316 research outputs found
MIMO-OFDMA Measurements; Reception, Testing, and Evaluation of WiMAX-MIMO Signals with a Single Channel Receiver
Abstract-The number of MIMO-OFDMA systems is expected to increase sharply in the near future. Engineers who need to test these systems face two difficulties. First, the lack of descriptive instructions to conduct reliable measurements. Second, the increased hardware cost due to the need for multiple transmitters and receivers. This paper first introduces all measurable parameters of MIMO-OFDMA systems and provides a clear guide to perform the measurements specific to various parts of the system. Then, it proposes to implement reception of MIMO-OFDMA signals using a single receiver rather than multiple receivers. For this purpose, impairments related to each of the RF front-end components are investigated. Challenges of MIMO-OFDMA measurements are addressed in comparison with SISO. A complete procedure is provided to receive and do impairment estimation for WiMAX MIMO signals using a single receiver according to the IEEE 802.16 standards
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Performance evaluation of fixed WiMax physical layer under high fading channels
This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.A radio channel characteristic modelling is essential in every network planning. This project deals with the performance of WiMax networks in an outdoor environment while using fading channel models. The radio channels characteristics are analyzed by simulations have been done using Matlab programming. Stanford University Interim(SUI) Channels set was proposed to simulate the fixed broadband wireless access channel environments where IEEE 802.16d is to be deployed. It has six channel models that are grouped into three categories according to three typical different outdoor Terrains, in order to give a comprehensive study of fading channels on the overall performance of the system, WiMax system has been tested under SUI channels that modified into account for 30o directional antennas, with 90% cell coverage and with 99.9% reliability in its geographical covered area. Furthermore, in order to combat the fading which occurs in urban areas and improve the capacity and the throughput of the system, multiples antennas at both ends of communication link are used, the transmission gain obtained when using multiple antennas instead of only a single antenna. Space-time coding and maximum ratio combining for more than one transmit and receive antenna is implemented to allow performance investigations in various MIMO scenarios. It has been concluded that uses multiple antennas at the receiver offers a significant improvement of 3 dB of gain in the channel SNR. This thesis also contain implementation of all compulsory features of the WiMax OFDM physical layer specified in IEEE 802.16-2004 using Matlab coding. In order to combat the temporal variations in quality on a multipath fading channel, an adaptive modulation technique is used. This technique employs multiple modulation schemes to instantaneously adapt to the variations in the channel SNR, thus maximizing the system throughput and improving BER performance. WiMax transceiver has been tested with and without encoding and studied the effect of encoding on multipath channel. Testing the system with flexible channel bandwidth has been part of this thesis. Finally it has been explained in this thesis the affect of increasing the size of cyclic prefix on overall performance of WiMax system
A real-time FPGA-based implementation of a high-performance MIMO-OFDM mobile WiMAX transmitter
The Multiple Input Multiple Output (MIMO)-Orthogonal
Frequency Division Multiplexing (OFDM) is considered a key technology
in modern wireless-access communication systems. The IEEE 802.16e
standard, also denoted as mobile WiMAX, utilizes the MIMO-OFDM
technology and it was one of the first initiatives towards the roadmap of
fourth generation systems. This paper presents the PHY-layer design, implementation
and validation of a high-performance real-time 2x2 MIMO
mobile WiMAX transmitter that accounts for low-level deployment issues
and signal impairments. The focus is mainly laid on the impact of
the selected high bandwidth, which scales the implementation complexity
of the baseband signal processing algorithms. The latter also requires
an advanced pipelined memory architecture to timely address the datapath
operations that involve high memory utilization. We present in this
paper a first evaluation of the extracted results that demonstrate the
performance of the system using a 2x2 MIMO channel emulation.Postprint (published version
Rapid Prototyping for Evaluating Vehicular Communications
[Abstract] This Thesis details the different elements of a rapid prototyping system able to
implement and evaluate vehicular communications fast, according to the continuously
evolving requirements of the industry. The system is basically composed of a testbed
and a channel emulator, which allow evaluating communication transceivers in realistic
vehicular scenarios.
Two different testbeds are introduced: a generic 2x2 system and a vehicular platform.
The former is used to compare and study space-time block coding (STBC) transmissions
at 2.4 GHz over different indoor channels. The latter makes use of software
transceivers whose performance is evaluated when they work under artificial high-speed
Rayleigh-fading scenarios.
