280 research outputs found
Data acquisition techniques based on frequency-encoding applied to capacitive MEMS microphones
Mención Internacional en el título de doctorThis thesis focuses on the development of capacitive sensor readout circuits
and data converters based on frequency-encoding. This research
has been motivated by the needs of consumer electronics industry, which
constantly demands more compact readout circuit for MEMS microphones
and other sensors. Nowadays, data acquisition is mainly based
on encoding signals in voltage or current domains, which is becoming
more challenging in modern deep submicron CMOS technologies.
Frequency-encoding is an emerging signal processing technique based
on encoding signals in the frequency domain. The key advantage of
this approach is that systems can be implemented using mostly-digital
circuitry, which benefits from CMOS technology scaling. Frequencyencoding
can be used to build phase referenced integrators, which can
replace classical integrators (such as switched-capacitor based integrators)
in the implementation of efficient analog-to-digital converters and
sensor interfaces. The core of the phase referenced integrators studied in
this thesis consists of the combination of different oscillator topologies
with counters and highly-digital circuitry.
This work addresses two related problems: the development of capacitive
MEMS sensor readout circuits based on frequency-encoding, and the
design and implementation of compact oscillator-based data converters
for audio applications.
In the first problem, the target is the integration of the MEMS sensor
into an oscillator circuit, making the oscillation frequency dependent on
the sensor capacitance. This way, the sound can be digitized by measuring
the oscillation frequency, using digital circuitry. However, a MEMS
microphone is a complex structure on which several parasitic effects can
influence the operation of the oscillator. This work presents a feasibility
analysis of the integration of a MEMS microphone into different oscillator
topologies. The conclusion of this study is that the parasitics of the
MEMS limit the performance of the microphone, making it inefficient.
In contrast, replacing conventional ADCs with frequency-encoding based
ADCs has proven a very efficient solution, which motivates the next
problem.
In the second problem, the focus is on the development of high-order
oscillator-based Sigma-Delta modulators. Firstly, the equivalence between classical
integrators and phase referenced integrators has been studied, followed
by an overview of state-of-art oscillator-based converters. Then,
a procedure to replace classical integrators by phase referenced integrators
is presented, including a design example of a second-order oscillator based
Sigma-Delta modulator. Subsequently, the main circuit impairments that
limit the performance of this kind of implementations, such as phase
noise, jitter or metastability, are described.
This thesis also presents a methodology to evaluate the impact of
phase noise and distortion in oscillator-based systems. The proposed
method is based on periodic steady-state analysis, which allows the rapid
estimation of the system dynamic range without resorting to transient
simulations. In addition, a novel technique to analyze the impact of
clock jitter in Sigma-Delta modulators is described.
Two integrated circuits have been implemented in 0.13 μm CMOS
technology to demonstrate the feasibility of high-order oscillator-based Sigma-Delta modulators. Both chips have been designed to feature secondorder
noise shaping using only oscillators and digital circuitry. The first
testchip shows a malfunction in the digital circuitry due to the complexity
of the multi-bit counters. The second chip, implemented using
single-bit counters for simplicity, shows second-order noise shaping and
reaches 103 dB-A of dynamic range in the audio bandwidth, occupying
only 0.04 mm2.Esta tesis se centra en el desarrollo de conversores de datos e interfaces
para sensores capacitivos basados en codificación en frecuencia. Esta
investigación está motivada por las necesidades de la industria, que constantemente
demanda reducir el tamaño de este tipo de circuitos. Hoy en
día, la adquisición de datos está basada principalmente en la codificación
de señales en tensión o en corriente. Sin embargo, la implementación
de este tipo de soluciones en tecnologías CMOS nanométricas presenta
varias dificultades.
La codificación de frecuencia es una técnica emergente en el procesado
de señales basada en codificar señales en el dominio de la frecuencia.
La principal ventaja de esta alternativa es que los sistemas pueden implementarse
usando circuitos mayoritariamente digitales, los cuales se
benefician de los avances de la tecnología CMOS. La codificación en
frecuencia puede emplearse para construir integradores referidos a la
fase, que pueden reemplazar a los integradores clásicos (como los basados
en capacidades conmutadas) en la implementación de conversores
analógico-digital e interfaces de sensores. Los integradores referidos a la
fase estudiados en esta tesis consisten en la combinación de diferentes
topologías de osciladores con contadores y circuitos principalmente digitales.
