audienceThe inherent nonlinear effects associated to Semiconductor Optical Amplifiers (SOAs) may translate into a transmission performance loss for non-constant envelope modulation formats. However, a variety of linearization schemes may be adopted for coping with these impairments and offering an effective system design. In this paper, an envelope tracking (ET) technique is investigated for linearizing an SOA-based Coherent Optical OFDM transmitter. An optimized design of the ET subsystem is performed under various scenarios, with the eventual joint use of Peak-to-Average Power Ratio (PAPR) reduction either via hard-clipping or nonlinear companding. A thorough carrier density analysis is performed in the amplifier, for various target gain values, so as to assess the effectiveness of the proposed scheme. Morever, we investigate the robustness of the proposed approach against some parameters variation both inside the ET path (DAC characteristics and bandwidth limited envelope generation). Extensive simulations performed with a precise SOA model show that up to 8 dB (resp. 7 dB) BER improvement can be achieved via the proposed scheme in the case of 4-QAM/OFDM (resp. 16-QAM/OFDM), compared to the conventional system with no linearization, and that even an envelope quantized with 2 bits still enables a significant performance increase
Low-Dimensional Reconciliation for Continuous-Variable Quantum Key Distribution
We propose an efficient logical layer-based reconciliation method for
continuous-variable quantum key distribution (CVQKD) to extract binary
information from correlated Gaussian variables. We demonstrate that by
operating on the raw-data level, the noise of the quantum channel can be
corrected in the low-dimensional (scalar) space and the reconciliation can be
extended to arbitrary dimensions. The CVQKD systems allow an unconditionally
secret communication over standard telecommunication networks. To exploit the
real potential of CVQKD a robust reconciliation technique is needed. It is
currently unavailable, which makes it impossible to reach the real performance
of the CVQKD protocols. The reconciliation is a post-processing step separated
from the transmission of quantum states, which is aimed to derive the secret
key from the raw data. The reconciliation process of correlated Gaussian
variables is a complex problem that requires either tomography in the physical
layer that is intractable in a practical scenario, or high-cost calculations in
the multidimensional spherical space with strict dimensional limitations. To
avoid these issues we define the low-dimensional reconciliation. We prove that
the error probability of one-dimensional reconciliation is zero in any
practical CVQKD scenario, and provides unconditional security. The results
allow to significantly improve the currently available key rates and
transmission distances of CVQKD.Comment: 43 pages, Journal-ref: Appl. Sci. (accepted
A Multicarrier Technique for Monte Carlo Simulation of Electrothermal Transport in Nanoelectronics
The field of microelectronics plays an important role in many areas of engineering and science, being ubiquitous in aerospace, industrial manufacturing, biotechnology, and many other fields. Today, many micro- and nanoscale electronic devices are integrated into one package. e capacity to simulate new devices accurately is critical to the engineering design process, as device engineers use simulations to predict performance characteristics and identify potential issues before fabrication. A problem of particular interest is the simulation of devices which exhibit exotic behaviors due to non-equilibrium thermodynamics and thermal effects such as self-heating. Frequently, it is desirable to predict the level of heat generation, the maximum temperature and its location, and the impact of these thermal effects on the current-voltage (IV) characteristic of a device. is problem is furthermore complicated by nanoscale device dimensions. As the ratio of surface area to volume increases, boundary effects tend to dominate the transfer of energy through a device. Effects such as quantum confinement begin to play a role for nanoscale devices as geometric feature sizes approach the wavelength of the particles involved. Classical approaches to charge transport and heat transfer simulation such as the drift-diffusion approach and Fourier’s law, respectively, do not provide accurate results at these length scales. Instead, the transport processes are governed by the semi-classical Boltzmann transport equation (BTE) with quantum corrections derived from the Schrodinger equation ̈ (SE). In this work, a technique is presented for coupling a 3D phonon Monte Carlo (MC) simulation to an electron multi-subband Monte Carlo (MSBMC) simulation. Both carrier species are first examined separately. An electron MC simulation of bulk silicon, a silicon n-i-n diode, and an intrinsic-channel fin-field effect transistor (FinFET) structure are also presented. A 3D phonon MC algorithm is demonstrated in bulk silicon, a silicon thin film, and a silicon nanoconstriction. These tests verify the correctness of the MC framework. Finally, a novel carrier scattering system which directly accounts for the interaction be- tween the two particle populations inside a nanoscale device is shown. e tool developed supports quantum size effects and is shown to be capable of modeling the exchange of energy between thermal and electronic particle systems in a silicon FinFET
