10 research outputs found
Performance Analysis of CP-Based and CAZAC Training Sequence-Based Synchronization in OFDM System
Orthogonal Frequency Division Multiplexing (OFDM) is a popular wireless data transmission scheme. However, its synchronization is still being a major problem when it is applied in real hardware. Cyclic Prefix (CP) based synchronization is one of the solutions in this problem, but CP has high crest factor. In the other hand, CAZAC sequence is another solution with lower crest factor but the higher complexity and also CAZAC has potential in security and channel estimation implementation. The performance between CP and CAZAC sequence based synchronization in OFDM system is analyzed in this paper. The real hardware, Universal Software Rado Peripheral (USRP), is used to prove the analysis. The CAZAC sequence has 10% performance increased in frequency offset than CP based synchronization
A Novel estimation and Correction of Channel errors in LTE SYSTEMS
The increase in the number of RF devices and the requirement for large data rates places major role in increasing demand on bandwidth. This necessitates the need for RF communication systems with increased throughput and capacity. MIMO-OFDM is one way to meet this basic requirement. OFDM is used in many (WCD) wireless communication devices and offers high spectral efficiency and resilience to multipath channel effects. Though OFDM is very sensitive to synchronization errors, it makes the task of channel equalization simple. MIMO utilize the multiple antennas to increase throughput without increasing transmitter power or bandwidth. This project presents an introduction to the (MPC) multipath fading channel and describes an appropriate channel model. Many modulation schemes are presented (i.e. BPSK, QPSK, QAM) that are often used in Conjunction with OFDM. Mathematical modeling and analysis of OFDM are given along with a discrete implementation common to modern RF communication systems. Synchronization errors are modeled mathematically and simulated, as well as techniques to estimate and correct those errors at the receiver accurately
Spectrally Efficient Waveforms for the Return Link in Satellite Communication Systems
In this paper, we study the applicability of terrestrial mobile waveforms in the return link of a high throughput satellite (HTS) communication system. These include orthogonal frequency division multiple access (OFDMA), single-carrier frequency division multiple access (SC-FDMA) and filter bank multi-carrier (FBMC). Key solutions to the challenges in a geostationary orbit (GEO) satellite channel, such as synchronization and non-linear distortion, are presented. A global-positioning-system-(GPS)-based approach for synchronization acquisition is proposed, while suitable algorithms are studied for timing/frequency offset estimation and synchronization tracking. The spectral and power efficiencies of the schemes are optimized by means of an intermodulation interference (IMI) cancelling receiver, and these are compared to state-of-the-art time division multiple access (TDMA). Finally, end-to-end simulations validate the system performance
SYNCHRONIZATION AND RESOURCE ALLOCATION IN DOWNLINK OFDM SYSTEMS
The next generation (4G) wireless systems are expected to provide
universal personal and multimedia communications with seamless connection
and very high rate transmissions and without regard to the users’ mobility and
location. OFDM technique is recognized as one of the leading candidates to
provide the wireless signalling for 4G systems. The major challenges in
downlink multiuser OFDM based 4G systems include the wireless channel, the
synchronization and radio resource management. Thus algorithms are required
to achieve accurate timing and frequency offset estimation and the efficient
utilization of radio resources such as subcarrier, bit and power allocation.
The objectives of the thesis are of two fields. Firstly, we presented the
frequency offset estimation algorithms for OFDM systems. Building our work
upon the classic single user OFDM architecture, we proposed two FFT-based
frequency offset estimation algorithms with low computational complexity.
The computer simulation results and comparisons show that the proposed
algorithms provide smaller error variance than previous well-known algorithm.
Secondly, we presented the resource allocation algorithms for OFDM
systems. Building our work upon the downlink multiuser OFDM architecture,
we aimed to minimize the total transmit power by exploiting the system
diversity through the management of subcarrier allocation, adaptive
modulation and power allocation. Particularly, we focused on the dynamic
resource allocation algorithms for multiuser OFDM system and multiuser
MIMO-OFDM system. For the multiuser OFDM system, we proposed a lowiv
complexity channel gain difference based subcarrier allocation algorithm. For
the multiuser MIMO-OFDM system, we proposed a unit-power based
subcarrier allocation algorithm. These proposed algorithms are all combined
with the optimal bit allocation algorithm to achieve the minimal total transmit
power. The numerical results and comparisons with various conventional nonadaptive
and adaptive algorithmic approaches are provided to show that the
proposed resource allocation algorithms improve the system efficiencies and
performance given that the Quality of Service (QoS) for each user is
guaranteed.
