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Dissertations / Theses on the topic 'Affine Frequency Division Multiplexing'

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Published: 25 May 2024

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1

Bemani, Ali. "Affine Frequency Division Multiplexing (AFDM) for Wireless Communications." Electronic Thesis or Diss., Sorbonne université, 2023. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2023SORUS610.pdf.

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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
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2

Recio, Adolfo Leon. "Spectrum-Aware Orthogonal Frequency Division Multiplexing." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/30193.

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Reconfigurable computing architectures are well suited for the dynamic data flow processing requirements of software-defined radio. The software radio concept has quickly evolved to include spectrum sensing, awareness, and cognitive algorithms for machine learning resulting in the cognitive radio model. This work explores the application of reconfigurable hardware to the physical layer of cognitive radios using non-contiguous multi-carrier radio techniques. The practical tasks of spectrum sensing, frame detection, synchronization, channel estimation, and mutual interference mitigation are challenges in the communications and the computing fields that are addressed to optimally utilize the capacity of opportunistically allocated spectrum bands. FPGA implementations of parameterizable OFDM and filter bank multi-carrier (FBMC) radio prototypes with spectrum awareness and non-contiguous sub-carrier allocation were completed and tested over-the-air. Sub-carrier sparseness assumptions were validated under practical implementation and performance considerations. A novel algorithm for frame detection and synchronization with mutual interference rejection applicable to the FBMC case was proposed and tested.
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3

Challakere, Nagaravind. "Carrier Frequency Offset Estimation for Orthogonal Frequency Division Multiplexing." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1423.

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This thesis presents a novel method to solve the problem of estimating the carrier frequency set in an Orthogonal Frequency Division Multiplexing (OFDM) system. The approach is based on the minimization of the probability of symbol error. Hence, this approach is called the Minimum Symbol Error Rate (MSER) approach. An existing approach based on Maximum Likelihood (ML) is chosen to benchmark the performance of the MSER-based algorithm. The MSER approach is computationally intensive. The thesis evaluates the approximations that can be made to the MSER-based objective function to make the computation tractable. A modified gradient function based on the MSER objective is developed which provides better performance characteristics than the ML-based estimator. The estimates produced by the MSER approach exhibit lower Mean Squared Error compared to the ML benchmark. The performance of MSER-based estimator is simulated with Quaternary Phase Shift Keying (QPSK) symbols, but the algorithm presented is applicable to all complex symbol constellations.
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4

Zhang, Hua. "Orthogonal Frequency Division Multiplexing for Wireless Communications." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4960.

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OFDM is a promising technique for high-data-rate wireless communications because it can combat inter-symbol interference (ISI) caused by the dispersive fading of wireless channels. The proposed research focuses on techniques that improve the performance of OFDM-based wireless communications and its commercial and military applications. In particular, we address the following aspects of OFDM: inter-channel interference (ICI) suppression, interference suppression for clustered OFDM, clustered OFDM based anti-jamming modulation, channel estimation for MIMO-OFDM, MIMO transmission with limited feedback. For inter-channel interference suppression, a frequency domain partial response coding (PRC) scheme is proposed to mitigate ICI. We derive the near-optimal weights for PRC that is independent on the channel power spectrum. The error floor resulting from ICI can be reduced significantly using a two-tap or a three-tap PRC. Clustered OFDM is a new technique that has many advantages over traditional OFDM. In clustered OFDM systems, adaptive antenna arrays are used for interference suppression. To calculate weights for interference suppression, we propose a polynomial-based parameter estimator to combat the severe leakage of the DFT based estimator due to the small size of the cluster. An adaptive algorithm is developed to obtain optimal performance. For high data rate military communications, we propose a clustered OFDM base spread spectrum modulation to provide both anti-jamming and fading suppression capability. We analyze the performance of uncoded and coded system. Employing multiple transmit and receive antennas in OFDM systems (MIMO-OFDM) can increase the spectral efficiency and link reliability. We develop a minimum mean-square-error (MMSE) channel estimator that takes advantage of the spatial-frequency correlations in MIMO-OFDM systems to minimize the estimation error. We investigate the training sequence design and two optimal training sequence designs are given for arbitrary spatial correlations. For a MIMO system, the diversity and array gains can be obtained by exploiting channel information at the transmitter. For MIMO-OFDM systems, we propose a subspace tracking based approach that can exploit the frequency correlations of the OFDM system to reduce the feedback rate. The proposed approach does not need recalculate the precoding matrix and is robust to multiple data stream transmission.
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5

Kim, Dukhyun. "Orthogonal frequency division multiplexing for digital broadcasting." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13704.

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6

Bledowski, Ian A. "Frequency-division-multiplexing technique for imaging metrology." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9286.

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An algorithm to multiplex multiple image captures simultaneously onto a single image sensor at full frame resolution was developed for imaging metrology. Parseval’s theorem was used to obtain the image intensity from image time-series of around typically 256 frames captured by the imaging sensor at typically 60 fps, though kHz frame rates are possible, hardware permitting. The time-series contained contributions from each image channel in the system, which were created by periodically modulating the intensity of the light source which defined that channel. The modulating time-series was converted to a frequency representation by Fourier transform and from that the channels could be identified by their peaks in the spectrum. Peaks corresponding to each channel were then isolated with a window function and Parseval’s theorem applied on a pixel by pixel basis to convert the signal strength back to an image containing the information from that channel only. The FDM algorithm was then applied to two imaging metrology methods. First, an in-plane, two-channel shearography system was multiplexed with FDM in such a way as to allow time-division multiplexed measurements to be taken on the same deformations with the same instrument so as to allow comparison of results from other methods. FDM was found to produce good quality results comparable with current methods. Interferometric planar Doppler velocimetry was performed, multiplexing the reference phase channel signal and a signal channel for both a wheel and a gas jet. FDM was found to suppress the effects of phase drifts in the system which would lead to velocity offsets in the results, and gave velocities which varied from the model by only up to ~5%. Finally, an error analysis was performed on the FDM algorithm, comparing the technique with time-averaging and single image capture through simulation and practical methods. It was shown that FDM strongly suppresses the noise and background in a measurement, and can produce good images from low intensity signals. It could be concluded that the FDM algorithm offers significant advantages over time-averaging a signal when applied to a multi-channel imaging metrology system.
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Clark, Alan. "On Coding for Orthogonal Frequency Division Multiplexing Systems." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/1092.

