Dissertations / Theses: 'OFDM'

1

Nowak, Dan. "Adaptivní OFDM." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219140.

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The purpose of this paper is to study the possibilities of the OFDM system adaptive modulation. The study presents mechanism for acquiring the necessary data of every frequency subchannel using pilot signals and application of these data for system adjustment. The paper introduces the water-filling principle for subchannel power allocation on the basis of their SNR and adaptive modulation mechanisms for variety of OFDM usage. These mechanisms are implemented into a MATLAB model. The code is then transformed into graphical representation and using USRP2, the signal is transmitted by real world channel.

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2

Gharba, Mohamed. "Study and evaluation of a frequential multiplexing based on OFDM/OQAM." Phd thesis, Conservatoire national des arts et metiers - CNAM, 2012. http://tel.archives-ouvertes.fr/tel-00767401.

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This thesis is dedicated to the study of the OFDM/OQAM modulation as an alternative to the OFDM modulation. We treat more especially the multi-user environment. In this respect, synchronization aspects are crucial. The different options plus the choice of the waveform are examined in this point of view. Another objective is to precisely show how the OFDM/OQAM can be adapted to a cellular transmission type, taking as reference the 3GPP/LTE system. The main contributions we have made are : 1) Analysis of the desynchronization phenomena : we analyze the effect of desynchronization, according to the time and frequency axes, on the performance of OFDM/OQAM at the receiver side. 2) Synchronization method : we analyze a method of temporal synchronization defined in a single user OFDM/OQAM transmission and we adapt it to a multi-user scenario type. 3) Proposing for a multiple access scheme : we propose a multiple access scheme based on theOFDM/OQAM modulation, alternative to the known techniques OFDMA and SC-FDMA, for the UL transmission in a 3GPP/LTE context.

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3

Wang, Tiejun. "Mobile OFDM communications." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3211276.

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Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed June 7, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 104-111).

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4

Armour, Simon Martin Daniel. "Combined OFDM-equalisation." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369530.

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5

Xu, Lei. "OFDM turbo transceivers." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/64480/.

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In this thesis a variety of different techniques designed for the sake of improving the attainable efficiency of wireless system are considered in the context of Orthogonal Frequency Division Multiplexing (OFDM). More explicitly, powerful turbo transceivers invoking Sphere Packing (SP) modulation are designed using EXtrinsic Information Transfer (EXIT) charts for both single-user and multi-user transmission. In order to provide an attractive suite of single-user OFDM transceivers, we contrive a SP-aided OFDM scheme for maximizing the achievable coding advantage. The corresponding capacity equation shows that the SP-OFDM scheme exhibits a higher capacity than its counterpart dispensing with SP. Furthermore, a carefully designed Sphere Packing symbol To Sub-Carrier Mapping (SPTSCM) scheme is contrived, which results in an improved Discrete Input Continuous Output Memoryless Channel (DCMC) capacity. This is achieved by reducing the correlation between the multiple OFDM sub-carriers conveying a specific SP symbol. In order to enhance the attainable BER performance of the SP-OFDM scheme, iterative detection is invoked for exchanging extrinsic information between the SP symbol-to-bit demapper and the channel decoder. In contrast to the classic SP signal construction, sophisticated SP schemes are designed with the aid of EXIT charts for the sake of improving the convergence behaviour of the iteratively detected schemes. Explicitly, an approximately 0.15bit/s/Hz DCMC capacity improvement is achieved and the proposed iterative detection aided SP-OFDM scheme becomes capable of performing within 2.1dB of the maximum achievable rate limit obtained using EXIT charts at BER = 10−4. Some of the proposed advances are then extended to a multi-user Space Division Multiple Access (SDMA) OFDM scheme. Novel turbo MUDs are designed and investigated in terms of their complexity, EXIT characteristics and BER performance. More explicitly, the linear turbo MUDs considered include the Complex-valued Minimum Mean Square Error (SIC-CMMSE) scheme, the Soft Interference Cancellation based Real-valued Minimum Mean Square Error (SIC-RMMSE) arrangement and the Soft Interference Cancellation based Minimum Bit-Error Rate (SIC-MBER) MUD schemes. The SIC-RMMSE is only applicable in the context of BPSK modulated schemes. A Reduced-complexity Minimum Bit-Error Rate (RMBER) is also designed for the sake of arriving at a complexity reduction by slightly compromising the attainable performance in comparison to the SIC-MBER MUD. Furthermore, a hybrid scheme was designed to eliminate the performance degradation imposed by the RMBER MUD. In contrast to above-mentioned linear schemes, Bayesian turbo MUD and the K-best iterative Sphere Decoder (SD) belong to the family of non-linear MUDs. Then a general complexityreduction technique was contrived in order to reduce the complexity imposed by the turbo MUDs, which was referred to as the A-priori-LLR-Threshold (ALT) aided MUD algorithm, which was introduced for the sake of striking an attractive trade-off between the attainable complexity-reduction and the performance degradation imposed. Finally, the novel framework of Transmit Domain Processing based Detectors (TDPD) was contrived for a generalized multi-access or multiplexing based channel model in order to circumvent the exponentially increasing complexity imposed by the Maximum Likelihood (ML) MUD as a function of both the number of antennas and the number of bits per symbol. Explicitly, the TDPD may be separated into three basic steps including the MUD’s Search Center (SC) calculation, detection candidate list generation and LLR output calculation. A range of different schemes were considered for each of the three steps, and the SIC-CMMSE SC aided hybrid K-best subset combination based iterative TDPD was capable of achieving a similar BER performance to the optimal ML detector at a significantly reduced-complexity.

