86 research outputs found
On the Optimal Transmission Strategies for Sources without Channel State Information
With the growth of multimedia services, it is essential to find
new transmission schemes to support higher data rates
in wireless networks. In this thesis, we study
networks in which the Channel State
Information (CSI) is only available at the destination.
We focus on the analysis of three different network setups. For
each case, we propose a transmission scheme which maximizes
the average performance of the network.
The first scenario, which is studied in Chapter 2,
is a multi-hop network in which the channel gain of each hop
changes quasi-statically from one transmission block to the other.
Our main motivation to study this network is the recent advances
in deployment of relay nodes in wireless networks (e.g., LTE-A and IEEE 802.16j).
In this setup, we assume that all nodes are equipped with a single
antenna and the relay nodes are not capable of data buffering over
multiple transmission blocks. The proposed
transmission scheme is based on
infinite-layer coding at all nodes (the source and all relays)
in conjunction with the Decode-and-Forward DF relaying.
The objective is to maximize the statistical average of
the received rate per channel use at the destination.
To find the optimal parameters of this code, we
first formulate the problem for a two-hop scenario
and describe the code design algorithm for this
two-hop setting. The optimality
of infinite-layer DF coding is also discussed
for the case of two-hop networks. The
result is then generalized to multi-hop scenarios. To show
the superiority of the proposed scheme, we also evaluate
the achievable average received rate of
infinite-layer DF coding and compare it with the performance of
previously known schemes.
The second scenario, studied in Chapter 3, is a single-hop
network in which both nodes are equipped with multiple antennas, while the channel gain
changes quasi-statically and the CSI is not available at the source.
The main reason for selecting this network setup is to
study the transmission of video signals (compressed using
a scalable video coding technique, e.g., SVC H.264/AVC)
over a Multiple-Input Multiple-Output (MIMO) link.
In this setup,
although scalable video coding
techniques compress the video signal into layers with different importance (for video reconstruction),
the source cannot adapt the number of transmitted layers to the capacity of the channel
(since it does not have the CSI in each time slot). An alternative approach
is to always transmit all layers of the compressed video signal, but
use unequal error protection for different layers. With this motivation,
we focus on the design of multilayer codes for a MIMO
link in which the destination is only
able to perform successive decoding (not joint-decoding). In this chapter,
we introduce a design rule for construction of multilayer codes for MIMO systems.
We also propose a algorithm that uses this design rule to determine
the parameters of the multilayer code. The performance analysis of the proposed scheme
is also discussed in this chapter.
In the two previous scenarios, the ambiguity of the source regarding the channel state
comes from the fact that the channel gains randomly change in each transmission block
and there is no feedback to notify the source about the current state of the channel.
Apart from these, there are some scenarios in which the channel state is unknown at the source,
even though the channel gain is fixed and the source knows its value.
The third scenario of this thesis
presents an example of such network setups.
More precisely, in Chapter 4, we study a multiple access network with K users and one Access Point
(AP), where all nodes are equipped with multiple antennas.
To access the network, each user independently decides whether to transmit in a
time slot or not (no coordination between users). Considering a
two-user random access network, we first derive
the optimal value of network average Degrees of Freedom (DoF) (introduced in Section 4.1).
Generalizing the result to multiuser networks, we propose an upper-bound for the
network average DoF of a K-user random access network. This upper-bound is
then analyzed for different network configurations to identify the network classes in
which the proposed upper-bound is tight. It is also shown that simple single-stream data transmission
achieves the upper-bound in most network settings. However, for
some network configurations, we need to apply multi-stream data transmission in conjunction
with interference alignment to reach the upper-bound. Some illustrative examples
are also presented in this chapter
Solutions for New Terrestrial Broadcasting Systems Offering Simultaneously Stationary and Mobile Services
221 p.[EN]Since the first broadcasted TV signal was transmitted in the early decades of
the past century, the television broadcasting industry has experienced a series of
dramatic changes. Most recently, following the evolution from analogue to digital
systems, the digital dividend has become one of the main concerns of the
broadcasting industry. In fact, there are many international spectrum authorities
reclaiming part of the broadcasting spectrum to satisfy the growing demand of
other services, such as broadband wireless services, arguing that the TV services
are not very spectrum-efficient.
