Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaf 157). Also available via the Internet.

Thesis (MScEng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The aim of this thesis was to investigate the use of behavioral level models in receiver simulations using the capabilities of Agilent's Advanced Design System. Behavioral level modeling has become increasingly attractive because it offers faster and easier results for system level simulations. The work in this thesis focused strongly on nonlinear measurements to characterize the various nonlinear phenomena that are present in amplifiers and mixers. Measurement automation software was developed to automate the process. An error correction technique was also developed to increase the accuracy of spectrum analyzer measurements. The measured data was used to implement the behavioral level amplifier and mixer models in ADS. The accuracy of the models was compared to measured data and the different available models were compared. Finally the models were combined to realize different receivers and were used to do typical receiver tests. These test include gain and gain compression, two-tone intermodulation and spurious responses. The results are compared to measured data to test the accuracy and usefulness of the models and simulation techniques. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis was om stelsel-vlak gedrags-modelle te ondersoek soos hulle in Agilent se Advanced Design System (ADS) aangebied word. Die modellering van die stelselvlak-gedrag van komponente en stelsels is aantreklik aangesien dit 'n hoë vlak beskrywing van komplekse kommunikasie stelsels moontlik maak. Akkurate stelsel-vlak simulasies sal lei tot vinnige ontwikkeling en evaluasie van nuwe sisteme. Die resultate wat verkry word is egter afhanklik van die beskikbaarheid van akkurate stelsel-vlak gedragsmodelle Die tesis het baie sterk op metings staat gemaak om die nie-liniêre gedrag van versterkers en mengers te karakteriseer. Meet sagteware is ontwikkel om die verskillende metings te automatiseer. Fout korreksie vir spetrum-analiseerder-metings is ook ontwikkel. Die gemete data is gebruik om die nie-liniêre gedrags-modelle in ADS te implementer. Die modelle is in simulasies gebruik en die akuraatheid van die simulasies is teen gemete data getoets. Die finale deel van die tesis gebruik die modelle om tipiese ontvanger karakteristieke te voorspel. Die volgende toetse is gedoen: aanwins en kompressie, twee-toon intermodulasie en hoer orde meng produkte. Die resultate van die toetse is met gemete data vergelyk om die akuraatehied en bruikbaarheid van die verskillende modelle te vergelyk.

abstract: The Kilopixel Array Pathfinder Project (KAPPa) advances the number of coherent high-frequency terahertz (THz) receivers that could be packed into a single focal plane array on existing submm telescopes. The KAPPa receiver, at 655-695 GHz, is a high frequency heterodyne receiver that can achieve system temperatures of less than 200 K, the specification for ALMA band-9. The KAPPa receiver uses a novel design of a permanent magnet to suppress the noise generated by the DC Josephson effect. This is in stark contrast to the benchmark solution of an electromagnet that is both too expensive and too large for use in kilo-pixel arrays. I present a simple, robust design for a single receiver element that can be tessellated throughout a telescope's focal plane to make a ~1000 pixel array, which is much larger than the current state-of-the-art array, SuperCam, at 64 pixels and ~345 GHz. While the original goal to develop receiver technologies has been accomplished, the path to this accomplishment required a far more holistic approach than originally anticipated. The goal of the present work has expended exponentially from that of KAPPas promised technical achievements. In the present work, KAPPa and its extension, I present solutions ranging from 1) the creation of large scale astronomical maps, 2) metaheuristic algorithms that solve tasks too complex for humans, and 3) detailed technical assembly of microscopic circuit components. Each part is equally integral for the realization of a ~1000 pixel THz arrays. Our automated tuning algorithm, Alice, uses differential evolution techniques and has been extremely successful in its implementation. Alice provides good results for characterizing the extremely complex tuning topology of THz receivers. More importantly, it has accomplished rapid optimization of an entire array without human intervention. In the age of big data astronomy, I have prepared THz heterodyne receiver arrays by making cutting edge community-oriented data analysis tools for the future of large-scale discovery. I present a from-scratch reduction and analysis architecture developed for observations of 100s of square degree on-the-sky maps with SuperCam to address the gulf between observing with single dish antennas versus a truly integrated focal plane array. / Dissertation/Thesis / Doctoral Dissertation Astrophysics 2016

