MULTICARRIER TRANSMISSION TECHNIQUES

In this thesis, multicarrier transmission techniques envisioned for the fifth-generation wireless networks are studied. First, three basic techniques, namely orthogonal frequency-division multiplexing (OFDM), filter-bank multicarrier offset quadrature amplitude modulation (FBMC-OQAM), and generalized frequency-division multiplexing (GFDM) are reviewed in detail. In particular, the block-based structure and cyclic prefixing of OFDM are discussed and its bit error rate (BER) performance is analyzed. Then it is demonstrated that with offset QAM the orthogonality between subcarriers in FBMC-OQAM is preserved. Next, the roles of tail biting technique and circular convolution in GFDM are explained. An efficient implementation of GFDM is also described. Second, circular filterbank multicarrier offset QAM (CFBMC-OQAM), a technique which combines the block-based structure of GFDM and offset QAM of FBMC-OQAM, is presented. Then a precoded scheme is proposed, in which the Walsh-Hadamard (WH) transform is applied to CFBMC-OQAM system, resulting in a precoded scheme called WH-CFBMC-OQAM. The proposed system has a block-based structure and can be implemented efficiently using fast Fourier transform (FTT) and inverse FFT (IFFT). In addition, a cyclic prefix can be inserted to facilitate simple equalization at the receiver. WH-CFBMC-OQAM exploits the frequency diversity by averaging the signal-to-noise ratios (SNRs) over all subcarriers. A theoretical approximation for the bit error rate performance of WH-CFBMC-OQAM over a frequency-selective channel is derived. Under the same system configuration, simulation results demonstrate the excellent performance of the proposed scheme when compared to the performance of other techniques. Simulation also verifies that the theoretical results match perfectly with simulation results for any SNR value

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

Novas técnicas de précodificação e equalização para sistemas multiportadoras

Tese [doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.Nesta tese, novas técnicas de equalização e précodificação para sistemas multiportadora foram propostas e analisadas. Primeiramente, foi analisado o desempenho de erro dos sistemas multiportadoras baseados em bancos de filtros (FBMC) précodificados. Foi descoberto que este desempenho é altamente sensível à completa equalização dos subcanais. Quando há interferência intersimbólica residual proveniente de equalização imperfeita do subcanal, há uma perda de diversidade; esta diversidade pode ser restaurada adotando um número de subcanais suficiente para que o subcanal sofra desvanecimento plano ou utilizando um equalizador de subcanal com comprimento suficiente para compensar a resposta em frequência deste. Após isto, uma aproximação para a distribuição para a relação sinal/ruído+interferência (SINR) de sistemas SC-FDE utilizando equalização linear MMSE foi proposta. Esta aproximação usa a distribuição lognormal com a menor distância de Kullback-Leibler para a verdadeira distribuição, e se mostrou precisa no desempenho de erro; ela serve como uma abstração do sistema. Com esta abstração, foi proposto um método preciso para obter o desempenho de erro codificado analítico desses sistemas. Finalmente, précodificadores Tomlinson-Harashima (THP) e equalizadores (lineares e de decisão realimentada) utilizando o processamento largamente linear para sistemas SC-FDE foram propostos. Estes précodificadores e equalizadores têm um desempenho de erro melhor quando comparados com suas versões estritamente lineares se sinais provenientes de uma constelação imprópria são transmitidos. Além disso, o desempenho de erro quando equalizadores com realimentação de decisão são utilizados é menos sensível ao comprimento do filtro realimentado. Quando précodificadores largamente lineares são utilizados, este desempenho torna-se menos sensível a erros de estimação do cana

FBMC system: an insight into doubly dispersive channel impact

It has been claimed that filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, intersymbol interference (ISI), intercarrier interference (ICI), interblock interference (IBI), and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that under harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur

Nouvelles Techniques de Précodage et d Égalisation pour les Systèmes Multiporteuses

