116 research outputs found
Iterative analog-digital multi-user equalizer for wideband millimeter wave massive MIMO systems
Most of the previous work on hybrid transmit and receive beamforming focused on narrowband channels. Because the millimeter wave channels are expected to be wideband, it is crucial to propose efficient solutions for frequency-selective channels. In this regard, this paper proposes an iterative analog-digital multi-user equalizer scheme for the uplink of wideband millimeter-wave massive multiple-input-multiple-output (MIMO) systems. By iterative equalizer we mean that both analog and digital parts are updated using as input the estimates obtained at the previous iteration. The proposed iterative analog-digital multi-user equalizer is designed by minimizing the sum of the mean square error of the data estimates over the subcarriers. We assume that the analog part is fixed for all subcarriers while the digital part is computed on a per subcarrier basis. Due to the complexity of the resulting optimization problem, a sequential approach is proposed to compute the analog phase shifters values for each radio frequency (RF) chain. We also derive an accurate, semi-analytical approach for obtaining the bit error rate (BER) of the proposed hybrid system. The proposed solution is compared with other hybrid equalizer schemes, recently designed for wideband millimeter-wave (mmWave) massive MIMO systems. The simulation results show that the performance of the developed analog-digital multi-user equalizer is close to full-digital counterpart and outperforms the previous hybrid approach.publishe
Multi-user linear equalizer and precoder scheme for hybrid sub-connected wideband systems
Millimeter waves and massive multiple-input multiple output (MIMO) are two promising
key technologies to achieve the high demands of data rate for the future mobile communication
generation. Due to hardware limitations, these systems employ hybrid analog–digital architectures.
Nonetheless, most of the works developed for hybrid architectures focus on narrowband channels,
and it is expected that millimeter waves be wideband. Moreover, it is more feasible to have a
sub-connected architecture than a fully connected one, due to the hardware constraints. Therefore,
the aim of this paper is to design a sub-connected hybrid analog–digital multi-user linear equalizer
combined with an analog precoder to efficiently remove the multi-user interference. We consider
low complexity user terminals employing pure analog precoders, computed with the knowledge
of a quantized version of the average angles of departure of each cluster. At the base station,
the hybrid multi-user linear equalizer is optimized by using the bit-error-rate (BER) as a metric over
all the subcarriers. The analog domain hardware constraints, together with the assumption of a flat
analog equalizer over the subcarriers, considerably increase the complexity of the corresponding
optimization problem. To simplify the problem at hand, the merit function is first upper bounded,
and by leveraging the specific properties of the resulting problem, we show that the analog equalizer
may be computed iteratively over the radio frequency (RF) chains by assigning the users in an
interleaved fashion to the RF chains. The proposed hybrid sub-connected scheme is compared with a
fully connected counterpart.publishe
Hybrid multi-user equalizer for massive MIMO millimeter-wave dynamic subconnected architecture
This paper proposes a hybrid multi-user equalizer for the uplink of broadband millimeterwave massive multiple input/multiple output (MIMO) systems with dynamic subarray antennas. Hybrid
subconnected architectures are more suitable for practical applications since the number of required phase
shifters is lower than in fully connected architectures. We consider a set of only analog precoded users
transmitting to a base station and sharing the same radio resources. At the receiver end, the hybrid multi-user
equalizer is designed by minimizing the sum of the mean square error (MSE) of all subcarriers, considering
a two-step approach. In the first step, the digital part is iteratively computed as a function of the analog
part. It is considered that the digital equalizers are computed on a per subcarrier basis, while the analog
equalizer is constant over the subcarriers and the digital iterations due to hardware constraints. In the second
step, the analog equalizer with dynamic antenna mapping is derived to connect the best set of antennas to
each radio frequency (RF) chain. For each subset of antennas, one antenna and a quantized phase shifter are
selected at a time, taking into account all previously selected antennas. The results show that the proposed
hybrid dynamic two-step equalizer achieves a performance close to the fully connected counterpart, although
it is less complex in terms of hardware and signal processing requirements.publishe
Multiuser equalizer for hybrid massive MIMO mmWave CE-OFDM systems
This paper considers a multiuser broadband uplink massive multiple input multiple
output (MIMO) millimeter-wave (mmWave) system. The constant envelope orthogonal frequency
division multiplexing (CE-OFDM) is adopted as a modulation technique to allow an efficient power
amplification, fundamental for mmWave based systems. Furthermore, a hybrid architecture is
considered at the user terminals (UTs) and base station (BS) to reduce the high cost and power
consumption required by a full-digital architecture, which has a radio frequency (RF) chain per
antenna. Both the design of the UT’s precoder and base station equalizer are considered in this work.
