Littérature scientifique sur le sujet « Beyond OFDM »

Computational complexity is one of the drawbacks of orthogonal frequency division multiplexing (OFDM)-index modulation (IM) systems. In this study, a novel IM technique is proposed for OFDM systems by considering the null subcarrier locations (NSC-OFDM-IM) within a predetermined group in the frequency domain. So far, a variety of index modulation techniques have been proposed for OFDM systems. However, they are almost always based on modulating the active subcarrier indices. We propose a novel index modulation technique by employing the part of the transmitted bit group into the null subcarrier location index within the predefined size of the subgroup. The novelty comes from modulating null subcarriers rather than actives and reducing the computational complexity of the index selection and index detection algorithms at the transmitter and receiver, respectively. The proposed method is physically straightforward and easy to implement owing to the size of the subgroups, which is defined as a power of two. Based on the results of our simulations, it appeared that the proposed NSC-OFDM-IM does not suffer from any performance degradation compared to the existing OFDM-IM, while achieving better bit error rate (BER) performance and improved spectral efficiency (SE) compared to conventional OFDM. Moreover, in terms of computational complexity, the proposed approach has a significantly reduced complexity over the traditional OFDM-IM scheme.

Non-orthogonal multiple access (NOMA) is a promising applicant innovation for 5G cell systems. By and by MIMO-OFDM remote innovations are utilizing in 4G LTE development remote correspondence. This paper examine about the job of MIMO-OFDM and NOMA as principal contributing execution factors in past 4G LTE Remote Transmission Innovation from a specialized point of view. Long Term Evolution (LTE) utilizes Orthogonal Frequency Division Multiplexing (OFDM) along with MIMO (Multiple Input Multiple Output) reception apparatus innovation standard to accomplish high radio spectral efficiency and multicarrier approach for multiple accesses.

F-OFDM (Filtered-OFDM) is a flexible waveform that has been considered suitable for 5G and beyond systems for its improved spectrum utilization, moderates PAPR, low OOB emission, multiple asynchronous sub-band transmission, and high robustness to frequency selectivity. It can attain a desirable balance between frequency and time localizations for narrow bandwidths. It is also MIMO friendly. In this paper, a comprehensive design and analysis have been made to evaluate the performance of MIMO (4×4) CP-OFDM and F-OFDM systems for message bits transmission using several digital modulation techniques (16-QAM, 16-PSK, 16-DPSK, 64-QAM, 64-PSK, and 64-DPSK), RA channel coding, different windowed (Hanning, Hamming, Blackman, Blackman-Harris, RRC) sinc FIR filters for length N = 513, and MMSE signal detection technique. From MATLAB based simulation results, it is observed that F-OFDM reduces spectrum leakage thus enhances spectrum efficiency than conventional CP-OFDM. F-OFDM based system offers lower BER (Bit Error Rate) performance than CP-OFDM based system.

As one of the techniques beyond 3G, because of the effective performance of high spectrum utilization and anti-fading for frequency selecting and adopted multi-carrier modulation technique that meets the requirement of the explosive traffic capacity, Orthogonal Frequency Division Multiplexing (OFDM) has carried great weight in wireless communications. This paper expounds OFDM technical characteristics and performs computer simulation on the OFDM system based on Inverse Fast Fourier Transform (IFFT) by means MATLAB. During the course of simulation, comparison between OFDM and traditional single-carrier technology is performed. The simulation results have great significance for research and applications in the field.

Although orthogonal frequency division multiplexing (OFDM) has been standardized for 5G, filter bank multi-carrier (FBMC) and filtered orthogonal frequency division multiplexing (F-OFDM) remain competitive as candidates for future generations of wireless technologies beyond 5G, due to their reduced spectrum leakage and thus enhanced spectrum efficiency. In this article, we developed a unified spectrum expression for OFDM, FBMC, and F-OFDM, which provides comparative insights into those techniques. A representative sideband quantification is included at the end of this article.