Este trabajo aborda dos cuestiones relacionadas: el desarrollo de circuitos
de lectura para sensores MEMS capacitivos basados en codificación
temporal, y el diseño e implementación de conversores de datos
compactos para aplicaciones de audio basados en osciladores.
En el primer caso, el objetivo es la integración de un sensor MEMS
en un oscilador, haciendo que la frecuencia de oscilación depe capacidad del sensor. De esta forma, el sonido puede ser digitalizado
midiendo la frecuencia de oscilación, lo cual puede realizarse usando circuitos
en su mayor parte digitales. Sin embargo, un micrófono MEMS es
una estructura compleja en la que múltiples efectos parasíticos pueden
alterar el correcto funcionamiento del oscilador. Este trabajo presenta
un análisis de la viabilidad de integrar un micrófono MEMS en diferentes
topologías de oscilador. La conclusión de este estudio es que los parasíticos
del MEMS limitan el rendimiento del micrófono, causando que esta
solución no sea eficiente. En cambio, la implementación de conversores
analógico-digitales basados en codificación en frecuencia ha demostrado
ser una alternativa muy eficiente, lo cual motiva el estudio del siguiente
problema.
La segunda cuestión está centrada en el desarrollo de moduladores Sigma-Delta de alto orden basados en osciladores. En primer lugar se ha estudiado
la equivalencia entre los integradores clásicos y los integradores
referidos a la fase, seguido de una descripción de los conversores basados
en osciladores publicados en los últimos años. A continuación se
presenta un procedimiento para reemplazar integradores clásicos por integradores
referidos a la fase, incluyendo un ejemplo de diseño de un
modulador Sigma-Delta de segundo orden basado en osciladores. Posteriormente
se describen los principales problemas que limitan el rendimiento de este
tipo de sistemas, como el ruido de fase, el jitter o la metaestabilidad.
Esta tesis también presenta un nuevo método para evaluar el impacto
del ruido de fase y de la distorsión en sistemas basados en osciladores. El
método propuesto está basado en simulaciones PSS, las cuales permiten
la rápida estimación del rango dinámico del sistema sin necesidad de
recurrir a simulaciones temporales. Además, este trabajo describe una
nueva técnica para analizar el impacto del jitter de reloj en moduladores Sigma-Delta.
En esta tesis se han implementado dos circuitos integrados en tecnología
CMOS de 0.13 μm, con el fin de demostrar la viabilidad de los
moduladores Sigma-Delta de alto orden basados en osciladores. Ambos chips han
sido diseñados para producir conformación espectral de ruido de segundo
orden, usando únicamente osciladores y circuitos mayoritariamente digitales.
El primer chip ha mostrado un error en el funcionamiento de los
circuitos digitales debido a la complejidad de las estructuras multi-bit
utilizadas. El segundo chip, implementado usando contadores de un solo
bit con el fin de simplificar el sistema, consigue conformación espectral
de ruido de segundo orden y alcanza 103 dB-A de rango dinámico en el
ancho de banda del audio, ocupando solo 0.04 mm2.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Georges G.E. Gielen.- Secretario: José Manuel de la Rosa.- Vocal: Ana Rus
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Fully-passive switched-capacitor techniques for high performance SAR ADC design
In recent years, SAR ADC becomes more and more popular in various low-power applications such as wireless sensors and low energy radios due to its circuit simplicity, high power efficiency, and scaling compatibility. However, its speed is limited by its successive approximation procedures and its power efficiency greatly reduces with the ADC resolution going beyond 10 bit. To address these issues, this thesis proposes to embed two techniques: 1) compressive sensing (CS) and 2) noise shaping (NS) to a conventional SAR ADC. The realization of both techniques are based on fully-passive switched-capacitor techniques.