To show the capabilities of both platforms, three software transceivers have been
developed following the specifications for the physical layers of the standards IEEE
802.11p, IEEE 802.11a and IEEE 802.16e (Mobile WiMAX). The present work details
the different elements that make up each transceiver and indicates how to connect them
to the rest of the system to perform evaluation measurements.
Finally, single-antenna and multi-antenna performances are measured thanks to the
design and implementation of three FPGA-based channel emulators that are able to
recreate up to seven different vehicular scenarios that include urban canyons, suburban
areas and highways[Resumo] A presente Tese detalla os elementos necesarios para constituir un sistema basado en
prototipado rápido capaz de levar a cabo e avaliar comunicacións vehiculares. O hardware
do sistema está composto básicamente por unha plataforma de probas (testbed)
e un emulador de canal, os cales permiten avaliar o rendemento de transceptores
inartiamicos recreando diferentes escenarios vehiculares.
Inicialmente, este traballo céntrase na descripción do hardware do sistema, detallando
a construcción e proba dunha plataforma multi-antena e un testebed vehicular.
Estos sistemas permitiron, respectivamente, estudar o comportamento de códigos STBC
(space-time block codes) en interiores e medir o rendemento de tranceptores software
ao traballar a distintas velocidades vehiculares en canais con desvaecemento Rayleigh.
Tres transceptores software foron creados seguindo as especificacións das capas
físicas dos estándares IEEE 802.11p, IEEE 802.11a e IEEE 802.16e (Mobile WiMAX).
Este traballo detalla os diferentes componentes de cada transceptor, indicando cómo
conectalos ao resto do sistema para realizar a avaliacition do seu rendemento. Dita
avaliación realizouse coa axuda de tres emuladores de canal basados en tecnoloxía
FPGA (Field Programmable Gate Array), os cales son capaces de recrear ata sete
escenarios vehiculares distintos, incluindo cañóns urbanos, zonas suburbanas e autopistas.[Resumen] La presente Tesis detalla los elementos necesarios para constituir un sistema basado
en prototipado rtiapido capaz de llevar a cabo y evaluar comunicaciones vehiculares.
El hardware del sistema está compuesto por una plataforma de pruebas (testbed) y
un emulador de canal, los cuales permiten evaluar el rendimiento de transceptores
inaltiambricos recreando diferentes escenarios vehiculares.
Inicialmente, este trabajo se centra en la descripcition del hardware del sistema,
detallando la construccition y prueba de una plataforma multi-antena y un testebed
vehicular. Estos sistemas han permitido, respectivamente, estudiar el comportamiento
de ctiodigos STBC (space-time block codes) en interiores y medir el rendimiento en
canal con desvanecimiento Rayleigh de tranceptores software a distintas velocidades
vehiculares.
Tres transceptores software han sido creados siguiendo las especificaciones de las
capas físicas de los estandares IEEE 802.11p, IEEE 802.11a e IEEE 802.16e (Mobile
WiMAX). Este trabajo detalla los diferentes componentes de cada transceptor,
indicando ctiomo conectarlos al resto del sistema para realizar la evaluacition de su
rendimiento. Dicha evaluacition se realiztio con la ayuda de tres emuladores de canal
basados en FPGAs (Field Programmable Gate Array), los cuales son capaces de recrear
comunicaciones multi-antena en hasta siete escenarios vehiculares distintos, incluyendo
cañones urbanos, zonas suburbanas y autopistas
Assessment and Real Time Implementation of Wireless Communications Systems and Applications in Transportation Systems
Programa Oficial de Doutoramento en Tecnoloxías da Información e das Comunicacións en Redes Móbiles. 5029V01[Resumo]
Os sistemas de comunicación sen fíos de cuarta e quinta xeración (4G e 5G) utilizan unha capa física
(PHY) baseada en modulacións multiportadora para a transmisión de datos cun gran ancho de banda.
Este tipo de modulacións proporcionan unha alta eficiencia espectral á vez que permiten corrixir de
forma sinxela os efectos da canle radio.
Estes sistemas utilizan OFDMA como mecanismo para a repartición dos recursos radio dispoñibles
entre os diferentes usuarios. Este repartimento realízase asignando un subconxunto de subportadoras a
cada usuario nun instante de tempo determinado. Isto aporta unha gran flexibilidade ó sistema que lle
permite adaptarse tanto ós requisitos de calidade de servizo dos usuarios como ó estado da canle radio.