Abstract Advanced receiver structures capable of suppressing multiple-access interference in code-division multiple-access (CDMA) systems operating in frequency-selective fading channels are considered in this thesis. The aim of the thesis is to develop and validate novel receiver concepts suitable for future wideband cellular CDMA systems. Data detection and synchronization both for downlink and uplink receivers are studied. The linear minimum mean squared error (LMMSE) receivers are derived and analyzed in frequency-selective fading channels. Different versions of the LMMSE receivers are shown to be suitable for different data rates. The precombining LMMSE receiver, whichis also suitable for relatively fast fading channels, is shown to improve the performance of the conventional RAKE receivers signicantly in the FRAMES wideband CDMA concept. It is observed that the performance of the conventional RAKE receivers is degraded signicantly with highest data rates due to multiple-access interference (MAI) as well as due to inter-path interference. Based on a general convergence analysis, it is observed that the postcombining LMMSE receivers are mainly suited to the high data rate indoor systems. The blind adaptive LMMSE-RAKE receiverdeveloped for relatively fast fading frequency-selective channels gives superior rate of convergence and bit error rate (BER) performance in comparison to other blind adaptive receivers based on least mean squares algorithms. The minimum variance method based delay estimation in blind adaptive receivers is shown to result in improved delay acquisition performance in comparison to the conventional matched filter and subspace based acquisition schemes. A novel delay tracking algorithm suitable to blind least squares receivers is also proposed. The analysis shows improved tracking performance in comparison to the standard delay-locked loops. Parallel interference cancellation (PIC) receivers are developed for the uplink. Data detection, channel estimation, delay acquisition, delay tracking, inter-cell interference suppression, and array processing in PIC receivers are considered. A multistage data detector with the tentative data decision and the channel estimate feedback from the last stage is developed. Adaptive channel estimation filters are used to improve the channel estimation accuracy. The PIC method is also applied to the timing synchronization of the receiver. It is shown that the PIC based delay acquisition and tracking methods can be used to improve the performance of the conventional synchronization schemes. Although the overall performance of the PIC receiver is relatively good in the single-cell case, its performance is signicantly degraded in a multi-cell environment due to unknown signal components which degrade the MAI estimates and subsequently the cancellation efficiency. The blind receiver concepts developed for the downlink are integrated into the PIC receivers for inter-cell interference suppression. The resulting LMMSE-PIC receiver is capable of suppressing residual interference and results in good BER performance in the presence of unknown signal components.

Abstract In this thesis, iterative detection and estimation algorithms for digital communications systems in the presence of parametric uncertainty are explored and further developed. In particular, variational methods, which have been extensively applied in other research fields such as artificial intelligence and machine learning, are introduced and systematically used in deriving approximations to the optimal receivers in various channel conditions. The key idea behind the variational methods is to transform the problem of interest into an optimization problem via an introduction of extra degrees of freedom known as variational parameters. This is done so that, for fixed values of the free parameters, the transformed problem has a simple solution, solving approximately the original problem. The thesis contributes to the state of the art of advanced receiver design in a number of ways. These include the development of new theoretical and conceptual viewpoints of iterative turbo-processing receivers as well as a new set of practical joint estimation and detection algorithms. Central to the theoretical studies is to show that many of the known low-complexity turbo receivers, such as linear minimum mean square error (MMSE) soft-input soft-output (SISO) equalizers and demodulators that are based on the Bayesian expectation-maximization (BEM) algorithm, can be formulated as solutions to the variational optimization problem. This new approach not only provides new insights into the current designs and structural properties of the relevant receivers, but also suggests some improvements on them. In addition, SISO detection in multipath fading channels is considered with the aim of obtaining a new class of low-complexity adaptive SISOs. As a result, a novel, unified method is proposed and applied in order to derive recursive versions of the classical Baum-Welch algorithm and its Bayesian counterpart, referred to as the BEM algorithm. These formulations are shown to yield computationally attractive soft decision-directed (SDD) channel estimators for both deterministic and Rayleigh fading intersymbol interference (ISI) channels. Next, by modeling the multipath fading channel as a complex bandpass autoregressive (AR) process, it is shown that the statistical parameters of radio channels, such as frequency offset, Doppler spread, and power-delay profile, can be conveniently extracted from the estimated AR parameters which, in turn, may be conveniently derived via an EM algorithm. Such a joint estimator for all relevant radio channel parameters has a number of virtues, particularly its capability to perform equally well in a variety of channel conditions. Lastly, adaptive iterative detection in the presence of phase uncertainty is investigated. As a result, novel iterative joint Bayesian estimation and symbol a posteriori probability (APP) computation algorithms, based on the variational Bayesian method, are proposed for both constant-phase channel models and dynamic phase models, and their performance is evaluated via computer simulations.

