A Novel Frequency Synchronization Algorithm and its Cramer Rao Bound in Practical UWB Environment for MB-OFDM Systems

This paper presents an efficient time-domain coarse frequency offset (FO) synchronizer (TCFS) for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for practical ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier FOs and different channel responses in different bands to keep the analysis and simulation compatible for practical multiband UWB scenario. Performance of the algorithm is studied by means of bit error rate (BER) analysis of MBOFDM system. We derive the Cramer Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1-CM4. Both analysis and simulation show that TCFS can estimate coarse carrier FO more efficiently in UWB fading channels for MB-OFDM applications compared to the other reported results in literature. Also, computational complexity of the proposed algorithm is analyzed for its usability evaluation

Módulo transmissor e receptor OFDM sintetizado em hardware FPGA

Trabalho de Conclusão de Curso (graduação)—Universidade de Brasília, Faculdade UnB Gama, Engenharia Eletrônica, 2019.As dificuldades existentes no sistema de comunicação de única portadora, como por exemplo, condições ruins do meio, atenuação de altas frequências, interferência inter-símbolo, interferência causada por múltiplos caminhos, despertam estudos e análises sobre essas dificuldades. Uma maneira para analisar esse problema é o desenvolvimento, implementação e análise de um transmissor e receptor OFDM na linguagem de descrição de Hardware VHDL. O principal objetivo desse trabalho é implementar um modulador e um receptor OFDM em descrição de Hardware e utilizar um osciloscópio para a análise do sinal modulado. Para o presente projeto, foi necessário um estudo minucioso do sincronismo e a realização de um método, que contribuiu para uma eficiente implementação e visualização dos blocos no osciloscópio. A maioria dos estudos na área de codificação do sistema OFDM não apresenta de forma detalhada a implementação do sistema em linguagem de hardware, o que não demonstra a correta elaboração do sincronismo dos subsistemas da OFDM. Os subsistemas IFFT e FFT foram implementadas de forma eficiente, as quais apresentaram uma taxa de erro de apenas 3.2% e apresentaram rapidez nas realizações dos cálculos, embora sejam limitadas ao lidar com quantidades de bits muito elevadas, ou seja, problemas de overflow e limitadas quando realizam cálculos em ponto flutuante. Os subsistemas IFFT e FFT foram comparados com os valores adquiridos do software Matlab. Foi possível também, observar o sinal do transmissor no osciloscópio e utilizou a validação por escrita em arquivo na linguagem VHDL para verificação dos resultados do transmissor e receptor. A taxa de erro para o transmissor e o receptor é inferior a 8%. Os resultados obtidos por meio do trabalho realizado contribuirão para aprofundar estudos posteriores nessa área, ampliar a complexidade do subsistema da IFFT e também do transmissor OFDM.Difficulties in the single-carrier, communication system, such as poor media conditions, high-frequency attenuation, inter-symbol interference, multipath interference, trigger studies and analysis of these difficulties. One way to analyze this problem is the development, implementation and analysis of an OFDM transmitter and receiver in the VHDL Hardware description language. The main objective of this work is to implement a modulator and OFDM receiver in hardware description and to use an oscilloscope to analyzze the modulated signal. For the present project, it was necessary a detailed study of synchronism and the realization of a method, which contributed to an efficient implementation and visualization of the blocks in the oscilloscope. Most studies in the coding area of the OFDM system do not detail the system implementation in hardware language, which does not demonstrate the correct elaboration of OFDM subsystem synchronism. The IFFT and FFT subsystems were implemented efficiently, which had an error rate of only 3.2% and were quick to perform the calculation, although they are limited when dealing with very high bit amounts. The IFFT and FFT subsystems were compared with the values acquired from Matlab software. It was also possible to observe the transmitter signal on the oscilloscope and used file-written validation in the VHDL language to verify the transmitter and receiver results. The error rate for transmitter and receiver is less than 8%. The results obtained through the work performed will contribute to further studies in this area, increasing the complexity of the IFFT subsystem and also the OFDM transmitter