Apart from that, it must be taken into account that, even if up to now the
mobile broadcasting has not been considered a major requirement, this will
probably change in the near future. In fact, it is expected that the global mobile
data traffic will increase 11-fold between 2014 and 2018, and what is more, over
two thirds of the data traffic will be video stream by the end of that period.
Therefore, the capability to receive HD services anywhere with a mobile device is
going to be a mandatory requirement for any new generation broadcasting system.
The main objective of this work is to present several technical solutions that
answer to these challenges. In particular, the main questions to be solved are the
spectrum efficiency issue and the increasing user expectations of receiving high
quality mobile services. In other words, the main objective is to provide technical
solutions for an efficient and flexible usage of the terrestrial broadcasting spectrum
for both stationary and mobile services.
The first contributions of this scientific work are closely related to the study of
the mobile broadcast reception. Firstly, a comprehensive mathematical analysis of
the OFDM signal behaviour over time-varying channels is presented. In order to
maximize the channel capacity in mobile environments, channel estimation and
equalization are studied in depth. First, the most implemented equalization
solutions in time-varying scenarios are analyzed, and then, based on these existing
techniques, a new equalization algorithm is proposed for enhancing the receivers’
performance.
An alternative solution for improving the efficiency under mobile channel
conditions is treating the Inter Carrier Interference as another noise source.
Specifically, after analyzing the ICI impact and the existing solutions for reducing
the ICI penalty, a new approach based on the robustness of FEC codes is
presented. This new approach employs one dimensional algorithms at the receiver
and entrusts the ICI removing task to the robust forward error correction codes.
Finally, another major contribution of this work is the presentation of the
Layer Division Multiplexing (LDM) as a spectrum-efficient and flexible solution
for offering stationary and mobile services simultaneously. The comprehensive
theoretical study developed here verifies the improved spectrum efficiency,
whereas the included practical validation confirms the feasibility of the system and
presents it as a very promising multiplexing technique, which will surely be a strong
candidate for the next generation broadcasting services.[ES]Desde el comienzo de la transmisión de las primeras señales de televisión a
principios del siglo pasado, la radiodifusión digital ha evolucionado gracias a una
serie de cambios relevantes. Recientemente, como consecuencia directa de la
digitalización del servicio, el dividendo digital se ha convertido en uno de los
caballos de batalla de la industria de la radiodifusión. De hecho, no son pocos los
consorcios internacionales que abogan por asignar parte del espectro de
radiodifusión a otros servicios como, por ejemplo, la telefonía móvil, argumentado
la poca eficiencia espectral de la tecnología de radiodifusión actual.
Asimismo, se debe tener en cuenta que a pesar de que los servicios móviles no
se han considerado fundamentales en el pasado, esta tendencia probablemente
variará en el futuro cercano. De hecho, se espera que el tráfico derivado de
servicios móviles se multiplique por once entre los años 2014 y 2018; y lo que es
más importante, se pronostica que dos tercios del tráfico móvil sea video streaming
para finales de ese periodo. Por lo tanto, la posibilidad de ofrecer servicios de alta
definición en dispositivos móviles es un requisito fundamental para los sistemas de
radiodifusión de nueva generación.
El principal objetivo de este trabajo es presentar soluciones técnicas que den
respuesta a los retos planteados anteriormente. En particular, las principales
cuestiones a resolver son la ineficiencia espectral y el incremento de usuarios que
demandan mayor calidad en los contenidos para dispositivos móviles. En pocas
palabras, el principal objetivo de este trabajo se basa en ofrecer una solución más
eficiente y flexible para la transmisión simultánea de servicios fijos y móviles.
La primera contribución relevante de este trabajo está relacionada con la
recepción de la señal de televisión en movimiento. En primer lugar, se presenta un
completo análisis matemático del comportamiento de la señal OFDM en canales
variantes con el tiempo. A continuación, con la intención de maximizar la
capacidad del canal, se estudian en profundidad los algoritmos de estimación y
ecualización. Posteriormente, se analizan los algoritmos de ecualización más
implementados, y por último, basándose en estas técnicas, se propone un nuevo
algoritmo de ecualización para aumentar el rendimiento de los receptores en tales
condiciones.