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The main contribution of this thesis is the statistical analysis of orthogonal frequency di- vision multiplexing (OFDM) systems operating over wireless channels that are both fre- quency selective and Rayleigh fading. We first describe the instantaneous capacity of such systems using a central limit theorem, as well as the asymptotic capacity of a power lim- ited OFDM system as the number of subcarriers approaches infinity. We then analyse the performance of uncoded OFDM systems by first developing bounds on the block error rate. Next we show that the distribution of the number of symbol errors within each block may be tightly approximated, and derive the distribution of an upper bound on the total variation distance. Finally, the central result of this thesis proposes the use of lattices for encodingOFDMsystems. For this, we detail a particular method of using lattices to encode OFDMsystems, and derive the optimalmaximumlikelihood decodingmetric. Generalised Minimum Distance (GMD) decoding is then introduced as a lower complexity method of decoding lattice encoded OFDM. We derive the optimal reliability metric for GMD decod- ing of OFDM systems operating over frequency selective channels, and develop analytical upper bounds on the error rate of lattice encoded OFDM systems employing GMD decod- ing.
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李世榮 and Sai-weng Lei. "Adaptive interleaving for orthogonal frequency division multiplexing systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31224702.

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Lepley, Jason J. "Frequency stabilisation for dense wavelength division multiplexing systems." Thesis, University of Essex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310059.

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10

Wang, Samuel Y. "Perfect shuffle optical frequency division multiplexing (PS/OFDM)." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14255.

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11

Bouziane, R. "Real-time optical orthogonal frequency division multiplexing transceivers." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1383794/.

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Optical orthogonal frequency division multiplexing (O-OFDM) is a potential candidate for 100 Gigabit Ethernet (GbE) and beyond due to its high spectral efficiency and strong resilience towards chromatic and polarization mode dispersion. In this thesis, investigations have been performed into the feasibility of O-OFDM in high speed optical fibre communications. First, an overview of OFDM fundamentals and optical fibre communications is given. Numerical simulations which were performed to characterise and optimise real-time OFDM transceivers are then presented. The effects of a variety of design parameters on the performance of the system are studied. Amongst the key parameters included in the study are the quantisation and clipping noise in data converters, and the quantisation errors in the fast Fourier transform and its inverse (FFT/IFFT). Optimum parameters that give the best trade-off between performance and cost in terms of bit precision are determined. It was found that these parameters depend on the modulation format as well as the size of the FFT used in the system. The thesis then presents the design of a multi-gigabit real-time O-OFDM transmitter based on field programmable gate array (FPGA) implementation. The 21.4 GS/s real-time transmitter was built and used to transmit 8.36 Gb/s directly-detected single sideband QPSK-OFDM signals over 1600 km of uncompensated standard single mode fibre. This was one of the first demonstrations of real-time OFDM transmitters operating at such high line rates. It remains the longest transmission distance achieved with a real-time OFDM transmitter. The next step in confirming the feasibility of O-OFDM involves the design and assessment of application-specific integrated circuit (ASIC) implementations. In the final part of the thesis, digital signal processing (DSP) circuits for 21.8 Gb/s and 43.7 Gb/s QPSK- and 16-QAM-encoded O-OFDM transceivers with 50 data subcarriers were designed at the register-transfer-level, and synthesis and simulations were carried out to assess their performance, power consumption, and chip area. The aim of the study is to determine the suitability of OFDM technology for low-cost optical interconnects. Power calculations based on synthesis for a 65nm standard-cell library show that the DSP components of the transceiver consume 18.2 mW/Gb/s and 12.8 mW/Gb/s in the case of QPSK and 16-QAM respectively. The effects of modulation format and FFT size on the area and power consumption of the transceivers are also quantified. Finally, characterisation results showing the trade-offs between energy consumption and chip footprint are presented and analysed to help designers optimise the transceivers according the requirements and specifications.
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Omomukuyo, O. O. "Orthogonal frequency division multiplexing for optical access networks." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1400463/.

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Orthogonal Frequency Division Multiplexing (OFDM) is a modulation scheme with numerous advantages that has for years been employed as the leading physical interface in many wired and wireless communication systems. Recently, with advancements made in digital signal processing, there has been a surge of interest in applying OFDM techniques for optical communications. This thesis presents extensive research on optical OFDM and how it is being applied in access networks. With the aid of theoretical analysis, simulations and experiments, it is shown that the system performance of direct-detection optical OFDM (DD-OOFDM) in the presence of MZM non-linear distortion can be improved by proper biasing and selection of appropriate drive to the MZM. Investigations are conducted to illustrate how a variation in the number of subcarriers and the modulation format influences the sensitivity of the DD-OOFDM system to the MZM non-linear distortion. The possibility of improving the spectral efficiency by reduction of the width of the guard band is also investigated. This thesis also looks into the radio-over-fibre (RoF) transmission of Multiband OFDM UWB as a transparent and low-cost solution for distributing multi-Gbit/s data to end-users in FTTH networks. Due to relaxed regulatory requirements and the wide bandwidth available, UWB operation in the 60-GHz band is also considered for this FTTH application scenario. Four techniques for enabling MB-OFDM UWB RoF operation in the 60-GHz band are experimentally demonstrated. The impacts of various parameters on the performance of the techniques as well as the limitations imposed by fibre distribution are illustrated. Finally, a digital pre-distorter is proposed for compensating for the MZM non-linearity. Experimental demonstration of this digital pre-distortion in an UWB over fibre transmission system shows an increased tolerance to the amplitude of the driving OFDM signal as well as an increase in the optimum modulation index of the OFDM signal.
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Lei, Sai-weng. "Adaptive interleaving for orthogonal frequency division multiplexing systems /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk:8888/cgi-bin/hkuto%5Ftoc%5Fpdf?B23295065.

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14

Cai, Kun, and 蔡琨. "Bayesian carrier frequency offset estimation in orthogonal frequency division multiplexing systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841367.

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Cai, Kun. "Bayesian carrier frequency offset estimation in orthogonal frequency division multiplexing systems." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42841367.

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16

Rende, Deniz. "Bit-interleaved space-frequency coded modulation for orthogonal frequency-division multiplexing systems." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006420.

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17

Deckert, Thomas. "Orthogonal frequency division multiplexing based medium access under rate constraints." Dresden Vogt, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=3002150&prov=M&dok_var=1&dok_ext=htm.

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18

Chen, Yingkan [Verfasser]. "Orthogonal Frequency-Division Multiplexing in Fiber-Optic Communication / Yingkan Chen." München : Verlag Dr. Hut, 2016. http://d-nb.info/1136601260/34.

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Li, Kai. "Fast orthogonal frequency division multiplexing (Fast-OFDM) for wireless communications." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/17220/.