The simulation work of this project is based on hand written codes in the
platform of the MATLAB R2007b
Underwater 3D positioning on smart devices
The emergence of water-proof mobile and wearable devices (e.g., Garmin
Descent and Apple Watch Ultra) designed for underwater activities like
professional scuba diving, opens up opportunities for underwater networking and
localization capabilities on these devices. Here, we present the first
underwater acoustic positioning system for smart devices. Unlike conventional
systems that use floating buoys as anchors at known locations, we design a
system where a dive leader can compute the relative positions of all other
divers, without any external infrastructure. Our intuition is that in a
well-connected network of devices, if we compute the pairwise distances, we can
determine the shape of the network topology. By incorporating orientation
information about a single diver who is in the visual range of the leader
device, we can then estimate the positions of all the remaining divers, even if
they are not within sight. We address various practical problems including
detecting erroneous distance estimates, addressing rotational and flipping
ambiguities as well as designing a distributed timestamp protocol that scales
linearly with the number of devices. Our evaluations show that our distributed
system running on underwater deployments of 4-5 commodity smart devices can
perform pairwise ranging and localization with median errors of 0.5-0.9 m and
0.9-1.6
MIMO Spread Spectrum
[ES] Esta tesis aborda el análisis de la estimación del canal en sistemas MIMO (Multiple-Input MultipleOutput) con un canal de desvanecimiento de Rayleigh selectivo en frecuencia, bajo la condición de haber empleado técnicas de Espectro Ensanchado de Secuencia Directa y haber mantenido la ortogonalidad de los códigos mediante el uso de secuencias Zadoff-Chu, asà como el empleo de Prefijos CÃclicos.[EN] This thesis deals with the analysis of channel estimation in MIMO (Multiple-Input MultipleOutput) systems with a Frequency Selective Rayleigh Fading Channel, under the condition of having employed Direct Sequence Spread Spectrum techniques and have maintained the orthogonality of the codes by using Zadoff-Chu sequences as well as employing Cyclic Prefix.Ballester Palacios, P. (2022). MIMO Spread Spectrum. Universitat Politècnica de València. http://hdl.handle.net/10251/18781
Implementação de um sistema de comunicações móveis para o Uplink
Mestrado em Engenharia Electrónica e TelecomunicaçõesÉ evidente que actualmente cada vez mais a internet móvel está presente na
vida das sociedades. Hoje em dia é relativamente fácil estar ligado à internet
sempre que se quiser, independentemente do lugar onde se encontra
(conceito: anytime and anywhere). Desta forma existe um número crescente
de utilizadores que acedem a serviços e aplicações interactivas a partir dos
seus terminais móveis. Há, portanto, uma necessidade de adaptar o mundo
das telecomunicações a esta nova realidade, para isso é necessário
implementar novas arquitecturas que sejam capazes de fornecer maior largura
de banda e reduzir os atrasos das comunicações, maximizando a utilização
dos recursos disponÃveis do meio/rede e melhorando assim a experiência do
utilizador final.
O LTE representa uma das tecnologias mais avançadas e de maior relevância
para o acesso sem fios em banda larga de redes celulares. OFDM é a
tecnologia base que está por traz da técnica de modulação, bem como as
tecnologias adjacentes, OFDMA e SC-FDMA, usadas especificamente no LTE
para a comunicação de dados descendente (downlink) ou ascendente (uplink),
respectivamente. A implementação de múltiplas antenas em ambos os
terminais, potenciam ainda mais o aumento da eficiência espectral do meio
rádio permitindo atingir grandes taxas de transmissão de dados.
Nesta dissertação é feito o estudo, implementação e avaliação do
desempenho da camada fÃsica (camada 1 do modelo OSI) do LTE, no entanto
o foco será a comunicação de dados ascendente e a respectiva técnica de
modelação, SC-FDMA. Foi implementada uma plataforma de simulação
baseada nas especificações do LTE UL onde foram considerandos diferentes
esquemas de antenas. Particularmente para o esquema MIMO, usou-se a
técnica de codificação no espaço-frequência proposta por Alamouti. Foram
também implementados vários equalizadores.