A capa de acceso ó medio (MAC) destes sistemas encárgase de configurar os diversos parámetros
proporcionados pola capa física OFDMA, ademais de xestionar os diversos fluxos de información de
cada usuario, transformando os paquetes de capas superiores en paquetes da capa física.
Neste traballo estúdase o deseño e implementación das capas MAC e PHY de sistemas de
comunicación 4G ademais da súa aplicabilidade en sistemas de transporte ferroviarios.
Por unha parte, abórdase o deseño e implementación en tempo real do estándar WiMAX. Estúdanse
os mecanismos necesarios para establecer comunicacións bidireccionais entre unha estación base e
múltiples dispositivos móbiles. Ademais, estúdase como realizar esta implementación nunha arquitectura
hardware baseada en DSPs e FPGAs, na que se implementan as capas MAC e PHY. Dado que esta
arquitectura ten uns recursos computacionais limitados, tamén se estudan as necesidades de cada módulo
do sistema para poder garantir o funcionamento en tempo real do sistema completo.
Por outra parte, tamén se estuda a aplicabilidade dos sistemas 4G a sistemas de transporte públicos.
Os sistemas de comunicacións e sinalización son unha parte vital para os sistemas de transporte
ferroviario e metro. As comunicacións sen fíos utilizadas por estes sistemas deben ser robustas e
proporcionar unha alta fiabilidade para permitir a supervisión, control e seguridade do tráfico ferroviario.
Para levar a cabo esta avaliación de viabilidade realízanse simulacións de redes de comunicacións
LTE en contornos de transporte ferroviarios, comprobando o cumprimento dos requisitos de fiabilidade
e seguridade. Realízanse diferentes simulacións do sistema de comunicacións para poder ser avaliadas e
seleccionar a configuración e arquitectura do sistema máis axeitada en función do escenario considerado.
Tamén se efectúan simulacións de redes baseadas en Wi-Fi, dado que é a solución máis utilizada nos
metros, para confrontar os resultados cos obtidos para LTE.
Para que os resultados das simulacións sexan realistas débense empregar modelos de propagación
radio axeitados. Nas simulacións utilízanse tanto modelos deterministas como modelos baseados nos
resultados de campañas de medida realizadas nestes escenarios.
Nas simulacións empréganse os diferentes fluxos de información destes escenarios para comprobar
que se cumpren os requisitos de calidade de servicio (QoS). Por exemplo, os fluxos críticos para o control
ferroviario, como European Train Control System (ETCS) ou Communication-Based Train Control (CBTC), necesitan unha alta fiabilidade e un retardo mínimo nas comunicacións para garantir o correcto
funcionamento do sistema.[Resumen]
Los sistemas de comunicación inalámbricos de cuarta y quinta generación (4G y 5G) utilizan una capa
física (PHY) basada en modulaciones multiportadora para la transmisión de datos con un gran ancho
de banda. Este tipo de modulaciones han demostrado tener una alta eficiencia espectral a la vez que
permiten corregir de forma sencilla los efectos del canal radio.
Estos sistemas utilizan OFDMA como mecanismo para el reparto de los recursos radio disponibles
entre los diferentes usuarios. Este reparto se realiza asignando un subconjunto de subportadoras a cada
usuario en un instante de tiempo determinado. Esto aporta una gran flexibilidad al sistema que le permite
adaptarse tanto a los requisitos de calidad de servicio de los usuarios como al estado del canal radio.
La capa de acceso al medio (MAC) de estos sistemas se encarga de configurar los diversos parámetros
proporcionados por la capa física OFDMA, además de gestionar los diversos flujos de información de
cada usuario, transformando los paquetes de capas superiores en paquetes de la capa física.
En este trabajo se estudia el diseño e implementación de las capas MAC y PHY de sistemas de
comunicación 4G además de su aplicabilidad en sistemas de transporte ferroviarios.
Por una parte, se aborda el diseño e implementación en tiempo real del estándar WiMAX. Se
estudian los mecanismos necesarios para establecer comunicaciones bidireccionales entre una estación
base y múltiples dispositivos móviles. Además, se estudia cómo realizar esta implementación en una
arquitectura hardware basada en DSPs y FPGAs, en la que se implementan las capas MAC y PHY. Dado
que esta arquitectura tiene unos recursos computacionales limitados, también se estudian las necesidades
de cada módulo del sistema para poder garantizar el funcionamiento en tiempo real del sistema completo.