The current generation (5G) mobile communication system promises to accommodate a wide range of new applications and use scenarios, resulting in more flexible and unified connection. To satisfy the required criteria, the current waveform was replaced with new UF-OFDM, which combines the advantages of OFDM with enhanced spectral characteristics and greater resilience against time-frequency misalignments. However, its biggest disadvantage is the transmitter's computational complexity, which may be up to two hundred times that of OFDM if there is no reduction in complexity. The majority of current research on unique waveforms has focused on filter modification or performance enhancement strategies. UFMC with the use of adaptive filter (UFMC -FSK) is offered as a revolutionary technique in this study. The filter designed and used to transport information through the index modulation technique. As a result, each UF-OFDM sub band's used filter is chosen, so the data rate is enhanced according to a filter configured depending on original input data bits. The combined Maximum-likelihood (ML) decision metric for each sub band that is calculated at the receiver. Each sub band has a filter as well as data symbols that provide the minimal metric for making decisions are discovered. Furthermore, the bit error rate and power spectrum density are enhanced over the UF-OFDM technique, however there is some trade-off. Overall, the proposed system outperform typical UF-OFDM. Matlab simulations are used to assess the performance of the Adaptive UFMC system.

The vision towards 6G and beyond communication systems demands higher rate transmission, massive amount of data processing, and low latency communication. Orthogonal Frequency Division Modulation (OFDM) has been adopted in the current 5G networks and has become one of the potential candidates for the future communication systems. Although OFDM offers many benefits including high spectrum efficiency and high robustness against the multipath fading channels, it has major challenges such as frequency offset and high Peak to Power Ratio (PAPR). In 5G communication network, there is a significant increase in the number of sensors and other low-power devices where users or devices may create large amount of connection and dynamic data processing. In order to deal with the increasingly complex communication network, Machine Learning (ML) has been increasingly utilised to create intelligent and more efficient communication network. This paper discusses challenges and the impacts of embedding ML in OFDM-based communication systems.

Nowadays, multicarrier modulation schemes are being widely used in wireless communication system than single-carrier modulation techniques. Single-carrier modulation schemes are less capable of dealing with multipath fading channels than multicarrier modulation schemes, which results in lower spectral efficiency. Multicarrier modulation schemes have the ability to overcome multipath fading channels. Multicarrier modulation technique currently used in 4G technology in many countries is OFDM and it is easy for implementation, immune to interference, and provide fast data rate. However, the rising users demand on wireless communication resulted in need for further advancement of wireless communication system. The present OFDM transmission does not fulfill the requirements of 5G wireless communication system and beyond due to major limitations such as out of band emission and usage of cyclic prefix. To overcome the challenges of OFDM, different modulation schemes like Filter Bank Multicarrier with Offset-QAM, Filter Bank Multicarrier with QAM, Universal Filter Multicarrier, Filtered-OFDM, and Weighted Overlap and Added-OFDM are proposed. In this study, the Filter Bank Multicarrier with QAM using Hermite prototype filter is proposed to overcome drawbacks of OFDM and all other proposed waveforms. The performances of each multicarrier technique are analyzed based on power spectral density and bit error rate. Simulation result shows that the power spectral density of FBMC with QAM using Hermite filter resulted in 4.7 dB reduction of out of band emission compared to FBMC with QAM using PHYDYAS filter. The bit error rate is also reduced for Vehicular A, Vehicular B, Pedestrian A, and Pedestrian B channel models.

