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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.

The objective of Diploma thesis is design of analysis tool for equalizers used in FMT modulation. The model of transmission channel was designed for simulations with FMT. The transmission path is modeled by test loop, which corresponds to DSL line. For this reason, some principles of DSL technology is described in the thesis. The principles of multicarrier modulation are introduced in first part. The multicarrier modulation with filter bank (FMT) is described in detail.The different methods of design the fiter bank are given and compared. Channel equalization are introduced in second part. The attention was focused on minimum mean square error filtering (MMSE). Decision feedback channel equalizer (DFE) is extended from linear MMSE equalizer. DFE equalizers were programmed in analysis tool. For computation of equalizer coeficients was used also equalizers based on adaptive algorithms and MMSE. The last part describes the results of DFE equalizers used in communication system with FMT modulation. Analysis tool was programmed in MATLAB with a graphical user interface. It allows to show mean square error, signal-to-noise ratio and transmission speed dependence on delay between original and distorted signal. Signal-to-noise ration is displayed also in individual subchannels and users can display mean square error dependence on different orders of DFE filters.

No description available.

No / Orthogonal frequency division multiplexing (OFDM) is pronounced in wireless communication systems. Methods for improving the performance of the OFDM-based systems are mostly sought. A method of doing this involves error correction coding and another, a better multicarrier modulation kernel. In this work, convolutional error correction coding with interleaving is introduced in wavelet multicarrier modulation OFDM system (wavelet-OFDM) to improve the performance of multicarrier systems as the signal traverses the multipath and noisy transmission channels. This is compared with FFT-based multicarrier modulation (FFT-OFDM). Results show that coded wavelet-OFDM saves more than a half of the transmit power than the uncoded wavelet. Also it will be shown that, the interleaved and non-interleaved coded wavelet-OFDM well outperform interleaved coded and non-interleaved coded FFT-OFDM systems respectively.

[pt] crescimento dos sistemas de comunicações móveis celulares e dos sistemas de rádio difusão de sinais de áudio e vídeo tem despertado grande interesse na pesquisa de novos métodos para a transmissão de sinais nestas redes. A necessidade de se transmitir dados em altas taxas, com significante eficiência no uso da largura de faixa de freqüências disponível, e por meio de um canal de propagação ruidoso e variante no tempo, constitui o principal problema para o desenvolvimento de novas técnicas de trasmissão de sinais. Dentro deste contexto, esta dissertação trata do uso dos conceitos de transmissão digital e filtragem adaptativa para a demodulação de sinais OFDM (Orthogonal Frequency Division Multiplexing). A equalização de sinais antes e após o estágio de DFT (Discrete Fourier Transform) no receptor e as técnicas de estimação de canal são o objeto principal de estudo deste trabalho. Os resultados dos experimentos são analisados em termos da taxa de erro de bit média obtida e da convergência dos algoritmos empregados nas etapas de equalização e estimação de canal no receptor. / [en] The growth of cellular mobile communication systems and audio and video broadcasting systems has stimulated great interest in the research of new methods for the signal transmission in these networks. The high rate data transmission, with significant efficiency in the use of the available bandwidth, in a noisy and time variant channel, constitutes the main problem for the development of new techniques for signal transmission. In this context, this dissertation deals with the use of the concepts of digital transmission and adaptive filtering for the demodulation of OFDM (Orthogonal Frequency Division Multiplexing) signals. The equalization pre and post DFT (Discrete Fourier Transform) in the receiver and the channel estimation techniques are the main object of study in this work. The results of the experiments are analyzed in terms of the mean bit error rate achieved and the convergence for the algorithms used in the stages of equalization and channel estimation in the receiver.

