Rozprawy doktorskie: „OFDM (Orthogonal Frequency Division Multiplexing)”

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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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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.
Ph. D.

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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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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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Chen, Jianwu, i 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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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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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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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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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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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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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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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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Chen, Zhiqiang, i 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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Baxley, Robert John. "OFDM communications over peak-limited channels". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/29631.

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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Zhou, G. Tong; Committee Member: Johnson, Ellis; Committee Member: Kenney, J. Stevenson; Committee Member: Li, Ye; Committee Member: Ma, Xiaoli. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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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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Pan, Xinyue, i 潘新月. "Symbol synchronization in OFDM-based systems". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39793850.

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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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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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Stinchcombe, Timothy Edward. "Aperiodic correlations of length 2'm sequences, complementarity and power control for OFDM". Thesis, Royal Holloway, University of London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325865.

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Rodrigues, Miguel Raul Dias. "Modelling and performance assessment of OFDM communication systems in the presence of non-linearities". Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268393.

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He, Lanlan, i 何兰兰. "Data detection for OFDM systems under high mobility". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B45876642.

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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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Chen, Wei Zhang Ruifeng. "Time- frequency- selective channel estimation of ofdm systems /". Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/616.

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Sharma, Ragahv. "Behavioral Modeling and FPGA Synthesis of IEEE 802.11n Orthogonal Frequency Division Multiplexing (OFDM) Scheme". Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6584.

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In the field of communications, a high data rate and low multi-path fading is required for efficient information exchange. Orthogonal Frequency Division Multiplexing (OFDM) is a widely accepted IEEE 802.11n (and many others) standard for usage in communication systems operating in fading dispersive channels. In this thesis, we modeled the OFDM algorithm at the behavioral level in VHDL/Verilog that was successfully synthesized/verified on an FPGA. Due to rapid technology scaling, FPGAs have become popular and are low-cost and high performance alternatives to (semi-) custom ASICs. Further, due to reprogramming flexibility, FPGAs are useful in rapid prototyping. As per the IEEE standard, we implemented both transmitter and receiver with four modulation schemes (BPSK, QPSK, QAM16, and QAM64). We extensively verified the design in simulation as well as on Altera Stratix IV EP4SGX230KF40C2 FPGA (Terasic DE4 Development Board). The synthesized design ran at 100 MHz clock frequency incurring 54 µ sec. end-to-end latency and 8% logic utilization.

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Zhang, Rong. "Estimation and compensation of I/Q imbalance in OFDM-based systems /". View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20ZHANGR.

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Modhe, Sandesh. "Performance Analysis of Orthogonal Frequency Division Multiplexing (OFDM) and Bandwidth Extension using Carrier Aggregation (CA)". University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1430336307.

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Ho, Ka Ming. "Cross-layer design of FDD-OFDM system based on ACK/NAK feedbacks /". View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?ECED%202007%20HO.

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Erdogan, Ahmet Yasin. "Analysis of the effects of phase noise and frequency offset in orthogonal frequency division multiplexing (OFDM) systems". Thesis, Monterey California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1712.

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Approved for public release, distribution is unlimited
Orthogonal frequency division multiplexing (OFDM) is being successfully used in numerous applications. It was chosen for IEEE 802.11a wireless local area network (WLAN) standard, and it is being considered for the fourthgeneration mobile communication systems. Along with its many attractive features, OFDM has some principal drawbacks. Sensitivity to frequency errors is the most dominant of these drawbacks. In this thesis, the frequency offset and phase noise effects on OFDM based communication systems are investigated under a variety of channel conditions covering both indoor and outdoor environments. The simulation performance results of the OFDM system for these channels are presented.
Lieutenant Junior Grade, Turkish Navy

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Sen, Mumtaz Bilgin. "Channel estimation techniques for single and multiple transmit antenna orthogonal frequency division multiplexing (OFDM) systems". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FSen.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2005.
Thesis Advisor(s): Roberto Cristi, Murali Tummala. Includes bibliographical references (p. 71-72). Also available online.