Por otra parte, también se estudia la aplicabilidad de los sistemas 4G a sistemas de transporte
públicos. Los sistemas de comunicaciones y señalización son una parte vital para los sistemas de
transporte ferroviario y metro. Las comunicaciones inalámbricas utilizadas por estos sistemas deben ser
robustas y proporcionar una alta fiabilidad para permitir la supervisión, control y seguridad del tráfico
ferroviario.
Para llevar a cabo esta evaluación de viabilidad se realizan simulaciones de redes de comunicaciones
LTE en entornos de transporte ferroviarios, comprobando si se cumplen los requisitos de fiabilidad y
seguridad. Se realizan diferentes simulaciones del sistema de comunicaciones para poder ser evaluados y
seleccionar la configuración y arquitectura del sistema más adecuada en función del escenario planteado.
También se efectúan simulaciones de redes basadas en Wi-Fi, dado que es la solución más utilizada en
los metros, para comparar los resultados con los obtenidos para LTE.
Para que los resultados de las simulaciones sean realistas se deben utilizar modelos de propagación
radio apropiados. En las simulaciones se utilizan tanto modelos deterministas como modelos basados en
los resultados de campañas de medida realizadas en estos escenarios.
En las simulaciones se utilizan los diferentes flujos de información de estos escenarios para
comprobar que se cumplen sus requisitos de calidad de servicio. Por ejemplo, los flujos críticos para el control ferroviario, como European Train Control System (ETCS) o Communication-Based Train
Control (CBTC), necesitan una alta fiabilidad y un retardo bajo en las comunicaciones para garantizar el
correcto funcionamiento del sistema.[Abstract]
The fourth and fifth generation wireless communication systems (4G and 5G) use a physical layer (PHY)
based on multicarrier modulations for data transmission using high bandwidth. This type of modulations
has shown to provide high spectral efficiency while allowing low complexity radio channel equalization.
These systems use OFDMA as a mechanism for distributing the available radio resources among
different users. This allocation is done by assigning a subset of subcarriers to each user in a given instant
of time. This provides great flexibility to the system that allows it to adapt to both the quality of service
requirements of users and the radio channel state.
The media access layer (MAC) of these systems is in charge of configuring the multiple OFDMA
PHY layer parameters, in addition to managing the data flows of each user, transforming the higher layer
packets into PHY layer packets.
This work studies the design and implementation of MAC and PHY layers of 4G communication
systems as well as their applicability in rail transport systems.
On the one hand, the design and implementation in real time of the WiMAX standard is addressed.
The required mechanisms to establish bidirectional communications between a base station and several
mobile devices are also evaluated. Moreover, a MAC layer and PHY layer implementation is
presented, using a hardware architecture based in DSPs and FPGAs. Since this architecture has limited
computational resources, the requirements of each processing block of the system are also studied in
order to guarantee the real time operation of the complete system.
On the other hand, the applicability of 4G systems to public transportation systems is also studied.
Communications and signaling systems are a vital part of rail and metro transport systems. The
wireless communications used by these systems must be robust and provide high reliability to enable
the supervision, control and safety of rail traffic.
To carry out this feasibility assessment, LTE communications network simulations are performed in
rail transport environments to verify that reliability and safety requirements are met. Several simulations
are carried out in order to evaluate the system performance and select the most appropriate system
configuration in each case. Simulations of Wi-Fi based networks are also carried out, since it is the
most used solution in subways, to compare the results with those obtained for LTE.
To perform the simulations correctly, appropriate radio propagation models must be used. Both
deterministic models and models based on the results of measurement campaigns in these scenarios are
used in the simulations.
