Efficient implementation of filter bank multicarrier systems using circular fast convolution

In this paper, filter bank-based multicarrier systems using a fast convolution approach are investigated. We show that exploiting offset quadrature amplitude modulation enables us to perform FFT/IFFT-based convolution without overlapped processing, and the circular distortion can be discarded as a part of orthogonal interference terms. This property has two advantages. First, it leads to spectral efficiency enhancement in the system by removing the prototype filter transients. Second, the complexity of the system is significantly reduced as the result of using efficient FFT algorithms for convolution. The new scheme is compared with the conventional waveforms in terms of out-of-band radiation, orthogonality, spectral efficiency, and complexity. The performance of the receiver and the equalization methods are investigated and compared with other waveforms through simulations. Moreover, based on the time variant nature of the filter response of the proposed scheme, a pilot-based channel estimation technique with controlled transmit power is developed and analyzed through lower-bound derivations. The proposed transceiver is shown to be a competitive solution for future wireless networks

Toward Early-Warning Detection of Gravitational Waves from Compact Binary Coalescence

Rapid detection of compact binary coalescence (CBC) with a network of advanced gravitational-wave detectors will offer a unique opportunity for multi-messenger astronomy. Prompt detection alerts for the astronomical community might make it possible to observe the onset of electromagnetic emission from (CBC). We demonstrate a computationally practical filtering strategy that could produce early-warning triggers before gravitational radiation from the final merger has arrived at the detectors.Comment: 16 pages, 7 figures, published in ApJ. Reformatted preprint with emulateap

Frequency-Domain Signal Processing for Spectrally-Enhanced CP-OFDM Waveforms in 5G New Radio

Orthogonal frequency-division multiplexing (OFDM) has been selected as the basis for the fifth-generation new radio (5G-NR) waveform developments. However, effective signal processing tools are needed for enhancing the OFDM spectrum in various advanced transmission scenarios. In earlier work, we have shown that fast-convolution (FC) processing is a very flexible and efficient tool for filtered-OFDM signal generation and receiver-side subband filtering, e.g., for the mixed-numerology scenarios of the 5G-NR. FC filtering approximates linear convolution through effective fast Fourier transform (FFT)-based circular convolutions using partly overlapping processing blocks. However, with the continuous overlap-and-save and overlap-and-add processing models with fixed block-size and fixed overlap, the FC-processing blocks cannot be aligned with all OFDM symbols of a transmission frame. Furthermore, 5G-NR numerology does not allow to use transform lengths shorter than 128 because this would lead to non-integer cyclic prefix (CP) lengths. In this article, we present new FC-processing schemes which solve the mentioned limitations. These schemes are based on dynamically adjusting the overlap periods and extrapolating the CP samples, which make it possible to align the FC blocks with each OFDM symbol, even in case of variable CP lengths. This reduces complexity and latency, e.g., in mini-slot transmissions and, as an example, allows to use 16-point transforms in case of a 12-subcarrier-wide subband allocation, greatly reducing the implementation complexity. On the receiver side, the proposed scheme makes it possible to effectively combine cascaded inverse and forward FFT units in FC-filtered OFDM processing. Transform decomposition is used to simplify these computations. Very extensive set of numerical results is also provided, in terms of radio-link performance and associated processing complexity.Comment: This work has been submitted to the IEEE Transactions on Wireless Communications for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