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Sonntag, Christoph. "Orthogonal frequency division multiplexing (OFDM) implementation as part of a software devined radio (SDR) environment". Thesis, Stellenbosch : University of Stellenbosch, 2005. http://hdl.handle.net/10019.1/2447.

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Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005.
Orthogonal Frequency Division Multiplexing (ODFM) has gained considerable attention the past couple of years. In our modern world the need for faster data transmission is never-ending. OFDM modulation provides us with a way of more densely packing modulated carriers in the frequency domain than other existing Frequency Multiplexing schemes, thus achieving higher data rates through communications channels. Software Defined Radio (SDR) creates a very good entry point for designing any communications system. SDR is an architecture that aims to minimise hardware components in electronic communications circuits by doing all possible processing in the software domain. Such systems have many advantages over existing hardware implementations and can be executed on various platforms and embedded systems, given that the appropriate analogue front ends are attached to the system.

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Han, Taewoo. "New signal processing in OFDM communication systems". Diss., Online access via UMI:, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3174448.

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Thesis (Ph. D.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Electrical & Computer Engineering, 2005.
Includes bibliographical references.

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Chheda, Shital Ratilal. "A Comparison Between Synchronous CDMA and Orthogonal Frequency Division Multiplexing (OFDM) for Fixed Broadband Wireless Access". Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/31896.

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The growth of broadband Internet access has paved the way for the development of many new technologies. As the cost of implementing broadband access soars, the best alternative will be to use fixed wireless for these services. This thesis addresses the possibility of 3rd Generation (3G) mobile cellular wireless systems as the basis for fixed broadband wireless service. Two of the 3G technologies aimed at providing fixed broadband wireless access are Time Division Synchronous Code Division Multiple Access (TD-SCDMA) and Orthogonal Frequency Division Multiplexing (OFDM).

This thesis aims to provide a preliminary study on using TD-SCDMA and OFDM for broadband wireless systems. Currently, there is not enough theory and information to establish the feasibility of using either of these technologies for broadband wireless access. First, the basic features and background on synchronous CDMA and OFDM are presented for the reader to better understand these technologies. Then, an example TD-SCDMA system is described, and some analytical and experimental results are presented. Finally, TD-SCDMAâ s technologies, along with this systemâ s attributes, are compared analytically to that of Vector OFDM (VOFDM).
Master of Science

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Zhou, Wen, i 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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Wicomb, Lindsay Paul. "OFDM modulation techniques for domestic power line communication". Thesis, Cape Peninsula University of Technology, 2005. http://hdl.handle.net/20.500.11838/1083.

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Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2005
With the growth of the personal computer industry, a number of households now contain two or more personal computers. The need to share resources such as printers, scanners and other PC peripherals has become evident. Communication between personal computers and other smart devices in the home is also required. This brings the emergence of home networking together with home automation. Home networking is the collection of elements to enable the connection and integration of multiple computing, control and communication devices. There are various options at this stage for home networking. One of the broadband options is indoor power line communication. The aim of the project was to evaluate a communication system capable of performing efficiently in South African Home Power line environment. In designing a communication system capable of performing in the harsh conditions which are presented in the home environment (noise, attenuation, phase distortion, etc.), a mathematical model that is representative of a typical suburban South African home power line is required. To aid the modeling process, an experimental network was constructed so measurements could be taken in a controlled environment. In conjunction with simulation, the model of the home power line network has aided the design of the data communication system. The project has involved: • Determining optimal specifications for the communication system. • Development of a home power line model representative of a typical South African suburban home environment. • Construction and measurement of an experimental power grid • Development of methods, algorithms and programs for the design of an OFDM PLC modem (in software) to optimal specifications. • Simulation development in MA1LAB of the OFDM Modem. • Comparison of different OFDM sub-modulation schemes for enhancing the communication system performance, In conclusion, the simulation model of the PLC modem correlates well with typical practical systems. Optimising throughput of the communication system and hardware development of the modem will form the basis for further research.

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Zhang, Lu. "Timing synchronization algorithm design for MB-OFDM UWB systems /". View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20ZHANGL.

