78 research outputs found
Reduced complexity detection in MIMO systems with SC-FDE modulations and iterative DFE receivers
This paper considers a Multiple-Input Multiple-Output (MIMO) system with P transmitting
and R receiving antennas and different overall noise characteristics on the different receiver antennas
(e.g., due to nonlinear effects at the receiver side). Each communication link employs a Single-Carrier
with Frequency-Domain Equalization (SC-FDE) modulation scheme, and the receiver is based on
robust iterative frequency-domain multi-user detectors based on the Iterative Block Decision Feedback
Equalization (IB-DFE) concept. We present low complexity efficient receivers that can employ low
resolution Analog-to-Digital Converters (ADCs) and require the inversion of matrices with reduced
dimension when the number of receive antennas is larger than the number of independent data
streams. The advantages of the proposed techniques are particularly high for highly unbalanced
MIMO systems, such as in the uplink of Base Station (BS) cooperation systems that aim for
Single-Frequency Network (SFN) operation or massive MIMO systems with much more antennas at
the receiver side.publishe
Approaching universal frequency reuse through base station cooperation
Base Station (BS) architectures are a promising cellular wireless solution to mitigate
the interference issues and to avoid the high frequency reuse factors implemented
in conventional systems. Combined with block transmission techniques, such as Orthogonal
Frequency-Division Multiplexing (OFDM) for the downlink and Single-Carrier with
Frequency-Domain Equalization (SC-FDE) for the uplink, these systems provide a significant
performance improvement to the overall system. Block transmission techniques are
suitable for broadband wireless communication systems, which have to deal with strongly
frequency-selective fading channels and are able to provide high bit rates despite the channel
adversities. In BS cooperation schemes users in adjacent cells share the same physical
channel and the signals received by each BS are sent to a Central Processing Unit (CPU)
that combines the different signals and performs the user detections and/or separation,
which can be regarded as a Multi-User Detection (MUD) technique. The work presented
in this thesis is focused on the study of uplink transmissions in BS cooperations systems,
considering single carrier block transmission schemes and iterative receivers based on the
Iterative-Block Decision Feedback Equalization (IB-DFE) concept, which combined with
the employment of Cyclic Prefix (CP)-assisted block transmission techniques are appropriate
to scenarios with strongly time-dispersive channels. Furthermore, the impact of the
sampling and quantization applied to the received signals from each Mobile Terminal (MT)
to the corresponding BS is studied, with the achievement of the spectral characterization
of the quantization noise. This thesis also provides a conventional analytical model for the
BER (Bit Error Rate) performance complemented with an approach to improve its results.
Finally, this thesis addresses the contextualization of BS cooperation schemes in clustered
C-RAN (Centralized-Radio Access Network)-type solutions.As arquitecturas BS cooperation são uma solução promissora de redes celulares sem
fios para atenuar o problema da interferência e evitar os factores de reuso elevados, que
se encontram implementados nos sistemas convencionais. Combinadas com técnicas de
transmissão por blocos, como o OFDM para o downlink e o SC-FDE no uplink, estes
sistemas fornecem uma melhoria significativa no desempenho geral do sistema. Técnicas
de transmissão por blocos são adequadas para sistemas de comunicações de banda larga
sem fios, que têm que lidar com canais que possuem um forte desvanescimento selectivo
na frequência e são capazes de fornecer ligações com taxas de transmissão altas apesar
das adversidades do canal. Em esquemas BS cooperation os terminais móveis situados em
células adjacentes partilham o mesmo canal fÃsico e os sinais recebidos em cada estação
de base são enviados para uma Unidade Central de Processamento (CPU) que combina
os diferentes sinais recebidos associados a um dado utilizador e realiza a detecção e/ou
separação do mesmo, sendo esta considerada uma técnica de Detecção Multi-Utilizador
(MUD). O trabalho apresentado nesta tese concentra o seu estudo no uplink de transmissões
em sistemas BS cooperation, considerando transmissões em bloco de esquemas monoportadoras
e receptores iterativos baseados no conceito B-DFE, em que quando combinados
com a implementação de técnicas de transmissao por blocos assistidas por prefixos cÃclicos
(CP) são apropriados a cenários com canais fortemente dispersivos no tempo. Além disso, é
estudado o impacto do processo de amostragem e quantização aplicados aos sinais recebidos
de cada terminal móvel para a estação de base, com a obtenção da caracterização espectral
do ruÃdo de quantização. Esta tese também fornece um modelo analÃtico convencional para
a computação do desempenho da taxa de erros de bit (BER), com um método melhorado
para o mesmo. Por último, esta tese visa a contextualização dos sistemas BS cooperation
em soluções do tipo C-RAN
Performance analysis of massive MIMO receivers
We face now an exponential increase in wireless devices and to allow good user experience, it is imperative that the next generation of mobile (5G) communications
ensures reliable connections, high data transfer rates and low latency.
