114 research outputs found
Wireless Channel Model and LDM-Based Transmission with Unequal Error Protection for Inside Train Communications
Although the deployment of wireless systems is widespread, there are still sectors where they are not used due to their lack of reliability in comparison to wired systems. Sectors like industry or vehicle communications consider their environment hostile because the wireless signals suffer a lot of interferences. One of such environments is the railway sector, where wiring removal will allow more flexibility for both control and monitoring systems. This thesis analyzes wireless communications inside train cars, aiming at modelling their behavior and at proposing techniques to increase the reliability of the critical signals among train systems, wich can coexist with other lower priority systems. After proposing a novel model of an inside train wireless channel, a transmission system based on Layered Division Multiplexing (LDM) has been proposed which theoretically promises higher capacities than traditional TDM or FDM. This capacity gain is used to provide higher reliability to critical data using Unequal Error Protection (UEP) while maintaining the same bit rate as equivalent TDM or FDM based systems. In the final part of the thesis, simulation results of the proposed LDM system are provided, combined with Alamouti space time coding and different coding rates. Multiantenna extensions of the proposed LDM schemes are also simulated, providing BER and throughput results. These results will be used to shed light about how to reduce BER of an inside train wireless communication system.Aunque el despliegue de los sistemas inalámbricos está muy extendido, aun hay sectores donde no se utiliza por la poca fiabilidad que proporcionan comparado con los sistemas cableados. Sectores como la industria o las comunicaciones vehiculares consideran el entorno donde trabajan como entorno hostil, debido a que las señales inalámbricas sufren muchas interferencias. Uno de estos entornos es el de las comunicaciones en ferrocarril donde la eliminación de cables permitiría mayor flexibilidad entre los sistemas de control y monitorización. En esta tesis se analiza el canal de comunicación inalámbrico dentro de los trenes, con el objetivo de modelar su comportamiento y proponer técnicas que permitan aumentar la fiabilidad de la información de tipo crítico transmitida entre los sistemas del tren, repercutiendo lo menos posible en otros sistemas de menor prioridad. Tras proponer el modelo de canal inalámbrico dentro del tren, se ha propuesto un sistema de transmisión basado en Layered Division Multiplexing (LDM) que analizándolo teóricamente promete mayores capacidades que los tradicionales TDM o FDM. Esta capacidad se utilizará para obtener mayor redundancia de los datos críticos usando Unequal Error Protection (UEP) manteniendo la misma tasa de transferencia bits que los sistemas basados en TDM/FDM. En la parte final de la tesis, se obtienen resultados de las simulaciones realizadas con el sistema LDM propuesto, combinada con codificación espacio temporal como Alamouti y diferentes ratios de codificación. También se han simulado configuraciones multiantena obteniendo resultados de BER y throughput. Estos resultados servirán para arrojar luz sobre cómo reducir el BER en las comunicaciones inalámbricas dentro de los trenes.Haririk gabeko sistemak oso hedatuak dauden arren oraindik erabiltzen ez dituen sektoreak badaude ematen duten fidagarritasuna txikia delako kableatutako sistemekin alderatuz. Industria bezalako sektoreek edo ibilgailuetako komunikazioek lan egiten duten ingurua oso zaratatsua izaten da eta seinaleek interferentzia asko jasaten dituzte. Tesi honetan tren barruko haririk gabeko komunikazio kanala aztertzen da, bere portaera aztertu eta modelatzeko asmotan. Jakintza honekin zein teknika izan daitekeen erabilgarriak aztertuko da datuen fidagarritasuna handitzeko helburuarekin, lehentasun gutxiago duten sistemetan eragin txikiena izanik. Modeloa atera ondoren proposatu den transmisio sistema Layered Division Multiplexing (LDM) izan da, non azterketa teorikoek TDM edo FDM sistemek baino kapazitate gehiago dutela frogatzen dute. Kapazitate hau sistemaren datu kritikoei erredundantzia gehiago emateko erabiliko da Unequal Error Protection (UEP) erabiliz, TDM/FDM sistemetan bidaltzen den bit tasa kopurua mantenduz. Tesiaren azken partean, proposatutako LDM sistemaren simulazio emaitzak ematen dira, Alamouti espazio denbora kodifikazioarekin konbinatuak eta kodigo ratio desberdinekin. Antena anitzezko konfigurazioak ere simulatu dira BER eta throughput emaitzak lortuz. Emaitza hauek haririk gabeko tren barruko komunikazioetan BER-a nola gutxitu daitekeen jakiten lagunduko digute
The electronically steerable parasitic array radiator antenna for wireless communications : signal processing and emerging techniques
Smart antenna technology is expected to play an important role in future wireless
communication networks in order to use the spectrum efficiently, improve the
quality of service, reduce the costs of establishing new wireless paradigms and
reduce the energy consumption in wireless networks. Generally, smart antennas
exploit multiple widely spaced active elements, which are connected to separate
radio frequency (RF) chains. Therefore, they are only applicable to base stations
(BSs) and access points, by contrast with modern compact wireless terminals with
constraints on size, power and complexity. This dissertation considers an alternative
smart antenna system the electronically steerable parasitic array radiator
(ESPAR) which uses only a single RF chain, coupled with multiple parasitic elements.