With code division multiple access (CDMA) systems being the prominent multiple access scheme for the air interface for 3G cellular systems, most standardisation bodies have based their terrestrial cellular systems on DS-CDMA (W-CDMA, UMTS, cdma2000). With 4G systems fast approaching, bringing with them improved services and quality of service standards, there is growing interest in further investigating and developing more efficient multiple access techniques such as multicarrier CDMA (MC-CDMA) systems. MC-CDMA combines multicarrier modulation (MCM), namely OFDM, with CDMA profiting from the benefits of both multiplexing techniques; as such, MC-CDMA is emerging as a possible candidate for the air interface multiple access scheme for 4G cellular systems. Multiple access interference (MAI) is a limiting factor of CDMA systems in terms of system capacity as orthogonally designed spreading sequences lose their orthogonality in the presence of timing misalignments amongst mobile subscribers in a cell; such is the case over the uplink channel. Ensuring orthogonal code properties minimises the MAI over synchronous environments, however, it is when the users are allowed to transmit asynchronously, as is the case over the uplink channel, that MAI inflicts significant performance degradation. In CDMA systems, all subscribers are active on the same frequency band simultaneously and signal separation is facilitated upon reception via the properties of the assigned spreading codes. Under asynchronous conditions the code properties alone do not provide the necessary separation and an additive MAI term remains in the detection process. In addition to the separation abilities of the spreading codes, a further method of deciphering the desired subscriber signal from the interfering subscriber signals is sought. In this thesis we propose a statistical model for both the probability density function (pdf) of the total MAI power and the corresponding bit-error rate (BER) observed during asynchronous CDMA transmission. The modelling offers the full statistic the MAI power and resulting BER, not just the first and second order statistics. In addition to statistically quantifying the MAI power, the thesis also proposes a technique for the successful reduction of MAI caused by asynchronous transmission. This interference reduction technique is derived from an ambiguity domain analysis of the asynchronous CDMA detection problem and its application to both the DS-CDMA and MC-CDMA multiplexing techniques is presented and the results show significant MAI reduction, and thus an improved the BER. A methodology for the approximation of the total MAI power pdf and the resulting BER pdf is proposed for the asynchronous DS-CDMA and MC-CDMA techniques. This methodology is derived for the use of Walsh-Hadamard (WH) and Gold spreading sequences, however, it is applicable to any given set of deterministic spreading sequences. The total MAI power pdfs of both systems are statistically modelled as being Nakagamim distributed and the corresponding BER modelling is derived from the Nakagami-m formulation offering the full statistic of both the incurred MAI power and the achievable BER. The proposed pdf acquisition methodology and statistical models can be used as analysis tools to assess the relative performances of the DS-CDMA and MC-CDMA techniques for a variety of communications environments. Here the asynchronous uplink channel is considered in the absence of fading and the results show a clear distinction between the BER performances of the MC-CDMA and DS-CDMA systems, for which the MC-CDMA system offers a superior performance for the purely asynchronous channel considered. The results suggest a higher resistance to MAI in the MC-CDMA technique in comparison to the DS-CDMA system for the considered transmission scenario. Following ambiguity function analysis of the asynchronous CDMA detection problem, the concept of dual-frequency switching is introduced to the existing DS-CDMA and MC-CDMA techniques giving rise to the proposed dual-frequency DS-CDMA (DF/DSCDMA) and dual-frequency MC-CDMA (DF/MC-CDMA) schemes. Periodically switching the carrier frequency between dual frequency bands at consecutive symbol boundaries facilitates partial CDMA signal separation upon asynchronous reception. Such switching of the carrier frequency induces a separation in frequency between offset interference signals and the reference signal; this is equivalent to shifting the energy concentration of the interference signals away form the ambiguity domain origin (representing the decision variable of the matched filter). Further MAI reduction is demonstrated through careful design of the dual carrier frequencies. The newly proposed DF systems clearly outperform the standard DS-CDMA and MC-CDMA systems when adopting equivalent spreading factors. The DF/DS-CDMA technique in particular achieves the most MAI reduction and in doing so, surpasses all other considered techniques to offer the best BER performance for the purely asynchronous channel considered. In terms of bandwidth usage, the DF/DS-CDMA band width is 1.5 times that of the DF/MC-CDMA system and from the BER results presented, one may argue that DF/MC-CDMA offers the better BER given the bandwidth usage. The multicarrier systems presented, MC-CDMA and DF/MC-CDMA, offer attractive BER performances for the bandwidth used and it is concluded that MC-CDMA is a genuine candidate for the uplink air interface multiple access scheme for future mobile cellular technologies.