With the aim of maximizing the beamforming gain between each UT and the BS, the precoder analog
coefficients are computed as a function of the average angles of departure (AoD), which are assumed
to be known at the UTs. At the BS, the analog part is derived by assuming a system with no multi-user
interference. Then, a per carrier basis nonlinear/iterative multi-user equalizer, based on the iterative
block decision feedback equalization (IB-DFE) principle is designed, to explicitly remove both the
multi-user and residual inter carrier interferences, not tackled in the analog part. The equalizer
design metric is the sum of the mean square error (MSE) of all subcarriers, whose minimization is
shown to be equivalent to the minimization of a weighted error between the hybrid and the full
digital equalizer matrices. The results show that the proposed hybrid multi-user equalizer has a
performance close to the fully digital counterpart.publishe
Two-step multiuser equalization for hybrid mmWave massive MIMO GFDM systems
Although millimeter-wave (mmWave) and massive multiple input multiple output
(mMIMO) can be considered as promising technologies for future mobile communications (beyond
5G or 6G), some hardware limitations limit their applicability. The hybrid analog-digital architecture
has been introduced as a possible solution to avoid such issues. In this paper, we propose a two-step
hybrid multi-user (MU) equalizer combined with low complexity hybrid precoder for wideband
mmWave mMIMO systems, as well as a semi-analytical approach to evaluate its performance.
The new digital non-orthogonal multi carrier modulation scheme generalized frequency division
multiplexing (GFDM) is considered owing to its efficient performance in terms of achieving higher
spectral efficiency, better control of out-of-band (OOB) emissions, and lower peak to average power
ratio (PAPR) when compared with the orthogonal frequency division multiplexing (OFDM) access
technique. First, a low complexity analog precoder is applied on the transmitter side. Then, at the
base station (BS), the analog coefficients of the hybrid equalizer are obtained by minimizing the
mean square error (MSE) between the hybrid approach and the full digital counterpart. For the
digital part, zero-forcing (ZF) is used to cancel the MU interference not mitigated by the analog
part. The performance results show that the performance gap of the proposed hybrid scheme to the
full digital counterpart reduces as the number of radio frequency (RF) chains increases. Moreover,
the theoretical curves almost overlap with the simulated ones, which show that the semi-analytical
approach is quite accurate.publishe
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 hÃbrida, 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 domÃnios digital e analógico. Na literatura, a maioria dos esquemas
hÃbridos 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 hÃbrido 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 hÃbrido 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
Spatial modulation schemes and modem architectures for millimeter wave radio systems
The rapid growth of wireless industry opens the door to several use cases such as internet of things and device-to-device communications, which require boosting the reliability and the spectral efficiency of the wireless access network, while reducing the energy consumption at the terminals. The vast spectrum available in millimeter-wave (mmWave) frequency band is one of the most promising candidates to achieve high-speed communications. However, the propagation of the radio signals at high carrier frequencies suffers from severe path-loss which reduces the coverage area. Fortunately, the small wavelengths of the mmWave signals allow packing a large number of antennas not only at the base station (BS) but also at the user terminal (UT). These massive antenna arrays can be exploited to attain high beamforming and combining gains and overcome the path-loss associated with the mmWave propagation. In conventional (fully digital) multiple-input-multiple-output (MIMO) transceivers, each antenna is connected to a specific radio-frequency (RF) chain and high resolution analog-to-digital-converter. Unfortunately, these devices are expensive and power hungry especially at mmWave frequency band and when operating in large bandwidths. Having this in mind, several MIMO transceiver architectures have been proposed with the purpose of reducing the hardware cost and the energy consumption.
Fully connected hybrid analog and digital precoding schemes were proposed in with the aim of replacing some of the conventional RF chains by energy efficient analog devices. These fully connected mapping requires many analog devices that leads to non-negligible energy consumption. Partially connected hybrid architectures have been proposed to improve the energy efficiency of the fully connected transceivers by reducing the number of analog devices. Simplifying the transceiver’s architecture to reduce the power consumption results in a degradation of the attained spectral efficiency.