[ES] La estandarización de la Quinta Generación de redes móviles o 5G, ha concluido este año 2020. No obstante, en el año 2014 cuando la ITU empezó el proceso de estandarización IMT-2020, una de las principales interrogantes era cuál sería la forma de onda sobre la cual se construiría la capa física de esta nueva generación de tecnologías. El 3GPP se comprometió a entregar una tecnología candidata al proceso IMT-2020, y es así como dentro de este proceso de deliberación se presentaron varias formas de onda candidatas, las cuales fueron evaluadas en varios aspectos hasta que en el año 2016 el 3GPP tomó una decisión, continuar con CP-OFDM (utilizada en 4G) con numerología flexible. Una vez decidida la forma de onda, el proceso de estandarización continuó afinando la estructura de la trama, y todos los aspectos intrínsecos de la misma. Esta tesis acompañó y participó de todo este proceso. Para empezar, en esta disertación se evaluaron las principales formas de onda candidatas al 5G. Es así que se realizó un análisis teórico de cada forma de onda, destacando sus fortalezas y debilidades, tanto a nivel de implementación como de rendimiento. Posteriormente, se llevó a cabo una implementación real en una plataforma Software Defined Radio de tres de las formas de onda más prometedoras (CP-OFDM, UFMC y OQAM-FBMC), lo que permitió evaluar su rendimiento en términos de la tasa de error por bit, así como la complejidad de su implementación. Esta tesis ha propuesto también el uso de una solución armonizada como forma de onda para el 5G y sostiene que sigue siendo una opción viable para sistemas beyond 5G. Dado que ninguna de las forma de onda candidatas era capaz de cumplir por sí misma con todos los requisitos del 5G, en lugar de elegir una única forma de onda se propuso construir un transceptor que fuese capaz de construir todas las principales formas de onda candidatas (CP-OFDM, P-OFDM, UFMC, QAM-FBMC, OQAM-FBMC). Esto se consiguió identificando los bloques comunes entre las formas de onda, para luego integrarlos junto con el resto de bloques indispensables para cada forma de onda. La motivación para esta solución era tener una capa física que fuese capaz de cumplir con todos los aspectos del 5G, seleccionando siempre la mejor forma de onda según el escenario. Esta propuesta fue evaluada en términos de complejidad, y los resultados se compararon con la complejidad de cada forma de onda. La decisión de continuar con CP-OFDM con numerología flexible como forma de onda para el 5G se puede considerar también como una solución armonizada, ya que al cambiar el prefijo cíclico y el número de subportadoras, cambian también las prestaciones del sistema. En esta tesis se evaluaron todas las numerologías propuestas por el 3GPP sobre cada uno de los modelos de canal descritos para el 5G (y considerados válidos para sistemas beyond 5G), teniendo en cuenta factores como la movilidad de los equipos de usuario y la frecuencia de operación; para esto se utilizó un simulador de capa física del 3GPP, al que se hicieron las debidas adaptaciones con el fin de evaluar el rendimiento de las numerologías en términos de la tasa de error por bloque. Finalmente, se presenta un bosquejo de lo que podría llegar a ser la Sexta Generación de redes móviles o 6G, con el objetivo de entender las nuevas aplicaciones que podrían ser utilizadas en un futuro, así como sus necesidades. Completado el estudio llevado a cabo en esta tesis, se puede afirmar que como se propuso desde un principio la solución, tanto para el 5G como para beyond 5G, la solución es la armonización de las formas de onda. De los resultados obtenidos se puede corroborar que una solución armonizada permite alcanzar un ahorro computacional entre el 25-40% para el transmisor y del 15-25% para el receptor. Además, fue posible identificar qué numerología CP-OFDM es la más adecuada para cada escenario, lo que permitiría optimizar el diseño y despliegue de las redes 5G. Esto abriría la puerta a hacer lo mismo con el 6G, ya que en esta tesis se considera que será necesario abrir nuevamente el debate sobre cuál es la forma de onda adecuada para esta nueva generación de tecnologías, y se plantea que el camino a seguir es optar por una solución armonizada con distintas formas de onda, en lugar de solo una como sucede con el 5G.
