Goal of this thesis is to analyse basic algorithms for the carrier and time synchronisation in the OFDM systems in 5G networks. Firtly, basic introduction to OFDM systems, then parameters and properties of the OFDM are discussed. Then estimation and compensation timing and frequency offsets are analysed as well as algorythms for searhcing of the start of the symbols. Last but not least hardware setup, which will be prepared in the DREL department for test of the communication in the millimeter wave band, with frequency of 60GHz is slightly discribed. This thesis is just a introduction for the real future work on this setup.

Goal of this thesis is to analyse basic algorithms for the carrier and time synchronisation in the OFDM systems in 5G networks. Firtly, basic introduction to OFDM systems, then parameters and properties of the OFDM are discussed. Then estimation and compensation timing and frequency offsets are analysed as well as algorythms for searhcing of the start of the symbols. Last but not least hardware setup, which will be prepared in the DREL department for test of the communication in the millimeter wave band, with frequency of 60GHz is slightly discribed. This thesis is just a introduction for the real future work on this setup.

Light-emitting diode (LED) luminaires are ubiquitous and widely used in our daily life. Because of energy efficiency and illumination requirements, LED lamps are required to dim. In addition to the lighting function, visible light communication (VLC) is being considered as a potential technology beyond 5G. Orthogonal frequency-division multiplexing (OFDM) is a popular modulation choice and most recently spatial optical OFDM (SO-OFDM) has been used with multiple LEDs. SO-OFDM is a low complexity way of constructing OFDM signals by sending a series of narrow-band emissions from different LEDs and allowing them to sum in space. The integration of dimming within an SO-OFDM framework remains an open area of research. In this thesis, an optimal dimming strategy for optical power allocation is proposed based on SO-OFDM in visible light communication systems under different illumination requirements, i.e., dimming. Firstly, a non-convex problem is formulated to maximize the capacity of SO-OFDM under a specified dimming target. Furthermore, this non-convex problem is broken into a group of convex problems through approximations and constraint relaxation. The proposed scheme can optimize the power allocation in SO-OFDM and achieve the dimming target at the same time. According to the proposed power allocation scheme, more of the power is allocated to subcarriers with low noise variance. This phenomenon makes sense to take advantage of good channels when power is limited and is similar to the conventional water-filling method. When the dimming target and signal-to-noise ratio (SNR) is sufficiently high, the optimal distribution approaches a uniform distribution that agrees well with conventional water filling in a high SNR regime. Compared with traditional digital dimming, the proposed spatial dimming method can not only use spatial domain for dimming but also allocates power to different subcarriers according to channel conditions which is more efficient. Analytical and numerical results imply that the proposed scheme converges quickly and performs well compared with traditional power allocation methods. / Thesis / Master of Applied Science (MASc)

