Constant Envelope DCT- and FFT- based Multicarrier Systems

Discrete Cosine Transform (DCT)- and Fast Fourier Transform (FFT)- based Orthogonal Frequency Division Multiplexing (OFDM) systems with a variety of angle modulations are considered for data transmission. These modulations are used with the purpose of achieving Constant Envelope (CE) transmitted signals, for superior power efficiency with nonlinear High Power Amplifier (HPA), typically used at the transmitter in OFDM systems. Specifically, four angle modulations are considered: i) Phase Modulation (PM); ii) Frequency Modulation (FM); iii) Continuous Phase Modulation (CPM); and iv) Continuous Phase Chirp Modulation (CPCM). Descriptions of DCT- and FFT- based OFDM systems with M-ary Pulse Amplitude Modulation (MPAM) mapper, with these modulations, are given and expressions for transmitted signals are developed. The detection of these signals in Additive White Gaussian Noise (AWGN) and multipath fading channels is addressed. The receiver structure consists of arctangent demodulator followed by the optimum OFDM receiver for memoryless PM and FM modulations. However, for CPM and CPCM modulations that have inherent memory, arctangent demodulator followed by correction with oversampling technique is used prior to the optimum OFDM receiver. Closed-form expressions for Bit Error Rate (BER) have been derived and are function of: i) Signal-to-Noise Ratio, (Eb/N0); ii) Modulation parameters; iii) Number of amplitude levels of M-PAM mapper; and iv) parameters of multipath fading environment. It is shown that, in general, BER performance of CE-DCT-OFDM system is superior compared to that of conventional DCT-OFDM system, when the effect of HPA in the system is taken into account. Also, it is observed that CE-DCT-OFDM system outperforms CE-FFT-OFDM system by nearly 3 dB. The DCT- and FFT- OFDM systems with CPM and CPCM modulations are superior in BER performance compared to PM and FM modulations in these systems. The use of CPCM in OFDM systems can provide attractive trade off between bandwidth and BER performance. The performance of CE-DCT-OFDM and CE-FFT-OFDM systems over Rayleigh and Rician frequency non-selective slowly-varying fading channels are illustrated as a function of channel parameters and the penalty in SNR that must be paid as consequence of the fading is determined

Transmissor para sistemas 5G

The current 4G systems are based on the OFDM modulation which, while providing great exibility and intricacy to the multipath propagation inherent in wireless systems, it has great variations in their temporal envelope which causes high PAPR and, consequently, obstacles in the PAs performance. In this sense, the emergence of 5G systems has given rise high hopes of reducing the above mentioned problems of 4G systems, allowing more eficient data transmission. In the simulation of wireless communication system there are two simulation domains that must be taken into account: the system analysis that allows the study of diferent modulations and the circuit analysis that, in turn, allows the study of nonlinear circuits, as is the case of PAs present in these systems. In this way, it becomes important to unite these two domains allowing the existence of a unifying simulation tool, which has been called the simulation platform. With this platform it is possible, besides joining two domains hitherto analyzed separately, not only to study the behaviour of a 5G system but also any other system due to its adaptability. Thus, the system analysis is performed with the help of MATLAB software, in which three types of digital modulation (QPSK, 16-QAM and 64-QAM modulation) will be studied along with OFDM modulation. For the circuit analysis it was used the ADS circuit simulation software, which will analyze the behavior of two types of PAs (a Class B and a Doherty). As a way of testing its functioning, the platform simulations were performed for three diferent con gurations: SISO, SISO in which the PA model was replaced by a polynomial approximation, and Alamouti 2x1 (particular case of the MISO con guration). Finally, the tests of functioning of the simulation platform are nalized with the comparison of the simulations using the BEROs atuais sistemas 4G são baseados na modulação Orthogonal Frequency Division Multiplexing (OFDM) que apesar de garantir uma grande exibilidade e robustez à propagação multi-percurso inerente aos sistemas sem fi os, possui grandes variações nas respetivas envolventes temporais o que causa um elevado Peak-to-Average Power Ratio (PAPR) e, consequentemente, limitações no desempenho dos ampli cadores de potência (do inglês, Power Ampli ers (PAs)). Neste sentido, o aparecimento dos sistemas 5G têm suscitado grandes esperanças na redução dos problemas mencionados anteriormente, permitindo uma transmissão de dados mais e ficiente. Na simulação de um sistema de comunicações sem fi os há dois domínios de simulação principais que se devem ter em consideração: a análise de sistema que permite o estudo de diferentes modulações e a análise de circuito que, por sua vez, permite o estudo de circuitos não-lineares, como é o caso dos PAs presentes nestes sistemas. Desta forma, torna-se importante unir estes dois domínios possibilitando a existência de uma ferramenta de simulação unifi cadora, à qual se atribuiu a designação de plataforma de simulação. Com a plataforma de simulação consegue-se, além de unir dois domínios até agora analisados separadamente, não só estudar o comportamento de um sistema 5G mas também de qualquer outro devido à sua adaptabilidade. Assim, a análise de sistema é efetuada com o auxílio do software MATLAB, onde são estudados três tipos de modulação digital (modulação Quadrature Phase Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (QAM) e 64-QAM) juntamente com a modulação OFDM. Para a análise de circuito recorreu-se ao software de simulação de circuitos Advanced Design System (ADS), onde se analisou o comportamento de dois tipos de PAs (um Classe B e um Doherty). Como forma de teste do funcionamento da plataforma, foi efetuada a simulação para três confi gurações diferentes: Single-Input Single-Output (SISO), SISO em que se substituiu o modelo do Power Ampli er (PA) por uma aproximação polinomial e Alamouti 2x1 (caso particular da configuração Multiple-Input Single-Output (MISO)). Por último, os testes do funcionamento da plataforma de simulação são fi nalizados com a comparação das simulações recorrendo ao Bit Error Rate (BER)Mestrado em Engenharia Eletrónica e Telecomunicaçõe