The simulations use the different information flows present in the railway transportation systems to
verify that its quality of service requirements are met. For example, critical flows for railway control,
such as the European Train Control System (ETCS) or Communication-Based Train Control (CBTC),
require high reliability and low delay communications to ensure the proper functioning of the system
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
Pattern Diversity Characterization of Reconfigurable Antenna Arrays for Next Generation Wireless Systems
The use of multi-antenna technology in wireless radio communications has attracted tremendous attention due to its potential to increase data rates without requiring additional bandwidth and transmission power. This has been driven by the burgeoning demand for high data rates and the need for instantaneous and ubiquitous access to information. It is therefore no surprise that current and future generation wireless standards such as LTE and WiMAX have adopted the use of adaptive multi-antenna systems also known as adaptive Multiple Input and Multiple Output (MIMO) as their de facto transmission technology. In this thesis work, we focus on the design of a smart wireless antenna system, and the study of relevant techniques that enable us to reap the benefits of their deployment in small wireless devices with MIMO capability. Specifically, we employ a new class of adaptive antenna systems known as Reconfigurable Antenna Systems (RAS) for portable devices. These antennas are capable of dynamically changing their electrical and radiation characteristics to suit the conditions of the wireless channel. The changing radiation patterns lead to pattern diversity gains that improve system performance. This is in contrast to conventional non-reconfigurable arrays which depend on signal processing techniques such as antenna grouping and beamforming to achieve performance gains. However, despite the demonstrable system-level performance benefits of RAS in adaptive MIMO, few of these antennas have been adopted and integrated in state-of-the-art wireless standards. Their usage has been partly inhibited by the prohibitive costs of implementation and operation in a real wireless infrastructure. As part of this thesis research effort we attempt to integrate these new antennas into a cost-effective real wireless MIMO testbed for use in current generation technologies. The solution integration is carried-out through the use of readily available software-defined radio frameworks. We first design, analyze and characterize the pattern diversity in RAS antenna arrays that resonate at frequencies suitable for 4G applications. We then study the benefits of pattern diversity obtained from RAS arrays over conventional space diversity approaches such as antenna grouping and beamforming. This dissertation also presents low-complexity adaptive physical layer models and algorithms to exploit the benefits of RAS array integration in MIMO wireless systems. We implement these algorithms in software-defined radio frameworks, experimentally test, and benchmark them against other established approaches in literature. And finally, integrate and test these RAS array design prototypes as part of the MIMO wireless system that leverages a state-of-the-art wireless base station and mobile terminals.Ph.D., Electrical Engineering -- Drexel University, 201
Design and evaluation of OFDM radio interfaces for high mobility communications
[Resumo]
Nas dúas últimas décadas, as modulacións multiportadora emerxeron como una solución de
baixa complexidade para combatir os efectos do multitraxecto en comuniacións sen fíos. Entre
elas, Orthogonal Frequency Division Multiplexing (OFOM) é posiblemente o esquema de
modulación máis estudado, e tamén amplamente adoptado como alicerce de estándares da
industria como WiMAX ou LTE. Sen embargo, OFDM é sensible a canles que varian ca tempo,
unha característica dos escenarios con mobilidade, debido á aparición da interferencia entre
portadoras (ICI).
A implementación de equipamento hardware para o usuario final faise normalmente en
chips dedicados, afnda que entornos de investigación, prefírense solucións máis flexibles. Unha
aproximación popular é a coñecida como Software Defined Radio (SOR), onde os algoritmos de
procesado de sinal se implementan en hardware reconfigurable como Digital Signal Processors
(OSPs) e Field Programmable Gate Arrays (FPGAs).
O obxectivo deste traballo é dobre. Por un lado, definir unha arquitectura para
implementacións de tempo real de capas físicas basadas en OFDM usando como referencia
O estándar WiMAX, probada Dunha plataforma composta por OSPs e FPGAs. Por outra banda,
estudar os efectos da selectividade en tempo no sinal OFDM, definindo métodos de estimación
de canle que teñen en conta a ICI, e evaluándoos tanto en simulación como con medidas
experimentais. Seguíronse dúas aproximacións para caracterizar o comportamento de formas de
onda OFDM baixo condicións de mobilidade, unha basada nun emulador de canle que traballa
en tempo real, e outra en inducir grandes ensanchamentos Doppler no sinal mediante a extensión
da duración do símbolo OFOM.[Resumen]
En las dos últimas décadas, las modulaciones multiportadora han emergido como una
solución de baja complejidad para combatir los efectos del multitrayecto en comunicaciones
iDalámbricas. Entre ellas, Orthogonal Frequency Division Mulriplexing (OFDM) es
posiblemente el esquema de modulación más estudiado, y también ampliamente adoptado
como fundamento de estándares de la industria como WiMAX o LTE. Sin embargo, OFDM es
sensible a canales que varían con el tiempo, una característica de los escenarios coo movilidad,
debido a la aparicióo de la interferencia entre portadoras (ICI).
La implementación de equipamiento hardware para el usuario final se hace normalmente en
chips dedicados, aunque eo entornos de investigación, son preferibles soluciones más Hexibles.