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Rice, Michael, i 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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Ma, Shaodan. "Semi-blind signal detection for MIMO and MIMO-OFDM systems". Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36846569.

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Ma, Shaodan, i 馬少丹. "Semi-blind signal detection for MIMO and MIMO-OFDM systems". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36846569.

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Wu, Nansong. "Resource Allocation, Scheduling and Feedback Reduction in Multiple Input Multiple Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) Systems". FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/637.

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The number of wireless systems, services, and users are constantly increasing and therefore the bandwidth requirements have become higher. One of the most robust modulations is Orthogonal Frequency-Division Multiplexing (OFDM). It has been considered as an attractive solution for future broadband wireless communications. This dissertation investigates bit and power allocation, joint resource allocation, user scheduling, and limited feedback problem in multi-user OFDM systems. The following dissertation contributes to improved OFDM systems in the following manner. (1) A low complexity sub-carrier, power, and bit allocation algorithm is proposed. This algorithm has lower computational complexity and results in performance that is comparable to that of the existing algorithms. (2) Variations of the proportional fair scheduling scheme are proposed and analyzed. The proposed scheme improves system throughput and delay time, and achieves higher throughput without sacrificing fairness which makes it a better scheme in terms of efficiency and fairness. (3) A DCT feedback compression algorithm based on sorting is proposed. This algorithm uses sorting to increase the correlation between feedback channel quality information of frequency selective channels. The feedback overhead of system is successfully reduced.

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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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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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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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Kwun, Byong-Ok. "Robust beamforming for collaborative MIMO-OFDM wireless systems". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100228.

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Collaborative beamforming is a powerful technique to increase communication energy efficiency and range in an energy-constrained network. To achieve high performance, collaborative beamforming requires accurate knowledge of channel state information (CSI) at the transmitters (collaborative nodes). In practice, however, such exact knowledge of CSI is not available. A robust transmitter design based on partial CSI is required to mitigate the effects of CSI mismatches.
This thesis focuses on the design and evaluation of a beamforming scheme that is robust to CSI mismatches for collaborative multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless systems. Using a max-min robust design approach, the robust beamformer is designed to maximize the minimum (worst-case) received signal-to-noise ratio (SNR) within a predefined uncertainty region at each OFDM subcarrier. In addition, several subcarrier power allocation strategies are investigated to further improve the robustness of collaborative systems. Numerical simulation results show that the robust beamformer offers improved performance over the nonrobust beamformers and the use of power allocation strategies among subcarriers further improves the system performance.

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Gao, Bo 1981. "Computationally efficient approaches for blind adaptive beamforming in SIMO-OFDM systems". Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115994.

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In single-input multiple-output (SIMO) systems based on orthogonal frequency division multiplexing (OFDM), adaptive beamforming at the receiver side can be used to combat the effect of directional co-channel interference (CCI). Since pilot-aided beamforming suffers from consuming precious channel bandwidth, there has been much interest in blind beamforming approaches that can adapt their weights by restoring certain properties of the transmitted signals. Within this class of blind algorithms, the recursive least squares constant modulus algorithm (RLS-CMA) is of particular interest due to its good overall CCI cancelation performance and fast convergence. Nevertheless, the direct use of RSL-CMA within a SIMO-OFDM receiver induces considerable computational complexity, since a distinct copy of the RLS-CMA must be run on each individual sub-carriers. In this thesis, we present two approaches to reduce the computational complexity of SIMO-OFDM beamforming based on the RLS-CMA, namely: frequency interpolation and distributed processing. The former approach, which exploits the coherence bandwidth of the broadband wireless channels, divides the sub-carriers into several contiguous groups and applies the RLS-CMA to a selected sub-carrier in each group. The weight vectors at other frequencies are then obtained by interpolation. The distributed processing approach relies on the partitioning of the receiving array into sub-arrays and the use of a special approximation in the RLS-CMA. This allows a partial decoupling of the algorithm which can then be run on multiple processors with reduced overall complexity. This approach is well-suited to collaborative beamforming i~ multi-node distributed relaying. Through numerical simulation experiments of a SIMO-OFDM system, it is demonstrated that the proposed modifications to the RLS-CMA scheme can lead to substantial computational savings with minimal losses in adaptive cancelation performance.