Os resultados provenientes da simulação demonstram tanto a eficiência dos
diversos modos de operação em termos da taxa de erro, como o excelente
funcionamento de processos de mapeamento e equalização, que visam
melhorar a taxa de recepção de dados.It is clear that mobile Internet is present in the life of societies. Nowadays it is
relatively easy to be connected to the internet whenever you want, no matter
where you are (concept: anytime and anywhere). Thus, there are a growing
number of users accessing interactive services and applications from their
handsets. Therefore, there is a need to adapt the world of telecommunications
to this new reality, for that it is necessary to implement new architectures that
are able to provide higher bandwidth and reduce communication delays,
maximizing use of available resources in the medium/network and thereby
improving end-user experience.
LTE represents one of the most advanced architectures and most relevant to
wireless broadband cellular networks. OFDM is the technology that is behind
the modulation technique and the underlying technologies, OFDMA and SCFDMA,
used specifically in LTE for data communication downward (downlink)
or upward (uplink), respectively. The implementation of multiple antennas at
both ends further potentiate the increase of spectral efficiency allowing to
achieve high rates of data transmission.
In this dissertation is done the study, implementation and performance
evaluation of the physical layer (OSI Layer 1) of the LTE, but the focus will be
communication and its upstream data modeling technique, SC-FDMA. We
implemented a simulation platform based on LTE UL specifications where were
considered different antenna schemes. Particularly for the MIMO scheme, we
used the technique of space-frequency coding proposed by Alamouti. We also
implemented several equalizers.
The results from the simulation demonstrate both the efficiency of different
modes of operation in terms of error rate, as the excellent operation of mapping
processes and equalization, designed to improve the rate of receiving data
Modelaçcão comportamental da camada fÃsica NB-IoT - Uplink
Mestrado em Engenharia Eletrónica e TelecomunicaçõesA Internet das Coisas (IoT) consiste numa rede sem fios de sensores/atuadores
ligados entre si e que têm a capacidade de recolher dados. Devido
ao crescimento rápido do mercado IoT, as redes de longa distância e baixa
potência (LPWAN) tornaram-se populares. O NarrowBand-IoT (NB-IoT),
desenvolvido pela 3rd Generation Partnership Project (3GPP), é um desses
protocolos.
O principal objectivo desta dissertação é a implementação de uma simulação
comportamental em MATLAB do NB-IoT no uplink, que será disponibilizada
abertamente. Esta será focada, primariamente, na camada fÃsica e nas
suas respetivas funcionalidades, nomeadamente turbo coding, modulação
SC-FDMA, modelos de simulação de canal, desmodulação SC-FDMA, estimação de canal, equalizador e turbo decoding. A estimação de canal é
feita usando sÃmbolos piloto previamente conhecidos. Os modelos de canal
utilizados são baseados nas especificações oficiais da 3GPP.
A taxa de bits errados (BER) é calculada e usada de forma a avaliar a performance
do turbo encoder e do equalizador zero forcing (ZF). Serve também
como comparação quando a implementação usa esquemas de modulação
diferentes (Binary Phase-Shift Keying (BPSK) e Quadrature Phase-Shift
Keying (QPSK)). Além disso, os sinais gerados em MATLAB são transmitidos
usando como front-end de radio-frequência (RF) uma Universal
Software Radio Peripheral (USRP). Posteriormente, são recebidos, desmodulados
e descodificados. Finalmente, é obtida a constelação do sinal, a BER
é calculada e os resultados são analisados.The Internet of Things (IoT) refers to a wireless network of interconnected
sensors/actuators with data-collecting technologies. Low Power Wide Area
Networks (LPWAN) have become popular due to the rapid growth of the
IoT market. Narrowband-IoT (NB-IoT), developed by 3rd Generation Partnership
Project (3GPP), is one of these protocols.
The main objective of this thesis is the implementation of an open-source uplink
behavioral simulator based on MATLAB. Its focus is primarily on Layer 1
(physical layer) relevant functionalities, namely turbo coding, Single-Carrier
Frequency-Division Multiple Access (SC-FDMA) modulation, channel modeling,
SC-FDMA demodulation, channel estimation, equalization and turbo
decoding. Channel estimation is performed using known pilot symbols. The
used channel models are based on the 3GPP o cial release specs.