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6

Gui, Bo. "Cooperative OFDM networking." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 156 p, 2009. http://proquest.umi.com/pqdweb?did=1654493791&sid=1&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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7

Skrzypczak, Alexandre. "Contribution à l'étude des modulations multiporteuses OFDM / OQAM et OFDM suréchantillonnées." Rennes 1, 2007. http://www.theses.fr/2007REN1S136.

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Actuellement, pour la transmission dans des canaux multi-trajets, le choix de la modulation se base surtout sur des schémas de transmission multiporteuse du fait de leur robustesse vis-à-vis de la sélectivité fréquentielle. Parmi ces solutions, la modulation OFDM est la modulation de référence. Mais cette modulation, basée sur une mise en forme spectrale rectangulaire, possède des inconvénients notables comme une densité spectrale de puissance ayant des lobes secondaires très élevés. D'autres modulations ont alors été développées pour lutter contre ce problème, parmi lesquelles l'OFDM/OQAM et l'OFDM suréchantillonné, ceci au prix de nouvelles contraintes. L'objectif de cette thèse est d'étudier ces modulations avec forme d'onde sur plusieurs aspects critiques des transmissions. Nous nous focalisons ainsi sur l'étude de la densité spectrale de puissance, du PAPR et de sa réduction, et de l'estimation de canal. Une application au courant porteur en ligne est enfin réalisée
Nowadays, for the transmission over multipath fading channel, the choice of multicarrier solutions becomes more and more frequent because of their remarkable robustness with respect to frequency selective distortions. The OFDM solution then stands for a reference modulation. However, this modulation, based on a rectangular pulse shape, exhibits some noticeable drawbacks, like a power spectral density with high sidelobes. In order to cope with this problem, new solutions have been developed using non-rectangular pulse shapes. Nevertheless, modulations like OFDM/OQAM and oversampled OFDM lead to specific constraints. This Ph. D. Thesis aims at studying these pulse-shaped multicarrier modulations on several critical aspects of transmission. We focus on the study of the power spectral density, the PAPR and its reduction, and the channel estimation problem. We finally apply these solutions to power line communications

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8

Serener, Ali. "Optimization of short block length LDPC codes for OFDM and spread OFDM /." Search for this dissertation online, 2005. http://wwwlib.umi.com/cr/ksu/main.

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9

Karampatsis, Dimitrios. "Modelling and performance assessment of OFDM and fast-OFDM wireless communication systems." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446778/.

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This thesis is mainly concerned with the design, modelling and performance assessment of modulation techniques for use in wireless communication systems. The work is divided, broadly in three areas; a multimode system proposal, an assessment of a new modulation scheme and a system optimisation technique. A multimode system architecture employing GSM and EDGE systems and an Orthogonal Frequency Division Multiplexing (OFDM) system is proposed. The OFDM system is designed to have similar frame structure, channel allocation and spectrum shape to those of the GSM and EDGE systems. The multimode system is evaluated under typical multipath fading environments specified for GSM/EDGE and adjacent-channel and co-channel interference. The results indicated that the proposed OFDM system can be perfectly integrated within the GSM/EDGE network core. Furthermore, a novel modulation technique is investigated. Fast-OFDM (FOFDM) is a variation of OFDM, which offers twice the bandwidth efficiency when compared to OFDM. However, the bandwidth efficiency only applies to one dimensional modulation schemes (BPSK or M-ASK). The suitability of FOFDM for wireless communications is assessed by studying its performance under receiver front-end distortions and multipath fading environments. The performance of the FOFDM system is compared with the performance of a similar OFDM system. The results indicated that under small distortion conditions, the performance of FOFDM and OFDM is comparable. Finally, the effect of interpolation filtering on OFDM systems in noise limited and interference limited environments is investigated. The aim of this study is to highlight that interference should be taken into consideration when designing systems for wireless communications. In addition, this study can be utilised in software defined radio schemes, offering optimised performance. Overall, this thesis presents work over a range of research areas, providing system proposals, modulation comparisons and system optimisation techniques that can be used by developers of future mobile systems.

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Cheung, Bing-Leung Patrick. "Simulation of Adaptive Array Algorithms for OFDM and Adaptive Vector OFDM Systems." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/34915.

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The increasing demand for high data rate services necessitates the adoption of very wideband waveforms. In this case, the channel is frequency-selective, that is, a large number of resolvable multipaths are present in this environment and fading is not highly correlated across the band. Orthogonal frequency division multiplexing (OFDM) is well-known to be effective against multipath distortion. It is a multicarrier communication scheme, in which the bandwidth of the channel is divided into subcarriers and data symbols are modulated and transmitted on each subcarrier simultaneously. By inserting guard time that is longer than the delay spread of the channel, an OFDM system is able to mitigate intersymbol interference (ISI). Deploying an adaptive antenna array at the receiver can help separate the desired signal from interfering signals which originate from different spatial locations. This enhancement of signal integrity increases system capacity. In this research, we apply adaptive array algorithms to OFDM systems and study their performance in a multipath environment with the presence of interference. A novel adaptive beamforming algorithm based on the minimum mean-squared error (MMSE) criterion, which is referred to as frequency-domain beamforming, is proposed that exploits the characteristics of OFDM signals. The computational complexity of frequency-domain beamforming is also studied. Simulation results show employing an adaptive antenna array with an OFDM system significantly improves system performance when interference is present. Simulations also show that the computational complexity of the algorithm can be reduced by half without significant performance degradation. Adaptive array algorithms based on the maximum signal-to-noise ratio (MSNR) and the maximum signal-to-interference-plus-noise ratio (MSINR) criteria are also applied to adaptive vector OFDM systems (AV-OFDM). Simulation results show that the adaptive algorithm based on the MSNR criterion has superior performance in the multipath environment but performs worse than the one based on the MSINR criterion under the flat fading channel.
Master of Science

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11

Prasetyo, Bhimantoro Yudho. "Synchronisation in OFDM systems." Thesis, King's College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252282.