En esta tesis se tratan diversos aspectos que contribuyen a incrementar el desempeño de los sistemas de comunicaciones modernos. Entre los desafíos más importantes están la compen sación de los efectos del canal de comunicaciones, la sincroni-zación en frecuencia y las limitaciones en el ancho de banda de transmisión. Los estándares modernos son capaces de proveer a los usuarios diferentes tipos de calidad de servicio. Esto exige gran flexibilidad en el manejo de los recursos de radio y alta robustez frente a las interferencias. El multiplexa-do por división en frecuencias ortogonales (OFDM), es el es-quema de modulación multiportadora que se esta adoptando en la mayoría de los estándares para lograr dichas exigencias. Entre las desventajas de la implementación práctica de OFDM están la sensibilidad a errores de sincronismo en frecuencia y el alto consumo de potencia en la amplificación. El error de sincronismo en frecuencia destruye la ortogonalidad entre las subportadoras de OFDM lo que disminuye notablemente el desempeño del sistema, por ese motivo es necesario estimar y compensar dicho error. Para tal fin se propuso una familia de algoritmos de estimación de errores de sincronismo basados en una aproximación más exacta de la estadística de la señal de entrenamiento. En consecuencia, los estimadores obte-nidos tienen mejor desempeño que los propuestos anterior-mente. Considerando una incipiente línea de investigación, se propuso un estimador de frecuencia basado en filtrado notch que es útil para la estimación de errores de sincronismo en sistemas multiportadora. El algoritmo funciona de manera itera-tiva procesando la información en bloques, lo que resulta ade-cuado para estimaciones basadas en una secuencia de entre-namiento. El acceso mútiple por división de frecuencias ortogonales (OFDMA) está basado en OFDM y utiliza conjun-tos de subportadoras para trasmitir la información de cada usuario. En este caso también es necesario estimar y compen-sar los errores de sincronismo, operaciones que requieren una elevada carga computacional. En esta tesis se propone un esquema de compensación de errores de sincronismo que permite reducir notoriamente la complejidad del sistema sin degradar considerablemente el desempeño. La modulación multiportadora basada en banco de filtros (FBMC) se ha pro-puesto recientemente como alternativa a OFDMA ya que es menos sensible a errores de sincronismo en frecuencia. Con el fin de determinar cual sistema es el más adecuado, se pre-senta una comparación entre OFDMA y FBMC en un contexto realista, teniendo en cuenta tanto el desempeño como la complejidad de implementación. Además de las temáticas principales antes mencionadas, en esta tesis se tratan de manera complementaria cuestiones relacionadas con nuevos sistemas de comunicaciones en estado de desarrollo, que permiten abordar los problemas de escasez espectral y de amplificación de una señal de amplio rango dinámico. Estu-dios recientes demuestran que el espectro es un recurso escaso pero muchas veces desperdiciado. La solución para este problema puede ser la asignación dinámica de ancho de banda, lo que permite que varios sistemas o redes compartan la misma banda de frecuencias. Estos sistemas están compuestos por dispositivos llamados radios cognitivas que tienen que realizar tareas de sensado espectral a fin de determinar si alguna banda de interés está o no disponible. Se supone que las señales involucradas en el proceso de sen-sado son OFDM, debido a que este esquema es ampliamente utilizado en la actualidad. Por consiguiente, en esta tesis se estudian técnicas de detección y diferenciación de señales basadas en características estadísticas de dicha modulación. El alto rango dinámico de las señales OFDM produce un alto consumo de potencia que puede ser inaceptable, sobretodo en dispositivos móviles. Para evitar el problema es posible concebir un sistema híbrido en el cual se utilice OFDM en el enlace de bajada y modulacion de portadora simple en el enlace de subida. En este sistema la ecualización en el enlace de subida no es trivial como en el caso de OFDM. Se ha propuesto entonces, un ecualizador con realimentación de decisión en el dominio frecuencia y adaptación de mínimos cuadrados recursiva, que permite mejorar el desempeño tanto en la velocidad de convergencia de los coeficientes del filtro, como en el seguimiento de las variaciones del canal de comunicaciones. / In this thesis are discussed several aspects that contribute to increase the performance of modern communication systems. Among the most important challenges are the compensation of communication channel effects, frequency synchronization and transmission bandwidth limitations. Modern standards are able to provide different quality of services to the users. This requires a high flexibility in the management of radio resources and high robustness against channel interference. The ortho-gonal frequency-division multiplexing (OFDM), is the multi-carrier modulation scheme that is being adopted in most of modern standards to achieve the required specifications. Among the disadvantages of OFDM practical implementation are the sensitivity to frequency synchronization errors and the high consumption of the power amplifier. The frequency synchronization error destroys the orthogonality of OFDM subcarriers which decreases the system performance signi-ficantly, for this reason it is necessary to estimate and compensate this error. To that end, it is proposed a new family of algorithms for carrier frequency offset estimation, based on a more accurate approximation of the training signal statistics. As a consequence, obtained estimators have better performance that previous proposals. Considering an emerging line of research, it is also proposed a frequency estimator based on notch filtering that is useful for estimation of frequency synchronization errors in multicarrier systems. The algorithm is iterative and process the information in a bock basis, which results appropriate for estimations based on a training sequence. Orthogonal frequency division multiple access (OFDMA) is based on OFDM and employs a set of subcarriers to transmit the information of each user. In this case also it is necessary to estimate and compensate syn-chronization errors, operations that require a high computa-tional load. In this thesis is proposed a compensation scheme for frequency synchronization errors that allows to reduce significantly the system complexity without degrading noto-riously the performance. The filter bank based multicarrier (FBMC) modulation has been recently proposed as an alter-native to OFDMA since it is less sensitive to frequency syn-chronization errors. In order to establish which system is the more appropriate, it is presented a comparison between OFDMA and FBMC in a realistic context, taking into account performance and implementation complexity. In addition to the key issues mentioned above, in this thesis are discussed in a complementary manner topics related to new commu-nications systems in early development stages, that address the problems of spectral scarcity and high dynamic range power amplification. Recent studies show that the spectrum is a scarce resource but often wasted. The solution to this pro-blem may be the dynamic bandwidth allocation, allowing multiple systems or networks to share the same frequency band. These systems consist of devices called cognitive radios, that have to sense the spectrum to determine if the frequency band of interest is available or not.It is supposed that signals involved in the sensing process are OFDM, since this scheme is currently wide adopted. In conclusion, in this thesis are studied signal detection and differentiation tech-niques based on statistical features of this modulation. The high dynamic range of OFDM leads to a high power consump-tion that could be unacceptable, mainly in mobile devices. To avoid the problem is possible to conceive an hybrid system that employ OFDM in the downlink and single carrier modula-tion in the uplink. In this system the equalization in the uplink is not trivial as for the OFDM case. Then, it is proposed a frequency domain decision feedback equalizer and recursive least squares adaptation, that improves the performance both in convergence speed and tracking of communication channel variations.

