414 research outputs found
Frequency-domain transmit processing for MIMO SC-FDMA in wideband propagation channels
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Técnicas de equalização para MIMO massivo com amplificação não linear
The dawn of the new generation of mobile communications and the trafic
explosion that derives from its implementation pose great challenge. The
milimeter wave band and the use of massive number of antennas are technologies
which, when combined, allow the transmission of high data rate,
functioning in zones of the electromagnetic spectrum that are less explored
and with capability of allocation of dozens of GHz of bandwidth.
In this dissertation we consider a massive MIMO millimeter wave system
employing a hybrid architecture, i.e., the number of transmit and receive
antennas are lower than the number of radio frequency chains. As consequence,
the precoder and equalizers should be designed in both digital and
analog domains. In the literature, most of the proposed hybrid beamforming
schemes were evaluated without considering the effects of nonlinear amplifications. However, these systems face non-avoidable nonlinear effects due
to power amplifiers functioning in nonlinear regions. The strong nonlinear
effects throughout the transmission chain will have a negative impact on the
overall system performance and thus its study and the design of equalizers
that take into account these effects are of paramount importance.
This dissertation proposes a hybrid iterative equalizer for massive MIMO millimeter
wave SC-FDMA systems. The user terminals have low complexity,
just equipped with analog precoders based on average angle of departure,
each with a single radio frequency chain. At the base station it is designed
an hybrid analog-digital iterative equalizer with fully connected architecture
in order to eliminate both the multi-user interference and the nonlinear distortion
caused by signal amplification during the transmission. The equalizer
is optimized by minimizing the bit error rate, which is equivalent to minimize
the mean square error rate. The impact of the saturation threshold of the
amplifiers in the system performance is analysed, and it is demonstrated that
the iterative process can efficiently remove the multi-user interference and
the distortion, improving the overall system performance.O surgimento de uma nova geração de comunicações móveis e a explosão
de tráfego que advém da sua implementação apresenta grandes desafios. A
banda de ondas milimétricas e o uso massivo de antenas são tecnologias que,
combinadas, permitem atingir elevadas taxas de transmissão, funcionando
em zonas do espectro electromagnético menos exploradas e com capacidade
de alocação de dezenas de GHz para largura de banda.
Nesta dissertação foi considerado um sistema de MIMO massivo de ondas
milimétricas usando uma arquitectura híbrida, i.e., o número de antenas para
transmissão e recepção é menor que o número de cadeias de radiofrequência.
Consequentemente, o pré-codificador e equalizadores devem ser projectados
nos domínios digital e analógico. Na literatura, a maioria dos esquemas
híbridos de beamforming são avaliados sem ter em conta os efeitos de não linearidade
da amplificação do sinal. No entanto, estes sistemas sofrem
inevitavelmente de efeitos não lineares devido aos amplificadores de potência
operarem em regiões não lineares. Os fortes efeitos das não-linearidades ao
longo da cadeia de transmissão têm um efeito nefasto no desempenho do
sistema e portanto o seu estudo e projecto de equalizadores que tenham em
conta estes efeitos são de extrema importância.
Esta dissertação propõe um equalizador híbrido para sistemas baseados em
ondas milimétricas para MIMO massivo com modulação SC-FDMA. Os terminais
de utilizador possuem baixa complexidade, equipados apenas com
pré-codificadores analógicos baseados no ângulo médio de partida, cada um
com uma única cadeia de radiofrequência. Na estação base é projectado
um equalizador iterativo híbrido analógico-digital com arquitectura completamente
conectada de modo a eliminar a interferencia multi-utilizador e a
distorção causada pela amplificação do sinal aquando da transmissão. O
equalizador é optimizado minimizando a taxa de erro de bit, o que é equivalente
a minimizar a taxa de erro quadrático médio. O impacto do limiar
de saturação dos amplificadores no desempenho do sistema é analisado, e é
demonstrado que o processo iterativo consegue eliminar de modo eficiente
a interferência multi-utilizador e a distorção, melhorando o desempenho do
sistema.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
Design guidelines for spatial modulation
A new class of low-complexity, yet energyefficient Multiple-Input Multiple-Output (MIMO) transmission techniques, namely the family of Spatial Modulation (SM) aided MIMOs (SM-MIMO) has emerged. These systems are capable of exploiting the spatial dimensions (i.e. the antenna indices) as an additional dimension invoked for transmitting information, apart from the traditional Amplitude and Phase Modulation (APM). SM is capable of efficiently operating in diverse MIMO configurations in the context of future communication systems. It constitutes a promising transmission candidate for large-scale MIMO design and for the indoor optical wireless communication whilst relying on a single-Radio Frequency (RF) chain. Moreover, SM may also be viewed as an entirely new hybrid modulation scheme, which is still in its infancy. This paper aims for providing a general survey of the SM design framework as well as of its intrinsic limits. In particular, we focus our attention on the associated transceiver design, on spatial constellation optimization, on link adaptation techniques, on distributed/ cooperative protocol design issues, and on their meritorious variants
Simultaneous Wireless Information and Power Transfer in 5G communication
Green communication technology is expected to be widely adopted in future generation
networks to improve energy efficiency and reliability of wireless communication network.
