25 research outputs found
Establishing Multi-User MIMO Communications Automatically Using Retrodirective Arrays
Communications in the mmWave and THz bands will be a key technological pillar for next-generation wireless networks. However, the increase in frequency results in an increase in path loss, which must be compensated for by using large antenna arrays. This introduces challenging issues due to power consumption, signalling overhead for channel estimation, hardware complexity, and slow beamforming and beam alignment schemes, which are in contrast with the requirements of next-generation wireless networks. In this paper, we propose the adoption of a retro-directive antenna array (RAA) at the user equipment (UE) side, where the signal sent by the base station (BS) is reflected towards the source after being conjugated and phase-modulated according to the UE data. By making use of modified Power Methods for the computation of the eigenvectors of the resulting round-trip channel, it is shown that, in single and multi-user multiple-input multiple-output (MIMO) scenarios, ultra-low complexity UEs can establish parallel communication links automatically with the BS in a very short time. This is done in a blind way, also by tracking fast channel variations while communicating, without the need for ADC chains at the UE as well as without explicit channel estimation and time-consuming beamforming and beam alignment schemes
Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation
A new line of research on communications and signals design for Wireless
Power Transfer (WPT) has recently emerged in the communication literature.
Promising signal strategies to maximize the power transfer efficiency of WPT
rely on (energy) beamforming, waveform, modulation and transmit diversity, and
a combination thereof. To a great extent, the study of those strategies has so
far been limited to theoretical performance analysis. In this paper, we study
the real over-the-air performance of all the aforementioned signal strategies
for WPT. To that end, we have designed, prototyped and experimented an
innovative radiative WPT architecture based on Software-Defined Radio (SDR)
that can operate in open-loop and closed-loop (with channel acquisition at the
transmitter) modes. The prototype consists of three important blocks, namely
the channel estimator, the signal generator, and the energy harvester. The
experiments have been conducted in a variety of deployments, including
frequency flat and frequency selective channels, under static and mobility
conditions. Experiments highlight that a channeladaptive WPT architecture based
on joint beamforming and waveform design offers significant performance
improvements in harvested DC power over conventional
single-antenna/multiantenna continuous wave systems. The experimental results
fully validate the observations predicted from the theoretical signal designs
and confirm the crucial and beneficial role played by the energy harvester
nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication
2009 Index IEEE Antennas and Wireless Propagation Letters Vol. 8
This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index
2008 Index IEEE Transactions on Control Systems Technology Vol. 16
This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index
Architectures and synchronization techniques for distributed satellite systems: a survey
Cohesive Distributed Satellite Systems (CDSSs) is a key enabling technology for the future of remote sensing and communication missions. However, they have to meet strict synchronization requirements before their use is generalized. When clock or local oscillator signals are generated locally at each of the distributed nodes, achieving exact synchronization in absolute phase, frequency, and time is a complex problem. In addition, satellite systems have significant resource constraints, especially for small satellites, which are envisioned to be part of the future CDSSs. Thus, the development of precise, robust, and resource-efficient synchronization techniques is essential for the advancement of future CDSSs. In this context, this survey aims to summarize and categorize the most relevant results on synchronization techniques for Distributed Satellite Systems (DSSs). First, some important architecture and system concepts are defined. Then, the synchronization methods reported in the literature are reviewed and categorized. This article also provides an extensive list of applications and examples of synchronization techniques for DSSs in addition to the most significant advances in other operations closely related to synchronization, such as inter-satellite ranging and relative position. The survey also provides a discussion on emerging data-driven synchronization techniques based on Machine Learning (ML). Finally, a compilation of current research activities and potential research topics is proposed, identifying problems and open challenges that can be useful for researchers in the field.This work was supported by the Luxembourg National Research Fund (FNR), through the CORE Project COHEsive SATellite (COHESAT): Cognitive Cohesive Networks of Distributed Units for Active and Passive Space Applications, under Grant FNR11689919.Award-winningPostprint (published version
Estudio de los efectos producidos por la modulación temporal aplicada a una agrupación de antenas en sistemas de transmisión digital
Programa Oficial de Doutoramento en Tecnoloxías da Información e as Comunicacións en Redes Móbiles. 5032V0[Resumo]
Os selos de identidade das comunicacións móbiles e sen fíos de hoxe en día son a demanda
continua e crecente de mobilidade, capacidade e fiabilidade, xunto cun firme e definitivo compromiso
coa sustentabilidade. Baixo estas premisas, as antenas intelixentes –capaces de sensar a contorna
electromagnética e adaptar de xeito eficaz as súas características de radiación– están chamadas a xogar
un papel crucial nas ditas comunicacións. Neste senso, os estándares sen fíos actuais consideran técnicas
multi-antena encamiñadas a explotar a diversidade espacial, o multiplexado espacial e o conformado de
feixe, acadando así mellores niveis de fiabilidade e capacidade.