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Diao, Zhifeng, i 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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Shao, Lei. "Code design for MIMO-OFDM(A) systems /". Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/5859.

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Dayal, Avik. "Nonlinear Doppler Warp Correction for Acoustic OFDM". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/78157.

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The Underwater Acoustic (UWA) channel has been an area of interest for many researchers and engineers, but also a very challenging area. Compared to the over-the-air radio frequency (RF) channel, the underwater acoustic channel causes multiple distortions – due to multipath, frequency selectivity, noise, and Doppler – some of which are more severe. The increased distortion causes many techniques and assumptions made for typical RF communication systems to break down. One of the assumptions that breaks down is that the Doppler effect that the signal undergoes can be modelled with a simple shift in frequency, since the signals used to communicate in a UWA channel are effectively wideband. In this work the Doppler Effect that a signal undergoes is modelled as a nonlinear time warp. A procedure is developed to estimate the parameters of the time warp from the observed signal. These time warp parameters are then used to reverse the effect of the time warp. Two different methods for estimating the time warp parameters and correcting the Doppler are compared. The first technique uses sinusoids placed at the beginning and end of the signal to estimate the parameters of the warp that the signal undergoes. The second technique uses sinusoids that are present during the signal to estimate and correct for the warp. The frequencies of the sinusoids are outside of the frequency range used for the transmitted data signal, so there is no interference with the information that is being sent. The transmitted data signal uses Orthogonal Frequency Division Multiplexing (OFDM) to encode the data symbols, but the Doppler Correction technique will in principle work for other kinds of wideband signals as well. The results, which include MATLAB based simulations and over-the-air experiments, show that performance improvements can be realized using the time warp correction model.
Master of Science

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Mody, Apurva Narendra. "Signal Acquisition and Tracking for Fixed Wireless Access Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing". Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7624.

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The general objective of this proposed research is to design and develop signal acquisition and tracking algorithms for multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems for fixed wireless access applications. The algorithms are specifically targeted for systems that work in time division multiple access and frequency division multiple access frame modes. In our research, we first develop a comprehensive system model for a MIMO-OFDM system under the influence of the radio frequency (RF) oscillator frequency offset, sampling frequency (SF) offset, RF oscillator phase noise, frequency selective channel impairments and finally the additive white Gaussian noise. We then develop the acquisition and tracking algorithms to estimate and track all these parameters. The acquisition and tracking algorithms are assisted by a preamble consisting of one or more training sequences and pilot symbol matrices. Along with the signal acquisition and tracking algorithms, we also consider design of the MIMO-OFDM preamble and pilot signals that enable the suggested algorithms to work efficiently. Signal acquisition as defined in our research consists of time and RF synchronization, SF offset estimation and correction, phase noise estimation and correction and finally channel estimation. Signal tracking consists of RF, SF, phase noise and channel tracking. Time synchronization, RF oscillator frequency offset, SF oscillator frequency offset, phase noise and channel estimation and tracking are all research topics by themselves. A large number of studies have addressed these issues, but usually individually and for single-input single-output (SISO) OFDM systems. In the proposed research we present a complete suite of signal acquisition and tracking algorithms for MIMO-OFDM systems along with Cramr-Rao bounds for the SISO-OFDM case. In addition, we also derive the Maximum Likelihood (ML) estimates of the parameters for the SISO-OFDM case. Our proposed research is unique from the existing literature in that it presents a complete receiver implementation for MIMO-OFDM systems and accounts for the cumulative effects of all possible acquisition and tracking errors on the bit error rate (BER) performance. The suggested algorithms and the pilot/training schemes may be applied to any MIMO OFDM system and are independent of the space-time coding techniques that are employed.

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Hui, Shui-wing David. "Cross-layer design for OFDMA wireless system". View the Table of Contents & Abstract, 2007. http://sunzi.lib.hku.hk/hkuto/record/B36996439.

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