223 research outputs found
PAPR Reduction Method based on In-phase/Quadrature Data Symbol Components in MIMO-OFDM Systems
To overcome unpredictable spikes in the peak-toaverage power ratio (PAPR) in the presence of an orthogonal frequency-division multiplexing (OFDM) for multi-input-multioutput (MIMO) systems, implementation of a new SLM scheme is presented in this paper, which is extended from our previous study of IQ-SLM in SISO-OFDM system. In each transmit antenna, both real and imaginary parts of the base-band data symbol were modified independently using a corresponding phase element within a commonly generated phase vector, instead of modifying the complex data symbol as a single component. After applying an inverse fast Fourier transform (IFFT) for the real, imaginary, and original base-band vectors, the minimum PAPR component was observed. Therefore, the phase vector that introduced the minimal PAPR was considered to convert the original data block for transmission. This technique is called the In-phase/Quadrature-SLM (IQ-SLM) scheme. In this proposal, only U phase vectors were generated to treat all Nt data blocks, simultaneously, unlike the conventional MIMO-SLM techniques which generate UNt candidate phase blocks. The thing which, in turn, can be considered as a further computational complexity reduction, specifically in data-phase conversion stages. As a result, in terms of the complementary cumulative distribution function of PAPR performance(CCDF-PAPR), the proposal achieved a greater decibel reduction than conventional SLM methods such as dSLM, oSLM, and sSLM, at different subcarrier lengths N, candidate phase vectors U, transmit antennas Nt. Also, it shows a comparable BER performances over the dSLM scheme referencing to the theoretical curves, in the case where Nt ≤ Nr for both zero-forcing (ZF) and ZF with vertical Bell laboratories layered space-time (V-BLAST) detector
Ubiquitous Cell-Free Massive MIMO Communications
Since the first cellular networks were trialled in the 1970s, we have
witnessed an incredible wireless revolution. From 1G to 4G, the massive traffic
growth has been managed by a combination of wider bandwidths, refined radio
interfaces, and network densification, namely increasing the number of antennas
per site. Due its cost-efficiency, the latter has contributed the most. Massive
MIMO (multiple-input multiple-output) is a key 5G technology that uses massive
antenna arrays to provide a very high beamforming gain and spatially
multiplexing of users, and hence, increases the spectral and energy efficiency.
It constitutes a centralized solution to densify a network, and its performance
is limited by the inter-cell interference inherent in its cell-centric design.
Conversely, ubiquitous cell-free Massive MIMO refers to a distributed Massive
MIMO system implementing coherent user-centric transmission to overcome the
inter-cell interference limitation in cellular networks and provide additional
macro-diversity. These features, combined with the system scalability inherent
in the Massive MIMO design, distinguishes ubiquitous cell-free Massive MIMO
from prior coordinated distributed wireless systems. In this article, we
investigate the enormous potential of this promising technology while
addressing practical deployment issues to deal with the increased
back/front-hauling overhead deriving from the signal co-processing.Comment: Published in EURASIP Journal on Wireless Communications and
Networking on August 5, 201
On the optimal user grouping in NOMA system technology
This paper provides a state-of-art analysis of the most relevant studies on optimal user-aggregation strategies for non-orthogonal multiple access (NOMA) technology. The main ideas behind are i) to highlight how, in addition to the adoption of an optimal power allocation scheme, an optimal user-aggregation strategy represents an important key factor for improving NOMA system performance, and ii) to provide an exhaustive survey of the most relevant studies which can serve as useful starting point for the definition of new channel state-aware user-aggregation strategies for NOMA systems which, at the time of writing, represents a research field that still remains to be investigated more in depth. A detailed and complete analysis, which permits to point out the need to guarantee a certain relationship between users’ channel gain, is provided for each cited work
Thirty Years of Machine Learning: The Road to Pareto-Optimal Wireless Networks
Future wireless networks have a substantial potential in terms of supporting
a broad range of complex compelling applications both in military and civilian
fields, where the users are able to enjoy high-rate, low-latency, low-cost and
reliable information services. Achieving this ambitious goal requires new radio
techniques for adaptive learning and intelligent decision making because of the
complex heterogeneous nature of the network structures and wireless services.
Machine learning (ML) algorithms have great success in supporting big data
analytics, efficient parameter estimation and interactive decision making.
Hence, in this article, we review the thirty-year history of ML by elaborating
on supervised learning, unsupervised learning, reinforcement learning and deep
learning. Furthermore, we investigate their employment in the compelling
applications of wireless networks, including heterogeneous networks (HetNets),
cognitive radios (CR), Internet of things (IoT), machine to machine networks
(M2M), and so on. This article aims for assisting the readers in clarifying the
motivation and methodology of the various ML algorithms, so as to invoke them
for hitherto unexplored services as well as scenarios of future wireless
networks.Comment: 46 pages, 22 fig
Equalizador híbrido 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 à
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 híbrida, 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 flexível, 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 híbrido multiutilizador totalmente conectado, i.e., cada cadeia RF
está ligada a todas as antenas, combinado com um pré-codificador híbrido,
de baixa complexidade para sistemas MIMO massivo de banda larga. O
equalizador híbrido é otimizado, minimizando o erro quadrático médio entre a
abordagem híbrida e a contraparte totalmente digital. Os resultados mostram
que o desempenho do esquema híbrido proposto está muito próximo do
equivalente digital, à medida que o número de cadeias de RF aumenta.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
D6.3 Intermediate system evaluation results
The overall purpose of METIS is to develop a 5G system concept that fulfil s the requirements of the beyond-2020 connected information society and to extend today’s wireless communication systems for new usage cases. First, in this deliverable an updated view on the
overall METIS 5G system concept is presented.
Thereafter, simulation results for the most promising technology components supporting the METIS 5G system concept are reported.
Finally, s
imulation results are presented for
one
relevant
aspect of each Horizontal Topic:
Direct Device
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to
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Device Communication, Massive Machine Communication, Moving Networks,
Ultra
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Dense Networks, and Ultra
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Reliable Communication.Popovski, P.; Mange, G.; Fertl, P.; Gozálvez - Serrano, D.; Droste, H.; Bayer, N.; Roos, A.... (2014). D6.3 Intermediate system evaluation results. http://hdl.handle.net/10251/7676
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