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This thesis presents research that has addressed various design issues related to an adapted orthogonal frequency division multiplexing scheme, namely Fast-OFDM. A comparative study of the system with conventional OFDM in various signal mapping conditions has been investigated. The thesis reports on performance assessment in terms of bit-error-rate (BER) performance, spectral efficiency, peak-to-average-power ratio (PAPR), nonlinear effects and adjacent channel interference (ACI) analysis. The results show that the performance of Fast-OFDM is comparable to OFDM for single dimensional modulation scheme, whereas for complex modulation schemes, the performance of Fast-OFDM degrades severely due to the loss of orthogonality between subcarriers. Two multi-carrier CDMA schemes, multi-carrier direct sequence CDMA (MC DS-CDMA) and multi-tone CDMA (MT-CDMA), have been studied in different modulation scenarios. The performance of the overlapping multi-carrier CDMA schemes compared to OFDM and Fast-OFDM has been evaluated in terms of BER, spectral efficiency, PAPR and ACI analysis. The results reveal that the overlapping multi-carrier CDMA systems are comparable to the Fast-OFDM system under single user condition. It is thus feasible to apply multi-carrier CDMA detection techniques in Fast-OFOM systems. Therefore, two different types of linear detectors, zero-forcing (ZF) and minimum mean square error (MMSE) have been employed in complex modulated Fast-OFDM, leading to improvement of system performance. Overall, the theoretical design and performance assessment issues addressed in this thesis provide an insight into the performance of Fast-OFDM in the presence of additive white Gaussian noise (AWGN). The results obtained can be used by receiver designers for improving signal recovery of complex modulated Fast-OFDM in future wireless communication systems.
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Guan, Karen Min 1978. "Quadrature amplitude modulated codes for orthogonal frequency division multiplexing applications." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/87226.

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21

Ansari, Ashlaghi Aria. "100 GBPS Orthogonal Frequency Division Multiplexing optical fiber communication network." Thesis, California State University, Long Beach, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1604879.

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Optical fiber communication has emerged as a high potential substitute for communication methods such as twisted pair and coaxial wire. The main advantage of optical fiber over previous methods is to have higher capacity of data rate transmission. The conventional types of modulation and demodulation technique, which have been used through optical fiber communication system are Wavelength Division Multiplexing (WDM) technique and Dense Wavelength Division Multiplexing (DWDM) technique so far.

In this thesis, the Orthogonal Frequency Division Multiplexing (OFDM) is applied through the modulation and demodulation parts due to some advantages over WDM and DWDM to reach to 100 Gbps data transmission. The main advantage of OFDM-optical fiber is that it only needs one optical source to modulate and one optical source to demodulate the signals at transmitter side and receiver side, which results in a reduction of the cost of the system. Also, by using the OFDM, the chromatic dispersion can be eliminated or decreased.

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Simões, Gaspar Ivan. "Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-201875.

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To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation. This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed. The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms. In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels.
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Welling, Kenneth. "Coded Orthogonal Frequency Division Multiplexing for the Multipath Fading Channel." International Foundation for Telemetering, 1999. http://hdl.handle.net/10150/608525.

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International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada
This paper presents a mathematical model for Coded Orthogonal Frequency Division Multiplexing (COFDM) in frequency selective multipath encountered in aeronautical telemetry. The use of the fast Fourier transform (FFT) for modulation and demodulation is reviewed. Error control coding with interleaving in frequency is able to provide reliable data communications during frequency selective multipath fade events. Simulations demonstrate QPSK mapped COFDM performs well in a multipath fading environment with parameters typically encountered in aeronautical telemetry.
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Lee, King F. "Space-time and space-frequency coded orthogonal frequency division multiplexing transmitter diversity techniques." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/14981.

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Wong, Kar Lun (Clarence). "Space-time-frequency channel estimation for multiple-antenna orthogonal frequency division multiplexing systems." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100244.

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We propose a linear mean square error channel estimator that exploits the joint space-time-frequency (STF) correlations of the wireless fading channel for applications in multiple-antenna orthogonal frequency division multiplexing systems. Our work generalizes existing channel estimators to the full dimensions including transmit spatial, receive spatial, time, and frequency. This allows versatile applications of our STF channel estimator to any fading environment, ranging from spatially-uncorrelated slow-varying frequency-flat channels to spatially-correlated fast-varying frequency-selective channels.
The proposed STF channel estimator reduces to a time-frequency (TF) channel estimator when no spatial correlations exist. In another perspective, the lower-dimension TF channel estimator can be viewed as an STF channel estimator with spatial correlation mismatch for space-time-frequency selective channels.
Computer simulations were performed to study the mean-square-error (MSE) behavior with different pilot parameters. We then evaluate the suitability of our STF channel estimator on a space-frequency block coded OFDM system. Bit error rate (BER) performance degradation, with respect to perfect coherent detection, is limited to less than 2 dB at a BER of 10-5 in the modified 3GPP fast-fading suburban macro environment. Modifications to the 3GPP channel involves reducing the base station angle spread to imitate a high transmit spatial correlation scenario to emphasize the benefit of exploiting spatial correlation in our STF channel estimator.
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Oz, Ersoy. "A comparison of timing methods in orthogonal frequency division multiplexing (OFDM) systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sep%5FOz.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, Sept. 2004.
Thesis Advisor(s): Roberto Cristi, Murali Tummala. Includes bibliographical references (p. 169-173). Also available online.
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Chen, Jianwu, and 陳建武. "Frequency synchronization in OFDM-based systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687338.

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Chen, Jianwu. "Frequency synchronization in OFDM-based systems." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B40687338.

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Karaoglu, Bulent. "A comparison of frequency offset estimation methods in Orthogonal Frequency Division Multiplexing (OFDM) systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FKaraoglu.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, Dec. 2004.
Thesis Advisor(s): Roberto Cristi, Murali Tummala. Includes bibliographical references (p. 45-46). Also available online.
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30

Kaur, Amandeep. "Comparison of Different Predistortion Techniques for Orthogonal Frequency Division Multiplexing Systems." Thesis, California State University, Long Beach, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13426595.

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Wireless channels have significant problems like multipath fading, delay spread, frequency selective fading. Guard bands/channel equalization techniques are employed to overcome these. However, these solutions are complex and don’t solve the issue of bandwidth scarcity. Thus, Orthogonal Frequency Division Multiplexing was introduced; a special case of Frequency Division Multiplexing where orthogonal subcarriers overlap in the frequency domain using lesser bandwidth without any inter-symbol interference.

The next challenge is to reduce the error rate in transmission. This thesis focuses on the noise created because of the non-linear input/output relationship of the power amplifier used. Different techniques used to linearize power amplifiers are compared. Predistortion was found to be most effective. Various predistortion schemes are compared and error rate performance evaluated for the Orthogonal Frequency Division Multiplexing system with and without Predistortion as well as for different modulation techniques. Dynamic Digital Predistortion paired with 8 Quadrature Amplitude Modulation was found to work most efficiently.