The ESPAR antenna is of significant interest because of its
flexibility in beamforming by tuning a number of easy-to-implement reactance loads connected
to parasitic elements; however, parasitic elements require no expensive RF circuits.
This work concentrates on the study of the ESPAR antenna for compact
transceivers in order to achieve some emerging techniques in wireless communications.
The work begins by presenting the work principle and modeling of the ESPAR
antenna and describes the reactance-domain signal processing that is suited to the
single active antenna array, which are fundamental factors throughout this thesis.
The major contribution in this chapter is the adaptive beamforming method
based on the ESPAR antenna. In order to achieve fast convergent beamforming
for the ESPAR antenna, a modified minimum variance distortionless response
(MVDR) beamfomer is proposed. With reactance-domain signal processing, the
ESPAR array obtains a correlation matrix of receive signals as the input to the
MVDR optimization problem. To design a set of feasible reactance loads for a desired
beampattern, the MVDR optimization problem is reformulated as a convex
optimization problem constraining an optimized weight vector close to a feasible
solution. Finally, the necessary reactance loads are optimized by iterating the convex problem and a simple projector. In addition, the generic algorithm-based
beamforming method has also studied for the ESPAR antenna.
Blind interference alignment (BIA) is a promising technique for providing an optimal
degree of freedom in a multi-user, multiple-inputsingle-output broadcast
channel, without the requirements of channel state information at the transmitters.
Its key is antenna mode switching at the receive antenna. The ESPAR
antenna is able to provide a practical solution to beampattern switching (one
kind of antenna mode switching) for the implementation of BIA. In this chapter,
three beamforming methods are proposed for providing the required number of
beampatterns that are exploited across one super symbol for creating the channel
fluctuation patterns seen by receivers. These manually created channel
fluctuation
patterns are jointly combined with the designed spacetime precoding in order to
align the inter-user interference. Furthermore, the directional beampatterns designed
in the ESPAR antenna are demonstrated to improve the performance of
BIA by alleviating the noise amplification.
The ESPAR antenna is studied as the solution to interference mitigation in small
cell networks. Specifically, ESPARs analog beamforming presented in the previous
chapter is exploited to suppress inter-cell interference for the system scenario,
scheduling only one user to be served by each small BS at a single time. In
addition, the ESPAR-based BIA is employed to mitigate both inter-cell and intracell
interference for the system scenario, scheduling a small number of users to be
simultaneously served by each small BS for a single time.
In the cognitive radio (CR) paradigm, the ESPAR antenna is employed for spatial
spectrum sensing in order to utilize the new angle dimension in the spectrum
space besides the conventional frequency, time and space dimensions. The twostage
spatial spectrum sensing method is proposed based on the ESPAR antenna
being targeted at identifying white spectrum space, including the new angle dimension.
At the first stage, the occupancy of a specific frequency band is detected
by conventional spectrum-sensing methods, including energy detector and
eigenvalue-based methods implemented with the switched-beam ESPAR antenna. With the presence of primary users, their directions are estimated at the second
stage, by high-resolution angle-of-arrival (AoA) estimation algorithms. Specifically, the compressive sensing technology has been studied for AoA detection with
the ESPAR antenna, which is demonstrated to provide high-resolution estimation
results and even to outperform the reactance-domain multiple signal classification
Optimization of Spectrum Management in Massive Array Antenna Systems with MIMO
Fifth generation (5G), is being considered as a revolutionary technology in the telecommunication
domain whose the challenges are mainly to achieve signal quality and great ability to
work with free spectrum in the millimetre waves. Besides, other important innovations are the
introduction of a more current architecture and the use of multiple antennas in transmission
and reception. Digital communication using multiple input and multiple output (MIMO) wireless
links has recently emerged as one of the most significant technical advances in modern communications.