Del mismo modo, se plantea un nuevo enfoque para mejorar la eficiencia de
los servicios móviles basado en tratar la interferencia entre portadoras como una
fuente de ruido. Concretamente, tras analizar el impacto del ICI en los receptores
actuales, se sugiere delegar el trabajo de corrección de dichas distorsiones en
códigos FEC muy robustos.
Finalmente, la última contribución importante de este trabajo es la
presentación de la tecnología LDM como una manera más eficiente y flexible para
la transmisión simultánea de servicios fijos y móviles. El análisis teórico presentado
confirma el incremento en la eficiencia espectral, mientras que el estudio práctico
valida la posible implementación del sistema y presenta la tecnología LDM c
Reception performance studies for the evaluation and improvement of the new generation terrestrial television systems
270 p.La industria de la TV ha experimentado grandes cambios en las últimas décadas. Las expectativas cada vez mayores de los espectadores y la reducción del espectro disponible para los servicios de TV han provocado la necesidad de sistemas más robustos de Televisión Digital Terrestre (TDT).El primer intento de cumplir estos requisitos es el estándar europeo DVB-T2 (2009). La publicación de un nuevo estándar significa el inicio de un proceso de evaluación del rendimiento del mismo mediante, por ejemplo, estudios de cobertura u obtención de valores de umbral de relación señal / ruido (SNR). Al inicio de esta tesis, este proceso estaba casi terminado para recepción fija y móvil. Sin embargo, la recepción en interiores no se había estudiado en detalle. Por esta razón, esta tesis completa la evaluación de DVB-T2 en interiores y define una nueva metodología de evaluación optimizada para este escenario.A pesar de que DVB-T2 emplea tecnologías muy avanzadas, el sistema se definió hace casi diez años y desde entonces han aparecido nuevas técnicas avanzadas, como por ejemplo nuevos códigos de corrección de errores o la nueva técnica de multiplexación por división en capas (LDM). Estas nuevas técnicas tampoco han sido evaluadas en entornos de interior, por lo que esta tesis incluye el análisis de las mismas evaluando su idoneidad para mejorar el rendimiento de DVB-T2. Además, se ha comprobado que los algoritmos tradicionales de los receptores TDT no están optimizados para los nuevos escenarios en los que se consideran las señales multicapa y recepción móvil. Por esta razón, se han propuesto nuevos algoritmos para mejorar la recepción en este tipo de situaciones.El último intento de hacer frente a los altos requisitos actuales de TDT es el estándar americano ATSC 3.0 (2016). Al igual que con DVB-T2, se necesita proceso completo de evaluación del sistema. Por ello, en esta tesis se han realizado simulaciones y pruebas de laboratorio para completar el estudio de rendimiento de ATSC 3.0 en diferentes escenarios
Spatial diversity in MIMO communication systems with distributed or co-located antennas
The use of multiple antennas in wireless communication systems has gained much attention during the last decade. It was shown that such multiple-input multiple-output (MIMO) systems offer huge advantages over single-antenna systems. Typically, quite restrictive assumptions are made concerning the spacing of the individual antenna elements. On the one hand, it is typically assumed that the antenna elements at transmitter and receiver are co-located, i.e., they belong to some sort of antenna array. On the other hand, it is often assumed that the antenna spacings are sufficiently large, so as to justify the assumption of independent fading. In this thesis, the above assumptions are relaxed. In the first part, it is shown that MIMO systems with distributed antennas and MIMO systems with co-located antennas can be treated in a single, unifying framework. In the second part this fact is utilized, in order to develop appropriate transmit power allocation strategies for co-located and distributed MIMO systems. Finally, the third part focuses on specific synchronization problems that are of interest for distributed MIMO systems
Rede neural de função de base radial de transmissão de fase complexa para decodificação mimo-ofdm massiva