In this PhD dissertation, we propose novel modulation schemes and massive MIMO transceiver design to combat the challenges at the mmWave cellular systems. The structure of the doctoral manuscript can be expressed as
In Chapter 1, we introduce the transceiver design challenges at mmWave cellular communications. Then, we illustrate several state of the art architectures and highlight their limitations. After that, we propose scheme that attains high-energy efficiency and spectrum efficiency.
In chapter 2, first, we mathematically describe the state of the art of the SM and highlight the main challenges with these schemes when applied at mmWave frequency band. In order to combat these challenges (for example, high cost and high power consumption), we propose novel SM schemes specifically designed for mmWave massive MIMO systems. After that, we explain how these schemes can be exploited in attaining energy efficient UT architecture. Finally, we present the channel model, systems assumptions and the transceiver devices power consumption models.
In chapter 3, we consider single user SM system. First, we propose downlink (DL) receive SM (RSM) scheme where the UT can be implemented with single or multiple radio-frequency chains and the BS can be fully digital or hybrid architecture. Moreover, we consider different precoders at the BS and propose low complexity and efficient antenna selection schemes for narrowband and wideband transmissions. After that, we propose joint uplink-downlink SM scheme where we consider RSM in the DL and transmit SM (TSM) in the UL based on energy efficient hybrid UT architecture.
In chapter 4, we extend the SM system to the multi-user case. Specifically, we develop joint multi-user power allocation, user selection and antenna selection algorithms for the broadcast and the multiple access channels.
Chapter 5 is presented for concluding the thesis and proposing future research directions.Considerando los altos requerimientos de los servicios de nueva generación, las infraestructuras de red actual se han visto obligadas a evolucionar en la forma de manejar los diferentes recursos de red y computación. Con este fin, nuevas tecnologÃas han surgido para soportar las funcionalidades necesarias para esta evolución, significando también un gran cambio de paradigma en el diseño de arquitecturas para la futura implementación de redes.En este sentido, este documento de tesis doctoral presenta un análisis sobre estas tecnologÃas, enfocado en el caso de redes inter/intra Data Centre. Por consiguiente, la introducción de tecnologÃas basadas en redes ópticas ha sido estudiada, con el fin de identificar problemas actuales que puedan llegar a ser solucionados mediante el diseño y aplicación de nuevas técnicas, asimismo como a través del desarrollo o la extensión de los componentes de arquitectura de red.Con este propósito, se han definido una serie de propuestas relacionadas con aspectos cruciales, asà como el control de dispositivos ópticos por SDN para habilitar el manejo de redes hÃbridas, la necesidad de definir un mecanismo de descubrimiento de topologÃas ópticas capaz de exponer información precisa, y el analizar las brechas existentes para la definición de una arquitectura común en fin de soportar las comunicaciones 5G.Para validar estas propuestas, se han presentado una serie de validaciones experimentales por medio de escenarios de prueba especÃficos, demostrando los avances en control, orquestación, virtualización y manejo de recursos con el fin de optimizar su utilización. Los resultados expuestos, además de corroborar la correcta operación de los métodos y componentes propuestos, abre el camino hacia nuevas formas de adaptar los actuales despliegues de red respecto a los desafÃos definidos en el inicio de una nueva era de las telecomunicaciones.Postprint (published version
Equalizador hÃbrido na banda das ondas milimétricas para sistemas GFDM
Wireless communication using very-large multiple-input multiple-output
(MIMO) antennas has been regarded as one of the enabling technologies
for the future mobile communication. It refers to the idea of equipping
cellular base stations (BSs) with a very large number of antennas giving the
possibility to focusing the transmitted signal energy into very short-range
areas, which will provide huge improvements in the capacity, in addition
to the spectral and energy efficiency. Concurrently, this demand for high
data rates and capacity led to the necessity of exploiting the enormous
amount of spectrum in the millimeter wave (mmWave) bands. However,
the combination of millimeter-wave communications arrays with a massive
number of antennas has the potential to dramatically enhance the features
of wireless communication. This combination implies high cost and power
consumption in the conventional full digital architecture, where each RF chain
is dedicated to one antenna. The solution is the use of a hybrid architecture,
where a small number of RF chains are connected to a large number of
antennas through a network of phase shifters.