Submitted by Carolina Neves (carolinapon@uefs.br) on 2016-08-09T01:01:22Z No. of bitstreams: 1 Karine_Souza_de_Almeida_Dissertacao_Final.pdf: 13569698 bytes, checksum: 81752dfa3be4ee9493654f5c61524c5a (MD5) / Made available in DSpace on 2016-08-09T01:01:22Z (GMT). No. of bitstreams: 1 Karine_Souza_de_Almeida_Dissertacao_Final.pdf: 13569698 bytes, checksum: 81752dfa3be4ee9493654f5c61524c5a (MD5) Previous issue date: 2016-05-24 / Funda??o de Amparo ? Pesquisa do Estado da Bahia - FAPEB / By using the Orthogonal Frequency Division Multiplexing (OFDM), it is possible to transmit by a channel a more robust signal and less susceptible to interferences. When such technique, based on orthogonal subcarriers, is combined with the use of propagation models, which are relevant tools for simulating the signal behavior in respect to environmental parameters and antenna configurations, it is feasible to have an evaluation about the performance of these systems, improving their project phase. Therefore, this work presents the use of OFDM technique applied to two propagation models: a two-ray geometric model and a microcellular model adapted to the Paulista Avenue, S?o Paulo, SP, having as objective the analysis of a mobile communication system through Bit Error Rate (BER). In the developed application using the MAtrix LABoratory (MATLAB) software, the mobile communication system based on OFDM admits several scenarios during the simulation, so that scenarios are related to positioning of the antennas, heights, type of modulation, size of the bit sequence to be sent, and others. The adopted OFDM architecture has been the IFFT/FFT and based on it, the system performs the transmission and reception of a bit set through a channel with interference by using different digital modulations, making appropriate comparisons. / Atrav?s da utiliza??o da t?cnica de Multiplexa??o por Divis?o de Frequ?ncias Ortogonais (OFDM, do ingl?s, Orthogonal Frequency Division Multiplexing), ? poss?vel transmitir por um canal um sinal mais robusto e menos propenso a interfer?ncias. Quando tal t?cnica, baseada na utiliza??o de subportadoras ortogonais, ? aliada ao uso de modelos de propaga??o, que s?o ferramentas relevantes para a simula??o do comportamento do sinal em rela??o aos par?metros do ambiente e as configura??es das antenas, ? poss?vel ter uma avalia??o a respeito do desempenho desses sistemas, melhorando a fase de projeto dos mesmos. Sendo assim, este trabalho apresenta o uso da t?cnica OFDM aplicada a dois modelos de propaga??o: um modelo geom?trico de dois raios e um modelo microcelular adaptado para a Avenida Paulista, S?o Paulo, SP, possuindo como objetivo a an?lise de um sistema de comunica??o m?vel atrav?s do c?lculo da Taxa de Erro de Bit (BER, do ingl?s, Bit Error Rate). Na aplica??o desenvolvida utilizando o software MATLAB (MATrix LABoratory), o sistema de comunica??o m?vel baseado em OFDM assume diversos cen?rios durante as simula??es, de forma que esses cen?rios s?o relacionados ao posicionamento das antenas, alturas, tipo de modula??o, tamanho da sequ?ncia de bits a ser enviada, entre outras. A arquitetura OFDM adotada foi a IFFT/FFT e baseado nela, o sistema realiza a transmiss?o e a recep??o de um conjunto de bits por um canal com interfer?ncias utilizando diferentes modula??es digitais, fazendo as devidas compara??es.

This thesis deals with computer simulation of the communication chain using the OFDM modulation. In the beginning of my thesis there is a brief description of digital modulations, especially OFDM. The model of the transmitter, radio channel and receiver, including a simple timing and frequency synchronization and equalization is designed and simulated in the Matlab environment. There is a designed communication system implemented into USRP development board in the Simulink environment. The development board could not work simultaneously as a transmitter and as a receiver. Function of the transmitter was verified by measuring on spectrum analyzer. Testing OFDM signal using the arbitrary waveform generator CompuGen 4302 was generated for the verification of the function of the receiver. Testing signal was received and demodulated on the development board which works as a receiver.

Vu que la modulation multi-porteuses est largement utilisée dans les communications sans fil et la radio cognitive (CR pour “Cognitive Radio”) améliore l’utilisation des ressources radio et du spectre, nous nous concentrons sur les réseaux radio cognitifs (CR) pour faire progresser l’allocation des ressources, le routage, et l’ajustement de la puissance d’émission vers les récepteurs (synthèse de faisceaux ou beamforming) dans cette thèse. Nous étudions deux types de modulations multi-porteuses :Orthogonal Frequency-Division Multiplexing (OFDM) à base d’ondelettes (WOFDM pourWavelet OFDM) et OFDM dans sa forme classique ou traditionnelle (OFDM s’appuyant sur la transformation de Fourier pour partager les ressources). WOFDM adopte Wavelet Packet Modulation (WPM) pour obtenir des lobes secondaires beaucoup plus faibles dans la densité spectrale de puissance du signal transmis en comparaison à OFDM. WPM permet de surcroit à WOFDM de s’affranchir du Préfixe Cyclique (indispensable à OFDM) et d’exploiter l’égalisation pour combattre l’Interférence entre Symboles (ISI). Nous évaluons la performance de WOFDM sous différentes conditions du canal radio. Nous comparons la performance de WOFDM, qui s’appuie sur l’égalisation dans le domaine temporel, à celle de OFDM, qui requiert l’utilisation du Préfixe Cyclique et opère dans le domaine fréquentiel / In view of the wide usage of multicarrier modulation in wireless communications and the prominent contribution of Cognitive Radio (CR) to deal with critical shortage of spectrum resource, we focus on multicarrier based cognitive radio networks to investigate general resource allocation issues: subcarrier allocation, power allocation, routing, and beamforming in this thesis. We investigate two types of multicarrier modulation: Wavelet-based Orthogonal Frequency Division Multiplexing (WOFDM) and Fourier-based Orthogonal Frequency Division Multiplexing (OFDM). WOFDM adopts Wavelet Packet Modulation (WPM). Compared with fourier-based OFDM, wavelet-based OFDM achieves much lower side lobe in the transmitted signal. Wavelet-based OFDM excludes Cyclic Prefix (CP) which is used in fourier-based OFDM systems. Wavelet-based OFDM turns to exploit equalization to combat Inter-Symbol Interference (ISI). We evaluate the performance of WOFDM under different channel conditions. We compare the performance of wavelet-based OFDM using equalization in the time domain to that of fourier-based OFDM with CP and the equalization in the frequency domain