MIMO technology is able to offer a large increase in the capacity of these systems,
without requiring a considerable increase in bandwidth or power required for transmission.
This dissertation presents an overview of theoretical concepts of MIMO systems. With such a
system a spatial diversity gain can be obtained by using space-time codes, which simultaneously
exploit the spatial domain and the time domain. SISO, SIMO and MISO systems are differentiated
by their channel capacity and their configuration in relation to the number of antennas in the
transmitter/receiver. To verify the effectiveness of the MIMO systems a comparison between the
capacity of SISO and MIMO systems has been performed using the Shannon’s principles. In the
MIMO system some variations in the number of antennas arrays have been considered, and the
superiority of transmission gains of the MIMO systems have been demonstrated. Combined with
millimetre waves (mmWaves) technology, massive MIMO systems, where the number of antennas
in the base station and the number of users are large, is a promising solution.
SDR implementations have been performed considering a platform with Matlab code applied to
MIMO 2x2 Radio and Universal Software Peripheral Radio (USRP). A detailed study was initially
conducted to analyze the architecture of the USRP. Complex structures of MIMO systems can
be simplified by using mathematical methods implemented in Matlab for the synchronization of
the USRP in the receiver side. SISO transmission and reception techniques have been considered
to refine the synchronization (with 16-QAM), thus facilitating the future implementation of the
MIMO system. OpenAirInterface has been considered for 4G and 5G implementations of actual
mobile radio communication systems. Together with the practical MIMO, this type of solution is
the starting point for future hardware building blocks involving massive MIMO systems.A quinta geração (5G) está sendo considerada uma tecnologia revolucionária no setor de telecomunicações,
cujos desafios são principalmente a obtenção de qualidade de sinal e grande capacidade
de trabalhar com espectro livre nas ondas milimétricas. Além disso, outras inovações
importantes são a introdução de uma arquitetura mais atual e o uso de múltiplas antenas em
transmissão e recepção. A comunicação digital usando ligaçõe sem fio de múltiplas entradas e
múltiplas saídas (MIMO) emergiu recentemente como um dos avanços técnicos mais significativos
nas comunicações modernas. A tecnologia MIMO é capaz de oferecer um elevado aumento na
capacidade, sem exigir um aumento considerável na largura de banda ou potência transmitida.
Esta dissertação apresenta uma visão geral dos conceitos teóricos dos sistemas MIMO. Com esses
sistemas, um ganho de diversidade espacial pode ser obtido utilizando códigos espaço-tempo
reais. Os sistemas SISO, SIMO e MISO são diferenciados pela capacidade de seus canais e a sua
configuração em relação ao número de antenas no emissor/receptor. Para verificar a eficiência
dos sistemas MIMO, realizou-se uma comparação entre a capacidade dos sistemas SISO e MIMO
utilizado os princípios de Shannon. Nos sistemas MIMO condecideraram-se algumas variações no
número de agregados de antenas, e a superioridade dos ganhos de transmissão dos sistemas MIMO
foi demonstrada. Combinado com a tecnologia de ondas milimétricas (mmWaves), os sistemas
massivos MIMO, onde o número de antenas na estação base e o número de usuários são grandes,
são uma solução promissora.
As implementações do SDR foram realizadas considerando uma plataforma com código Matlab
aplicado aos rádios MIMO 2x2 e Universal Software Peripheral Radio (USRP). Um estudo detalhado
foi inicialmente conduzido para analisar a arquitetura da USRP. Estruturas complexas de sistemas
MIMO podem ser simplificadas usando métodos matemáticos implementados no Matlab para a
sincronização do USRP no lado do receptor. Consideraram-se técnicas de transmissão e recepção
SISO para refinar a sincronização (com 16-QAM), facilitando assim a implementação futura do
sistema MIMO . Considerou-se o OpenAirInterface para implementações 4G e 5G de sistemas
reais de comunicações móveis. Juntamente com o MIMO na pratica, este tipo de solução é
o ponto de partida para futuros blocos de construção de hardware envolvendo sistemas MIMO
massivos
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