Orientador: Dalton Soares ArantesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Os esquemas de transmissão MIMO (multiple-input multiple-output) se tornaram as técnicas escolhidas para aumentar a eficiência espectral em áreas congestionadas. No entanto, o projeto de receptores de baixo custo para canais MIMO continua sendo uma tarefa desafiadora. O detector de máxima verossimilhança pode atingir um desempenho excelente, geralmente o melhor, mas sua complexidade computacional é um fator limitante na implementação prática. Neste trabalho, um novo esquema MIMO é proposto com um algoritmo de decodificação pratico e viável baseado na PTRBFNN (rede neural de função de base radial de transmitância de fase). O esquema proposto atinge uma complexidade computacional bastante competitiva em relação à decodificação de Máxima Verossimilhança, aumentando substancialmente a aplicabilidade do algoritmo. Os resultados da simulação são apresentados para MIMO-OFDM sob desvanecimento Rayleigh em canais sem fio, para que uma comparação de desempenho justa com outras técnicas de referência possa ser estabelecidaAbstract: Multi-Input Multi-Output (MIMO) transmission schemes have become the techniques of choice for increasing spectral efficiency in bandwidth-congested areas. However, the design of cost-effective receivers for MIMO channels remains a challenging task. The maximum likelihood detector can achieve excellent performance, usually the best, but its computational complexity is a limiting factor in practical implementation. In this work, a new MIMO scheme is proposed with a practically feasible decoding algorithm based on the phase transmittance radial basis function neural network (PTRBFNN). The proposed scheme achieves a computational complexity that is quite competitive relative to the Maximum Likelihood decoding, thus substantially increasing the applicability of the algorithm. Simulation results are presented for MIMO-OFDM under wireless Rayleigh fading channels so that a fair performance comparison with other reference techniques can be establishedMestradoTelecomunicações e TelemáticaMestre em Engenharia Elétrica132545/2019-5CNP
Investigation of Vehicular S-LSTM NOMA Over Time Selective Nakagami-m Fading with Imperfect CSI, Journal of Telecommunications and Information Technology, 2022, nr 4
In this paper, the performance of a deep learning based multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) system is investigated for 5G radio communication networks. We consider independent and identically distributed (i.i.d.) Nakagami-m fading links to prove that when using MIMO with the NOMA system, the outage probability (OP) and end-to-end symbol error rate (SER) improve, even in the presence of imperfect channel state information (CSI) and successive interference cancellation (SIC) errors. Further more, the stacked long short-term memory (S-LSTM) algorithm is employed to improve the system’s performance, even under time-selective channel conditions and in the presence of terminal’s mobility. For vehicular NOMA networks, OP, SER, and ergodic sum rate have been formulated. Simulations show that an S-LSTM-based DL-NOMA receiver outperforms least square (LS) and minimum mean square error (MMSE) receivers. Furthermore, it has been discovered that the performance of the end-to-end system degrades with the growing amount of node mobility, or if CSI knowledge remains poor. Simulated curves are in close agreement with the analytical results
Satellite Communications
This study is motivated by the need to give the reader a broad view of the developments, key concepts, and technologies related to information society evolution, with a focus on the wireless communications and geoinformation technologies and their role in the environment. Giving perspective, it aims at assisting people active in the industry, the public sector, and Earth science fields as well, by providing a base for their continued work and thinking
Radio Communications
In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks
MIMO Systems
In recent years, it was realized that the MIMO communication systems seems to be inevitable in accelerated evolution of high data rates applications due to their potential to dramatically increase the spectral efficiency and simultaneously sending individual information to the corresponding users in wireless systems. This book, intends to provide highlights of the current research topics in the field of MIMO system, to offer a snapshot of the recent advances and major issues faced today by the researchers in the MIMO related areas. The book is written by specialists working in universities and research centers all over the world to cover the fundamental principles and main advanced topics on high data rates wireless communications systems over MIMO channels. Moreover, the book has the advantage of providing a collection of applications that are completely independent and self-contained; thus, the interested reader can choose any chapter and skip to another without losing continuity
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