University, Diss., 2002--Essen.

Techn. University, Diss., 2005--Kaiserslautern.

Techn. University, Diss., 2005--Kaiserslautern.

Cette thèse est consacrée à l’étude de la modulation OFDM/OQAM en tant qu’alternative à la modulation OFDM. Nous traitons plus particulièrement le contexte multiusagers. De ce point de vue, les aspects de synchronisation sont déterminants. Les différentes options plus le choix de la forme d’onde sont donc examinés de ce point de vue. Un autre objectif est de montrer de manière précise comment la modulation OFDM/OQAM peut s’adapter à une transmission de type cellulaire, en prenant comme référence le système 3GPP/LTE. Les principales contributions que nous avons apportées sont : 1) Une analyse des phénomènes de désynchronisation : nous analysons l’effet de la désynchronisation, suivant les axes temporel et fréquentiel, sur les performances de l’OFDM/OQAM au récepteur. 2) Méthode de synchronisation : nous analysons une méthode de synchronisation temporelle définie dans un contexte de transmission OFDM/OQAM mono-usager et nous l’adaptons à un scénario de type multi-usagers. 3) Proposition d’un schéma d’accès multiple : nous proposons un schéma d’accès multiple basé sur la modulation OFDM/OQAM, alternatif aux techniques connues OFDMA et SC-FDMA, pour la transmission en liaison montante dans un contexte de type 3GPP/LTE. / 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.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-20T15:37:28Z No. of bitstreams: 1 guilhermeribeirocolen.pdf: 1980646 bytes, checksum: 55067533570f6bd2d5a1ab3288db464d (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-24T16:49:37Z (GMT) No. of bitstreams: 1 guilhermeribeirocolen.pdf: 1980646 bytes, checksum: 55067533570f6bd2d5a1ab3288db464d (MD5) / Made available in DSpace on 2017-04-24T16:49:37Z (GMT). No. of bitstreams: 1 guilhermeribeirocolen.pdf: 1980646 bytes, checksum: 55067533570f6bd2d5a1ab3288db464d (MD5) Previous issue date: 2012-09-06 / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / Esta dissertação tem como objetivo investigar, propor e analisar esquemas para reduzir a complexidade computacional de algoritmos implementados na camada física de transceptores para comunicação de dados via rede elétrica - power line communication (PLC) que são baseados em multiplexação por divisão de frequência ortogonal - orthogonal frequency division multiplexing (OFDM). Inicialmente, o Clustered-OFDM é investigado e analisado com o intuito de reduzir a complexidade computacional dos transceptores PLC. Além disto, uma relação entre complexidade computacional e desempenho é demonstrada para Clustered-OFDM e múltiplo acesso por divisão de frequência ortogonal - orthogonal frequency division multiple access (OFDMA). Os resultados computacionais quantificam a relação entre complexidade computacional e redução da capacidade do canal para o Clustered-OFDM em comparação com o OFDMA. Em seguida, é proposto e analisado um esquema Clustered-OFDM para comunicação com múltiplas entradas e múltiplas saídas - multiple-input and multiple-output (MIMO) 2×2, denominado MIMO-Clustered-OFDM, que tem como base um código de bloco espacial e temporal. Os resultados de comparações revelam que a proposta MIMO-Clustered-OFDM pode reduzir a capacidade do canal para atingir uma menor complexidade computacional, comparado ao MIMO-OFDMA. Por último, é introduzido um processo para analisar estatisticamente a degradação gerada pelo agrupamento de subportadoras contíguas para o uso de algoritmos de alocação de bits. Um estudo de caso com canais PLC revela que o critério aplicado para agrupar subportadoras contíguas pode proporcionar diferentes níveis de reduções de rendimento, bem como de outras perdas de desempenho se o tamanho do grupo é variável. / This thesis aims at investigating, proposing, and analyzing techniques to reduce the computational complexity of algorithms implemented in the physical layer of power line communication (PLC) transceivers which are based on orthogonal frequency division multiplexing (OFDM). First, the clustered-OFDM is investigated and analyzed to reduce computational complexity. Also, a trade between computational complexity and performance is demonstrated for clustered-OFDM and orthogonal frequency division multiple access (OFDMA). Performance results quantify what kind of tradeoff between computational complexity and capacity reduction can be achieved in comparison with OFDMA. Second, a clustered-OFDM scheme for 2×2 multiple input multiple output (MIMO) communication based on space time block code, named MIMO-clustered-OFDM, is proposed and analyzed. Comparison results reveal that the proposed MIMO-clustered-OFDM can trade capacity with computational complexity and can achieve lower computational complexity than MIMO-OFDMA. Third, a procedure to statistically analyze the degradation yielded by the use of granularity for grouping a set of contiguous subcarriers to be used by bitloading algorithm is introduced. A case study with PLC channels reveals that the criterion applied to group of contiguous subcarriers can offer different levels of throughput reductions and other performance losses if the size of the group is varied.

WiMAX provides broadband wireless access and uses OFDM as the underlying modulation technique. In an OFDM based wireless communication system, the channel will distort the transmitted signal and the performance is seriously degraded by synchronization mismatches between the transmitter and receiver. Therefore such systems require extensive digital signal processing of the received signal for retrieval of the transmitted information. In this master thesis, parts of an IEEE 802.16d (WiMAX) receiver have been implemented on a programmable baseband processor. The implemented parts constitute baseband algorithms which compensates for the effects from the channel and synchronization errors. The processor has a new innovative architecture with an instruction set optimized for baseband applications. This report includes theory behind the baseband algorithms as well as a presentation of how they are implemented on the processor. An impartial evaluation of the processor performance with respect to the algorithms used in the reference model is also presented in the report.