[CA] L'estandardització de la Quinta Generació de xarxes mòbils o 5G, ha conclòs enguany 2020. No obstant això, l'any 2014 quan la ITU va començar el procés d'estandardització IMT-2020, uns dels principals interrogants era quina seria la forma d'onda sobre la qual es construiria la capa física d'esta nova generació de tecnologies. El 3GPP es va comprometre a entregar una tecnologia candidata al procés IMT-2020, i és així com dins d'este procés de deliberació es van presentar diverses formes d'onda candidates, les quals van ser avaluades en diversos aspectes fins que l'any 2016 el 3GPP va prendre una decisió, continuar amb CP-OFDM (utilitzada en 4G) amb numerología flexible. Una vegada decidida la forma d'onda, el procés d'estandardització va continuar afinant la frame structure (no se m'ocorre nom en espanyol), i tots els aspectes intrínsecs de la mateixa. Esta tesi va acompanyar i va participar de tot este procés. Per a començar, en esta dissertació es van avaluar les principals formes d'onda candidates al 5G. És així que es va realitzar una anàlisi teòrica de cada forma d'onda, destacant les seues fortaleses i debilitats, tant a nivell d'implementació com de rendiment. Posteriorment, es va dur a terme una implementació real en una plataforma Software Defined Radio de tres de les formes d'onda més prometedores (CP-OFDM, UFMC i OQAM-FBMC), la qual cosa va permetre avaluar el seu rendiment en termes de la taxa d'error per bit, així com la complexitat de la seua implementació. Esta tesi ha proposat també l'ús d'una solució harmonitzada com a forma d'onda per al 5G i sosté que continua sent una opció viable per a sistemes beyond 5G. Atés que cap de les forma d'onda candidates era capaç de complir per si mateixa amb tots els requeriments del 5G, en compte de triar una única forma d'onda es va proposar construir un transceptor que fóra capaç de construir totes les principals formes d'onda candidates (CP-OFDM, P-OFDM, UFMC, QAM-FBMC, OQAM-FBMC). Açò es va aconseguir identificant els blocs comuns entre les formes d'onda, per a després integrar-los junt amb la resta de blocs indispensables per a cada forma d'onda. La motivació per a esta solució era tindre una capa física que fóra capaç de complir amb tots els aspectes del 5G, seleccionant sempre la millor forma d'onda segons l'escenari. Esta proposta va ser avaluada en termes de complexitat, i els resultats es van comparar amb la complexitat de cada forma d'onda. La decisió de continuar amb CP-OFDM amb numerología flexible com a forma d'onda per al 5G es pot considerar també com una solució harmonitzada, ja que al canviar el prefix cíclic i el número de subportadores, canvien també les prestacions del sistema. En esta tesi es van avaluar totes les numerologías propostes pel 3GPP sobre cada un dels models de canal descrits per al 5G (i considerats vàlids per a sistemes beyond 5G), tenint en compte factors com la mobilitat dels equips d'usuari i la freqüència d'operació; per a açò es va utilitzar un simulador de capa física del 3GPP, a què es van fer les degudes adaptacions a fi d'avaluar el rendiment de les numerologías en termes de la taxa d'error per bloc. Finalment, es presenta un esbós del que podria arribar a ser la Sexta Generació de xarxes mòbils o 6G, amb l'objectiu d'entendre les noves aplicacions que podrien ser utilitzades en un futur, així com les seues necessitats. Completat l'estudi dut a terme en esta tesi, es pot afirmar que com es va proposar des d'un principi la solució, tant per al 5G com per a beyond 5G, la solució és l'harmonització de les formes d'onda. dels resultats obtinguts es pot corroborar que una solució harmonitzada permet aconseguir un estalvi computacional entre el 25-40% per al transmissor i del 15-25% per al receptor. A més, va ser possible identificar què numerología CP-OFDM és la més adequada per a cada escenari, la qual cosa permetria optimitzar el disseny i desplegament de les xarxes 5G. Açò obriria la porta a fer el mateix amb el 6G, ja que en esta tesi es considera que serà necessari obrir novament el debat sobre quina és la forma d’onda adequada per a esta nova generació de tecnologies, i es planteja que el camí que s’ha de seguir és optar per una solució harmonitzada amb distintes formes d’onda, en compte de només una com succeïx amb el 5G.