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12

Tan, Edward S. "Hyper-wideband OFDM system." Thesis, Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55056.

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Hyper-wideband communications represent the next frontier in spread spectrum RF systems with an excess of 10 GHz instantaneous bandwidth. In this thesis, an end-to-end physical layer link is implemented featuring 16k-OFDM with a 4 GHz-wide channel centered at 9 GHz. No a priori channel state information is assumed; channel information is derived from the preamble and comb pilot structure. Due to the unique expansive spectral properties, the channel estimator is primarily composed of least squares channel estimates combined with a robust support vector statistical learning approach using autonomously selected parameters. The system’s performance is demonstrated through indoor wireless experiments, including line-of-sight and near-line-of-sight links. Moreover, it is shown that the support vector approach performs superior to linear and cubic spline inter/extrapolation of the least squares channel estimates.

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13

Ilunga, Lou. "Adaptive, Turbo-coded OFDM." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/34578.

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Wireless technologies, such as satellite, cellular, and wireless internet are now commercially driven by ever more demanding consumers, who are ready for seamless integration of communication networks from the home to the car, and into the office. There is a growing need to quickly transmit information wirelessly and accurately. Engineers have already combine techniques such as orthogonal frequency division multiplexing (OFDM) suitable for high data rate transmission with forward error correction (FEC) methods over wireless channels.

In this thesis, we enhance the system throughput of a working OFDM system by adding turbo coding and adaptive modulation (AD). Simulation is done over a time varying, frequency selective Rayleigh fading channel. The temporal variations in the simulated wireless channel are due to the presence of Doppler, a sign of relative motion between transmitter and receiver. The wideband system has 48 data sub-channels, each is individually modulated according to channel state information acquired during the previous burst. The end goal is to increase the system throughput while maintaining system performance under a bit error rate (BER) of 10-2. The results we obtained are preliminary. The lack of resources prevented us from producing detailed graphs of our findings.
Master of Science

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14

Montojo-Bennassar, Juan I. "Adaptive OFDM-based UWB." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3356337.

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Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed July 9, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 114-118).

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15

Fischer, Volker. "Aufwandsgünstige Verfahren zur Interkanalinterferenzunterdrückung bei OFDM /." Göttingen : Sierke, 2008. http://d-nb.info/99084692X/04.

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16

Raileanu, Alexandru. "Sistemi OFDM: prestazioni di livello fisico." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amslaurea.unibo.it/2405/.

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I primi studi su Orthogonal Frequency Division Multiplexing (OFDM) sono stati fatti fin dal 1960, ma negli ultimi anni la modulazione OFDM è emersa come una tecnica di modulazione chiave commerciale per i sistemi di comunicazione ad alta velocità. La ragione principale di questo crescente interesse è dovuto alla sua capacità di fornire dati ad alta velocità impiegando sistemi con complessità bassa e contrastando l'interferenza intersimbolo (ISI) e quella intercanale (ICI). Per questo motivo la modulazione OFDM è stata adottata da diversi sistemi digitali wireline e wireless standard, come Digital Audio Broadcasting (DAB), Asymmetric Digital Subscriber Line (ADSL), Wireless Local Area Network (IEEE 802.11 a,g,n) oppure per WiMAX e LTE.

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17

Zhou, Wen, and 周雯. "A study of channel estimation for OFDM systems and system capacity forMIMO-OFDM systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45555850.

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18

Thompson, Steve C. "Constant envelope OFDM phase modulation /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2005. http://wwwlib.umi.com/cr/ucsd/fullcit?p3208635.

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19

Osesina, Olukayode Isaac, Yafan Zhang, and Shirisha Pagoti. "OFDM Carrier Frequency Offset Estimation." Thesis, Karlstad University, Division for Information Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-343.

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This thesis discusses and investigates the estimation of carrier offset frequency in

orthogonal frequency division multiplexing (OFDM) mobile systems. The investigation

starts by using Mobile WiMAX wireless communication specifications described

in IEEE 802.16e as the primary system setup. Under this setup orthogonal

frequency division multiple access (OFDMA) is used as a physical layer scheme; it

also involves the use of pilots in the OFDM symbol for channel estimation.

Although OFDM is resistant to multipath fading, it requires a high degree of synchronisation

to maintain sub-carrier orthogonality. Therefore the level of performance

of the system depends first on the accuracy in estimating the carrier frequency

offset and then the estimation of the channel. Maximum likelihood estimator

is used for estimating carrier frequency offset; its performance under different conditions

for example SNR, number of virtual carriers needed for estimation etc. are

simulated and compared with theoretical results. The optimality of IEEE 802.16e

specifications was also examined during the simulations and results analysis.

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20

Gursan, Hakan Yesari. "Frame Synchronization In Ofdm Systems." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605782/index.pdf.