CS is a recently emerging sampling paradigm, stating that the sparsity of a signal can be exploited to reduce the ADC sampling rate below the Nyquist rate. Different from conventional CS frameworks which require dedicated analog CS encoders, this thesis proposes a fully-passive CS-SAR ADC architecture which only requires minor modification to a conventional SAR ADC. Two chips are fabricated in a 0.13 µm process to prove the concept. One chip is a single-channel CS-SAR ADC which can reduce the ADC conversion rate by 4 times, thus reducing the ADC power by 4 times. In many wireless sensing applications, multiple ADCs are commonly required to sense multi-channel signals such as multi-lead ECG sensing and parallel neural recording. Therefore, the other chip is a multi-channel CS-SAR ADC which can simultaneously convert 4-channel signals with a sampling rate of one channel’s Nyquist rate. At 0.8 V and 1 MS/s, both chips achieve an effective Walden FoM of around 5 fJ/conversion-step.
This thesis also proposes a novel NS SAR ADC architecture that is simple, robust and low power for high-resolution applications. Compared to conventional ∆Σ ADCs, it replaces the power-hungry active integrator with a passive integrator which only requires one switch and two capacitors. Compared to previous 1st-order NS SAR ADC works, it achieves the best NS performance and can be easily extended to 2nd-order. A 1st-order 10-bit NS SAR ADC is fabricated in a 0.13 µm process. Through NS, SNDR increases by 6 dB with OSR doubled, achieving a 12- bit ENOB at OSR = 8. An improved version of a 2nd-order 9-bit NS SAR ADC is designed and simulated in a 40 nm process. The SNDR increases by 10 dB with OSR doubled, achieving a 14-bit ENOB at OSR = 16. At a bandwidth of 312.5 kHz, the Schreier FoM is 181 dB and the Walden FoM is 12.5 fJ/conversion-step, proving that the proposed NS SAR ADC architecture can achieve high resolution and high power efficiency simultaneously.Electrical and Computer Engineerin
Flexible Coherent Optical Access: Architectures, Algorithms, and Demonstrations
To cope with the explosive bandwidth demand, significant progress has been
made in the ITU-T standardization sector to define a higher-speed passive
optical network (PON) with a 50Gb/s line rate. Recently, 50G PON becomes mature
gradually, which means it is time to discuss beyond 50G PON. For ensuring an
acceptable optical power budget, beyond 50G PON will potentially use coherent
technologies, which can simultaneously promote the applications of flexible
multiple access such as time/frequency-domain multiple access (TFDMA). In this
paper, we will introduce the architectures, algorithms, and demonstrations for
TFDMA-based coherent PON. The system architectures based on an ultra-simple
coherent transceiver and specific signal spectra are designed to greatly reduce
the cost of ONUs. Meanwhile, fast and low-complexity digital signal processing
(DSP) algorithms are proposed for dealing with upstream and downstream signals.
Based on the architectures and algorithms, we experimentally demonstrate the
first real-time TFDMA-based coherent PON, which can support at most 256 end
users, and peak line rates of 100Gb/s and 200Gb/s in the upstream and
downstream scenarios, respectively. In conclusion, the proposed technologies
for the coherent PON make it more possible to be applied in the future beyond
50G PON.Comment: The paper has been submitted to the Journal of Lightwave Technolog
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
ワイヤレス通信のための先進的な信号処理技術を用いた非線形補償法の研究
The inherit nonlinearity in analogue front-ends of transmitters and receivers have had primary impact on the overall performance of the wireless communication systems, as it gives arise of substantial distortion when transmitting and processing signals with such circuits. Therefore, the nonlinear compensation (linearization) techniques become essential to suppress the distortion to an acceptable extent in order to ensure sufficient low bit error rate. Furthermore, the increasing demands on higher data rate and ubiquitous interoperability between various multi-coverage protocols are two of the most important features of the contemporary communication system. The former demand pushes the communication system to use wider bandwidth and the latter one brings up severe coexistence problems. Having fully considered the problems raised above, the work in this Ph.D. thesis carries out extensive researches on the nonlinear compensations utilizing advanced digital signal processing techniques. The motivation behind this is to push more processing tasks to the digital domain, as it can potentially cut down the bill of materials (BOM) costs paid for the off-chip devices and reduce practical implementation difficulties. The work here is carried out using three approaches: numerical analysis & computer simulations; experimental tests using commercial instruments; actual implementation with FPGA. The primary contributions for this thesis are summarized as the following three points: 1) An adaptive digital predistortion (DPD) with fast convergence rate and low complexity for multi-carrier GSM system is presented. Albeit a legacy system, the GSM, however, has a very strict requirement on the out-of-band emission, thus it represents a much more difficult hurdle for DPD application. It is successfully implemented in an FPGA without using any other auxiliary processor. A simplified multiplier-free NLMS algorithm, especially suitable for FPGA implementation, for fast adapting the LUT is proposed. Many design methodologies and practical implementation issues are discussed in details. Experimental results have shown that the DPD performed robustly when it is involved in the multichannel transmitter. 