Receiver design for the uplink of base station cooperation systems employing SC-FDE modulations

The presented paper considers the uplink transmission in base station (BS) cooperation schemes where mobile terminals (MTs) in adjacent cells share the same physical channel. We consider single-carrier with frequency-domain equalization (SC-FDE) combined with iterative frequency-domain receivers based on the iterative block decision feedback equalization (IB-DFE). We study the quantization requirements when sending the received signals, from different MTs, at different BSs to a central unit that performs the separation of different MTs using iterative frequency-domain receivers. Our performance results show that a relatively coarse quantization, with only 4 bits in the in-phase and quadrature components of the complex envelope already allows close-to-optimum macro-diversity gains, as well as an efficient separation of the transmitted signals associated with each MT

Iterative receiver combining IB-DFE with MRC for massive MIMO schemes

Once we are moving to the 5G system it is imperative to reduce the complexity of massive MIMO (Multiple-Input, Multiple Output) receivers. This paper considers the uplink transmission using massive MIMO combined with SC-FDE (Single-Carrier with Frequency-Domain Equalization). We propose an iterative frequency-domain receiver merging IB-DFE (Iterative Block Decision-Feedback Equalizer) with MRC (Maximal Ratio Combining). We propose a novel approach to reduce the complexity of the receiver by avoiding matrix inversions while maintaining a level of performance very close to the Matched Filter Bound (MFB), which makes it an excellent option for 5G systems.info:eu-repo/semantics/acceptedVersio

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

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 preferível 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

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 físico 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 cíclicos (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 ruído de quantização. Esta tese também fornece um modelo analítico 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