[EN] The standardization of the Fifth Generation of mobile networks or 5G is still ongoing, although the first releases of the standard were completed two years ago and several 5G networks are up and running in several countries around the globe. However, in 2014 when the ITU began the IMT-2020 standardization process, one of the main questions was which would be the waveform to be used on the physical layer of this new generation of technologies. The 3GPP committed to submit a candidate technology to the IMT-2020 process, and that is how within this deliberation process several candidate waveforms were presented. After a thorough evaluation regarding several aspects, in 2016 the 3GPP decided to continue with CP-OFDM (used in 4G) but including, as a novelty, the use of a flexible numerology. Once the waveform was decided, the standardization process continued to fine-tune the frame structure and all the intrinsic aspects of it. This thesis accompanied and participated in this entire process. To begin with, this dissertation evaluates the main 5G candidate waveforms. Therefore, a theoretical analysis of each waveform is carried out, highlighting its strengths and weaknesses, both at the implementation and performance levels. Subsequently, a real implementation on a Software Defined Radio platform of three of the most promising waveforms (CP-OFDM, UFMC, and OQAM-FBMC) is presented, which allows evaluating their performance in terms of bit error rate, as well as the complexity of its implementation. This thesis also proposes the use of a harmonized solution as a waveform for 5G and argues that it remains a viable option for systems beyond 5G. Since none of the candidate waveforms was capable of meeting on its own with all the requirements for 5G, instead of choosing a single waveform, this thesis proposes to build a transceiver capable of building all the main waveforms candidates (CP-OFDM, P-OFDM, UFMC, QAM-FBMC, OQAM-FBMC). This is achieved by identifying the common blocks between the waveforms and then integrating them with the rest of the essential blocks for each waveform. The motivation for this solution is to have a physical layer that is capable of complying with all aspects of beyond 5G technologies, always selecting the best waveform according to the scenario. This proposal is evaluated in terms of complexity, and the results are compared with the complexity of each waveform. The decision to continue with CP-OFDM with flexible numerology as a waveform for 5G can also be considered as a harmonized solution, since changing the cyclic prefix and the number of subcarriers, changes also the performance of the system. In this thesis, all the numerologies proposed by the 3GPP are evaluated on each of the channel models described for 5G (and considered valid for beyond 5G systems), taking into account factors such as the mobility of the user equipment and the operating frequency. For this, a 3GPP physical layer simulator is used, and proper adaptations are made in order to evaluate the performance of the numerologies in terms of the block error rate. Finally, a sketch of what could become the Sixth Generation of mobile networks or 6G is presented, with the aim of understanding the new applications that could be used in the future, as well as their needs. After the completion of the study carried out in this thesis, it can be said that, as stated from the beginning, for both 5G and beyond 5G systems, the solution is the waveform harmonization. From the results obtained, it can be corroborated that a harmonized solution allows achieving computational savings between 25-40% for the transmitter and 15-25% for the receiver. In addition, it is possible to identify which CP-OFDM numerology is the most appropriate for each scenario, which would allow optimizing the design and deployment of 5G networks. This would open the door to doing the same with 6G, i.e., a harmonized solution with different waveforms, instead of just one as in 5G.
Flores De Valgas Torres, FJ. (2020). Study on Air Interface Variants and their Harmonization for Beyond 5G Systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164442
TESIS