2) The next generation system (5G) will unquestionably use wider bandwidth to support higher throughput, which poses stringent needs for using high-speed data converters. Herein the analog-to-digital converter (ADC) tends to be the most expensive single device in the whole transmitter/receiver systems. Therefore, conventional DPD utilizing high-speed ADC becomes unaffordable, especially for small base stations (micro, pico and femto). A digital predistortion technique utilizing spectral extrapolation is proposed in this thesis, wherein with band-limited feedback signal, the requirement on ADC speed can be significantly released. Experimental results have validated the feasibility of the proposed technique for coping with band-limited feedback signal. It has been shown that adequate linearization performance can be achieved even if the acquisition bandwidth is less than the original signal bandwidth. The experimental results obtained by using LTE-Advanced signal of 320 MHz bandwidth are quite satisfactory, and to the authors’ knowledge, this is the first high-performance wideband DPD ever been reported. 3) To address the predicament that mobile operators do not have enough contiguous usable bandwidth, carrier aggregation (CA) technique is developed and imported into 4G LTE-Advanced. This pushes the utilization of concurrent dual-band transmitter/receiver, which reduces the hardware expense by using a single front-end. Compensation techniques for the respective concurrent dual-band transmitter and receiver front-ends are proposed to combat the inter-band modulation distortion, and simultaneously reduce the distortion for the both lower-side band and upper-side band signals.電気通信大学201
Energy efficient and low complexity techniques for the next generation millimeter wave hybrid MIMO systems
The fifth generation (and beyond) wireless communication systems require increased
capacity, high data rates, improved coverage and reduced energy consumption.
This can be potentially provided by unused available spectrum such
as the Millimeter Wave (MmWave) frequency spectrum above 30 GHz. The high
bandwidths for mmWave communication compared to sub-6 GHz microwave frequency
bands must be traded off against increased path loss, which can be compensated
using large-scale antenna arrays such as the Multiple-Input Multiple-
Output (MIMO) systems. The analog/digital Hybrid Beamforming (HBF) architectures
for mmWave MIMO systems reduce the hardware complexity and power
consumption using fewer Radio Frequency (RF) chains and support multi-stream
communication with high Spectral Efficiency (SE). Such systems can also be
optimized to achieve high Energy Efficiency (EE) gains with low complexity but
this has not been widely studied in the literature. This PhD project focussed on
designing energy efficient and low complexity communication techniques for next
generation mmWave hybrid MIMO systems.
Firstly, a novel architecture with a framework that dynamically activates the
optimal number of RF chains was designed. Fractional programming was used
to solve an EE maximization problem and the Dinkelbach Method (DM) based
framework was exploited to optimize the number of active RF chains and the data
streams. The DM is an iterative and parametric algorithm where a sequence of
easier problems converge to the global solution. The HBF matrices were designed
using a codebook-based fast approximation solution called gradient pursuit which
was introduced as a cost-effective and fast approximation algorithm. This work
maximizes EE by exploiting the structure of RF chains with full resolution
sampling unlike existing baseline approaches that use fixed RF chains and aim
only for high SE.
Secondly, an efficient sparse mmWave channel estimation algorithm was developed
with low resolution Analog-to-Digital Converters (ADCs) at the receiver.
The sparsity of the mmWave channel was exploited and the estimation problem
was tackled using compressed sensing through the Stein's unbiased risk estimate
based parametric denoiser. The Expectation-maximization density estimation
was used to avoid the need to specify the channel statistics. Furthermore, an
energy efficient mmWave hybrid MIMO system was developed with Digital-to-
Analog Converters (DACs) at the transmitter where the best subset of the active
RF chains and the DAC resolution were selected. A novel technique based on the
DM and subset selection optimization was implemented for EE maximization.