On the other hand, another important factor that affect the transmission
quality is the modulation technique, which plays an important role in the
performance of the transmission process, for instance, GFDM is a flexible
non-orthogonal multicarrier modulation concept, that introduces additional
degrees of freedom when compared to other multicarrier techniques. This
flexibility makes GFDM a promising solution for the future cellular generations,
because it can achieve different requirements, such as higher spectrum
efficiency, better control of out-of-band (OOB) emissions, as well as achieving
low peak to average power ratio (PAPR).
In this work, we present an analog-digital transmitter and receiver structures.
Considering a GFDM modulation technique to be implemented in the digital
part, while in the analog part, we propose a full connected hybrid multiuser
linear equalizer, combined with low complexity hybrid precoder for wideband
millimeter-wave massive MIMO systems. The hybrid equalizer is optimized by
minimizing the mean square error between the hybrid approach and the full
digital counterpart.
The results show that the performance of the proposed hybrid scheme is very
close to the full digital counterpart and the gap reduces as the number of RF
chains increases.O uso de um número elevado de antenas, também designado por MIMO
massivo, tem sido considerada uma das tecnologias mais promissoras para
os futuros sistemas de comunicação sem fios. Esta tecnologia, refere-se Ã
ideia de equipar as estações base (BSs) com um número muito grande de
antenas, dando a possibilidade de focar a energia do sinal transmitido em
áreas de alcance muito restritas, o que proporcionará grandes melhorias na
capacidade, além das espectrais e eficiência energética. Simultaneamente,
a exigência por taxas de dados elevadas e capacidade levou à necessidade
de explorar uma enorme quantidade de espectro nas bandas de ondas
milimétricas (mmWave). A combinação de comunicação na banda das ondas
milimétricas com terminais equipados com um grande número de antenas
tem o potencial de melhorar drasticamente os recursos da comunicação sem
fios. Considerando no entanto uma arquitetura digital, usada em sistemas
MIMO convencionais, em que cada cadeia de RF é dedicada a uma antena,
implica um custo e um consumo de energia elevados. A solução é o uso
de uma arquitetura hÃbrida, na qual um pequeno número de cadeias de
RF é conectado a um grande número de antenas através de um conjunto
de deslocadores de fase. Outro fator importante que afeta a qualidade da
transmissão é a técnica de modulação usada, que desempenha um papel
importante no desempenho do processo de transmissão. O GFDM é um
conceito de modulação de portadora múltipla, não ortogonal e flexÃvel, que
introduz graus de liberdade adicionais, quando comparado a outras técnicas
de portadora múltipla, como o OFDM. Essa flexibilidade faz do GFDM uma
solução promissora para as futuras gerações celulares, pois pode atender
a diferentes requisitos, como maior eficiência de espectro, melhor controle
das emissões fora de banda (OOB), além de atingir baixo rácio de potência
média / pico ( PAPR).
Neste trabalho, é assumido uma arquitetura hibrida no transmissor e
recetor. Considera-se uma técnica de modulação GFDM a ser implementada
na parte digital, enquanto na parte analógica, é proposto um equalizador
linear hÃbrido multiutilizador totalmente conectado, i.e., cada cadeia RF
está ligada a todas as antenas, combinado com um pré-codificador hÃbrido,
de baixa complexidade para sistemas MIMO massivo de banda larga. O
equalizador hÃbrido é otimizado, minimizando o erro quadrático médio entre a
abordagem hÃbrida e a contraparte totalmente digital. Os resultados mostram
que o desempenho do esquema hÃbrido proposto está muito próximo do
equivalente digital, à medida que o número de cadeias de RF aumenta.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
Esquemas de pré-codificação e equalização para arquiteturas hÃbridas sub-conectadas na banda de ondas milimétricas
In the last years, the demand for high data rates increased substantially and the mobile communications are currently a necessity for our society. Thus, the number of users to access interactive services and applications has increased. The next generation of wireless communications (5G) is expected to be released in 2020 and it is projected to provide extremely high data rates for the users. The millimeter wave communications band and the massive MIMO are two promising keys technologies to achieve the multi Gbps for the future generations of mobile communications, in particular the 5G. The conjugation of these two technologies, allows packing a large number of antennas in the same volume than in the current frequencies and increase the spectral efficiency. However, when we have a large number of antennas, it is not reasonable to have a fully digital architecture due to the hardware constrains. On the other hand, it is not feasible to have a system that works only in the analog domain by employing a full analog beamforming since the performance is poor. Therefore, it is required a design of hybrid analog/digital architectures to reduce the complexity and achieve a good performance. Fully connected and sub-connected schemes are two examples of hybrid architectures. In the fully connected one, all RF chain connect to all antenna elements while in the sub-connected architecture, each RF chain is connected to a group of antennas. Consequently, the sub-connected architecture is more attractive due to the low complexity when compared to the fully connected one. Also, it is expected that millimeter waves be wideband, however, most of the works developed in last years for hybrid architectures are mainly focused in narrowband channels.