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Mohamed, Salma Darwish Abd Elaziz. "Modified Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing (MACO-OFDM) system." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25820.

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A modification to the Asymmetrically Clipped Optical OFDM (ACO-OFDM) technique, a well reported non-coherent optical implementation is proposed. A Modified ACO-OFDM (MACO-OFDM) system is developed to improve system performance at the expense of spectral efficiency. A MACO-OFDM system model is defined underpinned by a detailed mathematical framework verified through Monte Carlo simulations. System performance is compared to that of conventional ACO-OFDM. A 1.5 dB saving is achieved in the Bit Error Rate (BER) performance of 4-QAM ACO-OFDM after applying the proposed modification; the theoretical and simulation results are in good agreement. As the constellation size increases, the improvement in BER performance decreases. The research then treats the impact of atmospheric turbulence on the performance of both conventional ACO-OFDM and the proposed MACO-OFDM system. A Single Input Multiple Output (SIMO) approach using multiple receivers is employed to mitigate the impact of atmospheric turbulence. The performance of MACO-OFDM outperforms that of ACO-OFDM by nearly 3 dB, 4 dB, and 5 dB as the number of receiving apertures (nRx) increases as 1, 2, and 4 respectively in weak atmospheric turbulence; in moderate turbulence the performance is improved by 2 dB, and 4.5 dB for nRx=2, and nRx=4; and in strong turbulence, the BER performance is enhanced by nearly 2 dB and 4 dB for nRx=2 and nRx=4. The channel capacity of MACO-OFDM has been shown to be half that of conventional ACO-OFDM. The capacity of SIMO MACO-OFDM architecture in atmospheric turbulent channel is evaluated.
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Acácio, Luís Carlos Lorenzo. "Equalização pré-FFT de sistemas baseados em orthogonal frequency-division multiplexing." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-17122004-154902/.

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Esta dissertação trata da equalização no domínio do tempo de sistemas de comunicações digitais baseados em orthoghonal frequency-division multiplexing (OFDM), normalmente referida na literatura técnica como equalização pré-FFT. Tais sistemas foram originalmente projetados de modo a não necessitar de equalização, porém podem se beneficiar com seu uso, como mostrado a seguir. Foi implementado, em programa de computador, um simulador não codificado do sistema de televisão digital terrestre utilizado na Europa, o digital video broadcasting (DVB-T), que é baseado em OFDM e se encontra implantado com sucesso há alguns anos. Diversas simulações foram executadas comparando o método tradicional de recepção do sistema DVB-T com a versão equalizada proposta. Foram utilizadas várias técnicas de processamento digital de sinais para simular: a geração do sinal, sua passagem por um canal de comunicação com multipercurso, presença de ruído branco Gaussiano aditivo, equalização LMS (Least Mean Square), entre outros fenômenos importantes. Para um firme embasamento, o trabalho apresenta estudos matemáticos sobre a teoria geral do OFDM, modelos de canais de comunicação e o princípio básico do algoritmo LMS. Tendo-se utilizado o DVB-T como estudo de caso prático, não poderia deixar de constar uma descrição técnica desse sistema em que são apresentados vários dos detalhes e problemas envolvidos na geração e recepção do sinal. Com a finalidade de posicionar o leitor histórica e tecnologicamente, o texto inclui ainda uma revisão dos principais fatos que marcaram o desenvolvimento do OFDM desde os estudos iniciais até os dias de hoje.
This dissertation deals with time-domain equalization of digital communications systems based on orthoghonal frequency-division multiplexing (OFDM), usually referred as pre-FFT equalization in the technical literature. Such systems were originally designed to require no time equalization but can profit from its use, as is shown in this work. An uncoded simulator of the OFDM-based European system for terrestrial digital television transmission, the digital video broadcasting (DVB-T), was implemented in software. Many simulations were run to compare the performance of the traditional DVB-T reception method with the equalized version proposed. Several digital signal processing techniques were used to simulate as diverse fenomena as: generation of the source signal, effect of multipath communications channels, presence of additive white Gaussian noise, LMS (Least Mean Square) equalization, among others. In order to develop a solid base, the work includes mathematical studies about the general OFDM theory, models of communications channels and the basic principle of operation of the LMS algorithm. Since the DVB-T was used as a practical study case, a technical description of the system is presented, in which many problems and aspects about its generation and reception are discussed. To provide the reader with a historical and technological insight on the subject, this work also includes a summary of the landmarks in the development of the OFDM since the first experiments.
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Hosseinpour, Ali. "Investigation of orthogonal frequency division multiplexing based Power Line Communication systems." Thesis, University of East London, 2015. http://roar.uel.ac.uk/4420/.

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Power Line Communication (PLC) has the potential to become the preferred technique for providing broadband to homes and offices with the advantage of eliminating the need for new wiring infrastructure and reducing the cost. Power line grids, however, present a hostile channel for data communication, since the fundamental purpose of the power line channel was only the transmission of electric power at 50/60 Hz frequencies. The development of PLC systems for providing broadband applications requires an adequate knowledge of the power line channel characteristics. Various types of noise and multipath effects are some of the limitations for power line channels which need to be considered carefully in designing PLC systems. An effect of an impulsive noise characterized with short durations is identified as one of the major impairment in PLC system. Orthogonal Frequency Division Multiplexing (OFDM) technique is one of the modulation approaches which has been regarded as the modulation technique for PLC systems by most researchers in the field and is used in this research study work. This is because it provides high robustness against impulsive noise and minimizes the effects of multipath. In case of impulsive noise affecting the OFDM system, this effect is spread over multiple subcarriers due to Discrete Fourier Transform (DFT) at the receiver. Hence, each of the transmitted communication symbols is only affected by a fraction of the impulsive noise. In order to achieve reliable results for data transmission, a proper power line channel with various noise models must be used in the investigations. In this research study work, a multipath model which has been widely accepted by many researchers in the field and practically proven in the Tanzanian power line system is used as the model for the power line channel. The effects of different scenarios such as variations in direct path length, path number, branch length and load on the channel frequency response are investigated in this research work. Simulation results indicate the suitability of multi-carrier modulation technique such as an OFDM over the power line channels. To represent the actual noise scenario in the power line channel, an impulsive noise and background noise are classified as the two main noise sources. A Middleton class A noise is modelled as an impulsive noise, whereas the background noise is modelled as an Additive White Gaussian Noise (AWGN). The performance of PLC system based on OFDM is investigated under Middleton Class A and AWGN noise scenarios. It is observed that Bit Error Rate (BER) for the impulsive noise is higher than the background noise. Since channel coding can enhance the transmission in a communication system, Block code and convolutional codes have been studied in this research work. The hamming code chosen as a type of the block code, whereas the Trellis Coded Modulation (TCM) selected from the category of the convolutional channel codes and modelled in Matlab2013b. Although TCM code produces improvements in the Signal-to-Noise Ratio (SNR), they do not perform well with Middleton class A noise. A rectangular 16-QAM TCM based on OFDM provides better BER rate compared to the general TCM.
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Erdogan, Ahmet Yasin. "Analysis of the effects of phase noise and frequency offest in orthogonal frequency division multiplexing (OFDM) systems /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FErdogan.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2004.
Thesis advisor(s): Murali Tummala, Roberto Cristi. Includes bibliographical references (p. 127-129). Also available online.
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Holder, Sade A. "Linear frequency modulated signals vs orthogonal frequency division multiplexing signals for synthetic aperture radar systems." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/42647.