This work exploits the low resolution sampling at the converting units and provides
more efficient solutions in terms of EE and channel estimation than existing
baselines in the literature.
Thirdly, the DAC and ADC bit resolutions and the HBF matrices were jointly
optimized for EE maximization. The flexibility in choosing the bit resolution
for each DAC and ADC was considered and they were optimized on a frame-by-frame
basis unlike the existing approaches, based on the fixed resolution sampling.
A novel decomposition of the HBF matrices to three parts was introduced to
represent the analog beamformer matrix, the DAC/ADC bit resolution matrix and
the baseband beamformer matrix. The alternating direction method of multipliers
was used to solve this matrix factorization problem as it has been successfully
applied to other non-convex matrix factorization problems in the literature. This
work considers EE maximization with low resolution sampling at both the DACs
and the ADCs simultaneously, and jointly optimizes the HBF and DAC/ADC bit
resolution matrices, unlike the existing baselines that use fixed bit resolution or
otherwise optimize either DAC/ADC bit resolution or HBF matrices
Ultra Wideband Communications: from Analog to Digital
Ultrabreitband-Signale (Ultra Wideband [UWB]) können einen
signifikanten Nutzen im Bereich drahtloser Kommunikationssysteme haben. Es
sind jedoch noch einige Probleme offen, die durch Systemdesigner und
Wissenschaftler gelöst werden müssen. Ein Funknetzsystem mit einer derart
großen Bandbreite ist normalerweise auch durch eine große Anzahl an
Mehrwegekomponenten mit jeweils verschiedenen Pfadamplituden
gekennzeichnet. Daher ist es schwierig, die zeitlich verteilte Energie
effektiv zu erfassen. Außerdem ist in vielen Fällen der naheliegende
Ansatz, ein kohärenter Empfänger im Sinne eines signalangepassten Filters
oder eines Korrelators, nicht unbedingt die beste Wahl. In der vorliegenden
Arbeit wird dabei auf die bestehende Problematik und weitere
Lösungsmöglichkeiten eingegangen.
Im ersten Abschnitt geht es um „Impulse Radio UWB”-Systeme mit
niedriger Datenrate. Bei diesen Systemen kommt ein inkohärenter Empfänger
zum Einsatz. Inkohärente Signaldetektion stellt insofern einen
vielversprechenden Ansatz dar, als das damit aufwandsgünstige und robuste
Implementierungen möglich sind. Dies trifft vor allem in Anwendungsfällen
wie den von drahtlosen Sensornetzen zu, wo preiswerte Geräte mit langer
Batterielaufzeit nötigsind. Dies verringert den für die Kanalschätzung
und die Synchronisation nötigen Aufwand, was jedoch auf Kosten der
Leistungseffizienz geht und eine erhöhte Störempfindlichkeit gegenüber
Interferenz (z.B. Interferenz durch mehrere Nutzer oder schmalbandige
Interferenz) zur Folge hat.
Um die Bitfehlerrate der oben genannten Verfahren zu bestimmen, wurde
zunächst ein inkohärenter Combining-Verlust spezifiziert, welcher
auftritt im Gegensatz zu kohärenter Detektion mit Maximum Ratio Multipath
Combining. Dieser Verlust hängt von dem Produkt aus der Länge des
Integrationsfensters und der Signalbandbreite ab.
Um den Verlust durch inkohärentes Combining zu reduzieren und somit die
Leistungseffizienz des Empfängers zu steigern, werden verbesserte
Combining-Methoden für Mehrwegeempfang vorgeschlagen. Ein analoger
Empfänger, bei dem der Hauptteil des Mehrwege-Combinings durch einen
„Integrate and Dump”-Filter implementiert ist, wird für UWB-Systeme
mit Zeit-Hopping gezeigt. Dabei wurde die Einsatzmöglichkeit von dünn
besetzten Codes in solchen System diskutiert und bewertet. Des Weiteren
wird eine Regel für die Code-Auswahl vorgestellt, welche die Stabilität
des Systems gegen Mehrnutzer-Störungen sicherstellt und gleichzeitig den
Verlust durch inkohärentes Combining verringert.