Review of Recent Trends

This work was partially supported by the European Regional Development Fund (FEDER), through the Regional Operational Programme of Centre (CENTRO 2020) of the Portugal 2020 framework, through projects SOCA (CENTRO-01-0145-FEDER-000010) and ORCIP (CENTRO-01-0145-FEDER-022141). Fernando P. Guiomar acknowledges a fellowship from “la Caixa” Foundation (ID100010434), code LCF/BQ/PR20/11770015. Houda Harkat acknowledges the financial support of the Programmatic Financing of the CTS R&D Unit (UIDP/00066/2020).MIMO-OFDM is a key technology and a strong candidate for 5G telecommunication systems. In the literature, there is no convenient survey study that rounds up all the necessary points to be investigated concerning such systems. The current deeper review paper inspects and interprets the state of the art and addresses several research axes related to MIMO-OFDM systems. Two topics have received special attention: MIMO waveforms and MIMO-OFDM channel estimation. The existing MIMO hardware and software innovations, in addition to the MIMO-OFDM equalization techniques, are discussed concisely. In the literature, only a few authors have discussed the MIMO channel estimation and modeling problems for a variety of MIMO systems. However, to the best of our knowledge, there has been until now no review paper specifically discussing the recent works concerning channel estimation and the equalization process for MIMO-OFDM systems. Hence, the current work focuses on analyzing the recently used algorithms in the field, which could be a rich reference for researchers. Moreover, some research perspectives are identified.publishersversionpublishe