A study of synchronization algorithms for WiMAX systems

Orientador: Luís Geraldo Pedroso MeloniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de ComputaçãoResumo: Esta dissertação apresenta uma análise de métodos de sincronização temporal e de portadora em sistemas WiMAX/OFDM. São analisados trabalhos clássicos publicados nos anos 90 até resultados obtidos recentemente. Uma ênfase especial é dada aos métodos de sincronização aplícáveis ao WiMAX. Grande parte dos trabalhos mais recentes na área de sincronização não podem ser utilizados no WiMAX pois não são aplicáveis aos preâmbulos e pilotos definidos para esta tecnologia. São estudados tanto os algoritmos que funcionam no domínio do tempo (pré-FFT) quanto aqueles que trabalham no domínio da frequência (pós-FFT), bem como a integração entre esses algoritmos em um receptor WiMAX completo. É também apresentada uma proposta de extensão ao algoritmo de Morelli. Essa proposta é comparada com outros métodos (Schmidl e Tufvesson) sob diversos tipos e condições de canal. A extensão ao algoritmo de Morelli tem características de detecção próximas da detecção ótima por filtro casado de Tufvesson, quando a SNR é moderada (acima de 5-8dB)Abstract: This dissertation presents an analysis of time and carrier frequency synchronization algorithms for OFDM/WiMAX systems. The most relevant works from the last 20 years are presented, emphasizing the ones applicable to WiMAX. A great number of recent studies in the field are not applicable in WiMAX systems, since the preamble/pilot patterns used in these studies are not defined in the 802.16 standard. In this work, the integration between pre-FFT and post-FFT synchronization methods is also discussed. An extension to Morelli's algorithm is also proposed and compared with Schmidl and Tufvesson algorithms, under several channel types and conditions. The proposed extension has detection properties that are similar to the optimum matched-filter detection (Tufvesson), when analised under fair SNR conditions (above 5-8dB)MestradoTelecomunicações e TelemáticaMestre em Engenharia Elétric

Signal-perturbation-free semi-blind channel estimation for MIMO-OFDM systems

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) has been considered as a strong candidate for the beyond 3G (B3G) wireless communication systems, due to its high data-rate wireless transmission performance. It is well known that the advantages promised by MIMO-OFDM systems rely on the precise knowledge of the channel state information (CSI). In real wireless environments, however, the channel condition is unknown. Therefore, channel estimation is of crucial importance in MIMO-OFDM systems. Semi-blind channel estimation as a combination of the training-based or pilot-assisted method and the pure blind approach is considered to be a feasible solution for practical wireless systems due to its better estimation accuracy as well as spectral efficiency. In this thesis, we address the semi-blind channel estimation issue of MIMO-OFDM systems with an objective to develop very efficient channel estimation approaches. In the first part of the dissertation, several nulling-based semi-blind approaches are presented for the estimation of time-domain MIMO-OFDM channels. By incorporating a blind constraint that is derived from MIMO linear prediction (LP) into a training-based least-square method, a semi-blind solution for the time-domain channel estimation is first obtained. It is revealed through a perturbation analysis that the semi-blind solution is not subject to signal perturbation and therefore is superior to pure blind estimation methods. The LP-based semi-blind method is then extended for the channel estimation of MIMO-OFDM systems with pulse-shaping. By exploiting the pulse-shaping filter in the transmitter and the matched filter in the receiver, a very efficient semi-blind approach is developed for the estimation of sampling duration based multipath channels. A frequency-domain correlation matrix estimation algorithm is also presented to facilitate the computation of time-domain second-order statistics required in the LP-based method. The nulling-based semi-blind estimation issue of sparse MIMO-OFDM channels is also addressed. By disclosing and using a relationship between the positions of the most significant taps (MST) of the sparse channel and the lags of nonzero correlation matrices of the received signal, a novel estimation approach consisting of the MST detection and the sparse channel estimation, both in a semi-blind fashion, is developed. An intensive simulation study of all the proposed nulling-based methods with comparison to some existing techniques is conducted, showing a significant superiority of the new methodologies. The second part of the dissertation is dedicated to the development of two signal-perturbation-free (SPF) semi-blind channel estimation algorithms based on a novel transmit scheme that bears partial information of the second-order statistics of the transmitted signal to receiver. It is proved that the new transmit scheme can completely cancel the signal perturbation error in the noise-free case, thereby improving largely the estimation accuracy of correlation matrix for channel estimation in noisy conditions. It is also shown that the overhead caused by the transmission of the 8PF data is negligible as compared to that of regular pilot signals. By using the proposed transmit scheme, a whitening rotation (WR)-based algorithm is first developed for frequency-domain MIMO-OFDM channel estimation. It is shown through both theoretical analysis and simulation study that the new WR-based algorithm significantly outperforms the conventional WR-based method and the nulling-based semi-blind method. By using MIMO linear prediction, the new WR-based algorithm utilizing the 8PF transmit scheme is then extended for time-domain MIMO-OFDM channel estimation. Computer simulations show that the proposed signal-perturbation-free LP-based semi-blind solution performs much better than the LP semi-blind method without using the proposed transmit scheme, the LS method as well as the nulling-based semi-blind method in terms of the MSE of the channel estimate