Dans cette thèse, de nouvelles techniques d'égalisation et de précodage pour des systèmes multiporteuses ont été proposées et analysées. D'abord, la performance d'erreur des systèmes multiporteuses à base de bancs de filtres (FBMC) précodées a été analysée. Il a été découvert que cette performance est très sensible à l'égalisation complète des sous-canaux. Quand il y a de l'interference inter-symbole residuel qui vient de l'égalisation imparfaite du sous-canaux, il y a une perte de diversité; cette diversité peut être recuperée avec l'adoption d'un nombre de sous-canaux assez grand pour que chaque sous-canaux subisse de l'évanouissement plat ou avec l'utilisation d'un égaliseur de sous-canaux avec une longueur assez suffisante pour compenser cette réponse en fréquence. Après, une approximation pour la distribution du rapport signal/bruit-plus-interfèrence (SINR) des systèmes SC-FDE qui utilisent égalisation MMSE linéaire a été proposée. Cette approximation utilise la distribution lognormal avec la plus petit distance de Kullback-Leibler vers la vraie distribution, et il s'est révélé qu'elle est precise dans la performance d'erreur; elle sert aussi comme une abstraction de cette système. Avec cette abstraction, une méthode précise pour obtenir la performance d'erreur analytique codée de ces systèmes a été proposée. Finalement, des précodeurs Tomlinson-Harashima (THP) et égaliseurs (linéaires et à retour de décision) largement linéaires pour des systèmes SC-FDE ont été proposés. Ces précodeurs et égaliseurs ont une performance d'erreur mieux quand comparés avec ses versions strictement linéaires si des signaux de constellations impropres sont transmises. Aussi, la performance d'erreur quand des égaliseurs à retour de décision sont utilisés est moins sensible au longueur du filtre de retour. Quand des précodeurs largement linéaires sont utilisés, cette performance devient moins sensible à des erreurs d'estimation du canaux.In this thesis, new precoding and equalization techniques for multicarrier systems were proposed and analyzed.First, the error performance of precoded filterbank multicarrier (FBMC) systems was analyzed. It was found out that this performance is highly sensitive to complete subchannel equalization. When there is residual intersymbol interference (ISI) stemming from imperfect subchannel equalization there is a loss of diversity; this loss can be prevented with the adoption of a number of subchannels large enough so that each subchannel suffers flat fading or with the utilization of a subchannel equalizer with sufficient length to compensate the subchannel frequency response.After that, an approximation for the signal to interference-plus-noise ratio (SINR) distribution of SC-FDE systems using linear MMSE equalization was proposed. This approximation uses the lognormal distribution with the smallest Kullback-Leibler distance to the true distribution, and was shown to be precise in the error performance sense; it serves as a system abstraction. With this abstraction, a precise method to obtain the analytical coded error performance of these systems was proposed.Finally, widely linear Tomlinson-Harashima precoders and equalizers (linear and decision-feedback) for SC-FDE systems were proposed. These precoders and equalizers have better error performance when compared to their strictly linear versions if signals coming from an improper constellation are transmitted. Their error performance when decision-feedback equalizers are used is less sensitive to the length of the feedback filter. When widely linear precoders are used, this error performance becomes less sensitive to channel estimation errors.PARIS-CNAM (751032301) / SudocSudocFranceF

Waveform Design for 5G and Beyond

5G is envisioned to improve major key performance indicators (KPIs), such as peak data rate, spectral efficiency, power consumption, complexity, connection density, latency, and mobility. This chapter aims to provide a complete picture of the ongoing 5G waveform discussions and overviews the major candidates. It provides a brief description of the waveform and reveals the 5G use cases and waveform design requirements. The chapter presents the main features of cyclic prefix-orthogonal frequency-division multiplexing (CP-OFDM) that is deployed in 4G LTE systems. CP-OFDM is the baseline of the 5G waveform discussions since the performance of a new waveform is usually compared with it. The chapter examines the essential characteristics of the major waveform candidates along with the related advantages and disadvantages. It summarizes and compares the key features of different waveforms.Comment: 22 pages, 21 figures, 2 tables; accepted version (The URL for the final version: https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119333142.ch2

Downlink scheduling and resource allocation for 5G MIMO-multicarrier: OFDM vs FBMC/OQAM

OAPA The definition of the next generation of wireless communications, so-called 5G networks, is currently underway. Among many technical decisions, one that is particularly fundamental is the choice of the physical layer modulation format and waveform, an issue for which several alternatives have been proposed. Two of the most promising candidates are: (i) orthogonal frequency division multiple (OFDM), a conservative proposal that builds upon the huge legacy of 4G networks, and (ii) filterbank multicarrier/offset quadrature amplitude modulation (FBMC/OQAM), a progressive approach that in frequency selective channels sacrifices subcarrier orthogonality in lieu of an increased spectral efficiency. The comparative merits of OFDM and FBMC/OQAM have been well investigated over the last few years but mostly, from a purely physical layer point of view and largely neglecting how the physical layer performance translates into user-relevant metrics at the upper-layers. This paper aims at presenting a comprehensive comparison of both modulation formats in terms of practical network indicators such as goodput, delay, fairness and service coverage, and under operational conditions that can be envisaged to be realistic in 5G deployments. To this end, a unifying cross-layer framework is proposed that encompasses the downlink scheduling and resource allocation procedures and that builds upon a model of the queueing process at the data-link control layer and a physical layer abstraction that can be chosen to model either OFDM or FBMC/OQAM. Extensive numerical results conclusively demonstrate that most of the apriori advantages of FBMC/OQAM over OFDM do indeed translate into improved network indicators, that is, the increase in spectral efficiency achieved by FBMC/OQAM makes up for the distortion caused by the loss of orthogonality.Peer ReviewedPostprint (published version