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Approved for public release; distribution is unlimited
The goal of this thesis is to investigate the effects of an orthogonal frequency-division multiplexing (OFDM) signal versus a linear frequency modulated or chirp signal on simulated synthetic aperture radar (SAR) imagery. Various parameters of the transmitted signal, such as pulse duration, transmitted signal energy, bandwidth, and (specifically for the OFDM signal) number of subcarriers and transmission scheme were examined to determine which parameters are most important to reconstructing a SAR image. Matched filtering and interpolation are two techniques used to reconstruct the SAR image. SAR systems are used in various military and civilian sector applications. Some SAR application examples include ground surveillance, reconnaissance and remote sensing. These applications demand high resolution imagery; therefore, knowledge of exactly which parameters of the transmitted radar signal are more important in producing fine resolution imagery is worth investigating. This research will also aid in providing flexibility in terms of what type of signal and signal parameters are best suited for a particular SAR application and associated military missions. In addition to improving the method attaining high resolution images, SAR process improvement can potentially reduce military SAR system design cost.
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Holguín-Sánchez, Fausto Daniel. "Spectral Shape Division Multiplexing (SSDM): Apparatus, Transmitter, Receiver and Detection." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/800.

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Wireless communication companies require to use the frequency spectrum to operate. Both frequency licenses and infrastructure to reuse frequencies are costly resources subject to increasing demand. This work introduces a novel multiplexing method that saves spectrum called Spectral Shape Division Multiplexing (SSDM). Under certain configurations, SSDM displays higher flexibility and throughput than other spectrally efficient methods. SSDM defines the structure of a wireless multi-carrier by software. It is similar to Orthogonal Frequency Division Multiplexing (OFDM) in that both use overlapped sub-carriers to make efficient use of allocated spectrum. However, SSDM has several advantages. Where OFDM organizes sub-carriers orthogonally, SSDM allows arbitrary frequency steps enabling higher spectral efficiency. Similarly, while OFDM and other spectrally efficient methods use sinusoidal pulse forms, SSDM can use non-standard pulses providing a greater control of the carrier. In this thesis, a SSDM transceiver is implemented to reduce the spectrum utilization. SSDM presents an increase in spectral efficiency of 20% average with respect to OFDM. The cost of this gain is higher computational speed and signal to noise ratio. The mathematical models and possible architecture for an SSDM system with sinusoidal pulses is developed. The modem is compared with other spectrally efficient methods. Similarly, the trade-offs between spectral efficiency, bit-error rates, dimension of the carrier and sub-carrier spacing are subject of analysis.
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Escayola, Elias Francesc Xavier. "Next generation passive optical networks based on orthogonal frequency division multiplexing techniques." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/334417.