One way to increase the data transfer rate is to use massive Multiple-Input,
Multiple-Output (MIMO) systems, that is, systems with multiple antennas to emit
and multiple antennas to receive thus allowing spatial diversity. In these systems,
to increase the battery life of the devices it is preferable to use the Single-Carrier
with Frequency-Domain Equalization modulation in the uplink as this modulation
reduces the complexity in the emitter, transferring it to the receiver, in this case
the Base Staion, where it is quite acceptable.
This dissertation studies the performance of massive MIMO receiver systems,
comparing it to the performance achieved with the Matched Filter Bound (MFB).
The Iterative Block Decision-Feedback Equalizer (IB-DFE) receiver presents a
very similar performance to the MFB, however, the algorithm requires matrix
inversions, which in the systems under study, where the size of the matrix is
high, implies an increase of the associated operations increases. Thus it is very
important that low complexity receivers, such as the Maximal-Ratio Combining
(MRC) or Equal Gain Combining are used.
In this dissertation, a simple receiver is proposed combining the IB-DFE receiver with the MRC receiver, thus creating a low complexity receiver with excellent performanceAtualmente, sente-se um aumento exponencial nos dispositivos wireless. De modo
a permitir uma boa experiência por parte dos utilizadores é fundamental que a
próxima geração de comunicações móveis (5G) assegure fiabilidade nas ligações,
uma elevada taxa de transferência de dados e baixa latência.
Uma maneira de elevar a taxa de transferência de dados é utilizar sistemas
massive Multiple-Input, Multiple-Output (MIMO), ou seja, sistemas com múltiplas antenas a emitir e múltiplas antenas a receber permitindo assim diversidade
espacial. Nestes sistemas, para aumentar a bateria dos dispositivos é preferÃvel
usar no uplink a modulação Single-Carrier with Frequency-Domain Equalization
pois esta modulação reduz a complexidade no emissor transferindo-a para o recetor, neste caso na Base Station, onde isso é bastante aceitável.
Esta dissertação estuda o desempenho dos recetores dos sistemas massive
MIMO, comparando o desempenho alcançado com o desempenho do Matched
Filter Bound (MFB). O recetor Iterative Block Decision-Feedback Equalizer (IBDFE) apresenta um desempenho muito semelhante ao do MFB no entanto, o
algoritmo do receptor inverte matrizes, o que nos sistemas em estudo, onde o
tamanho das matrizes é elevado, se reflecte no aumento da complexidade das operações associadas. Deste modo, é importante que sejam utilizados recetores de
baixa complexidade tal como o Maximal-Ratio Combining (MRC) ou o Equal Gain
Combining.