Danach liegt der Fokus auf digitalen Lösungen bei inkohärenter
Demodulation. Im Vergleich zum Analogempfänger besitzt ein
Digitalempfänger einen Analog-Digital-Wandler im Zeitbereich gefolgt von
einem digitalen Optimalfilter. Der digitale Optimalfilter dekodiert den
Mehrfachzugriffscode kohärent und beschränkt das inkohärente Combining
auf die empfangenen Mehrwegekomponenten im Digitalbereich. Es kommt ein
schneller Analog-Digital-Wandler mit geringer Auflösung zum Einsatz, um
einen vertretbaren Energieverbrauch zu gewährleisten. Diese Digitaltechnik
macht den Einsatz langer Analogverzögerungen bei differentieller
Demodulation unnötig und ermöglicht viele Arten der digitalen
Signalverarbeitung. Im Vergleich zur Analogtechnik reduziert sie nicht nur
den inkohärenten Combining-Verlust, sonder zeigt auch eine stärkere
Resistenz gegenüber Störungen. Dabei werden die Auswirkungen der
Auflösung und der Abtastrate der Analog-Digital-Umsetzung analysiert. Die
Resultate zeigen, dass die verminderte Effizienz solcher
Analog-Digital-Wandler gering ausfällt. Weiterhin zeigt sich, dass im
Falle starker Mehrnutzerinterferenz sogar eine Verbesserung der Ergebnisse
zu beobachten ist. Die vorgeschlagenen Design-Regeln spezifizieren die
Anwendung der Analog-Digital-Wandler und die Auswahl der Systemparameter in
Abhängigkeit der verwendeten Mehrfachzugriffscodes und der Modulationsart.
Wir zeigen, wie unter Anwendung erweiterter Modulationsverfahren die
Leistungseffizienz verbessert werden kann und schlagen ein Verfahren zur
Unterdrückung schmalbandiger Störer vor, welches auf Soft Limiting
aufbaut. Durch die Untersuchungen und Ergebnissen zeigt sich, dass
inkohärente Empfänger in UWB-Kommunikationssystemen mit niedriger
Datenrate ein großes Potential aufweisen.
Außerdem wird die Auswahl der benutzbaren Bandbreite untersucht, um einen
Kompromiss zwischen inkohärentem Combining-Verlust und Stabilität
gegenüber langsamen Schwund zu erreichen. Dadurch wurde ein neues Konzept
für UWB-Systeme erarbeitet: wahlweise kohärente oder inkohärente
Empfänger, welche als UWB-Systeme Frequenz-Hopping nutzen. Der wesentliche
Vorteil hiervon liegt darin, dass die Bandbreite im Basisband sich deutlich
verringert. Mithin ermöglicht dies einfach zu realisierende digitale
Signalverarbeitungstechnik mit kostengünstigen Analog-Digital-Wandlern.
Dies stellt eine neue Epoche in der Forschung im Bereich drahtloser
Sensorfunknetze dar.
Der Schwerpunkt des zweiten Abschnitts stellt adaptiven Signalverarbeitung
für hohe Datenraten mit „Direct Sequence”-UWB-Systemen in den
Vordergrund. In solchen Systemen entstehen, wegen der großen Anzahl der
empfangenen Mehrwegekomponenten, starke Inter- bzw.
Intrasymbolinterferenzen. Außerdem kann die Funktionalität des Systems
durch Mehrnutzerinterferenz und Schmalbandstörungen deutlich beeinflusst
werden. Um sie zu eliminieren, wird die „Widely Linear”-Rangreduzierung
benutzt. Dabei verbessert die Rangreduzierungsmethode das
Konvergenzverhalten, besonders wenn der gegebene Vektor eine sehr große
Anzahl an Abtastwerten beinhaltet (in Folge hoher einer Abtastrate).
Zusätzlich kann das System durch die Anwendung der R-linearen Verarbeitung
die Statistik zweiter Ordnung des nicht-zirkularen Signals vollständig
ausnutzen, was sich in verbesserten Schätzergebnissen widerspiegelt.