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In this thesis, we considered the problem of frame synchronization and channel estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems. Since framing error may cause severe ISI and may disturb the orthogonality of the subcarriers, frame synchronization must be accomplished at the OFDM receiver. Furthermore, the effects of channel must be compensated to obtain the symbols accurately. We investigated several frame synchronization algorithms including a maximum likelihood (ML) synchronizer which relies on the periodicity induced in the OFDM structure, and a robust synchronizer which uses a special training symbol. These algorithms are evaluated in AWGN and Rayleigh fading multipath channels and performances are compared in terms of percentage of ISI-free synchronization, mean squared error and symbol error rate. The IEEE 802.11a framework is used to compare these algorithms with the standard system which utilizes training symbols dedicated for synchronization. It is shown that an adjustment for the frame start estimates must be done to avoid the effects of the channel delay spread. It is also pointed that ideal synchronization is not necessary unless symbol boundaries are detected inside an ISI-free region and the error aroused in ISI-free synchronization can be compensated by applying channel estimation and equalization regarding the same symbol boundaries.

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21

Gurel, Ilker. "Channel Estimation For Ofdm Systems." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606940/index.pdf.

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In this thesis, various pilot symbol aided channel estimation and tracking methods are investigated and their performances are compared for an OFDM system with packet based communication on HF channel. For the HF channel, Watterson HF channel model is used. The compared methods are least squares (LS) channel estimation, linear minimum mean square error (LMMSE) channel estimation, least mean squares (LMS) channel tracking, recursive least squares (RLS) channel tracking, constant position model based Kalman filter channel tracking, and constant velocity model based Kalman filter channel tracking. For LMS and RLS methods some adaptive approaches are also investigated.

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22

Fifield, Jeffrey M. "A software defined OFDM modulator." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1439452.

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23

Chen, Zhiqiang. "Cyclic prefix in OFDM systems." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39558332.

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24

Nyirongo, Nyembezi. "Optimization Stratergies for OFDM Communications." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490341.

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Orthogonal frequency division multiplexing (OFDM) efficiently deals with multipath fading by using a cyclic prefix (CP) or zero pad (ZP) sequence that is longer than the channel excess delay. OFDM has been adopted in I number of standards including IEEE 802.11a/g, digital video broadcasting (DVB) and digital audio broadcasting (DAB).

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Chen, Zhiqiang, and 陳志強. "Cyclic prefix in OFDM systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39558332.

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26

Lam, Chi Wa. "Synchronization in OFDM communication systems." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/928/.

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Kamirah, Daniel K. "OFDM Performance on Aeronautical Channnels." International Foundation for Telemetering, 2009. http://hdl.handle.net/10150/606130.

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ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada
This paper provides an introduction to the Orthogonal Frequency Division Multiplexing (OFDM) scheme which has been proposed for future aeronautical telemetry applications. OFDM offers the potential for high data rates on radio channels with multipath such as aeronautical telemetry channels. This paper provides in introduction to OFDM and demonstrates how orthogonality is maintained over multipath channels by the introduction of a guard band and by the inclusion of a cyclic prefix. The simulation of OFDM in multipath is simulated and performance results are presented that show the degradation of this scheme on a multipath channel with and without the guard band and the cyclic prefix.

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Rice, Michael, and Kenneth Welling. "CODED OFDM FOR AERONAUTICAL TELEMETRY." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/606496.

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International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California
Three Quadrature Phase Shift Keying (QPSK) mapped COFDM systems demonstrating a continuum of complexity levels are simulated over an evolving three ray model of the multipath fading channel with parameters interpolated from actual channel sounding experiments. The first COFDM system uses coherent QPSK and convolutional coding with interleaving in frequency, channel equalization and soft decision decoding; the second uses convolutional coding with interleaving in frequency, Differential Phase Shift Keying (DPSK) and soft decision decoding; the third system uses a quaternary BCH code with DPSK mapping and Error and Erasure Decoding (EED). All three systems are shown to be able to provide reliable data communication during frequency selective fade events. Simulations demonstrate QPSK mapped COFDM with reasonable complexity performs well in a multipath frequency selective fading environment under parameters typically encountered in aeronautical telemetry.

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Said, Fatin. "Turbo coding from OFDM systems." Thesis, King's College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394250.

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Thottappilly, Arjun. "OFDM for Underwater Acoustic Communication." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/34873.

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Communicating wirelessly underwater has been an area of interest for researchers, engineers, and practitioners alike. One of the main reasons for the slow rate of progress in this area is that the underwater acoustic channel is in general much more hostile â in terms of multipath, frequency selectivity, noise, and the Doppler effect â than the over-the-air radio frequency channel. In this work a time warp based technique which can be used to model time-varying wideband Doppler shifts (as seen in an UWA channel) in MATLAB is proposed. A corresponding procedure to estimate the parameters from observed data, required for inverting the effect of the time warp, is also proposed. Two different Doppler correction methods are compared; both can be used to undo the Doppler effect in measured data from an experiment subject to the wideband Doppler effect. The techniques presented correct for the wideband Doppler effect as if it changed the time scale of the received signal. The first resampling based technique corrects for the average expansion/contraction over a packet, inherently assuming the relative velocity to be constant over the duration of the packet. The second time warp based technique models time-varying Doppler shift. Sinusoids, added to the beginning and end of each packet, are used to estimate the parameters required to invert the effect of the warp. The time warp based methods are demonstrated using Orthogonal Frequency Division Multiplexing (OFDM) signals, but will in principle work for other kinds of wideband signals also. The presented results â using MATLAB based simulations, and over-the-air experiments performed in such a way as to introduce the Doppler effect in the received signals â emphasize the improvements that can be attained by using the time warp based Doppler modeling and correction method. The thesis concludes with suggestions for future work.
Master of Science

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31

Horák, Martin. "Implementace OFDM v obvodu FPGA." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217465.