Con todo, ditas vantaxes obtéñense a expensas dun incremento da complexidade do sistema, factor
non sempre asumible en termos de tamaño e eficiencia enerxética. Consecuentemente, suscítanse unha
serie de retos de cara a desenvolver tecnoloxías de antena axeitadas e capaces de dar resposta ás anteriores
prestacións no espazo limitado que dita a mobilidade.
O concepto de agrupación de antenas modulada temporalmente (TMAs, do inglés time-modulated
arrays) é unha técnica multi-antena que achega unha simplificación hardware significativa: o seu
diagrama de radiación contrólase mediante a sinxela aplicación de pulsos periódicos de duración variable
ás excitacións individuais da agrupación. A natureza non lineal desta operación causa a aparición de
diagramas de radiación nas frecuencias harmónicas dos pulsos periódicos aplicados. A técnica pode
empregarse para mellorar a topoloxía do nivel dos lóbulos secundarios do diagrama de radiación na
frecuencia central e/ou para explotar de xeito proveitoso os diagramas dos harmónicos, dotando á antena
de capacidades de antena intelixente.
Esta tese é o resultado dunha investigación das TMAs dende unha perspectiva interdisciplinaria,
é dicir, non soamente dende a óptica do diagrama de radiación ou das agrupacións de antenas, senón
tamén dende un punto de vista de procesado do sinal. Máis concretamente, a tese é unha análise en
profundidade da aplicación das TMAs ás comunicacións dixitais, desenvolvida en catro etapas: 1) análise
matemática da posibilidade de transmitir sinais dixitais mediante TMAs, identificando as restricións
para salvagardar a integridade do sinal e cuantificando a potencia radiada, 2) caracterización da taxa
de erro de bit dun sistema de comunicación dixital que incorpora un TMA en recepción explotando o
seu modo fundamental e considerando canles con ruído branco Gaussiano, 3) estudo das prestacións
das TMAs –explotando os harmónicos– na recepción de sinais de comunicación dixitais con diversidade
angular en canles multitraxecto con esvaecemento, 4) caracterización de TMAs para conformado de feixe
mediante o uso de pulsos de suma de cosenos ponderados no lugar de pulsos rectangulares, chegando ás
denominadas TMAs melloradas, dotadas dunha resposta superior en termos de flexibilidade e eficiencia.[Resumen]
Hoy en día, los sellos de identidad de las comunicaciones inalámbricas son la demanda continua
y creciente de movilidad, capacidad y fiabilidad, junto con un firme y definitivo compromiso con
la sostenibilidad. Bajo estas premisas, las antenas inteligentes –capaces de sensar el entorno
electromagnético y adaptar de forma eficaz sus características de radiación– están llamadas a jugar
un papel crucial en dichas comunicaciones. En este sentido, los estándares inalámbricos actuales
consideran técnicas multiantena encaminadas a explotar la diversidad espacial, el multiplexado espacial
o el conformado de haz, alcanzando así mejores niveles de fiabilidad y capacidad.
Sin embargo, dichas ventajas se obtienen a expensas de un incremento de la complejidad del sistema,
factor no siempre asumible en términos de tamaño y eficiencia energética. En consecuencia, se plantean
una serie de retos en el desarrollo de tecnologías de antena adecuadas, capaces de dar respuesta a las
anteriores prestaciones en el espacio limitado que dicta la movilidad.
El concepto de agrupación de antenas modulada temporalmente (TMAs, del inglés time-modulated
arrays) es una técnica multiantena que aporta una simplificación hardware significativa: su diagrama
de radiación se controla mediante la sencilla aplicación de pulsos periódicos de duración variable a las
excitaciones individuales de la agrupación. La naturaleza no lineal de esta operación causa la aparición
de diagramas de radiación en las frecuencias armónicas de los pulsos periódicos aplicados. La técnica se
puede utilizar para mejorar la topología del nivel de los lóbulos secundarios del diagrama de radiación
en la frecuencia central y/o para explotar de forma beneficiosa los diagramas de armónicos, dotando a la
antena de capacidades de antena inteligente.