Una aproximación popular es la conocida como Software Defined Radio (SDR), donde los
algOritmos de procesado de señal se implementan en hardware reconfigurable como Digital
Signa! Processors (DSPs) y Field Programmable Gate AIrays (FPGAs).
El objetivo de este trabajo es doble. Por un lado. definir una arquitectura para
implementaciones de tiempo real de capas ¡lSicas basadas en OFDM usando como referencia
el estándar WiMAX, probada en una plataforma compuesta por DSPs y FPGAs. Por otro
lado, estudiar los efectos de la selectividad en tiempo en la señal OFDM, definiendo métodos
de estimacióo de canal que tengan eo cueota la ICI, y evaluándolos tanto en simulación
como con medidas experimenta1es. Se han seguido dos aproximaciones para caracterizar el
comportamiento de formas de onda OFDM bajo condiciones de mobilidad, una basada en
un emulador de canal que trabaja en tiempo real. y otra en inducir grandes ensanchamientos
Doppler en la señal mediante la extensión de la duración del símbolo OFDM.[Abstract]
In Ihe last two decades, multicarrier modulations have emerged as a low complexity solulion
to combal the effects of Ihe multipalh in wireless communicalions. Among Ihem, Orthogonal
Frequency Division Mulliplexing (OFOM) is possibly Ihe mosl sludied modulation scheme,
and has a1so been widely adopted as Ihe foundation of induslry standards such as WiMAX or
LTE. However, OFOM is sensitive lo time selective channels, which are featured in mobility
scenarlos, due lO Ihe appearance of Inler-Carrier Interference (ICI).
Implemenlation of hardware equipmenl for Ihe end user is usually implemenled in dedicaled
chips, bul in researeh environments, more flexible solutions are preferred. One popular
approach is the so ealled Software Defined Radio (SOR), where the signal processing
a1gorithms are implemented in reconfigurable hardware sueh as Digital Signal Processors
(DSPs) and Field Prograrnmable Gate Arrays (FPGAs).
The aim of Ibis work is two-fold. On the one hand, to define an architeclure for Ihe
implementation of real-time OFOM-based physical layers, using as a reference Ihe WiMAX
standard, and it is tested on a platform composed by DSPs and FPGAs. On the olher hand,
to study Ihe effeets of !he time seleetivity on !he OFOM signal, defining channel estimation
me!hods aware of !he ICI, and ils evaluation bo!h in simulation as well as experimental
measuremenls. Two approaches have been followed to assess the behavior of OFOM waveforms
under mobility conditions, one based on a real-time channel emulator, and the other on inducing
large Doppler spreads in !he signal by extending the duration of Ihe OFDM symbols
Implementação e avaliação no system generator de um sistema cooperativo para os futuros sistemas 5G
With the arrival of 5G it is expected the proliferation of services in the
different fields such as healthcare, utility applications, industrial automation,
4K streaming, that the former networks can not provide. Additionally,
the total number of wireless communication devices will escalate in such
a manner that the already scarce available frequency bandwidth won’t be
enough to pack the intended objectives. Cisco’s Annual Internet Report from
2018 predicts that by 2023 there will be nearly 30 billion devices capable of
wireless communication. Due to the exponential expiation of both services
and devices, the challenges upon both network data capacity and efficient
radio resourse use will be greater than ever, thus the urgency for solutions
is grand.
Both the capacity for wireless communications and spectral efficiency are
related to cell size and its users proximity to the access point. Thus,
shortening the distance between the transmitter and the receiver improves
both aspects of the network. This concept is what motivates the
implementation of heterogeneous networks, HetNets, that are composed
of many different small-cells, SCs, overlaid across the same coexisting
area of a conventional macro-cell, shortening the distance between the
cell users and its access point transceivers, granting a better coverage and
higher data rates. However, the HetNets potential does not come without
any challenges, as these networks suffer considerably from communication
interference between cells.