Conformação de pulso de formas de onda OFDM para a interface aérea 5G

Orientador: Luís Geraldo Pedroso MeloniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: As formas de onda com multiplexação ortogonal por divisão de freqüência (OFDM) foram utilizadas com sucesso na interface aérea 3GPP LTE para superar a seletividade do canal e proporcionar uma boa eficiência espectral e altas taxas de transmissão de dados. O próximo sistema de comunicações 5G tem como objetivo oferecer suporte a mais serviços do que o antecessor, como comunicações de banda larga móveis, comunicações de tipo máquina e comunicações de baixa latência, e considera muitos outros cenários de aplicação, como o uso de espectro fragmentado. Esta diversidade de serviços com diferentes requisitos não pode ser suportada pela OFDM convencional, pois OFDM configura toda a largura de banda com parâmetros que atendem a um serviço em particular. Além disso, pode ocorrer interferência interportadora (ICI) quando a OFDM convencional é usada com multiplexação assíncrona de múltiplos usuários e isso é devido às altas emissões fora de banda (OOB) das subportadoras e à violação da condição de ortogonalidade do sinal. Portanto, para atender aos requisitos das futuras aplicações sem fio 5G, o desenvolvimento de uma interface aérea inovadora com novas capacidades torna-se necessário, em particular, uma nova forma de onda mais espectralmente ágil do que OFDM capaz de suportar múltiplas configurações, suprimindo efetivamente a interferência entre usuários, e com integração direta com as camadas superiores. Este trabalho centra-se em duas técnicas de conformação de pulsos para reduzir a emissões fora de banda e melhorar o desempenho de formas de onda baseadas em OFDM. A conformação de pulsos pode permitir o uso de parametrizações múltiplas dentro da forma de onda e abandonar os paradigmas rígidos de ortogonalidade e sincronismo com uma degradação de desempenho causada por interferência intersymbol (ISI) e ICI relativamente baixa. A primeira parte aborda um método de modelagem de pulso baseado na filtragem por subportadora para reduzir a emissão fora de banda no transmissor e interferência de canal adjacente (ACI) no receptor. Ele pode ser implementado usando funções de janela e alguns formatos de janela são apresentados nesta parte. O primeiro usa o prefixo cíclico (CP) existente dos símbolos para suavizar as transições abruptas do sinal, portanto, os grandes lóbulos espectrais sinc causados pelos filtros retangulares. Isso garante a compatibilidade retroativa em sistemas que usam OFDM com prefixo cíclico (CP-OFDM). O formato da segunda janela estende o comprimento do CP para reter a capacidade da forma de onda para combater a propagação do atraso do canal. Os efeitos no desempenho do ISI e ICI são estudados em termos de relação de sinal para interferência (SIR) e taxa de erro de bit (BER) usando formas de onda LTE em um cenário de espectro fragmentado multi-usuário. A segunda parte deste trabalho aborda o desenho e análise de filtros para a contenção espectral flexível em transceptores com filtragem baseada em sub-banda. Este filtro, chamado aqui semi-equiripple, exibe melhor atenuação na banda de rejeição para reduzir as interferências entre subbandas do que os filtros equiripple e filtros sinc baseados em janelamento e também possui boas características de resposta ao impulso para reduzir o ISI. O projeto de filtros baseia-se no algoritmo Parks-McClellan para obter diferentes taxas de decaimento da banda de parada e atende a especificações arbitrárias de máscaras de emissão de espectro (SEM) com baixa distorção dentro da banda. Portanto, pode ser útil para obter baixas emissões fora da banda e configurar sub-bandas com parâmetros independentes, uma vez que a interferência assíncrona é contida pelos filtros. São estudadas três distorções de ISI no filtro: espalhamento de símbolos relacionado à causalidade do filtro, ecos de símbolos devido a ondulações na banda e amplificação de ISI devido a amostras de valores anômalas nas caudas de sua resposta de impulso. O desempenho do filtro é avaliado em termos de densidade de espectro de potência (PSD) e conformidade com SEMs, taxa de erro de modulação (MER) e operação em um esquema assíncrono multi-serviço usando uma única forma de onda. O SIR e o efeito da filtragem na precisão da modulação são avaliados usando formas de onda OFDM ISDB-T e LTE. Estruturas de hardware flexíveis também são propostas para implementações reais. Os resultados mostram que esses métodos de conformação de pulso permitem que a forma de onda explore os fragmentos de espectro disponíveis e ofereça suporte a múltiplos serviços sem uma penalidade de desempenho significativa, o que pode permitir uma interface aérea mais flexívelAbstract: Orthogonal frequency division multiplexing (OFDM) waveforms have been used successfully in the 3GPP Long Term Evolution (LTE) air interface to overcome the channel selectivity and to provide good spectrum efficiency and high transmission data rates. The forthcoming 5G communication system aims to support more services than its predecessor, such as enhanced mobile broadband, machine-type communications and low latency communications, and considers many other application scenarios such as the fragmented spectrum use. This diversity of services with different requirements cannot be supported by conventional OFDM since OFDM configures the entire bandwidth with parameters attending one service in particular. Also, substantial intercarrier interference (ICI) can occur when conventional OFDM is used with asynchronous multiuser multiplexing and this is due to the high out-of-band (OOB) emissions of the subcarriers and the violation of the signal orthogonality constraint. Therefore, to meet the requirements of future 5G wireless applications, the development of an innovative air interface with new capabilities becomes necessary, in particular, a new waveform more spectrally agile than OFDM capable of supporting multiple configurations, suppressing the inter-user interference effectively, and with straightforward integration with the upper layers. This work focuses on two pulse shaping techniques to reduce the OOB emission and improve the in-band and OOB performances of OFDM-based waveforms. Pulse shaping can enable the use of multiple parameterizations within the waveform and abandon the strict paradigms of orthogonality and synchronism with relatively low performance degradation caused by intersymbol interference (ISI) and ICI. The first part addresses a pulse shaping method based on per-subcarrier filtering to reduce both OOB emission in the transmitter and adjacent channel interference (ACI) in the receiver. It can be implemented using window functions and some window formats are presented in this part. The first uses the existing cyclic prefix (CP) of OFDM symbols to smooth abrupt transitions of the signal, thus the large sinc spectral sidelobes caused by the rectangular filters. This guarantees backwards compatibility in systems using conventional cyclic prefixed OFDM (CP-OFDM). The second window format extends the CP length to retain the waveform ability to combat channel delay spread. The effects on performance of ISI and ICI are studied in terms of the signal to interference ratio (SIR) and bit error rate (BER) using LTE waveforms in a multi-user fragmented spectrum scenario. The second part of this work addresses the design and analysis of a filters for flexible spectral containment in subband-based filtering transceivers. This filter, called here semi-equiripple, exhibits better stopband attenuation to reduce the inter-subband interferences than equiripple and windowed truncated sinc filters and also has good impulse response characteristics to reduce ISI. The design is based on the Parks-McClellan algorithm to obtain different stopband decay rates and meet arbitrary spectrum emission masks (SEM) specifications with low in-band distortion. Therefore, it can be useful to achieve low OOB emission and configure subbands with independent parameters since the asynchronous interference is contained by the filters. Three ISI distortions in the filter are studied: symbol spreading related to the filter causality, symbol echoes due to in-band ripples, and ISI amplification due to outlier samples in the tails of its impulse response. The performance of the filter is assessed in terms of the power spectrum density (PSD) and compliance with tight SEMs, modulation error rate (MER) and operation in a multi-service asynchronous scheme using a single waveform. The SIR and the effect of filtering on the modulation accuracy are evaluated using OFDM ISDB-T and LTE waveforms. Flexible hardware structures are also proposed for actual implementations. The results show that these pulse shaping methods enable the waveform to exploit the available spectrum fragments and support multiple services without significant performance penalty, which can allow a more flexible air interfaceMestradoTelecomunicações e TelemáticaMestre em Engenharia ElétricaCAPE