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In recent decades, the industry of communications has acquired huge significance, and nowadays constitutes an essential tool for the society information. Thus, the exponential growth in demand of broadband services and the increasing amount of information to be transmitted have spurred the evolution of the access network infrastructure to effectively meet the user needs in an effective way in terms of costs of both installation and maintenance. Passive optical networks (PON) are currently considered the most efficient and least costly alternative to deploy fiber to the home environment. In order to allow many users simultaneously coexist PONs based on time multiplexing (TDMA) have been developed. Looking ahead, however, it is expected that these techniques do not meet the requirements on access networks. In consequence, other multiple access techniques such as Wavelength Division Multiplexing Access (WDMA) or Orthogonal Frequency Division Multiplexing Access (OFDMA) are currently under study and development for use in the next generation of PONs. Particularly, in recent years OFDM has stood out among the scientific community to be considered a solution with great potential on future implementation of PONs. This is especially true due to the capacity of OFDM to work with multilevel modulations, its high tolerance to chromatic dispersion, and its high flexibility and granularity in terms of bandwidth management. Given the above, the aim of this Thesis is to study deeply the advantages and challenges of implementing the standard OFDM as an access network solution; likewise, it offers solutions to improve its performance. In order to evaluate the main structures and strategies for OFDM-based PON, a comparative analysis of all of them is performed firstly, highlighting their sensitivity levels, maximum range and number of users. A key aspect for network providers is the cost of operation, deployment and maintenance of networks. As a low-cost solution, this Thesis proposes a network model called Statistical-OFDMA-PON based on intensity modulation and direct detection. In addition, dynamic bandwidth management strategies are applied into this model getting an improvement in the power balance which in turn, allows to increase the maximum range and the scalability in number of users. One of the main OFDM problems is the Peak-to-Average Power Ratio (PAPR) which increases with the number of carriers. This thesis proposes a new algorithm based on folding the signal and transmitting auxiliary information in order to compensate the PAPR effect and thus increase the sensitivity of the optical system. On the other hand, OFDMA requires a large number of operations in the digital domain resulting in a high computational effort, which in turn results in an increased cost. For this reason, this Thesis presents a study on the optimization of the required resolution in the Digital-to-Analog / Analog-to-Digital Converters (DAC/ADCs) maintaining the transmission quality. The optimization of the computation time may make the OFDMA-based optical network more attractive for future PONs. Finally, another problem concerning the OFDM optical networks is their sensitivity to Phase Noise (PN). In this regard, this Thesis presents a study of the effect of the laser linewidth and its dependence on signal bandwidth. A mitigation technique based on pilot tones is implemented and the limiting values for the laser linewidth are found to be within the reach of present low-cost light sources.
En estas últimas décadas, la industria de las comunicaciones ha adquirido gran importancia y hoy en día, constituye una herramienta imprescindible para el funcionamiento en la sociedad de la información. Así pues, el crecimiento exponencial en la demanda de servicios de banda ancha y la carga de información cada vez mayor que se necesita transmitir ha estimulado la evolución de las infraestructuras del tramo de acceso a la red para poder satisfacer las necesidades del usuario de forma efectiva en términos de costes de instalación y de mantenimiento. Las redes ópticas pasivas (Passive Optical Networks, PON) son actualmente consideradas la alternativa más eficiente y de menor coste para desplegar fibra hasta los hogares. Con el fin de permitir que muchos usuarios coexistan simultáneamente se han desarrollado PONs basadas en multiplexación en tiempo (Time Division Multiplexing Access, TDMA). De cara al futuro, sin embargo, se prevé que estas técnicas no permitan cubrir las exigencias sobre las redes de acceso. En consecuencia, otras técnicas de acceso múltiple al medio como el acceso múltiple por división de longitud de onda (Wavelength Division Multiplexing Access, WDMA) o el acceso múltiple por división de frecuencia ortogonal (Orthogonal Frequency Division Multiplexing Access, OFDMA) se encuentran actualmente en proceso de estudio y desarrollo para su uso en la futura generación de PONs. En concreto, en los últimos años OFDM se ha destacado entre la comunidad científica al considerarse una solución con gran potencial para su futura implantación en redes de acceso pasivas. Esto es especialmente cierto debido a la capacidad que el OFDM para trabajar con modulaciones multinivel, así como su alta tolerancia a la dispersión cromática y a la gran flexibilidad y granularidad que posibilita en términos de gestión del ancho de banda. Por todo lo anterior, el objetivo de esta Tesis es estudiar con profundidad las ventajas y los retos de aplicar el estándar OFDM como solución de red de acceso; del mismo modo, ofrece soluciones para mejorar su rendimiento. Con el objetivo de evaluar las principales estructuras basadas en OFDM-PON, en primer lugar se realiza un análisis comparativo de todas ellas destacando sus niveles de sensibilidad, máximo alcance y número de usuarios. Un aspecto fundamental para los proveedores de red es el coste de operación, despliegue y mantenimiento de las redes. Como solución de bajo coste, esta Tesis propone un modelo de red llamado Statistical-OFDMA-PON que se basa en modulación de intensidad y detección directa. Además, este modelo se completa con estrategias de gestión dinámica del ancho de banda de los usuarios que conforman la estructura de red propuesta consiguiendo una mejora en el balance de potencias que permite aumentar distancia y número de usuarios. Uno de los principales problemas del OFDM es el alto nivel de la relación de potencia de pico a potencia media (Peak-to-Average Power Ratio, PAPR) creciente con el número de portadoras. Esta Tesis propone un nuevo algoritmo basado en el pliegue de la señal y la transmisión de información auxiliar para compensar el efecto del PAPR aumentando así la sensibilidad del sistema óptico. Por otro lado, OFDMA requiere un número elevado de operaciones en el dominio digital resultando en un alto esfuerzo computacional que a su vez se traduce en un aumento del coste. Por esta razón, esta Tesis presenta un estudio sobre la optimización de la resolución requerida en los conversores analógicodigital (Digital-to-Analog/Analog-to-Digital Converters, DAC/ADCs) manteniendo la calidad de transmisión. La optimización del tiempo de cómputo requerido puede dotar de un mayor atractivo la solución de red óptica basada en OFDMA. Finalmente, otro de los problemas que presentan las redes ópticas OFDM es su sensibilidad frente al ruido de fase (Phase Noise, PN). En este aspecto, esta Tesis presenta un estudio del efecto del ancho de línea del láser y su dependencia con el ancho de banda de la señal. Técnicas de mitigación basadas en tonos piloto han sido implementadas y se han encontrado los valores limitantes del ancho de línea dentro del alcance de los láseres de bajo coste.
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38

Shenoy, Dinesh Nandakumar. "Compressive Sensing| Performance of Sparse Channel Estimation in Orthogonal Frequency Division Multiplexing." Thesis, California State University, Long Beach, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10751778.

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Compressive Sensing is a signal processing technique that is based on the property that the sparsity concept of a given signal can be exploited to reconstruct the signal successfully while disobeying Shannon’s Nyquist Theorem with fewer samples than what is required.

Sparse estimation which is an application of Compressive Sensing is applied to an OFDM transmission, as the model provides a better performance along with controlled inter symbol interference (ISI).

The thesis is based on the assumption that a single OFDM block is essentially time invariant and the simulations are carried out based on these assumptions. This thesis uses training data to simulate the channel estimation and to successfully recover the transmitted information. Convex optimization techniques to minimize noise and obtain the transmitted signal are employed. The thesis estimates the bit error rate (BER) using a Rayleigh channel and AWGN to illustrate how sparse estimation can be used to increase the performance of the system. The BER is estimated using the output at the receiver end and then compared with the BER of Least Square Estimation technique.

Simulation results show that the BER results for a system based on Sparse estimation of the channel are much better than a system with Least Square Estimation at high signal to noise ratios (SNR).

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Schedler, Stephan [Verfasser]. "Generalized Frequency Division Multiplexing in the Two-Way-Relay Channel / Stephan Schedler." Aachen : Shaker, 2016. http://d-nb.info/1120863880/34.

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Craven, Michael P. "Inter-chip communications in an analogue neural network utilising frequency division multiplexing." Thesis, University of Nottingham, 1994. http://eprints.nottingham.ac.uk/13085/.