Although some interference management algorithms that allow coexistence
between cells have been proposed in recent years, most of them were
evaluated by software simulations and not implemented in real-time
platforms. Therefore, this master thesis aims to give the first step on the
implementation and evaluation of an interference mitigation technique in
hardware. Specifically, it is assumed a downlink scenario composed by a
macro-cell base station, a macro-cell primary user and a small cell user,
with the aim of implementing an algorithm that eliminates the downlink
interference that the base station may cause to the secondary users. The
study was carried out using the System Generator DSP tool, which is a tool
that generates code for hardware from schematics created in it. This tool
also offers a wide range of blocks that help the creation, and fundamentally,
the simulation and study of the system to be implemented, before being
translated into hardware. The results obtained in this work are a faithful
representation of the behavior of the implemented system, which can be
used for a future application for FPGA.Com a chegada do 5G, espera-se a proliferação de serviços nas mais diversas
áreas tal como assistência médica, automação industrial, transmissão em
4k, que não eram possíveis nas redes das gerações anteriores. Além deste
fenómeno, o número total de dispositivos capazes de conexões wireless
aumentará de tal maneira que a escassa largura de banda disponível não
será suficiente para abranger os objetivos pretendidos. O Relatório Anual
de 2018 sobre a Internet da Cisco prevê que até 2023 haverá quase 30
bilhões de dispositivos capazes de comunicação sem fio. Devido ao aumento
exponencial de serviços e dispositivos, os desafios sobre a capacidade de
dados da rede e o udo eficiente dos recursos de rádio serão maiores que
nunca. Por estes motivos, a necessidade de soluções para estas lacunas é
enorme.
Tanto a capacidade da rede e o uso eficiente do espectro de frequências
estão relacionados ao tamanho da célula e à proximidade dos usuários com
o ponto de acesso da célula. Ao encurtar a distância entre o transmissor e
o recetor ocorre um melhoramento destes dois aspetos da rede. Este é o
principal conceito na implementação de redes heterogéneas, HetNets, que
são compostas por diversas células pequenas que coexistem na área de uma
macro célula convencional, diminuído a distância entre os utilizadores da
célula e os pontos de acesso, garantindo uma melhor cobertura e taxa de
dados mais elevadas. No entanto, o potencial das HatNets não vem sem
nenhum custo, pois estas redes sofrem consideravelmente de interferência
entre as células.
Embora nos últimos anos foram propostos alguns algoritmos que permitem
a coexistência das células, a maioria destes foi só testado em simulações
de software e não em plataformas em tempo real. Por esse motivo, esta
dissertação de mestrado visa dar o primeiro passo na implementação e
a avaliação de uma técnica de mitigação de interferência em hardware.
Mais especificamente no cenário de downlink entre uma estação base de
uma macro célula, um utilizador primário da macro célula e um utilizador
secundário de uma célula pequena, com o principal objetivo de cancelar a
interferência que a estação base possa fazer ao utilizador secundário. O
estudo foi realizado utilizando a ferramenta System Generator DSP, que é
uma ferramenta que gera código para hardware a partir de esquemáticos
criados na mesma. Esta ferramenta também oferece uma vasta gama de
blocos que ajudam a criação, e fundamentalmente, a simulação e o estudo do
sistema a implementar antes de ser traduzido para hardware. Os resultados
obtidos neste trabalho são uma fiel representação do comportamento do
sistema implementado. O quais podem ser utilizados para uma futura
aplicação para FPGA.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
Cooperative diversity schemes for wireless communication systems
Mestrado em Engenharia Electrónica e TelecomunicaçõesA presente dissertação insere-se na área das comunicações sem fios, ou mais especificamente na temática da diversidade cooperativa.
Neste trabalho é feito o estudo, implementação e avaliação do desempenho de esquemas de diversidade cooperativa de baixa complexidade para sistemas de comunicação móvel. Estes esquemas são mapeados em modelos de simulação baseados em OFDMA e são completamente simulados em CoCentric System Studio.
Os resultados obtidos com os modelos desenvolvidos mostram que os esquemas
de diversidade cooperativa atenuam os efeitos do desvanecimento induzido pela propagação multipercurso, aumentando desta forma a capacidade e cobertura dos sistemas wireless. Os ganhos são particularmente altos quando as perdas de percurso são consideráveis, como é o caso das zonas urbanas densas.
ABSTRACT: This dissertation is inserted into the wireless communication, or more specifically, into the cooperative diversity field.
within this thesis, the performance of low-complexity cooperative diversity schemes projected for mobile communication systems are studied, implemented and evaluated.
These schemes are mapped into simulation models based on OFDMA and are fully simulated in the CoCentric System Studio environment. The obtained results show that the proposed cooperative schemes for the uplink communication
mitigate fading induced by multipath propagation, thereby increasing the capacity and coverage of wireless systems. Cooperation gains are particularly high when multipath losses are considerable, as is the case for dense urban regions
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