Ever since the proposal of turbo code in 1993, there has been extensive research carried out to improve both the performance and spectrum efficiency. One of the methods used to improve the spectrum efficiency was to combine turbo code with a trellis-coded modulation scheme, called turbo trellis-coded modulation (TTCM). The scheme is used in various applications such as deep-space communication, wireless communication and other fields. It is a well established fact that an increase in an interleaver size of a TTCM system results in an improved performance in the bit error rate (BER). In this thesis repeat-punctured turbo trellis-coded modulation (RPTTCM) is proposed. In RPTTCM, the effect of repeat-puncture is investigated on a TTCM system, repetition of the information bits increases the interleaver size, followed by an appropriate puncturing scheme to maintain the respective code rate. The TTCM and RPTTCM systems are simulated in an Additive White Gaussian Noise (AWGN) channel. To understand how the RPTTCM scheme will perform in a wireless channel, the Rayleigh flat fading channel (with channel state information known at the receiver) will be used. The BER performance bound for the TTCM scheme is derived for AWGN and Rayleigh flat fading channels. Thereafter repeat-punctured is introduced into the TTCM system. The BER performance bound is then extended to include repeat-puncturing. The performances of the TTCM and RPTTCM systems are then compared. It was found that the RPTTCM system performed better at high signal-to-noise ratio (SNR) in both AWGN and Rayleigh flat fading channels. The RPTTCM scheme achieved a coding gain of approximately 0.87 dB at a BER of for an AWGN channel and 1.9 dB at a BER of for a Rayleigh flat fading channel, for an information size of N=800. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

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Time-dependent cosmic ray modulation in the heliosphere is studied by using a two-dimensional time dependent modulation model. To compute realistic cosmic ray modulation a compound approach is used, which combines the effect of the global changes in the heliospheric magnetic field magnitude and the current sheet tilt angle to establish realistic time dependent diffusion and drift coefficients. This approach is refined by scaling down drifts additionally (compared to diffusion) towards solar maximum. The amount of drifts needed in the model to realistically compute 2.5 GV proton and electron and 1.2GV electron and helium intensities, as measured by Ulysses from 1990 to 2004, is established. It is shown that the model produces the correct latitudinal gradients evident from the observations during both the Ulysses fast latitude scan periods. Also, much can be learned on the magnitude of perpendicular diffusion in the polar direction, K┴θ, especially for solar minimum conditions and for polarity cycles when particles drift in from the poles. For these periods K┴θ = 0.12K║ in the polar regions (with K║ the parallel diffusion coefficient)and K┴θ /K║ can vary between 0.01 to even 0.04 in the equatorial regions depending on the enhancement factor toward the poles. The model is also applied to compute radial gradients for 2.5 GV cosmic ray electrons and protons in the inner heliosphere. It is shown that, for solar minimum, and in the equatorial regions, the protons (electrons) have a radial gradient of 1.9 %/AU (2.9 %/AU), increasing for both species to a very fluctuating gradient varying between 3 to 4 %/AU at solar maximum. Furthermore, the model also computes realistic electron to proton and electron to helium ratios when compared to Ulysses observations, and charge-sign dependent modulation is predicted up to the next solar minimum expected in 2007. Lastly the model is also applied to model simultaneously galactic cosmic ray modulation at Earth and along the Voyager 1 trajectory, and results are compared with> 70 MeV count rates from Voyager 1 and IMP8. To produce realistic modulation, this model gives the magnitude of perpendicular diffusion in the radial direction as K┴r/K║= 0.035 and that the modulation boundary seemed to be situated between at 120 AU and 140 AU. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2005.

