In electric power systems, the existence of constant power loads such as output-regulated power converters may bring instability problem to AC or DC distributed systems. Impedance based stability criteria has been proven a good tool for small-signal stability analysis. This works focuses on the developing of a comprehensive software tool which can extract DC or three phase AC impedances, and apply stability analysis. An algorithm is designed to select FFT window and adjust perturbation frequencies. This feature enables the software to accurately measure impedances even in existence of system line harmonics. Furthermore, multi-tone approach is developed to improve simulation time. The complete software tool is tested with simulation models and experiment results, to show the effectiveness. When multi-tone approach is applied on nonlinear loads, it gives incorrect results. The reason is that perturbation frequency will have overlapping with side-band harmonics. An algorithm is designed to avoid this problem. The algorithm is tested with 12-pulse diode rectifier simulation model, and 6-pulse diode rectifier simulation model and experimental test bed. Both simulation and experiment results verifies the concept. / Master of Science

Characterization of nonlinear systems is a challenging task as the output can not be expressed simply in terms of input signal. Therefore, a universal analysis method is essential to simplify this procedure. Modeling of the input signal is a crucial part of such analysis. In this thesis, multi-tone representation is employed to model arbitrary, stochastically not well-defined input signals and thereafter characterize nonlinear systems. In order to verify the validity of multitone representation, multi-tone modeling concept is primarily applied to real life amplifier characterization in single amplifier configuration. This experiment demonstrated potential of multi-tone modeling concept in nonlinear system characterization and encouraged application of the concept to analysis of feedforward linearizers, which are complicated systems due to the presence of two nonlinear amplifiers and the requirement of strict amplitude, phase and delay matching within two loops of the circuit. It has been assumed that main and error amplifiers can be modeled with third order AM/AM nonlinearities and there exists no delay mismatch within the loops. Hence, closed form expressions relating the main and adjacent channel power at the output of the feedforward system to the system parameters are obtained. The developed model is verified by RF and system simulations. As a result, a mathematical handy tool to specify circuit parameters rapidly for optimum linearity performance and efficiency is achieved.

This paper describes a method of estimating distance via Time-of-Flight (TOF) measurement using ultrasonic Orthogonal Frequency Division Multiplexing (OFDM) signals. Using OFDM signals allows the signals and their sub-carriers to remain orthogonal to each other while continuously transmitting. This estimation method is based on the change of phase of a traveling wave as it propagates through a medium (air for ultrasonic signals). By using signals containing multiple tones, the phase change between each frequency component is slightly different. This phase difference is dependent on the distance traveled and can thus be used to estimate distance. This paper studies the impact of tone (OFDM sub-carriers) separation on accuracy, maximum distance, and computation for two-tone and three-tone systems. The effects of the transducer channel bandwidth and channel noise are accounted for to build an accurate model for a single-transmitter single-receiver system. This study found that each additional tone provides one extra independent distance measurement which improves accuracy in the presence of noise. The inclusion of an additional tone while maintaining the same overall signal strength shows improved performance with a reduction in standard deviation of estimated distance from 5.64 mm to 3.42 mm in simulation. A four-tone system is also examined to show that this effect holds for additional tones.

This thesis presents System Identification based On-Line Health Monitoring to analyse the dynamic behaviour of the Switch-Mode Power Converter (SMPC), detect, and diagnose anomalies in passive electronic components. The anomaly detection in this research is determined by examining the change in passive component values due to degradation. Degradation, which is a long-term process, however, is characterised by inserting different component values in the power converter. The novel health-monitoring capability enables accurate detection of passive electronic components despite component variations and uncertainties and is valid for different topologies of the switch-mode power converter. The need for a novel on-line health-monitoring capability is driven by the need to improve unscheduled in-service, logistics, and engineering costs, including the requirement of Integrated Vehicle Health Management (IVHM) for electronic systems and components. The detection and diagnosis of degradations and failures within power converters is of great importance for aircraft electronic manufacturers, such as Thales, where component failures result in equipment downtime and large maintenance costs. The fact that existing techniques, including built-in-self test, use of dedicated sensors, physics-of-failure, and data-driven based health-monitoring, have yet to deliver extensive application in IVHM, provides the motivation for this research ... [cont.].

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / This paper introduces new telemetry equipment based on Digital Subscriber Loop DSL technology (high speed transmission over copper cables) for military and industrial applications. A brief xDSL technology overview is followed with introduction of the new ‘P3’ product. A number of new applications for remote data transmission are presented and further highlighted in the Australian Army report detailing their recent equipment operational deployments.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper introduces new telemetry (communications) equipment based on Digital Subscriber Loop DSL technology (high speed transmission over copper cables) for defense and industrial applications. A brief xDSL technology overview is followed with introduction of the new ‘P3’ product and its application, reviewing advantages of using copper as a communications medium whenever rapidly deployed data and voice links are essential. An Australian Army report, detailing a specific equipment deployment’s findings is reproduced as an independent reference material.