The Bit Error Rate (BER) is calculated in order to evaluate the turbo encoder
and the Zero Forcing (ZF) equalizer performance, and to compare
Binary Phase-Shift Keying (BPSK) and Quadrature Phase-Shift Keying
(QPSK) implementations. Furthermore, the MATLAB generated signal is
transmitted using a radio-frequency (RF) front-end consisting of an Universal
Software Radio Peripheral (USRP). Afterwards, the signal is received,
demodulated and decoded. A constellation is obtained, the BER is calculated
and the results are analyzed
Algoritmos en transmisión y recepción para OFDM en entornos multi-usuario
Desde su incursión en la vida de los ciudadanos de forma cotidiana, las comunicaciones móviles han ido adquiriendo cada vez más protagonismo. Lo que hace unos años era un elemento de lujo o causa de envidias, hoy es algo tan habitual como coger el autobús. Este auge en las comunicaciones móviles ha llevado consigo un aumento del número de usuarios de estos servicios, asà como una mayor exigencia por parte de éstos en cuanto a velocidad de transmisión, seguridad, servicios, calidad ... Por este motivo, se han ido introduciendo nuevas redes, asà como mejoras en las ya existentes. Actualmente estamos asistiendo al inicio de la implantación de las redes denominadas de tercera generación (3G). No obstante, estas redes 3G fueron de nidas a mediados de los años 90. En la actualidad nos encontramos en la de nición de lo que será la cuarta generación móvil (4G) a la que probablemente preceda una intermedia, tal vez Super 3G. Muchas son las tecnologÃas candidatas para esta Super 3G o para la 4G, pero es OFDM (Multiplexación por División en Frecuencias Ortogonales - Orthogonal Frequency Division Multiplexing) una de las más prometedoras para terminar siendo la tecnologÃa elegida, debido principalmente a la robustez que ofrece frente al multi-trayecto, la flexibilidad que proporciona por el hecho de dividir el ancho de banda en sub-portadoras que pueden ser moduladas independientemente para adaptarse a las condiciones especÃficas de los canales móviles y al aprovechamiento de la diversidad multi-usuario cuando se combina en OFDMA (Acceso múltiple por división en frecuencias ortogonales - Orthogonal Frequency Division Multiple Access). Sin embargo, para que estos sistemas OFDMA sean una realidad en redes futuras como la Super 3G o la 4G, es preciso reducir la complejidad que ellos conllevan, en aspectos como la sincronización multi-usuario o la implementación de la modulación adaptativa. Esta Tesis está enfocada a reducir la complejidad de implementación para que la tecnologÃa OFDMA pueda ser un hecho en las futuras redes inalámbricas. La sincronización en sistemas OFDMA, principalmente en escenarios ad-hoc plantea un reto importante a la hora de implementarla en este tipo de redes. Dado que existe una literatura extensa dedicada a resolver el problema de la sincronización en entornos OFDM mono-usuario, en esta Tesis se propone un procedimiento para reducir el problema de la sincronización multiusuario al caso mono-usuario, lo que permite la re-utilización de todas las técnicas propuestas en la literatura. Además de las buenas prestaciones incluso en situaciones de saturación de la red, permite un ahorro de la energÃa necesaria para la realización de las tareas de sincronización. Asimismo, a la vez que se resuelve la sincronización multi-usuario, también en esta Tesis se aporta un algoritmo para realizar el seguimiento de la desviación de frecuencia en sistemas tanto OFDM como OFDMA, de una forma sencilla y eficiente. Este algoritmo utiliza las sub-portadoras piloto de los sÃmbolos, y ofrece unas prestaciones razonables, incluso cuando el número de estas sub-portadoras piloto es reducido. La modulación adaptativa u otras técnicas avanzadas de comunicaciones como MIMO (Multiple Input Multiple Output) o el conformado de haz (beamforming), que se hacen más atractivas cuando se combinan con OFDM u OFDMA, requieren de cierta realimentación hacia el transmisor por parte del receptor, además de un conocimiento del canal bastante preciso. En esta Tesis se aportan algoritmos para la compresión de esta información (que puede ser muy elevada dependiendo de la granularidad de la adaptación y la variabilidad del canal), lo que permite un mejor aprovechamiento de los recursos radio, y simpli ca la implementación de este tipo de sistemas. Se consiguen reducciones superiores a cuatro veces la tasa original, lo que implica grandes ventajas en todos los sentidos. Además, se realiza un estudio teórico sobre cómo afectan los errores en la estimación de canal en la capacidad del sistema, obteniéndose dos cotas numéricas para ésta. Gracias a estas cotas se puede concluir que las técnicas actuales de estimación de canal son su cientemente buenas como para que las pérdidas producidas por los errores en esta estimación no sean muy significativas; No obstante, estas pérdidas aumentan a medida que se incrementa la relación señal a ruido, y, por tanto, es conveniente seguir mejorando la estimación de canal si se pretende que estos sistemas trabajen a altas relaciones señal a ruido. Por último, destacar que las simulaciones llevadas a cabo para examinar las prestaciones de los algoritmos desarrollados han proporcionado datos prácticos que ayudarán al diseño e implementación de futuras redes móviles 4G.Nowadays mobile communications are common in our society. In less than two decades they
have changed the way people understand personal communications. This interest is still growing
and makes users (every day larger in number) ask for more and more services, speed, security
and quality, at least comparable to the wired technologies.