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The thesis is focused on designing OFDM modem, which should be implemented into the FPGA device. The advantages of using OFDM signals in order to provide high baud rates together with high multipath immunity has provoked a mass expansion into media systems such as DSL, DVB, Wi-Fi, WLAN, etc. . Thanks to this technology we can quarantee high modulation rates with minimal negative disturbance eects. The rst part is dedicated to characterise OFDM signals, their generation and the algorithm producing the OFDM which is implemented in DSP devices. For the purpose of using the fastest algorithm, the Fast Fourier Transform using Cooley-Tukey algorithm was shown. Before we can implement OFDM modem into the FPGA device, we have to simulate its correct function. Because there is no OFDM analyser available at our departement, its necessary to prove its correct function by simulations. Therefore a large part of this thesis is focused on simulations using Matlab and ModelSim, in order to show comparison between the theoretical, and simulated results. Between the theoretical and practical simulations there is a part which shows the brief characteristics of available FPGA devices. Detailed view is presented just for the Virtex II device, which the implementation is made for. As a suitable FPGA device, we have chosen Virtex II XC2V1000 which is available for students. In the last part the measured results were shown to prove the corect function of the modem. Programming the FPGA using VHDL language is realized in the software ISE Xilinx (distributed in Xilinx software support). All programmed scrits and data used in this thesis are included on distributed media.

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32

Spalding, Scott A. Jr. "Adaptive OFDM Radar Signal Design." Miami University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=miami1335728143.

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Kováč, Michal. "Modulátor OFDM v obvodu FPGA." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221112.

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The master’s thesis deals with the design of modulator OFDM in the FPGA circuit. The thesis describes basic attributes of modulation OFDM, its pros and cons. With the help of created block level scheme, it describes all the components of the processing of the data signal on its way from the transmitter to the receiver. The Atlys Spartan-6 Development Board has been chosen for the implementation of the modulator. The other part of thesis is the design and realization of the analog-digital interface for the modulator OFDM. The interface consists of PCB, which is connected to the development board using expansion connector. The board is assembled with all the parts required for transmitting the signal as well as consecutive receiving, the description of used solutions is also a part of this master’s thesis. Proper function of both designed parts was verified using hardware co-simulation.

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VALENTIM, B. L. "Equalização para Sistemas OFDM Óptico." Universidade Federal do Espírito Santo, 2010. http://repositorio.ufes.br/handle/10/9594.

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Na ´ultima d´ecada a t´ecnica OFDM (Orthogonal Frequency Division Multiplex ) tem ganhado cada vez mais espa¸co nas comunica¸coes com e sem fio. A ´area das comunica¸coes ´opticas tamb´em se desenvolveu bastante nos ´ultimos anos. Recentemente iniciou-se a jun¸cao destes dois recursos: a t´ecnica OFDM e o canal ´optico. Dentro deste panorama, este trabalho se propoe a estudar a conjuga¸cao destes dois recursos e propor um sistema ´optico simples, onde a compensa¸cao de dispersao e o alocamento de banda ficam sob a resposabilidade da OFDM aplicando a t´ecnica de equaliza¸cao de canal utilizando tons piloto. A esta t´ecnica ´e dado o nome de OOFDM (Optical OFDM). Neste trabalho foi considerado um sistema ´optico de fibra monomodo padrao com modula¸cao de intensidade e detec¸cao direta (IM-DD - Intensity Modulation - Direct Detection), visando deixar a parte ´optica simples. Na transmissao OFDM foi utilizada a simetria hermitiana, para a transmissao em banda base, mapeamento 16-QAM e a aloca¸cao variada atrav´es do bit loading. Para corrigir a dispersao do canal foi implementada uma estima¸cao e equaliza¸cao de canal atrav´es de tons piloto e interpola¸cao linear. O sistema foi simulado e os resultados mostraram a possibilidade de uma transmissao em 20 km de fibra com taxa de 47 Gbps com BER ≈ 10−5 e EVM ≈ −22 dB. Os resultados possibilitam a atua¸cao desta t´ecnica em redes metropolitanas e como solu¸cao para enlaces de ´ultima milha em altas taxas de bits.

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35

Wunder, Gerhard. "A theoretical framework for the peak to average power control problem in OFDM transmission." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970360150.

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Leischner, Stefan. "Kompensation von Impulsstörungen in Multiträgersystemen." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=967531985.

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Kongara, Krishna Prasad. "Advances in the Analysis of Adaptive OFDM Systems." Thesis, University of Canterbury. Electrical and Computer Engineering, 2009. http://hdl.handle.net/10092/3835.