Recently, wireless network technology has grown at such a pace that scientific research has become a practical reality in a very short time span. One mobile system that features high data rates and open network architecture is 4G. Currently, the research community and industry, in the field of wireless networks, are working on possible choices for solutions in the 4G system. The researcher considers one of the most important characteristics of future 4G mobile systems the ability to guarantee reliable communications at high data rates, in addition to high efficiency in the spectrum usage. On mobile wireless communication networks, one important factor is the coverage of large geographical areas. In 4G systems, a hybrid satellite/terrestrial network is crucial to providing users with coverage wherever needed. Subscribers thus require a reliable satellite link to access their services when they are in remote locations where a terrestrial infrastructure is unavailable. The results show that good modulation and access technique are also required in order to transmit high data rates over satellite links to mobile users. The dissertation proposes the use of OFDM (Orthogonal Frequency Multiple Access) for the satellite link by increasing the time diversity. This technique will allow for an increase of the data rate, as primarily required by multimedia applications, and will also optimally use the available bandwidth. In addition, this dissertation approaches the use of Cooperative Satellite Communications for hybrid satellite/terrestrial networks. By using this technique, the satellite coverage can be extended to areas where there is no direct link to the satellite. The issue of Cooperative Satellite Communications is solved through a new algorithm that forwards the received data from the fixed node to the mobile node. This algorithm is very efficient because it does not allow unnecessary transmissions and is based on signal to noise ratio (SNR) measures.

Orthogonal Frequency-Division Multiplexing (OFDM) has been proved to be a promising technology that enables the transmission of higher data rate. Multicarrier Code-Division Multiple Access (MC-CDMA) is a transmission technique which combines the advantages of both OFDM and Code-Division Multiplexing Access (CDMA), so as to allow high transmission rates over severe time-dispersive multi-path channels without the need of a complex receiver implementation. Also MC-CDMA exploits frequency diversity via the different subcarriers, and therefore allows the high code rates systems to achieve good Bit Error Rate (BER) performances. Furthermore, the spreading in the frequency domain makes the time synchronization requirement much lower than traditional direct sequence CDMA schemes. There are still some problems when we use MC-CDMA. One is the high Peak-to-Average Power Ratio (PAPR) of the transmit signal. High PAPR leads to nonlinear distortion of the amplifier and results in inter-carrier self-interference plus out-of-band radiation. On the other hand, suppressing the Multiple Access Interference (MAI) is another crucial problem in the MC-CDMA system. Imperfect cross-correlation characteristics of the spreading codes and the multipath fading destroy the orthogonality among the users, and then cause MAI, which produces serious BER degradation in the system. Moreover, in uplink system the received signals at a base station are always asynchronous. This also destroys the orthogonality among the users, and hence, generates MAI which degrades the system performance. Besides those two problems, the interference should always be considered seriously for any communication system. In this dissertation, we design a novel MC-CDMA system, which has low PAPR and mitigated MAI. The new Semi-blind channel estimation and multi-user data detection based on Parallel Interference Cancellation (PIC) have been applied in the system. The Low Density Parity Codes (LDPC) has also been introduced into the system to improve the performance. Different interference models are analyzed in multi-carrier communication systems and then the effective interference suppression for MC-CDMA systems is employed in this dissertation. The experimental results indicate that our system not only significantly reduces the PAPR and MAI but also effectively suppresses the outside interference with low complexity. Finally, we present a practical cognitive application of the proposed system over the software defined radio platform.

Thesis deals with problems PLC (Power Line Communication) communication. It is aimed at drawing up a suitable model for testing power network PLC communication. The reader is aware of at the beginning of work with the basic principles of PLC systems, distribution and use in communication networks. Another part of the work deals with different types of interference, which occur in power networks and ways to defend against such interference. For example, an appropriate choice of modulation and coding relevant. As a source of interference in the proposed model is used AWGN channel (Additive White Gaussian Noise). Conclusion of work is dedicated to design and build a model for PLC communication. There are three models designed with different OFDM technology. Models therefore vary between different levels of key mapping in OFDM (QPSK, 16-QAM, 64-QAM). It made a detailed description of a set of blocks that were used to build models. The behavior and functionality of the proposed models for broadband PLC communication was verified in the simulation program Matlab Simulink. Finally, it is shown the comparison and evaluation of results of each modulation.

As the technology is advances the reduced size of hardware gives rise to an additive 1/f baseband noise. This additive 1/f noise is a system noise generated due to miniaturization of hardware and affects the lower frequencies. Though 1/f noise does not show much effect in wide band channels because of its nature to affect only certain frequencies, 1/f noise becomes a prominent in OFDM communication systems where narrow band channels are used. in this thesis, I study the effects of 1/f noise on the OFDM systems and implement algorithms for estimation and suppression of the noise using Kalman filter. Suppression of the noise is achieved by subtracting the estimated noise from the received noise. I show that the performance of the system is considerably improved by applying the 1/f noise suppression.