For this reason, new networks have been introduced in the scene, as well as improvements in
the already existing ones. At the moment we are witnessing the beginning of the deployment of
the so-called third generation networks (3G). However, these 3G networks were defined in the
middle of years 90. At the present time we are in the definition of what will be the fourth mobile
generation, which is called the 4G and probably an intermediate stage as Super 3G could be
defined first.
Many different technologies are in consideration, but OFDM (Orthogonal Frequency
Multiplexing Division) is one of most promising candidates to end up becoming the technology
to be used, due mainly to the robustness that it others to the multi-path channel, the flexibility
that it provides by the fact that it divides the bandwidth into sub-carriers which can be
modulated independently to adapt the signal to the specific channel conditions and to the
advantage of the multi-user diversity when it is used to multiplex several users in the form of
OFDMA (Orthogonal Frequency Division Multiple Access).
Nevertheless, in order for these OFDMA systems to be a reality in future networks as Super
3G or 4G, the reduction in complexity has to be considered, in aspects such as the multi-user
synchronization or the implementation of the Adaptive Modulation. This doctoral Thesis is
focused on reducing the implementation complexity in both multi-user synchronization and
Adaptive Modulation so that OFDMA technology can be a fact in the near future radio networks.
The synchronization in OFDMA systems, specially in ad-hoc scenarios, raises an important
challenge at the time of implementing this technology. Since an extensive literature is devoted to
solve the problem of the synchronization in single-user OFDM systems, in this Thesis we have
designed and proposed a procedure to reduce the multi-user synchronization problem to the
single-user case, and therefore it allows the reuse of all the already proposed techniques in the
literature. The procedure exhibits a good performance even in network saturation situations, and
in addition it does not incur in a high power consumption when performing the synchronization
tasks. Besides, solving the multi-user synchronization problem, the Thesis also proposes an
algorithm for frequency offset tracking in an efficient and simple way, for both OFDM and
OFDMA systems. This algorithm uses the pilot sub-carriers scattered in each OFDM symbol,
and o ers reasonable performance, even when the number of these pilot sub-carriers is small.
Adaptive Modulation and other advanced techniques as MIMO (Multiple Input Multiple
Output) or beamforming become more attractive when they are combined with OFDM or
OFDMA. However they require certain feedback information from receiver to the transmitter,
and in addition, a quite precise knowledge about channel conditions. In this Thesis several
algorithms for compressing the feedback information have been developed. This feedback
information can be very highly demanding (depending on the granularity of the adaptation
and the variability of the channel), and therefore this compression allows a better use of
the resources, and simplifies the implementation of this kind of systems. Reductions of more
than four times the original flow are obtained, which implies great advantages. In addition, a
theoretical study is made on how errors in channel estimation affect the channel capacity, and
several upper-bounds (one of them very tight) for this effect are obtained. One of the conclusions
is that the actual state of the art in channel estimation techniques is good enough to be used
without too much loss; However, the loss increases as the signal to noise ratio increases, and
therefore, it is suggested to continue improving channel estimation algorithms for improving
performance in high signal to noise ratio scenarios.
Finally, thanks to simulations and designs carried out in order to examine the performance
of the developed algorithms, some practical data are provided that will help in the future design
of new mobile networks as 4G