Allgemeine kann die Methode der „Widely Linear”-Rangreduzierung auch in
andern Bereichen angewendet werden, z.B. in „Direct
Sequence”-Codemultiplexverfahren (DS-CDMA), im MIMO-Bereich, im Global
System for Mobile Communications (GSM) und beim Beamforming.The aim of this thesis is to investigate key issues encountered in the
design of transmission schemes and receiving techniques for Ultra Wideband
(UWB) communication systems. Based on different data rate applications,
this work is divided into two parts, where energy efficient and robust
physical layer solutions are proposed, respectively.
Due to a huge bandwidth of UWB signals, a considerable amount of multipath
arrivals with various path gains is resolvable at the receiver. For low
data rate impulse radio UWB systems, suboptimal non-coherent detection is a
simple way to effectively capture the multipath energy. Feasible techniques
that increase the power efficiency and the interference robustness of
non-coherent detection need to be investigated. For high data rate direct
sequence UWB systems, a large number of multipath arrivals results in
severe inter-/intra-symbol interference. Additionally, the system
performance may also be deteriorated by multi-user interference and
narrowband interference. It is necessary to develop advanced signal
processing techniques at the receiver to suppress these interferences.
Part I of this thesis deals with the co-design of signaling schemes and
receiver architectures in low data rate impulse radio UWB systems based on
non-coherent detection.● We analyze the bit error rate performance of
non-coherent detection and characterize a non-coherent combining loss,
i.e., a performance penalty with respect to coherent detection with maximum
ratio multipath combining. The thorough analysis of this loss is very
helpful for the design of transmission schemes and receive techniques
innon-coherent UWB communication systems.● We propose to use optical
orthogonal codes in a time hopping impulse radio UWB system based on an
analog non-coherent receiver. The “analog” means that the major part of
the multipath combining is implemented by an integrate and dump filter. The
introduced semi-analytical method can help us to easily select the time
hopping codes to ensure the robustness against the multi-user interference
and meanwhile to alleviate the non-coherent combining loss.● The main
contribution of Part I is the proposal of applying fully digital solutions
in non-coherent detection. The proposed digital non-coherent receiver is
based on a time domain analog-to-digital converter, which has a high speed
but a very low resolution to maintain a reasonable power consumption.
Compared to its analog counterpart, itnot only significantly reduces the
non-coherent combining loss but also offers a higher interference
robustness. In particular, the one-bit receiver can effectively suppress
strong multi-user interference and is thus advantageous in separating
simultaneously operating piconets.The fully digital solutions overcome the
difficulty of implementing long analog delay lines and make differential
UWB detection possible. They also facilitate the development of various
digital signal processing techniques such as multi-user detection and
non-coherent multipath combining methods as well as the use of advanced
modulationschemes (e.g., M-ary Walsh modulation).● Furthermore, we
present a novel impulse radio UWB system based on frequency hopping, where
both coherent and non-coherent receivers can be adopted. The key advantage
is that the baseband bandwidth can be considerably reduced (e.g., lower
than 500 MHz), which enables low-complexity implementation of the fully
digital solutions. It opens up various research activities in the
application field of wireless sensor networks.
Part II of this thesis proposes adaptive widely linear reduced-rank
techniques to suppress interferences for high data rate direct sequence UWB
systems, where second-order non-circular signals are used. The reduced-rank
techniques are designed to improve the convergence performance and the
interference robustness especially when the received vector contains a
large number of samples (due to a high sampling rate in UWB systems). The
widely linear processing takes full advantage of the second-order
statistics of the non-circular signals and enhances the estimation
performance. The generic widely linear reduced-rank concept also has a
great potential in the applications of other systems such as Direct
Sequence Code Division Multiple Access (DS-CDMA), Multiple Input Multiple
Output (MIMO) system, and Global System for Mobile Communications (GSM), or
in other areas such as beamforming
Remote Sensing and Skywave Digital Communication from Antarctica
This paper presents an overview of the research activities undertaken by La Salle and the Ebro Observatory in the field of remote sensing. On 2003 we started a research project with two main objectives: implement a long-haul oblique ionospheric sounder and transmit the data from remote sensors located at the Spanish Antarctic station Juan Carlos I to Spain. The paper focuses on a study of feasibility of two possible physical layer candidates for the skywave link between both points. A DS-SS based solution and an OFDM based solution are considered to achieve a reliable low-power low-rate communication system between Antarctica and Spain
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