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This thesis analyzes and quantifes the performance of adaptive orthogonal frequency division multiplexing (OFDM) systems in conjunction with single and multi antenna systems operating over frequency selective Rayleigh and Rician fading environments. We introduce a generalized transceiver model for adaptive cyclic prefixed (CP)-OFDM and isotropic orthogonal transform algorithm (IOTA)-OFDM. Fundamental issues concerning the BER performance of CP-OFDM and IOTA-OFDM are investigated under typical system imperfections. Furthermore, a throughput comparison of these two types of adaptive systems is given. Next, the peak-to-average power ratio (PAPR) problem of adaptive OFDM is considered. Focusing on wideband channel variations in the frequency domain, we have developed a novel statistical analysis for adaptive multiple input multiple output (MIMO)-OFDM systems. In addition, a central limit theorem (CLT) was developed for a wide range of block-based performance metrics. This thesis aims to present a systematic study of channel variation with a statistical analysis of the MIMO-OFDM channel and system performance. In particular, we focus on the behavior of block based performance measurements by considering the correlation across the frequency bins of the OFDM block. In addition, we investigate the eigenvalue variation of MIMO-OFDM systems across frequency. We show that eigenvalue and link gain changes in frequency can be analyzed and have presented novel results on the distributions and moments of such changes. We have also given expressions for the autocorrelationfunctions (ACFs) of the maximum eigenvalue and the link gain. Of particular interest is the very simple approximation to the ACF of the maximum eigenvalue. This leads to accurate closed-form approximations to the variance and CDF of the eigenvalue differences. We consider three types of adaptive MIMO-OFDM systems; one is based on (diversity mode) maximal ratio transmission-maximal ratio combining (MRT- MRC), while the others are spatial multiplexing techniques using singular value decomposition (SVD) or minimum mean square error (MMSE) receivers with linear precoding. We derive closed-form expressions for the joint cumulative distribution function (CDF) of arbitrarily selected eigenvalues in the same bin and in different bins. Furthermore, for MIMO with MRT-MRC, and MIMO- SVD, the exact mean and variance of the number of bits transmitted per OFDM block has been computed analytically and veried with Monte Carlo simulations.

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Zhang, Wei. "On frequency synchronization in OFDM-based systems." [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:289-vts-58922.

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Diao, Zhifeng. "Adaptive packet scheduling in OFDM systems." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B32059541.

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Larsson, Oskar, and Jimmy Karlsson. "SDR radar demonstrator using OFDM-modulation." Thesis, Linköping University, Department of Electrical Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-21094.

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Today radars are used to measure the distance to almost anything. It is used to determine the position of airplanes as well as the level of an oiltank. To achieve high precision in level gauging radars high quality components are demanded. This makes them expensive.

In this project we evaluate the possibility to use relatively cheap components, used in radio communication, to measure distances with an OFDM-modulated signal. The components are cheap due to large production volumes rather than low performance.

To do this we started with working out the theory needed for length estimation. At our disposal we had the SDR SFF Development Platform from Lyrtech. A simulation model of the platform was built in MatLab. This model was used to verify the theory developed. Finally our algorithms was implemented on the development platform.

Both simulations and real life measurements show that OFDM can be used to measure distances. Even though the hardware used in this project is not dedicated for this application we managed to perform measurements with good accuracy at short range. We believe that with more suitable hardware OFDM-radars will be able to compete with todays high end level gauging radars at all ranges.

Nu för tiden används radar för att mäta avstånd i en rad olika sammanhang. Det används till allt från att bestämma positionen på flygplan till att mäta nivån i oljetankar. För att uppnå den höga precision som krävs vid nivåmätning ställs höga krav på de ingående komponenterna. Detta gör att radarn blir dyr.

I detta examensarbete utvärderar vi möjligheten att använda relativt billiga komponenter, som används inom radiokommunikation, för att mäta avstånd med hjälp av en OFDM-modulerad signal. Dessa komponenter är billiga till följd av stora tillverkningsvolymer, inte för att de är dåliga.

Till att börja med tog vi fram den teori som behövdes för att skatta avstånd. Till vårt förfogande hade vi Lyrtechs SDR SFF Developmemt Platform. En simuleringsmodell av platformen gjordes i MatLab vilken användes för att verifiera teorin. Slutligen implementerades algoritmerna på utvecklingsplattformen.

Både simuleringar och riktiga mätningar visar att OFDM kan användas för att mäta avstånd. Trots att hårdvaran som användts under examensarbetet inte är anpassad för avståndsmätning blev mätresultaten goda för korta avstånd. Vi är övertygade om att med en, för ändamålet, mer anpassad hårdvara kommer en OFDM-radar upppnå samma precision som dagens högpresterande nivåmätareäven för längre avstånd.

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Malkireddy, Sivakesava Reddy. "Spectrum Sensing of acoustic OFDM signals." Thesis, Linköpings universitet, Kommunikationssystem, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-86811.

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OFDM is a fast growing technology in the area of wireless communication due to its numerous advantages and applications. The current and future technologies in the area of wireless communications like WiMAX, WiFi, LTE, MBWA and DVB-T uses the OFDM signals. The OFDM technology is applicable to the radio communication as well as the acoustic communication. Though the licensed spectrum is intended to be used only by the spectrum owners, Cognitive radio is a concept of reusing this licensed spectrum in an unlicensed manner. Cognitive radio is motivated by the measurements of spectrum utilization . Cognitive radio must be able to detect very weak primary users signal and to keep the interference level at a maximum acceptable level. Hence spectrum sensing is an essential part of the cognitive radio. Spectrum is a scarce resource and spectrum sensing is the process of identifying the unused spectrum, without causing any harm to the existing primary user’s signal. The unused spectrum is referred to as spectrum hole or white space and this spectrum hole could be reused by the cognitive radio. This thesis work focuses on implementing primary acoustic transmitter to transmit the OFDM signals from a computer through loudspeaker and receive the signals through a microphone. Then by applying different detection methods on the received OFDM signal for detection of the spectrum hole, the performance of these detection methods is compared here. The commonly used detection methods are power spectrum estimation, energy detection and second–order statistics (GLRT approach, Autocorrelation Function (ACF) detection and cyclostationary feature detection ). The detector based on GLRT approach exploits the structure of the OFDM signal by using the second order statistics of the received data. The thesis mainly focuses on GLRT approach and ACF detectors and compare their performance.

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Nguyen, Xuan Huan Electrical Engineering &amp Telecommunications Faculty of Engineering UNSW. "OFDM receiver design with iterative techniques." Awarded by:University of New South Wales. School of Electrical Engineering and Telecommunications, 2006. http://handle.unsw.edu.au/1959.4/26776.