Emulation of Narrowband Powerline Data Transmission Channels and Evaluation of PLC Systems

This work proposes advanced emulation of the physical layer behavior of NB-PLC channels and the application of a channel emulator for the evaluation of NB-PLC systems. In addition, test procedures and reference channels are proposed to improve efficiency and accuracy in the system evaluation and classification. This work shows that the channel emulator-based solution opens new ways toward flexible, reliable and technology-independent performance assessment of PLC modems

An investigation into a DSP implementation of partial response signaling for 4800 bits per second full-duplex data communications over M.1020 telephone lines

Includes bibliographical references.This thesis investigates high-speed digital transmission over a conditioned, voice-grade telephone circuit (M.1020), using a technique known as partial response signaling, or PRS. In particular, the case where 4800 bps, full-duplex transmission is required in a CCI'PT V. 22 type format is investigated. The main v.22 criterion to be adhered to, is that frequency-division multiplexing (FDM) is to be used as the means of separating thetransmit and receive channels. The carrier frequencies should be 1200 Hz and 2400 Hz respectively. The investigation concerns the modulation and demodulation sections only

Waveform Design for 5G and beyond Systems

5G traffic has very diverse requirements with respect to data rate, delay, and reliability. The concept of using multiple OFDM numerologies adopted in the 5G NR standard will likely meet these multiple requirements to some extent. However, the traffic is radically accruing different characteristics and requirements when compared with the initial stage of 5G, which focused mainly on high-speed multimedia data applications. For instance, applications such as vehicular communications and robotics control require a highly reliable and ultra-low delay. In addition, various emerging M2M applications have sparse traffic with a small amount of data to be delivered. The state-of-the-art OFDM technique has some limitations when addressing the aforementioned requirements at the same time. Meanwhile, numerous waveform alternatives, such as FBMC, GFDM, and UFMC, have been explored. They also have their own pros and cons due to their intrinsic waveform properties. Hence, it is the opportune moment to come up with modification/variations/combinations to the aforementioned techniques or a new waveform design for 5G systems and beyond. The aim of this Special Issue is to provide the latest research and advances in the field of waveform design for 5G systems and beyond

Low-Complexity Multicarrier Waveform Processing Schemes fo Future Wireless Communications