Please read the abstract in the front matter this document / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

Wireless communication networks have evolved continuously over the last four decades in order to meet the traffic and security requirements due to the ever-increasing amount of traffic. However this increase is projected to be massive for the fifth generation of wireless networks (5G), with a targeted capacity enhancement of 1000× w.r.t. 4G networks. This enhanced capacity is possible by a combination of major approaches (a) overhaul of some parts and (b) elimination of overhead and redundancies of the current 4G. In this work we focus on OFDM reference signal or pilot tones, which are used for channel estimation, link adaptation and other crucial functions in Long-Term Evolution (LTE). We investigate two aspects of pilot signals pertaining to its evolution - (a) impact of targeted interference on pilots and its mitigation and (b) adaptation of pilot patterns to match the channel conditions of the user. We develop theoretical models that accurately quantify the performance degradation at the user’s receiver in the presence of a multi-tone pilot jammer. We develop and evaluate mitigation algorithms to mitigate power constrained multi-tone pilot jammers in SISO- and full rank spatial multiplexing MIMO-OFDM systems. Our results show that the channel estimation performance can be restored even in the presence of a strong pilot jammer. We also show that full rank spatial multiplexing in the presence of a synchronized pilot jammer (transmitting on pilot locations only) is possible when the channel is flat between two pilot locations in either time or frequency. We also present experimental results of multi-tone broadcast pilot jamming (Jamming of Cell Specific Reference Signal) in the LTE downlink. Our results show that full-band jamming of pilots needs 5 dB less power than jamming the entire downlink signal, in order to cause Denial of Service (DoS) to the users. In addition to this, we have identified and demonstrated a previously unreported issue with LTE termed ‘Channel Quality Indicator (CQI) Spoofing’. In this scenario, the attacker tricks the user terminal into thinking that the channel quality is good, by transmitting interference transmission only on the data locations, while deliberately avoiding the pilots. This jamming strategy leverages the dependence of the adaptive modulation and coding (AMC) schemes on the CQI estimate in LTE. Lastly, we investigate the idea of pilot pattern adaptation for SISO- and spatial multiplexing MIMO-OFDM systems. We present a generic heuristic algorithm to predict the optimal pilot spacing and power in a nonstationary doubly selective channel (channel fading in both time and frequency). The algorithm fits estimated channel statistics to stored codebook channel profiles and uses it to maximize the upper bound on the constrained capacity. We demonstrate up to a 30% improvement in ergodic capacity using our algorithm and describe ways to minimize feedback requirements while adapting pilot patterns in multi-band carrier aggregation systems. We conclude this work by identifying scenarios where pilot adaptation can be implemented in current wireless networks and provide some guidelines to adapt pilots for 5G. / Master of Science / Wireless communications have evolved continuously over the last four decades in order to meet the ever-increasing number of users. The next generation of wireless networks, named 5G, is expected to interconnect a massive number of devices called the Internet of Things (IoT). Compared to the current generation of wireless networks (termed 4G), 5G is expected to provide a thousandfold increase in data rates. In addition to this, the security of these connected devices is also a challenging issue that needs to be addressed. Hence in the event of an attack, even if a tiny fraction of the total number of users are affected, this will still result in a large number of users who are impacted. The central theme of this thesis is the evolution of <i>Orthogonal Frequency Division Multiplexing (OFDM) pilot signals</i> on the road from 4G to 5G wireless networks. In OFDM, pilot signals are sent in parallel to data in order to aid the receiver in mitigating the impairments of the wireless channel. In this thesis, we look at two perspectives of the evolution of pilots: a) targeted interference on pilot signals, termed as ‘Multi-tone pilot jamming’ and b) adapting pilot patterns to optimize throughput. In the first part of the thesis, we investigate the (a) impact of multi-tone pilot jamming and (b) propose and evaluate strategies to counter multi-tone pilot jamming. In particular, we propose methods that (a) have the potential to be implemented in the Third Generation Partnership Project Long-Term Evolution (3GPP LTE) standard, and (b) have the ability to maintain high data rates with a multi-antenna receiver, in the presence of a multi-tone pilot jammer. We also experiment and analyze the behavior of LTE in the presence of such targeted interference. In the second half of the thesis, we explore the idea of adapting the density of pilots to optimize throughput. Increasing the pilot density improves the signal reception capabilities, but reduces the resources available for data and hence, data rate. Hence we propose and evaluate strategies to balance between these two conflicting requirements in a wireless communication system. In summary, this thesis provides and evaluates ideas to mitigate interference on pilot signals, and design data rate-maximizing pilot patterns for future OFDM-based wireless networks.

The master thesis deals with G.fast and G.mgfast transmission technologies, including their parameters. The work deals with the principle of vector DMT modulation and the possibility of time duplex TDD and full-duplex FDX in two-way communication used in these technologies. The following is a description of the line using the KHM model, which is suitable for simulations in the transmission band using G.fast and G.mgfast technologies. Subsequently, the disturbing effects of crosstalk at the near end of NEXT and the far end of FEXT and their elimination with these technologies are discussing. Part of the work explains supporting calculations to determine the SNR and bit allocation to calculate the baud rate. The work describes the methods of compensation of crosstalk FEXT and NEXT, which affect the resulting baud rate. The work also includes an application for simulation of transmission speed as a function of distance for G.fast and G.mgfast technologies, allowing changing input parameters and adjusting the transmission bandwidth based on G.9700 and G.9701 standards. Also, in work, an application is created to display the compensation of the influence of the transmitted signal crosstalk FEXT and NEXT, which allow the import of measured crosstalk between individual participants. The issue of influencing crosstalk for accurate measurements in the laboratory is also discussing. An application in the MATLAB environment is creating to display the measured characteristics.