Abstract Subsampling can be used in a radio receiver to perform signal downconversion and sample-and-hold operations in order to relieve the operation frequency and bandwidth requirements of the subsequent discrete-time circuitry. However, due to the inherent aliasing behaviour of wideband noise and interference in subsampling, and the difficulty of implementing appropriate bandpass anti-aliasing filtering at high frequencies, straightforward use of a low subsampling rate can result in significant degradation of the receiver dynamic range. The aim of this thesis is to investigate and implement methods for integrating filtering into high-frequency signal sampling and downconversion by subsampling to alleviate the requirements for additional front-end filters and to mitigate the effects of noise and out-of-band signal aliasing, thereby facilitating use in integrated high-quality radio receivers. The charge-domain sampling technique studied here allows simple integration of both continuous-and discrete-time filtering functions into high-frequency signal sampling. Gated current integration results in a lowpass sin(x)/x(sinc(x)) response capable of performing built-in anti-aliasing filtering in baseband signal sampling. Weighted integration of several successive current samples can be further used to obtain an embedded discrete-time finite-impulse-response (FIR) filtering response, which can be used for internal anti-aliasing and image-rejection filtering in the downconversion of bandpass signals by subsampling. The detailed analysis of elementary charge-domain sampling circuits presented here shows that the use of integrated FIR filtering with subsampling allows acceptable noise figures to be achieved and can provide effective internal anti-aliasing rejection. The new methods for increasing the selectivity of elementary charge-domain sampling circuits presented here enable the integration of advanced, digitally programmable FIR filtering functions into high-frequency signal sampling, thereby markedly relieving the requirements for additional anti-aliasing, image rejection and possibly even channel selection filters in a radio receiver. BiCMOS and CMOS IF sampler implementations are presented in order to demonstrate the feasibility of the charge-domain sampling technique for integrated anti-aliasing and image-rejection filtering in IF signal quadrature downconversion by subsampling. Circuit measurements show that this sampling technique for built-in filtering results in an accurate frequency response and allows the use of high subsampling ratios while still achieving a competitive dynamic range.

It has been shown in ionospheric research that modelling total electron content (TEC) during storm conditions is a big challenge. In this study, mathematical equations were developed to estimate TEC over Sutherland (32.38⁰S, 20.81⁰E), during storm conditions, using the Empirical Orthogonal Function (EOF) analysis, combined with regression analysis. TEC was derived from GPS observations and a geomagnetic storm was defined for Dst ≤ -50 nT. The inputs for the model were chosen based on the factors that influence TEC variation, such as diurnal, seasonal, solar and geomagnetic activity variation, and these were represented by hour of the day, day number of the year, F10.7 and A index respectively. The EOF model was developed using GPS TEC data from 1999 to 2013 and tested on different storms. For the model validation (interpolation), three storms were chosen in 2000 (solar maximum period) and three others in 2006 (solar minimum period), while for extrapolation six storms including three in 2014 and three in 2015 were chosen. Before building the model, TEC values for the selected 2000 and 2006 storms were removed from the dataset used to construct the model in order to make the model validation independent on data. A comparison of the observed and modelled TEC showed that the EOF model works well for storms with non-significant ionospheric TEC response and storms that occurred during periods of low solar activity. High correlation coefficients between the observed and modelled TEC were obtained showing that the model covers most of the information contained in the observed TEC. Furthermore, it has been shown that the EOF model developed for a specific station may be used to estimate TEC over other locations within a latitudinal and longitudinal coverage of 8.7⁰ and 10.6⁰ respectively. This is an important result as it reduces the data dimensionality problem for computational purposes. It may therefore not be necessary for regional storm-time TEC modelling to compute TEC data for all the closest GPS receiver stations since most of the needed information can be extracted from measurements at one location.

No description available.

No description available.

No description available.