Esta dissertação propõe um recetor simples que combina um recetor IB-DFE
com um recetor MRC, criando desde modo um recetor de baixa complexidade e
com excelente desempenho
Analytical performance evaluation of massive MIMO techniques for SC-FDE modulations
SAICT-45-2017-02
UIDB/EEA/50008/2020In the Fifth Generation of telecommunications networks (5G), it is possible to use massive Multiple Input Multiple Output (MIMO) systems, which require efficient receivers capable of reaching good performance values. MIMO systems can also be extended to massive MIMO (mMIMO) systems, while maintaining their, sometimes exceptional, performance. However, we must be aware that this implies an increase in the receiver complexity. Therefore, the use of mMIMO in 5G and future generations of mobile receivers will only be feasible if they use very efficient algorithms, so as to maintain their excellent performance, while coping with increasing and critical user demands. Having this in mind, this paper presents and compares three types of receivers used in MIMO systems, for further use with mMIMO systems, which use Single-Carrier with Frequency-Domain Equalization (SC-FDE), Iterative Block Decision Feedback Equalization (IB-DFE) and Maximum Ratio Combining (MRC) techniques. This paper presents and compares the theoretical and simulated performance values for these receivers in terms of their Bit Error Rate (BER) and correlation factor. While one of the receivers studied in this paper achieves a BER performance nearly matching the Matched Filter Bound (MFB), the other receivers (IB-DFE and MRC) are more than 1 dB away from MFB. The results obtained in this paper can help the development of ongoing research involving hybrid analog/digital receivers for 5G and future generations of mobile communications.publishersversionpublishe
Analytical BER Performance Evaluation in SISO and MIMO Environments with SC-FDE Modulations and IB-DFE Receivers
This paper preseThis paper presents the analysis of the obtainment of the theoretical bit error rate (BER) performance in single-input-single-output and multiple-input-multiple-output systems with single-carrier with frequency-domain equalization modulations and iterative receivers based on the iterative block decision feedback equalization concept. Through the consideration of a Gaussian-based approach to obtain the BER performance, we present a simple and accurate model to improve such method by compensating the difference between the theoretical performance results and the ones obtained by simulation.info:eu-repo/semantics/acceptedVersio
Low-Complexity Equalisers for Offset Constellations in Massive MIMO Schemes
This work was supported in part by the European Regional Development Fund (FEDER), through the Competitiveness and Internationalization Operational Program of the Portugal 2020 Framework, in part by the Regional OP Centro under Grant POCI-01-0145-FEDER-030588, in part by the Regional OP Lisboa under Grant Lisboa-01-0145-FEDER-03058, in part by the FCT/MEC through national funds of MASSIVE5G Project under Grant SAICT-45-2017-02 and PES3N Project under Grant 2018-SAICT-45-2017-POCI-01-0145-FEDER-030629, in part by the UID/EEE/50008/2019 Project, and in part by the FCT Ph.D. under Grant SFRH/BD/108522/2015.Massive multi-input-multi-output (m-MIMO) schemes require low-complexity implementations at both the transmitter and the receiver side, especially for systems operation at millimeter wave (mmWave) bands. In this paper, we consider the use of offset constellations in m-MIMO systems operating at mmWave frequencies. These signals are designed to have either an almost constant envelope or be decomposed as the sum of constant-envelope signals, making them compatible with strongly nonlinear power amplifiers, which can have low-implementation complexity and high amplification efficient, making them particularly interesting for mmWave communications. We design and evaluate low-complexity frequency-domain receivers for offset signals. It is shown that the proposed receivers can have excellent performance/complexity trade-offs in m-MIMO scenarios, making them particularly interesting for future wireless systems operating at mmWave bands.publishersversionpublishe
Estimating the performance of mimo sc-fde systems using siso measurements
project 023304 UIDB/50008/2020The demand for ubiquitous telecommunications services forces operators to have a special concern about signal quality and the coverage area they offer to their customers. This was usually checked by using suitable propagation models for Single Input Single Output (SISO) systems, which are no longer the case for new and future mobile generations, such as 5G and beyond. To guarantee good signal quality coverage, operators started to replace these models with Multiple Input Multiple Output (MIMO) ones. To achieve the best results, these models are usually calibrated with Drive Test (DT) measures; however, the DTs available for MIMO propagation models are sparse, in contrast to SISO ones. The main contribution presented in this paper is a methodology to extend the propagation models of SISO systems so they can be applied in MIMO sytems with Single-Carrier and Frequency-Domain Equalization (SC-FDE), while still using DTs acquired for SISO systems. This paper presents the impact on Bit Error Rate (BER) performance and its coverage area resulting from the application of our proposed method. We consider a MIMO SC-FDE system with an Iterative Block Decision Feedback Equalization (IB-DFE) receiver and we present the improvement expressions for the BER that we illustrate with some simulations.publishersversionpublishe