Wireless communication systems deliver enormous variety of services and applications. Nowa- days, wireless communications play a key-role in many fields, such as industry, social life, education, and home automation. The growing demand for wireless services and applications has motivated the development of the next generation cellular radio access technology called fifth-generation new radio (5G-NR). The future networks are required to magnify the delivered user data rates to gigabits per second, reduce the communication latency below 1 ms, and en- able communications for massive number of simple devices. Those main features of the future networks come with new demands for the wireless communication systems, such as enhancing the efficiency of the radio spectrum use at below 6 GHz frequency bands, while supporting various services with quite different requirements for the waveform related key parameters. The current wireless systems lack the capabilities to handle those requirements. For exam- ple, the long-term evolution (LTE) employs the cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM) waveform, which has critical drawbacks in the 5G-NR context. The basic drawback of CP-OFDM waveform is the lack of spectral localization. Therefore, spectrally enhanced variants of CP-OFDM or other multicarrier waveforms with well localized spectrum should be considered. This thesis investigates spectrally enhanced CP-OFDM (E-OFDM) schemes to suppress the out-of-band (OOB) emissions, which are normally produced by CP-OFDM. Commonly, the weighted overlap-and-add (WOLA) scheme applies smooth time-domain window on the CP- OFDM waveform, providing spectrally enhanced subcarriers and reducing the OOB emissions with very low additional computational complexity. Nevertheless, the suppression perfor- mance of WOLA-OFDM is not sufficient near the active subband. Another technique is based on filtering the CP-OFDM waveform, which is referred to as F-OFDM. F-OFDM is able to provide well-localized spectrum, however, with significant increase in the computational com- plexity in the basic scheme with time-domain filters. Also filter-bank multicarrier (FBMC) waveforms are included in this study. FBMC has been widely studied as a potential post- OFDM scheme with nearly ideal subcarrier spectrum localization. However, this scheme has quite high computational complexity while being limited to uniformly distributed sub- bands. Anyway, filter-bank based waveform processing is one of the main topics of this work. Instead of traditional polyphase network (PPN) based uniform filter banks, the focus is on fast-convolution filter banks (FC-FBs), which utilize fast Fourier transform (FFT) domain processing to realize effectively filter-banks with high flexibility in terms of subcarrier bandwidths and center frequencies. FC-FBs are applied for both FBMC and F-OFDM waveform genera- tion and processing with greatly increased flexibility and significantly reduced computational complexity. This study proposes novel structures for FC-FB processing based on decomposition of the FC-FB structure consisting of forward and inverse discrete Fourier transforms (DFT and IDFT). The decomposition of multirate FC provides means of reducing the computational complexity in some important specific scenarios. A generic FC decomposition model is proposed and analyzed. This scheme is mathematically equivalent to the corresponding direct FC imple- mentation, with exactly the same performance. The benefits of the optimized decomposition structure appear mainly in communication scenarios with relatively narrow active transmis- sion band, resulting in significantly reduced computational complexity compared to the direct FC structure. The narrowband scenarios find their places in the recent 3GPP specification of cellular low- power wide-area (LPWA) access technology called narrowband internet-of-things (NB-IoT). NB-IoT aims at introducing the IoT to LTE and GSM frequency bands in coexistence with those technologies. NB-IoT uses CP-OFDM based waveforms with parameters compatible with the LTE. However, additional means are needed also for NB-IoT transmitters to improve the spec- trum localization. For NB-IoT user devices, it is important to consider ultra-low complexity solutions, and a look-up table (LUT) based approach is proposed to implement NB-IoT uplink transmitters with filtered waveforms. This approach provides completely multiplication-free digital baseband implementations and the addition rates are similar or smaller than in the basic NB-IoT waveform generation without the needed elements for spectrum enhancement. The basic idea includes storing full or partial waveforms for all possible data symbol combinations. Then the transmitted waveform is composed through summation of needed stored partial waveforms and trivial phase rotations. The LUT based scheme is developed with different vari- ants tackling practical implementations issues of NB-IoT device transmitters, considering also the effects of nonlinear power amplifier. Moreover, a completely multiplication and addition- free LUT variant is proposed and found to be feasible for very narrowband transmission, with up to 3 subcarriers. The finite-wordlength performance of LUT variants is evaluated through simulations

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