Among the green communication technologies,simultaneous wireless information and
power transfer (SWIPT) is adopted for its flexible energy harvesting technology through
the radio frequency (RF) signa lthati sused for information transmission. Even though
existing SWIPT techniques are flexible and adoptable for the wireless communication
networks, the power and time resources of the signal need to be shared between infor-
mation transmission and RF energy harvesting, and this compromises the quality of the
signal. Therefore,SWIP Ttechniques need to be designed to allow an efficient resource
allocation for communication and energy harvesting.
The goal oft his thesisis to design SWIP Ttechniques that allow efficient,reliable and
secure joint communications and power transference. A problem associated to SWIPT
techniques combined with multi carrier signals is that the increased power requirements
inherent to energy harvesting purposes can exacerbate nonlinear distortion effects at the
transmitter. Therefore, we evaluate nonlinear distortion and present feasible solutions to
mitigate the impact of nonlinear distortion effects on the performance.Another goal of
the thesisis to take advantage of the energy harvesting signals in SWIP Ttechniques for
channel estimation and security purposes.Theperformance of these SWIPT techniques is
evaluated analytically, and those results are validated by simulations. It is shownthatthe
proposed SWIPT schemes can have excellent performance, out performing conventional
SWIPT schemes.Espera-se que aschamadas tecnologiasde green communications sejam amplamente ado-
tadas em futuras redes de comunicação sem fios para melhorar a sua eficiência energética
a fiabilidade.Entre estas,encontram-se as tecnologias SWIPT (Simultaneous Wireless
Information and Power Transference), nas quais um sinal radio é usado para transferir
simultaneamente potência e informações.Embora as técnicas SWIPT existentes sejam fle-
xíveis e adequadas para as redes de comunicações sem fios, os recursos de energia e tempo
do sinal precisam ser compartilhados entre a transmissão de informações e de energia, o
que pode comprometer a qualidade do sinal. Deste modo,as técnicas SWIPT precisam ser
projetadas para permitir uma alocação eficiente de recursos para comunicação e recolha
de energia.
O objetivo desta tese é desenvolver técnicas SWIPT que permitam transferência de
energia e comunicações eficientes,fiáveis e seguras.Um problema associado às técnicas
SWIPT combinadas com sinais multi-portadora são as dificuldades de amplificação ine-
rentes à combinação de sinais de transmissão de energia com sinais de transferência de
dados, que podem exacerbar os efeitos de distorção não-linear nos sinais transmitidos.
Deste modo, um dos objectivos desta tese é avaliar o impacto da distorção não-linear em
sinais SWIPT, e apresentar soluções viáveis para mitigar os efeitos da distorção não-linear
no desempenho da transmissão de dados.Outro objetivo da tese é aproveitar as vantagens
dos sinais de transferência de energia em técnicas SWIPT para efeitos de estimação de
canal e segurança na comunicação.Os desempenhos dessas técnicas SWIPT são avaliados
analiticamente,sendo os respectivos resultados validados por simulações.É mostrado que
os esquemas SWIPT propostos podem ter excelente desempenho, superando esquemas
SWIPT convencionais
Doctor of Philosophy
dissertationThe use of multicarrier techniques has allowed the rapid expansion of broadband wireless communications. Orthogonal frequency division multiplexing (OFDM) has been the most dominant technology in the past decade. It has been deployed in both indoor Wi-Fi and cellular environments, and has been researched for use in underwater acoustic channels. Recent works in wireless communications include the extension of OFDM to multiple access applications. Multiple access OFDM, or orthogonal frequency division multiple access (OFDMA), has been implemented in the third generation partnership project (3GPP) long- term evolution (LTE) downlink. In order to reduce the intercarrier interference (ICI) when user's synchronization is relaxed, filterbank multicarrier communication (FBMC) systems have been proposed. The first contribution made in this dissertation is a novel study of the classical FBMC systems that were presented in 1960s. We note that two distinct methods were presented then. We show that these methods are closely related through a modulation and a time/frequency scaling step. For cellular channels, OFDM also has the weakness of relatively large peak-to-average power ratios (PAPR). A special form of OFDM for the uplink of multiple access networks, called single carrier frequency division multiple access (SC-FDMA), has been developed to mitigate this issue. In this regard, this dissertation makes two contributions. First, we develop an optimization method for designing an effective precoding method for SC-FDMA systems. Second, we show how an equivalent to SC-FDMA can be developed for systems that are based on FBMC. In underwater acoustic communications applications, researchers are investigating the use of multicarrier communication systems like OFDM in underwater channels. The movement of the communicating vehicles scales the received signal along the time axis, which is often referred to as Doppler scaling. To undo the signal degradation, researchers have investigated methods to estimate the Doppler scaling factor and restore the original signal using resampling. We investigate a method called nonuniform fast Fourier transform (NUFFT) and apply that to increase the precision in the detection and correction of the Doppler scaling factor. NUFFT is applied to both OFDM and FBMC and its performance over the experimental data obtained from at sea experiments is investigated
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