Yes / This paper investigates the performance of wavelet OFDM signals over a wireless communications link. The scheme is shown to be generally similar to Fourier based OFDM, but with some additional features, and improved characteristics. The sensitivity of both schemes to the nonlinear amplification in the transmitter is compared by monitoring the time domain output data and the adjacent channel power ratio (ACPR) performance.

No / In the study of OFDM systems, discrete wavelet transforms have been reported to perform better than Fast Fourier Transform in multicarrier systems (MCS) - in terms of spectral efficiency because they can operate without a cyclic prefix, have reduced side-lobes and improved BER. However all of the wavelet families do not perform alike. This study has investigated various wavelet families such as Daubechies, Symlet, Haar (or db1), biorthogonal, reverse-biorthogonal and Coiflets for OFDM system design over an AWGN and multipath channels. Results show that Daubechies, Symlet, Haar and Coiflet wavelet families perform considerably better than other families considered, thus these families could be better in OFDM.

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.

"As the demand for bandwidth increases, the inefficient use of the spectrum becomes more apparent and limiting. Currently, secondary (unlicensed) users can not use sparsely occupied portions of radio spectrum that are not allocated to them. In prior research, a variant of Orthogonal Frequency Division Multiplex (OFDM) called Non-Contiguous OFDM (NC-OFDM) was found to be a suitable transmission technique for enabling Dynamic Spectrum Access, which allows for multiple secondary users to share the spectrum. This thesis presents an algorithm for the synchronization of NC-OFDM. Moreover, a hardware architecture is proposed for the synchronization, and a pruned FFT/IFFT core is designed. At present, there has been minimal research into synchronization for NC-OFDM systems. As with any modulation scheme, synchronization is an important part for receiving the transmission successfully. The current synchronization scheme is simulated in variety of wireless channels to show that it can successfully communicate in the tested channels. Additionally a hardware architecture is laid out for the practical implementation of the synchronization algorithm. Since NC-OFDM does not use all of the carriers for transmission, the FFT and IFFT can have their computations reduced. Since the FFT and IFFT are important parts to the receiver and the transmitter, a pruned FFT/IFFT in hardware makes the most sense to be able to reduced the computation. The number of butterfly computations is reduced at the expense of a large increase in resource usage. "

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.

We examine the effect of precoding on OFDM systems. The precoding operation, which is also known as constellation rotation, leads to a gain in diversity order for fading channels. In this thesis, we examine the effect of precoding for different receivers such as Maximum Likelihood (ML), Minimum Mean Squared Error (MMSE), and Zero Forcing (ZF) receivers. The diversity gain due to precoding comes at no cost of bandwidth expansion or power increase. Therefore it is an attractive and practical alternative. We also examine the precoding gain, when some reduction of rate is tolerable and compare the performance of rate reduced system with the uncoded system with the system which is coded by rateless unitary precoders, and with the hard-decision decoded BCH coded coded system.