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Recent advances in iterative signal processing have allowed communication systems to obtain near optimal performance with manageable complexity. The idea of iteratively exchanging the reliability information among the components within a receiver to improve overall performance is known as the turbo concept or turbo processing. Based on the principle of turbo processing, this thesis investigates the key issues in designing a receiver for high data rate multicarrier wireless systems. The particular focus is on the orthogonal frequency division multiplexing (OFDM) technique which can be potentially targeted for the 4th generation communication systems. The first part of the thesis addresses the primary issues in an OFDM receiver such as channel estimation, carrier frequency offset (CFO) compensation, and decoding. Since the optimal solutions require a high load of computation, iterative algorithms are generally desirable. The soft information from the decoder/detector can be efficiently incorporated into the channel estimator/CFO compensator, which consequently results in better performance of the receiver. The thesis provides a framework of iterative algorithms for OFDM receivers in which the converged performances are close to those of the optimal solutions. In the second part of the thesis, the iterative algorithms for the spatial diversity channels, or in other words, multiple input multiple output (MIMO) channels, are investigated. Together with capacity potential, MIMO channels bring in some new challenges. With a number of antennas on both the transmitting and receiving sides, inter-antenna and co-antenna interference is the arising concern in addition to the conventional intersymbol interference problem. Also, most of the optimal signal processing algorithms within a receiver have complexities which are at least proportionally if not exponentially increasing with the number of antennas. This creates challenges for implementing signal processing algorithms at the receiver. We therefore investigate and design manageable-complexity iterative algorithms for spatial diversity channels. In particular, we develop novel decision feedback detectors for the single user scenario, and then propose a jointly iterative multiuser detection and cell-related interference cancellation scheme for the multiuser scenario. Again, it is verified that the iterative algorithms can be effectively used as near-optimal solutions for OFDM system with spatial diversity channels.

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Thanabalasingham, Thayaparan. "Resource allocation in OFDM cellular networks /." Connect to thesis, 2006. http://eprints.unimelb.edu.au/archive/00003227.

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Pan, Xinyue. "Symbol synchronization in OFDM-based systems." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39793850.

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Chen, Harry Zhi Bing. "Signal design for MIMO-OFDM systems." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23907.

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Orthogonal frequency division multiplexing (OFDM) combined with multiple-input multiple-output (MIMO) wireless technology is an attractive air-interface solution for wireless systems. The time-selective and dispersive nature of the wireless channel, however, poses challenges for signal design. To address these challenges, this dissertation investigates several physical layer aspects of signal design for MIMO-OFDM systems. To improve the information outage rate of certain MIMO systems with low-rank channel matrices, we propose two novel channel augmentation schemes, namely, the complex virtual antenna (CVA) and the real virtual antenna (RVA) schemes. For Bell labs space-time (BLAST) type architectures, both the CVA and the RVA schemes are more robust to channel correlations than a previously proposed scheme. For performance enhancement of coded MIMO-OFDM, we consider wrapped space-frequency coding (WSFC) and coded vertical BLAST (V-BLAST) with adaptive bit loading (ABL) and optimize both schemes. We show that bit-loaded WSFC and V-BLAST optimized for coded MIMO-OFDM can achieve error rate performances close to that of quasi-optimal MIMO-OFDM based on single value decomposition (SVD) of the channel, while their feedback requirements for loading are low. To exploit the spatial and frequency diversity in coded MIMO-OFDM systems, we propose cyclic space-frequency (CSF) filtering, which is applicable to both traditional MIMO systems with co-located transmit antennas and cooperative diversity systems with distributed transmit antennas. We further propose a robust CSF filtering scheme, which exploits imperfect channel state information at the transmitter (CSIT) and takes into account the reliability of the CSIT. To further improve robustness, we combine CSF filtering with space-time block coding (STBC) in the frequency domain. We also propose a linear prediction method for improving the quality of the CSIT via post-processing. For these CSF filtering schemes, design criteria are derived, closed-form solutions are given for certain special cases, and various design methods are provided for the general case. Simulation results confirm that robust CSF filtering is a promising solution for wireless communication systems.

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Piskonova, Galyna. "Transmission OFDM pour la téléphonie cellulaire." Mémoire, École de technologie supérieure, 2003. http://espace.etsmtl.ca/783/1/PISKONOVA_Galyna.pdf.