La recherche de nouvelles formes d'onde robustes, lorsque utilisées sur des canaux doublement sélectifs, est primordiale. De telles formes d'onde permettraient donc d'assurer des communications fiables pour les réseaux sans fil de nouvelle génération dans les scénarios de haute mobilité. Dans cette thèse, une nouvelle solution, le affine frequency division multiplexing (AFDM), est proposée. Cette nouvelle forme d'onde de type multichirps est basée sur la transformée de Fourier affine discrète (DAFT), une variante de la transformée de Fourier discrète caractérisée par deux paramètres pouvant être adaptés pour mieux faire face aux canaux doublement dispersifs. Cette thèse offre une enquête complète sur les principes de l'AFDM au sein des communications à haute mobilité. Elle fournit un aperçu de la relation explicite entrée-sortie dans le domaine DAFT, révélant l'impact conséquent des paramètres de l'AFDM. Le manuscrit détaille le réglage précis des paramètres DAFT qui permette d'assurer une représentation complète délai-Doppler du canal de propagation sans fil. À travers des démonstrations analytiques, il est affirmé que l'AFDM atteint de manière optimale l'ordre de diversité des canaux doublement dispersifs en raison de la représentation complète délai-Doppler du canal qu'il permet d'obtenir. La thèse propose également deux algorithmes de détection à faible complexité pour l'AFDM, tirant parti de la parcimonie inhérente du canal. Le premier est un détecteur de type minimum mean squared error (MMSE) à faible complexité basé sur la factorisation LDL. Le deuxième est un égaliseur de type decision feedback equalizer (DFE) à faible complexité basé sur la combinaison cohérente, grace à la méthode maximum ratio combining (MRC), de différentes copies des symboles d'entrée du canal ayant été altérés par différents trajets de ce dernier. De plus, la thèse présente une technique de type embedded d'estimation de canal pour les systèmes AFDM, exploitant la capacité de l'AFDM à obtenir une représentation complète délai-Doppler du canal. Dans cette approche, un seul symbole pilote est inséré dans le domain DAFT du symbole AFDM, et les interférences que ce pilote pourrait générer pour les symboles de donnée sont évitées par des intervalles de garde. Un algorithme pratique d'estimation de canal, compatible avec ce schéma de transmission de pilote et basé sur une approche de type approximate maximum likelihood (ML), est aussi proposé. La thèse est conclue en se penchant sur de possibles applications de l'AFDM au delà de celles conçues pour les environnements marqués par une haute mobilité, spécifiquement les applications de type integrated sensing and communication (ISAC) et les communications dans les bandes de hautes fréquences. Il est démontré que pour identifier tous les composants de délai et de Doppler liés au milieu de propagation, on peut utiliser soit le signal AFDM complet, soit seulement sa partie pilote constituée d'un symbole de domaine DAFT et de son intervalle de garde. De plus, la nature chirp de l'AFDM permet une annulation simple de l'auto-interférence, éliminant ainsi le besoin de méthodes coûteuses normalement nécessaires dans les systèmes full duplex. La thèse met également en évidence les bonnes performances de l'AFDM pour les communications sans fil dans les bandes de hautes fréquences sans ou avec mobilité, grâce à la répartition maximale du signal AFDM en temps et en fréquences, assurant un gain de couverture. Contrairement à d'autres formes d'onde, l'AFDM ne fournit pas seulement une répartition maximale temps-fréquences mais assure également une détection robuste et efficace et une résilience au décalage de fréquence de porteuse et au bruit de phase
In the realm of next-generation wireless systems (beyond 5G/6G), the vision is clear: to support a broad range of services and applications. This includes ensuring reliable communications in environments marked by high mobility, such as high-speed railway systems and various vehicular communications. Despite the deployment of various multicarrier techniques like orthogonal frequency division multiplexing (OFDM) and single-carrier frequency division multiple access (SC-FDMA) in standardized communication systems, the challenge persists. These techniques, while effective in time-invariant frequency selective channels, face performance degradation in high mobility scenarios due to the destruction of orthogonality among subcarriers caused by significant Doppler frequency shifts. Addressing this, the search for new, robust modulation techniques is paramount. It stands as a key area of investigation aiming to resolve the reliable communications issue for next-generation wireless networks within doubly-selective wireless channels. In this thesis, a novel solution, affine frequency division multiplexing (AFDM), is proposed. This new chirp-based multicarrier waveform is based on the discrete affine Fourier transform (DAFT), a variant of the discrete Fourier transform characterized with two parameters that can be adapted to better cope with doubly dispersive channels. This thesis provides a comprehensive investigation into the principles of AFDM within high mobility communications. It provides insight into the explicit input-output relation in the DAFT domain, unveiling the consequential impact of AFDM parameters. The manuscript details the precise setting of DAFT parameters, ensuring a full delay-Doppler representation of the channel. Through analytical demonstrations, it asserts that AFDM optimally achieves the diversity order in doubly dispersive channels due to its full delay-Doppler representation. The thesis also proposes two low-complexity detection algorithms for AFDM, taking advantage of its inherent channel sparsity. The first is a low complexity MMSE detector based on LDL factorization. The second is a low complexity iterative decision feedback equalizer (DFE) based on weighted maximal ratio combining (MRC) of the channel impaired input symbols received from different paths. Additionally, the thesis presents an embedded channel estimation strategy for AFDM systems, leveraging AFDM's ability to achieve full delay-Doppler representation of the channel. In this approach, an AFDM frame contains a pilot symbol and data symbols, with zero-padded symbols employed as guard intervals to prevent interference. A practical channel estimation algorithm based on an approximate maximum likelihood (ML) approach and compatible with this pilot scheme is also provided. The thesis concludes by delving into the expanded applications of AFDM, specifically in integrated sensing and communication (ISAC) and extremely high frequency (EHF) band communications. It is demonstrated that to identify all delay and Doppler components linked with the propagation medium, one can use either the full AFDM signal or only its pilot part consisting of one DAFT domain symbol and its guard interval. Furthermore, the chirp nature of AFDM allows for unique and simple self-interference cancellation with a single pilot, eliminating the need for costly full-duplex methods. The thesis also highlights AFDM's efficient performance in high-frequency bands (with or without mobility), where the maximal spreading of its signal in time and frequency ensures a coverage gain. Unlike other waveforms, AFDM not only provides maximal time-frequency spreading but also ensures robust and efficient detection, characterized by one-tap equalization and resilience to carrier frequency offset (CFO) and phase noise