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As advances have been made in semiconductor processing technology, the number of transistors on a chip has increased out of step with the number of input/output pins, which has introduced a communications ’bottle-neck’ in the design of computer architectures. This is a major issue in the hardware design of parallel structures implemented in either digital or analogue VLSI, and is particularly relevant to the design of neural networks which need to be highly interconnected. This work reviews hardware implementations of neural networks, with an emphasis on analogue implementations, and proposes a new method for overcoming connectivity constraints, by the use of Frequency Division Multiplexing (FDM) for the inter-chip communications. In this FDM scheme, multiple analogue signals are transmitted between chips on a single wire by modulating them at different frequencies. The main theoretical work examines the number of signals which can be packed into an FDM channel, depending on the quality factors of the filters used for the demultiplexing, and a fractional overlap parameter which was defined to take into account the inevitable overlapping of filter frequency responses. It is seen that by increasing the amount of permissible overlap, it is possible to communicate a larger number of signals in a given bandwidth. Alternatively, the quality factors of the filters can be reduced, which is advantageous for hardware implementation. Therefore, it was found necessary to determine the amount of overlap which might be permissible in a neural network implementation utilising FDM communications. A software simulator is described, which was designed to test the effects of overlap on Multilayer Perceptron neural networks. Results are presented for networks trained with the backpropagation algorithm, and with the alternative weight perturbation algorithm. These were carried out using both floating point and quantised weights to examine the combined effects of overlap and weight quantisation. It is shown using examples of classification problems, that the neural network learning is indeed highly tolerent to overlap, such that the effect on performance (i.e. on convergence or generalisation) is negligible for fractional overlaps of up to 30%, and some tolerence is achieved for higher overlaps, before failure eventually occurs. The results of the simulations are followed up by a closer examination of the mechanism of network failure. The last section of the thesis investigates the VLSI implementation of the FDM scheme, and proposes the use of the operational transconductance amplifier (OTA) as a building block for implementation of the FDM circuitry in analogue VLSI. A full custom VLSI design of an OTA is presented, which was designed and fabricated through Eurochip, using HSPICE/Mentor Graphics CAD tools and the Mietec 2.4µ CMOS process. A VLSI architecture for inter-chip FDM is also proposed, using adaptive tuning of the OTA-C filters and oscillators.This forms the basis for a program of further work towards the VLSI realisation of inter-chip FDM, which is outlined in the conclusions chapter.
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Rajanna, Sowmya. "Orthogonal Frequency Division Multiplexing (OFDM) channel estimation using pilot based parametric scheme." Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10011270.

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This paper is aimed at parametric Multiple Input Multiple Output (MIMO) ? Orthogonal Frequency Division Multiplexing (OFDM) channel estimation that increases the spectrum efficiency of the wireless communication systems. OFDM technology has been widely used due to its high data rate and low multipath distortion. The estimation of channel for OFDM is required in vehicular environments and many other cutting-edge technology applications. To develop such reliable vehicular wireless communication systems, it is necessary to set up the standards and models of propagation channel with respect to the environment and scenarios. The proposed parametric scheme can accomplish super resolution by assessing the delays in arbitrary paths, making this scheme more suitable for wireless channels. The channel estimation precision is increased by using the spatial and temporal correlations in the wireless MIMO channel. The average pilot overhead for each antenna is reduced because of the temporal correlation of MIMO channels. Thus, the parametric scheme is promising for future wireless technologies as it accomplishes better spectral efficiency and better robustness for the multipath fading channels.

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Sahmel, Peter H. "Eigenspace Approach to Specific Emitter Identification of Orthogonal Frequency Division Multiplexing Signals." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/35987.

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Specific emitter identification is a technology used to uniquely identify a class of wireless devices, and in some cases a single device. Minute differences in the implementation of a wireless communication standard from one device manufacturer to another make it possi- ble to extract a wireless â fingerprintâ from the transmitted signal. These differences may stem from imperfect radio frequency (RF) components such as filters and power amplifiers. However, the problem of identifying a wireless device through analysis of these key signal characteristics presents several difficulties from an algorithmic perspective. Given that the differences in these features can be extremely subtle, in general a high signal to noise ratio (SNR) is necessary for a sufficient probability of correct detection. If a sufficiently high SNR is not guaranteed, then some from of identification algorithm which operates well in low SNR conditions must be used. Cyclostationary analysis offers a method of specific emitter iden- tification through analysis of second order spectral correlation features which can perform well at relatively low SNRs. The eigenvector/eigenvalue decomposition (EVD) is capable of separating principal components from uncorrelated gaussian noise. This work proposes a technique of specific emitter identification which utilizes the principal components of the EVD of the spectral correlation function which has been arranged into a square matrix. An analysis of this EVD-based SEI technique is presented herein, and some limitations are identified. Analysis is constrained to orthogonal frequency division multiplexing (OFDM) using the IEEE 802.16 specification (used for WiMAX) as a guideline for a variety of pilot arrangements.
Master of Science
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Du, Jinfeng. "Pulse Shape Adaptation and Channel Estimation in Generalised Frequency Division Multiplexing Systems." Licentiate thesis, Stockholm : Informations- och kommunikationsteknik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9457.

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Gemechu, Wasyhun Asefa. "Comparison of nonlinear frequency division multiplexing and OFDM for optical fiber transmissions." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLT021/document.

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La capacité ultime du canal dans les systèmes de transmission optique à longue distance est limitée par les effets non linéaires liés à la propagation dans les fibres optiques. Des techniques de compensation des effets non-linéaires, tel que la DBP (Digital Back Propagation), ont été proposées pour surmonter ces limitations et accroître la capacité. Compte tenu de leur complexité d’implémentation, leur gain en performance reste très limité. Cela a déclenché très récemment la recherche de nouvelles techniques de communication prenant en compte la non-linéarité de la fibre. Une nouvelle méthode de communication en régime non-linéaire, basée sur la théorie de la transformation spectrale inverse (IST pour Inverse Spectral Transform), a été proposée pour surmonter la limitation induite par ces effets. Cette méthode, proposée à l'origine par Hasegawa en 1993, encore appelée communication aux valeurs propres (ou multi-solitons), est basée sur l'observation fondamentale selon laquelle le spectre non linéaire d'un signal optique est invariant (à l'exception d'un déphasage linéaire trivial) lors de la propagation dans la fibre optique, comme décrit par l’équation non linéaire de Schrödinger (NLSE pour Non-Linear Schrödinger Equation). Cela signifie que si la transformée spectrale directe (DST) (également appelée NFT pour Nonlinear Fourier Transform) du signal reçu peut être calculée, le spectre de valeurs propres peut être entièrement récupéré.Cette thèse porte sur une technique de communication de type NFT connue sous le nom de multiplexage non linéaire en fréquence (NFDM pour Non-Linear Fourier Transform). Différentes configurations de systèmes optiques NFDM ont été évalués numériquement et validés expérimentalement. Dans un premier temps, la structure d’un système NFDM en mono-polarisation utilisant le spectre continu des fréquences non-linéaires dans une fibre en régime de dispersion normale est décrite. Pour ce faire, une forme NFT du vecteur NLSE, encore appelé système de Manakov, a été développé numériquement. Sur la base de ces algorithmes, la méthode NFDM a été étendue aux systèmes multiplexés par division de polarisation (PMD) et validée expérimentalement pour la première fois en utilisant le spectre continu. Finalement, l’expérience a été répliquée en régime de dispersion anormale. Afin d'étudier les contraintes de mise en œuvre, des études numériques supplémentaires ont été effectués pour la transmission de signaux NFDM utilisant la modulation du spectre continu
Nonlinear effects in optical fiber set the ultimate limit to the channel capacity in long-haul optical transmission systems. Advanced nonlinear compensation techniques such as digital backpropagation (DBP) have been proposed as a solution to overcome the channel capacity crunch. However, given theircomputational complexity, in a practical environment their performance gainremains very limited. This triggered a search for a novel communication system design that takes fiber nonlinearity into consideration. A new nonlinearcommunication method, based on the theory of the inverse spectral transform, has been proposed to overcome the nonlinear capacity crunch. Thismethod, originally proposed by Hasegawa in 1993 and called eigenvalue (ormulti-soliton) communication, is based on the fundamental observation thatthe nonlinear spectrum of an optical signal is invariant (except for a triviallinear phase shift) upon propagation in the fiber channel, as described bythe nonlinear Schrödinger equation (NLSE). This means that if the directspectral transform (also known as nonlinear Fourier transform (NFT)) ofthe received signal can be computed, the eigenvalue spectrum can be fullyrecovered.This thesis focuses on a NFT-based communication technique known as nonlinear frequency division multiplexing (NFDM). The NFDM optical systemis numerically assessed and experimentally demonstrated. First, the structure of the proposed single-polarization NFDM system using the continuousspectrum in the normal dispersion regime is presented. To that end, theNFT of the vector NLSE, or Manakov system, was numerically developed.Based on these algorithms the NFDM method was extended to polarizationdivision multiplexed (PMD) systems, and experimentally validated for thefirst time using the continuous spectrum. Finally, the experiment will bereplicated in the anomalous dispersion regime.Additional numerical studies are presented, in order to investigate the implementation challenges of the proposed NFDM techniques for the continuousspectrum modulation
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45