Performance Evaluation of Low Complexity Massive MIMO Techniques for SC-FDE Schemes
Massive-MIMO technology has emerged as a means to achieve 5G's ambitious goals;
mainly to obtain higher capacities and excellent performances without requiring the use of more
spectrum. In this thesis, focused on the uplink direction, we make a study of performance of low
complexity equalization techniques as well as we also approach the impact of the non-linear elements
located on the receivers of a system of this type. For that purpose, we consider a multi-user
uplink scenario through the Single Carrier with Frequency Domain Equalization (SC-FDE)
scheme. This seems to be the most appropriate due to the low energy consumption that it implies,
as well as being less favorable to the detrimental effects of high envelope fluctuations, that is, by
have a low Peak to Average Power Ratio (PAPR) comparing to other similar modulations, such
as the Orthogonal Frequency Division Multiplexing (OFDM). Due to the greater number of antennas
and consequent implementation complexity, the equalization processes for Massive-
MIMO schemes are aspects that should be simplified, that is, they should avoid the inversion of
matrices, contrary to common 4G, with the Zero Forcing (ZF) and Minimum Mean Square Error
(MMSE) techniques. To this end, we use low-complexity techniques, such as the Equal Gain
Combining (EGC) and the Maximum Ratio Combining (MRC). Since these algorithms are not
sufficiently capable of removing the entire Inter-Symbol Interference (ISI) and Inter-User Interference
(IUI), we combine them with iterative techniques, namely with the Iterative Block with
Decision Feedback Equalizer (IB-DFE) to completely remove the residual ISI and IUI. We also
take into account the hardware used in the receivers, since the effects of non-linear distortion can
impact negatively the performance of the system. It is expected a strong performance degradation
associated to the high quantization noise levels when implementing low-resolution Analog to
Digital Converters (ADCs). However, despite these elements with these configurations become
harmful to the performance of the majority of the systems, they are considered a desirable solution
for Massive-MIMO scenarios, because they make their implementation cheaper and more energy
efficient. In this way, we made a study of the impact in the performance by the low-resolution
ADCs. In this thesis we suggest that it is possible to bypass these negative effects by implementing
a number of receiving antennas far superior to the number of transmitting antennas
Low complexity detection for SC-FDE massive MIMO systems
Nowadays we continue to observe a big and fast growth of wireless com-munication usage due to the increasing number of access points, and fields of application of this technology. Furthermore, these new usages can require higher speed and better quality of service in order to create market. As example we can have: live 4K video transmission, M2M (Machine to Machine communication), IoT (Internet of Things), Tactile Internet, between many others.
As a consequence of all these factors, the spectrum is getting overloaded with communications, increasing the interference and affecting the system's per-formance. Therefore a different path of ideas has been followed and the commu-nication process has been taken to the next level in 5G by the usage of big arrays of antennas and multi-stream communication (MIMO systems) which in a greater scale are called massive MIMO schemes. These systems can be combined with an SC-FDE (Single-Carrier Frequency Domain Equalization) scheme to im-prove the power efficiency due to the low envelope fluctuations.
This thesis focused on the equalization in massive MIMO systems, more specifically in the FDE (Frequency Domain Equalization), studying the perfor-mance of different approaches, namely ZF (Zero Forcing), EGD (Equal Gain De-tector), MRD (Maximum Ratio Detector), IB-DFE (Iterative Block Decision Feed-back Equalizer) and a proposed receiver combining MRD (or EGD) and IB-DFE.With this approach we want to minimize the ICI (Inter Carrier Interference) in order to have almost independent data streams and to produce a low complexity code, so that the receiver's performance doesn't affect the total system's perfor-mance, with a final objective of increasing the data throughput in a great scale
Efficient frequency-domain detection for massive MIMO systems
Reduced-complexity implementations are critical for massive MIMO (Multiple Input, Multiple Output) systems. In this paper we consider the uplink of broadband massive MIMO systems employing SC-FDE (Single-Carrier with Frequency-Domain Equalization) schemes, where multiple users transmit to a single base station with a large number of antennas. We propose low-complexity frequency-domain detection schemes that allow excellent performance, but do not require matrix inversions.info:eu-repo/semantics/acceptedVersio
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