碩士
國立臺灣大學
電信工程學研究所
107
Enabling asynchronous multiuser uplink transmission is important and necessary for the next generation of wireless networks (5G) since it has to be able to meet the requirements for some scenarios, such as ultra-reliable low-latency communications (URLLC), and massive machine type communications (mMTC). In relaxed synchronization conditions, orthogonal frequency division multiplexing (OFDM) system, which is widely used in the fourth generation of the wireless network (4G), is easy to interfere adjacent users due to high out-of-subband emission (OSBE). Circularly pulse-shaped precoding orthogonal frequency division multiplexing (CPS-OFDM) system, a new waveform for 5G candidates, possesses the advantages of both low OSBE and low peak-to-average power ratio (PAPR) through precoding matrix design. In this thesis, the structure of frequency-domain equalizer (FDE) and its optimization problem design are proposed under the asynchronous multiuser uplink CPS-OFDM system. Simulation results show the BER performance of CPS-OFDM outperforms that of Filtered-OFDM (f-OFDM) and Weighted Overlap and Add based OFDM (WOLA-OFDM) by the proposed FDE. Thus, CPS-OFDM system will be one of the most developmental potentials in future 5G asynchronous transmission scenarios.

As one of the techniques beyond 3G, because of the effective performance of high spectrum utilization and anti-fading for frequency selecting and adopted multi-carrier modulation technique that meets the requirement of the explosive traffic capacity, Orthogonal Frequency Division Multiplexing (OFDM) has carried great weight in wireless communications. This paper expounds OFDM technical characteristics and performs computer simulation on the OFDM system based on Inverse Fast Fourier Transform (IFFT) by means MATLAB. During the course of simulation, comparison between OFDM and traditional single-carrier technology is performed. The simulation results have great significance for research and applications in the field.

We demonstrated a high-performance dual-color B5G DRoF system using delay compensation. A quad-level 6-Gbit/s 64-QAM OFDM signal was successfully transmitted over the proposed system, showing a much better performance compared to the conventional 1-bit system.