NOVEL OFDM SYSTEM BASED ON DUAL-TREE COMPLEX WAVELET TRANSFORM

The demand for higher and higher capacity in wireless networks, such as cellular, mobile and local area network etc, is driving the development of new signaling techniques with improved spectral and power efficiencies. At all stages of a transceiver, from the bandwidth efficiency of the modulation schemes through highly nonlinear power amplifier of the transmitters to the channel sharing between different users, the problems relating to power usage and spectrum are aplenty. In the coming future, orthogonal frequency division multiplexing (OFDM) technology promises to be a ready solution to achieving the high data capacity and better spectral efficiency in wireless communication systems by virtue of its well-known and desirable characteristics. Towards these ends, this dissertation investigates a novel OFDM system based on dual-tree complex wavelet transform (D

Advanced methods in automatic modulation classification for emerging technologies

Modulation classification (MC) is of large importance in both military and commercial communication applications. It is a challenging problem, especially in non-cooperative wireless environments, where channel fading and no prior knowledge on the incoming signal are major factors that deteriorate the reception performance. Although the average likelihood ratio test method can provide an optimal solution to the MC problem with unknown parameters, it suffers from high computational complexity and in some cases mathematical intractability. Instead, in this research, an array-based quasi-hybrid likelihood ratio test (qHLRT) algorithm is proposed, which depicts two major advantages. First, it is simple yet accurate enough parameter estimation with reduced complexity. Second the incorporation of antenna arrays offers an effective ability to combat fading. Furthermore, a practical array-based qHLRT classifier scheme is implemented, which applies maximal ratio combining (MRC) to increase the accuracy of both carrier frequency offset (CFO) estimation and likelihood function calculation in channel fading. In fact, double CFO estimations are executed in this classifier. With the first the unknown CFO, phase offsets and amplitudes are estimated as prerequisite for MRC operation. Then, MRC is performed using these estimates, followed by a second CFO estimator. Since the input of the second CFO estimator is the output of the MRC, fading effects on the incoming signals are removed significantly and signal-to-noise ratio (SNR) is augmented. As a result, a more accurate CFO estimate is obtained. Consequently, the overall classification performance is improved, especially in low SNR environment. Recently, many state-of-the-arts communication technologies, such as orthogonal frequency division multiplexing (OFDM) modulations, have been emerging. The need for distinguishing OFDM signal from single carrier has become obvious. Besides, some vital parameters of OFDM signals should be extracted for further processing. In comparison to the research on MC for single carrier single antenna transmission, much less attention has been paid to the MC for emerging modulation methods. A comprehensive classification system is proposed for recognizing the OFDM signal and extracting its parameters. An automatic OFDM modulation classifier is proposed, which is based on the goodness-of-fittest. Since OFDM signal is Gaussian, Cramer-von Mises technique, working on the empirical distribution function, has been applied to test the presence of the normality. Numerical results show that such approach can successfully identify OFDM signals from single carrier modulations over a wide SNR range. Moreover, the proposed scheme can provide the acceptable performance when frequency-selective fading is present. Correlation test is then applied to estimate OFDM cyclic prefix duration. A two-phase searching scheme, which is based on Fast Fourier Transform (FFT) as well as Gaussianity test, is devised to detect the number of subcarriers. In the first phase, a coarse search is carried out iteratively. The exact number of subcarriers is determined by the fine tune in the second phase. Both analytical work and numerical results are presented to verify the efficiency of the proposed scheme

Receiver design for nonlinearly distorted OFDM : signals applications in radio-over-fiber systems

Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Universidade do Porto. Faculdade de Engenharia. 201

Performance analysis of modified asymmetrically-clipped optical orthogonal frequency-division multiplexing systems

A modification to the Asymmetrically-Clipped Optical Orthogonal Frequency-Division Multiplexing (ACO-OFDM) technique is proposed through unipolar encoding. A performance analysis of the Bit Error Rate (BER) is developed and Monte Carlo simulations are carried out to verify the analysis. Results are compared to that of the corresponding ACO-OFDM system under the same bit energy and transmission rate; an improvement of 1 dB is obtained at a BER of 10-4. In addition, the performance of the proposed system in the presence of atmospheric turbulence is investigated using single-input multiple-output (SIMO) configuration and its performance under that environment is compared to that of ACO-OFDM. Energy improvements of 4 dB and 2.2 dB are obtained at a BER of 10-4 for SIMO systems of 1 and 2 photodetectors at the receiver for the case of strong turbulence, respectively

Performance Analysis of Multicarrier Code Division Multiple Access (MC-CDMA) Systems

A thesis presented to the faculty of the College of Science and Technology at Morehead State University in partial fulfillment of the requirements for the Degree of Master of Science by Pravinkumar Patil on August 11, 2008