Leung, Edward Sau-Yee. "A successive interference cancelling receiver for orthogonal frequency division multiplexing in mobile communications." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0019/MQ37576.pdf.

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46

Yang, Runfeng. "Multiband orthogonal frequency division multiplexing modulation and demodulation for wireless universal serial bus." Thesis, University of Reading, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499368.

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Wireless Universal Serial Bus (W-USB) has been proposed to offer a mechanism in short range and high speed Wireless Personal Area Networks (WPAN). Wireless USB has now been standardized by utilizing the common WiMedia Ultra Wideband (UWB) radio platform to use the services of Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) as the transport mechanism. With regards to the high data rate mode using DCM modulation scheme, different DCM demapping methods resulting in different system performance are presented, which include soft bit demapping, Maximum Likelihood (ML) soft bit demapping and I Log Likelihood Ratio (LLR) demapping. The proposed Channel State Information (CSl) aided scheme coupled with the band hopping information is used as the further technique to improve the DCM demapping performance.
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47

Bagdiya, Anshul P. "Iterative receiver for flip orthogonal frequency division multiplexing and proposed 5G modulation techniques." Thesis, California State University, Long Beach, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10251768.

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In Optical Wireless Communication (OWC) systems, the technique of Flip-Orthogonal Frequency Division Multiplexing (Flip-OFDM) is applied, where the positive segment and negative segment of the signal are transmitted on two continuous OFDM sub-frames. Conventionally in Flip-OFDM, data is recovered by simply subtracting the negative sub-frame from the positive sub-frame. But the signal survey confirms that the information in both sub-frames gets disrupted during signal propagation and an incorrect detection of the received values takes place at the detector.

An iterative receiver is proposed that utilizes the input signal values along with the received signals sub-frames to improve the efficacy of the Flip-OFDM. The Matlab software is used to design the transmitter and iterative receiver. Features such as cyclic prefixing, frame multiplexing, and channel characterization are included in the design.

The results of the simulation depict that the suggested receiver delivers a superior Bit Error Rate (BER) and Signal to Noise Ratio (SNR) gain when compared to the conservative receiver.

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48

Neilson, Rob. "An investigation into the use of orthogonal frequency division multiplexing in packet radio." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/5139.

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Bibliography: leaves 56-58.
The concept of Orthogonal Frequency Division Multiplexing has been around since the 1960s. It has resurfaced over the last decade as being the modulation scheme of choice in some newer technologies like Digital Video Broadcasting (DVB) and Asynchronous Digital Subscriber lines (ADSL). Amateur packet radio started in 1978 and has attracted thousands of enthusiasts from around the world. The interest in packet radio has waned over the years due advances in the data transmission capabilities oflandline systems and also more widespread access to the Internet. The purpose of this thesis was to develop a simple software simulation model to determine whether or not OFDM could be used to increase the data rates currently available in packet radio systems. The thesis starts out with an introduction to packet radio and OFDM in Chapter 1. A slightly more detailed discussion on OFDM is given in Chapter 2 in order to develop a basic specification for the proposed OFDM model. Chapters 2,3 and 4 discuss the development of the Transmitter model, the Receiver model and the Channel model respectively using the Simulink software package. Chapter 6 discusses the problem of Peak-to-Average Power Ratios (PAPR) in OFDM and explores the use of A-law companding to reduce this problem. In Chapter 7, the developed models are simulated and their performance compared to theoretical expectations. The full system is also simulated in this chapter in order to ascertain the possible data rate through the modelled packet radio channel. Conclusions regarding the application of OFDM to packet radio are presented in Chapter 8.
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49

Paul, Prabal. "On The Peak-To-Average-Power-Ratio Of Affine Linear Codes." Thesis, 2006. https://etd.iisc.ac.in/handle/2005/350.

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Employing an error control code is one of the techniques to reduce the Peak-to-Average Power Ratio (PAPR) in an Orthogonal Frequency Division Multiplexing system; a well known class of such codes being the cosets of Reed-Muller codes. In this thesis, classes of such coset-codes of arbitrary linear codes are considered. It has been proved that the size of such a code can be doubled with marginal/no increase in the PAPR. Conditions for employing this method iteratively have been enunciated. In fact this method has enabled to get the optimal coset-codes. The PAPR of the coset-codes of the extended codes is obtained from the PAPR of the corresponding coset-codes of the parent code. Utility of a special type of lengthening is established in PAPR studies
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50

Paul, Prabal. "On The Peak-To-Average-Power-Ratio Of Affine Linear Codes." Thesis, 2006. http://hdl.handle.net/2005/350.

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Employing an error control code is one of the techniques to reduce the Peak-to-Average Power Ratio (PAPR) in an Orthogonal Frequency Division Multiplexing system; a well known class of such codes being the cosets of Reed-Muller codes. In this thesis, classes of such coset-codes of arbitrary linear codes are considered. It has been proved that the size of such a code can be doubled with marginal/no increase in the PAPR. Conditions for employing this method iteratively have been enunciated. In fact this method has enabled to get the optimal coset-codes. The PAPR of the coset-codes of the extended codes is obtained from the PAPR of the corresponding coset-codes of the parent code. Utility of a special type of lengthening is established in PAPR studies
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