Wavelet Theory
The wavelet is a powerful mathematical tool that plays an important role in science and technology. This book looks at some of the most creative and popular applications of wavelets including biomedical signal processing, image processing, communication signal processing, Internet of Things (IoT), acoustical signal processing, financial market data analysis, energy and power management, and COVID-19 pandemic measurements and calculations. The editor’s personal interest is the application of wavelet transform to identify time domain changes on signals and corresponding frequency components and in improving power amplifier behavior
Spectrally efficient FDM communication signals and transceivers: design, mathematical modelling and system optimization
This thesis addresses theoretical, mathematical modelling and design issues of Spectrally Efficient
FDM (SEFDM) systems. SEFDM systems propose bandwidth savings when compared to
Orthogonal FDM (OFDM) systems by multiplexing multiple non-orthogonal overlapping carriers.
Nevertheless, the deliberate collapse of orthogonality poses significant challenges on the
SEFDM system in terms of performance and complexity, both issues are addressed in this work.
This thesis first investigates the mathematical properties of the SEFDM system and reveals the
links between the system conditioning and its main parameters through closed form formulas
derived for the Intercarrier Interference (ICI) and the system generating matrices. A rigorous
and efficient mathematical framework, to represent non-orthogonal signals using Inverse Discrete
Fourier Transform (IDFT) blocks, is proposed. This is subsequently used to design simple
SEFDM transmitters and to realize a new Matched Filter (MF) based demodulator using the
Discrete Fourier Transforms (DFT), thereby substantially simplifying the transmitter and demodulator
design and localizing complexity at detection stage with no premium at performance.
Operation is confirmed through the derivation and numerical verification of optimal detectors
in the form of Maximum Likelihood (ML) and Sphere Decoder (SD). Moreover, two new linear
detectors that address the ill conditioning of the system are proposed: the first based on
the Truncated Singular Value Decomposition (TSVD) and the second accounts for selected ICI
terms and termed Selective Equalization (SelE). Numerical investigations show that both detectors
substantially outperform existing linear detection techniques. Furthermore, the use of the
Fixed Complexity Sphere Decoder (FSD) is proposed to further improve performance and avoid
the variable complexity of the SD. Ultimately, a newly designed combined FSD-TSVD detector
is proposed and shown to provide near optimal error performance for bandwidth savings of 20%
with reduced and fixed complexity.
The thesis also addresses some practical considerations of the SEFDM systems. In particular,
mathematical and numerical investigations have shown that the SEFDM signal is prone to high
Peak to Average Power Ratio (PAPR) that can lead to significant performance degradations.
Investigations of PAPR control lead to the proposal of a new technique, termed SLiding Window
(SLW), utilizing the SEFDM signal structure which shows superior efficacy in PAPR control
over conventional techniques with lower complexity. The thesis also addresses the performance
of the SEFDM system in multipath fading channels confirming favourable performance and
practicability of implementation. In particular, a new Partial Channel Estimator (PCE) that
provides better estimation accuracy is proposed. Furthermore, several low complexity linear
and iterative joint channel equalizers and symbol detectors are investigated in fading channels
conditions with the FSD-TSVD joint equalization and detection with PCE obtained channel
estimate facilitating near optimum error performance, close to that of OFDM for bandwidth
savings of 25%. Finally, investigations of the precoding of the SEFDM signal demonstrate a
potential for complexity reduction and performance improvement.
Overall, this thesis provides the theoretical basis from which practical designs are derived to
pave the way to the first practical realization of SEFDM systems
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