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Les communications numériques envahissent la quasi-totalité des domaines d'activités et la demande pour des systèmes de transmissions assurant des très hauts débits avec une qualité de service importante ne cesse de croître. De nombreuses applications sont apparues récemment sur la plupart des supports physiques de transmissions possibles (tant câblés que hertziens). Ceci a motivé la recherche de nouveaux modes de transmissions capables de supporter des transmissions à large bande. En effet le signal utile est perturbé par de nombreuses dégradations lors de sa transmission (pollution par du bruit et des parasites, atténuation et distorsion lors de la propagation,...). Pour cette raison, il est nécessaire de disposer de techniques de transmission efficaces combinées à des algorithmes de réception adéquats. En outre, le canal de propagation est généralement partagé entre plusieurs sources (la bande de fréquence est par exemple partagée entre les utilisateurs dans les systèmes cellulaires) ce qui nécessite des techniques d'accès multiples pour permettre plusieurs transmissions simultanées. Plusieurs techniques existent pour transmettre des données sur un canal de transmission. Celles ci peuvent être grossièrement divisées en 3 catégories: multiplexage en temps, par code ou en fréquence. Le multiplexage en temps (TDMA) est utilisé par exemple dans les systèmes de téléphonie cellulaire de 2e génération tandis que le multiplexage par code (CDMA) a été adopté pour les systèmes cellulaires de 3e génération UMTS. La 3e technique: le multiplexage fréquentiel, a été popularisée principalement par le succès des systèmes dits OFDM: Orthogonal Frequency Division Multiplexing [1]. Le principe des systèmes OFDM est d'utiliser plusieurs fréquences porteuses pour répartir un flot d'informations à transmettre à travers un canal de transmission à large bande sur plusieurs sous-canaux à bande étroite (chacun correspondant à une des fréquences). Ceci explique la dénomination de transmission multiporteuse qui est souvent utilisée pour parler des systèmes OFDM. Ce mémoire porte sur la conception des systèmes de transmission OFDM et étudie de nouveaux axes de recherche visant à améliorer leur performance et leur fiabilité. Il porte plus particulièrement sur l'un des problèmes les plus importants des systèmes OFDM: celui du facteur de crête ou PAPR: Peak to Average Power Ratio. Celui-ci est dû au fait que la transmission OFDM n'a pas la propriété d'être à enveloppe constante. En effet à cause de la modulation à l'émetteur des symboles à transmettre par la matrice d'IFFT, les symboles temporels transmis effectivement sur le canal ont un module qui n'est pas constant et varie largement. Ceci conduit à des problèmes de saturation de l'amplificateur de puissance utilisé pour amplifier le signal avant sa transmission via l'antenne émettrice. Il s'ensuit une distortion des symboles émis qui peut fortement dégrader les performances du système. Ce mémoire peut être vu comme étant formé de 2 parties qui sont interconnectées tout au long de ce document: - Conception et simulation d'un système OFDM traditionnel et adaptation de ce modèle à l'étude de la problématique mentionnée ci-dessus. Dans ce système, la structure des facteurs complexes de rotation est la même que la modulation de données QPSK. Par conséquent, on a besoin d'un canal supplémentaire pour la transmission de l'information concernant ces facteurs de rotation au récepteur. - Simulations et études des performances du système en utilisant l'approche PTS (Partial Transmit Sequences) modifiée pour diminuer la largeur de bande requise pour la transmission de l'information et du nombre de canaux utilisés. L'approche proposée change les valeurs des facteurs complexes de rotation et évite donc la transmission de l'information latérale concernant ces facteurs de rotation sur un canal supplémentaire. La structure proposée de l'approche PTS donne un bon compromis entre les performances au niveau de facteur de crête et la complexité du système. Elle permet de diminuer le rapport de PAPR de 2-3 dB dépendamment des valeurs des facteurs complexes de rotation comparativement au système OFDM-PTS classique.

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47

Weiß, Timo [Verfasser]. "OFDM-basiertes spectrum pooling / Timo Weiß." Karlsruhe : Inst. für Nachrichtentechnik, 2004. http://d-nb.info/1001463730/34.

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Chowdhury, Moyamer, and Aminul Alam. "Study Comparison of WCDMA and OFDM." Thesis, Blekinge Tekniska Högskola, Avdelningen för telekommunikationssystem, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-1363.

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Wideband Code Division Multiple Access (WCDMA) is one of the main technologies for the implementation of third-generation (3G) cellular systems. It is based on radio access technique proposed by ETSI Alpha group and the specifications was finalised 1999. WCDMA is also known as UMTS and has been adopted as a standard by the ITU under the name “IMT-2000 direct spread”. The implementation of WCDMA will be a technical challenge because of its complexity and versatility. The complexity of WCDMA systems can be viewed from different angles: the complexity of each single algorithm, the complexity of the overall system and the computational complexity of a receiver. In WCDMA interface different users can simultaneously transmit at different data rates and data rates can even vary in time. WCDMA increases data transmission rates in GSM systems by using the CDMA air interface instead of TDMA. WCDMA is based on CDMA and is the technology used in UMTS. WCDMA is the dominating 3G technology, providing higher capacity for voice and data and higher data rates. The gradual evolution from today's systems is driven by demand for capacity, which is required by new and faster data based mobile services. WCDMA enables better use of available spectrum and more cost-efficient network solutions. The operator can gradually evolve from GSM to WCDMA, protecting investments by re-using the GSM core network and 2G/2.5G services. Orthogonal Frequency Division Multiplexing (OFDM) - technique for increasing the amount of information that can be carried over a wireless network uses an FDM modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of crosstalk in signal transmissions. 802.11a WLAN, 802.16 and WiMAX technologies use OFDM. It's also used in the ETSI's HiperLAN/2 standard. In addition, Japan's Mobile Multimedia Access Communications (MMAC) WLAN broadband mobile technology uses OFDM. In frequency-division multiplexing, multiple signals, or carriers, are sent simultaneously over different frequencies between two points. However, FDM has an inherent problem: Wireless signals can travel multiple paths from transmitter to receiver (by bouncing off buildings, mountains and even passing airplanes); receivers can have trouble sorting all the resulting data out. Orthogonal FDM deals with this multipath problem by splitting carriers into smaller subcarriers, and then broadcasting those simultaneously. This reduces multipath distortion and reduces RF interference allowing for greater throughput. In this paper we have discussed about these two methods of third generation radio transmission system which are WCDMA and OFDM with various aspects. In between these two radio transmission technique, a better choice will be investigated.

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49

Diao, Zhifeng, and 刁志峰. "Adaptive packet scheduling in OFDM systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B32059541.

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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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Dissertations / Theses on the topic 'OFDM'

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