In the present study we aim to further our understanding of charged particle transport in a magnetized medium. To this end, we perform direct numerical simulations of particle transport in a turbulent magnetic field. From the particle trajectories we calculate diffusion and drift coefficients. In contrast to previous numerical simulations of this nature, we also consider a background magnetic field that contains a gradient perpendicular to the magnetic field direction. By using a non-uniform background magnetic field, we can investigate the simultaneous large scale drift due to the gradient in the background magnetic field and the diffusion due to the turbulence which is superimposed on this background magnetic field. Upon comparison with the simulated diffusion coefficients, the newly proposed weakly non-linear theory (WNLT) of Shalchi et al. (2004b) seems to be the most appropriate theory for the simultaneous description of parallel and perpendicular diffusion over a wide range of fluctuation amplitude and particle rigidity. As for the effect of large scale drift on perpendicular diffusion, we find that under conditions of small amplitude turbulence and/ or high particle rigidity the transport perpendicular to the background field can exhibit super-diffusive behaviour. Diffusive behaviour seems to be recovered for the cases when the turbulence amplitude is sufficiently large and/ or the particle rigidity is sufficiently small. We furthermore find that both the drift coefficient and the drift speed are reduced from their weak scattering counterparts in the presence of scattering, with the reduction becoming more pronounced with increasing turbulence amplitude. For the drift coefficient in particular, the reduction from its weak scattering counterpart behaves differently for the cases in which the background magnetic field is either uniform or non-uniform. For the former case the reduction is predominantly at small rigidities, while for the latter case the reduction is predominantly at large rigidities. The latter result might be of significance for heliospheric modulation models in which the background magnetic field is highly non-uniform. Finally, we use a two-dimensional steadystate cosmic ray modulation model to see how our improved understanding of the underlying transport processes influences the overall cosmic ray modulation in the heliosphere. We conclude that in the absence of a theory which connects large scale drift with small scale diffusion, any statements about the inadequacy of a two-dimensional steady-state modulation model might be premature. / Thesis (Ph.D. (Physics))--North-West University, Potchefstroom Campus, 2006.

The objective of the proposed research is to investigate the performance of advanced modulation formats, specifically modified duobinary return-to zero (MD-RZ) modulation scheme and its long-haul repeaterless transmission over standard single mode fiber (SMF). This research also focuses on phase modulation formats like differential phase shift keying (DPSK) and differential quadrature phase shift keying (DQPSK), specifically free spectral range (FSR) optimization and wavelength offset tolerance in direct detection of these phase modulated systems. In this research we present a novel and cost effective technique to generate a modified duobinary return-to-zero (MD-RZ) signal. Next, we attained experimental results for single channel and WDM repeaterless transmission using these MD-RZ signals. A numerical comparison is also drawn with other conventional MD-RZ transmitters. MD-RZ transmission characteristics are also studied numerically for 40 Gb/s WDM signals and compared with other two leading constant intensity phase modulated formats like DPSK and DQPSK. We also have presented experimental results for FSR optimization of DQPSK de-modulator for ultra-high data-rate systems in the presence of strong optical filtering. Choice of an optimal FSR beyond 1-bit delay in Mach-Zehnder delay interferometer (MZ-DI) helps relieving some of the degradations due to strong optical filtering. Wavelength offset tolerance is also experimentally measured and numerically investigated for DPSK and DQPSK modulation formats with different transmitter schemes employing intensity or phase modulators to achieve required phase shifts.

Thesis (M.Eng.)--University of South Australia, 1995

Thesis (M.Eng.)--University of South Australia, 1995

Thesis (M.S.)--University of Wyoming, 2007. / Title from PDF title page (viewed on July 28, 2008). Includes bibliographical references (p. 61-62).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 141-143). Also available via the Internet.

Three-phase voltage source inverters are increasingly employed in power systems and industrial applications. Various pulse width modulation strategies have been applied to control the voltage source inverters. This dissertation presents a hybrid 2D-3D space vector modulation algorithm for three-phase voltage source inverters with both three-wire and four-wire topologies. The voltage magnitude and phase angle of the inverters fundamental output phase voltage are precisely controlled under either balanced or unbalanced load conditions, and hence, the space vector algorithm offers synchronization controllability over generation control in distributed generation systems. The numerical efficiency and simplicity of the proposed algorithm are validated through conducting MATLAB/Simulink simulations and hardware experiments. Mathematical description and harmonic analyses of output phase voltages of three-phase voltage source inverter which employs a hybrid 2D-3D SVM are presented in this dissertation. Explicit time domain representation of the harmonic components in addition to the total harmonic distortion of the output phase voltages are given in terms of system and switching parameters. The dissertation also investigates the harmonic characteristics and low total harmonic distortion performance against the linearity of modulation region which helps in the harmonic performance and design studies of such inverters employing the hybrid 2D-3D SVM. Experimental results are used to validate these analyses. In addition, the performance and the harmonic contents of the inverter output phase voltage when applying the proposed hybrid 2D-3D SVM are compared to that obtained from conventional 2D SVM and 3D SVM. As a result, the proposed new algorithm shows advantages in terms of low total harmonic distortion and reduced harmonic contents in both three-wire and four-wire systems.