Esta tesis es el resultado de una investigación de las TMAs desde una perspectiva interdisciplinar,
es decir, no solamente desde la óptica del diagrama de radiación o de las agrupaciones de antenas, sino
también desde un punto de vista de procesado de señal. Más concretamente, la tesis es un análisis en
profundidad de la aplicación de las TMAs a las comunicaciones digitales, desarrollada en cuatro etapas:
1) análisis matemático de la factibilidad de transmitir señales digitales mediante TMAs, identificando
las restricciones para salvaguardar la integridad de la señal y cuantificando la potencia radiada, 2)
caracterización de la tasa de error de bit de un sistema de comunicación digital que incorpora una TMA
en recepción explotando su modo fundamental y considerando canales con ruido blanco Gaussiano,
3) estudio de las prestaciones de las TMAs –explotando los armónicos– en la recepción de señales
digitales con diversidad angular en canales multitrayecto con desvanecimiento, 4) caracterización de
TMAs para conformado de haz mediante el uso de pulsos de suma de cosenos ponderados en lugar de
pulsos rectangulares, llegando a las denominadas TMAs mejoradas, dotadas de una respuesta superior
en términos de flexibilidad y eficiencia.[Abstract]
An ever-increasing demand for higher mobility, capacity and reliability, together with a definitive
compromise with sustainability, are the hallmarks of mobile and wireless communications systems
nowadays. Under these premises, smart antenna devices –capable of sensing the electromagnetic
environment and suitably adapting its radiation features– are correspondingly called to play a crucial
role. In this sense, today’s wireless standards consider multiple-antenna techniques in order to exploit
space diversity, spatial multiplexing and beamforming to achieve better levels of reliability and capacity.
Such advantages, however, are obtained at the expense of increased system complexity which may be
unaffordable in terms of size and energy efficiency. Consequently, some technical challenges remain to
develop the adequate antenna technologies capable of supporting the aforementioned features in a limited
physical space that the mobility demand dictates.
The concept of time-modulated array (TMA) is a feasible multi-antenna technique that provides a
significant hardware simplification: its radiated power pattern is controlled by the simple application of
variable-width periodical pulses to the individual array excitations. The nonlinear nature of such an array
operation causes the appearance of radiation patterns at the harmonic frequencies of the applied periodic
pulses. The technique can be used for improving the side-lobe level topology of the radiation pattern at
the central frequency and/or to profitably exploit the harmonic patterns in order to supply smart antenna
capabilities.
This thesis is the result of an investigation of TMAs from an interdisciplinary perspective, i.e., not
only under a radiation pattern or an antenna array outlook but also from a signal processing point of
view. More specifically, the thesis deals with an in-depth analysis of the application of TMAs in digital
communications developed in four stages: 1) mathematical analysis of the feasibility of transmission
of digital signals over TMAs, identifying the restrictions to safeguard the integrity of the signal and
quantifying the radiated power, 2) characterization of the bit error rate of a digital communication
system that incorporates a receive-TMA exploiting its fundamental mode and considering additive white
Gaussian noise channels, 3) study of the performance of TMAs –exploiting their harmonics– for the angle
diversity reception of digital communication signals over multipath fading channels, 4) an approach
to the characterization of beamforming TMAs which use sum of weighted cosines pulses instead of
rectangular ones, leading to the so-called enhanced time-modulated arrays, which endows them with a
better response in terms of flexibility and efficiency
1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface
A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance
Non-Radiative Calibration of Active Antenna Arrays
Antenna arrays offer significant benefits for modern wireless communication systems
but they remain difficult and expensive to produce. One of the impediments of utilising
them is to maintain knowledge of the precise amplitude and phase relationships between
the elements of the array, which are sensitive to errors particularly when each element
of the array is connected to its own transceiver. These errors arise from multiple
sources such as manufacturing errors, mutual coupling between the elements, thermal
effects, component aging and element location errors. The calibration problem of
antenna arrays is primarily the identification of the amplitude and phase mismatch, and
then using this information for correction.
This thesis will present a novel measurement-based calibration approach, which uses a
fixed structure allowing each element of the array to be measured. The measurement
structure is based around multiple sensors, which are interleaved with the elements of
the array to provide a scalable structure that provides multiple measurement paths to
almost all of the elements of the array. This structure is utilised by comparison based
calibration algorithms, so that each element of the array can be calibrated while
mitigating the impact of the additional measurement hardware on the calibration
accuracy. The calibration was proven in the investigation of the experimental test-bed,
which represented a typical telecommunications basestation. Calibration accuracies of
±0.5dB and 5o were achieved for all but one amplitude outlier of 0.55dB. The
performance is only limited by the quality of the coupler design. This calibration
approach has also been demonstrated for wideband signal calibration