Therefore, in this dissertation it is designed a low complex analog precoder at the user terminals and a hybrid analog-digital multi-user linear equalizer for broadband sub-connected millimeter wave massive MIMO at the base station. The analog precoder at the transmitter considers a quantized version of the average angle of departure of each cluster for its computation. In order to remove the multi-user interference, it is considered a hybrid sub-connected approach that minimizes the bit error rate (BER). The performance results show that the proposed hybrid sub-connected scheme is close to the hybrid full-connected design. However, due to the large number of connections, the full-connected scheme is slightly better than the proposed sub-connected scheme but with higher complexity. Therefore, the proposed analog precoder and hybrid sub-connected equalizer are more feasible to practical applications due to the good trade-off between performance and complexity.Nos últimos anos, a necessidade por elevadas taxas de transmissão de dados tem vindo a aumentar substancialmente uma vez que as comunicações móveis assumem cada vez mais um papel fundamental na sociedade atual. Por isso, o número de utilizadores que acedem a serviços e aplicações interativas tem vindo a aumentar. A próxima geração de comunicações móveis (5G) é esperada que seja lançada em 2020 e é projetada para fornecer elevadas taxas de transmissão de dados aos seus utilizadores. A comunicação na banda das ondas milimétricas e o MIMO massivo são duas tecnologias promissoras para alcançar os multi Gb/s para as comunicações móveis futuras, em particular o 5G. Conjugando essas duas tecnologias, permite-nos colocar um maior número de antenas no mesmo volume comparativamente à s frequências atuais, aumentando assim a eficiência espectral. No entanto, quanto se tem um grande número de antenas, não é viável ter uma arquitetura totalmente digital devido à s restrições de hardware. Por outro lado, não é viável ter um sistema que trabalhe apenas no domÃnio analógico. Assim sendo, é necessária uma arquitetura hÃbrida analógica-digital de modo a remover a complexidade geral do sistema. É esperado que os sistemas de comunicação baseados em ondas milimétricas sejam de banda larga, no entanto, a maioria dos trabalhos feitos para arquiteturas hÃbridas são focados em canais de banda estreita. Dois exemplos de soluções hÃbridas são as arquiteturas completamente conectada e sub-conectada. Na primeira, todas as cadeias RF estão ligadas a todas as antenas enquanto na arquitetura sub-conectada cada cadeia RF é ligada apenas a um grupo de antenas. Consequentemente, a arquitetura sub-conectada é mais interessante do ponto de vista prático devido à sua menor complexidade quando comparada à arquitetura completamente conectada.
Nesta dissertação é projetado um pré-codificador analógico de baixa complexidade no terminal móvel, combinado com um equalizador multiutilizador desenhado para uma arquitetura hÃbrida sub-conectada, implementado na estação base. O pré-codificador no transmissor assume um conhecimento parcial da informação do canal e, de modo a remover eficientemente a interferência multiutilizador, é proposta também uma arquitetura hÃbrida sub-conectada que minimiza a taxa média de erro. Os resultados de desempenho mostram que o esquema hÃbrido sub-conectado proposto está próximo da arquitetura hÃbrida completamente conectada. No entanto, devido ao grande número de conexões, a arquitetura hÃbrida completamente conectada é ligeiramente melhor que a arquitetura sub-conectada proposta à custa de uma maior complexidade. Assim sendo, o pré-codificador analógico e o equalizador sub-conectado hÃbrido proposto são mais viáveis para aplicações práticas devido ao compromisso entre o desempenho e a complexidade.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
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