Highly efficient switched‐mode transmitter using a current mode class‐D RF amplifier

This article presents a switched‐mode transmitter architecture using a current mode class‐D (CMCD) amplifier. To achieve high average efficiency for a modulated signal the envelope of the complex baseband signal is transformed into pulses such that the CMCD amplifier is operated either at its peak efficiency or completely switched off. The CMCD amplifier has been designed based on single‐tone active harmonic load‐pull measurements to achieve a power‐added efficiency (PAE) of 61.5% with 25 W output power at 900 MHz using LDMOS FETs. Removing the losses of the demodulation filter and of the amplifier a 10% higher efficiency than in an ideal class‐B amplifier can be obtained for burst‐mode operation with a peak‐to‐average power ratio of 10 dB. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Facets of the Fully Mixed Nash Equilibrium Conjecture

In this work, we continue the study of the many facets of the Fully Mixed Nash Equilibrium Conjecture, henceforth abbreviated as the FMNE\mathsf{FMNE} Conjecture, in selfish routing for the special case of n identical users over two (identical) parallel links. We introduce a new measure of Social Cost, defined as the expectation of the square of the maximum congestion on a link; we call it Quadratic Maximum Social Cost. A Nash equilibrium is a stable state where no user can improve her (expected) latency by switching her mixed strategy; a worst-case Nash equilibrium is one that maximizes Quadratic Maximum Social Cost. In the fully mixed Nash equilibrium, all mixed strategies achieve full support.     

Modeling and control of the doubly fed induction generator wind turbine

The present paper deals with the modeling of wind turbine generation systems. The model of a doubly fed induction generator, along with the corresponding converter, crow bar protection and electrical grid is described. The different level control strategies both in normal operation and under voltage dig conditions are discussed, including speed control, torque and reactive power control for the rotor-side converter, reactive and DC voltage control for the grid-side converter and the corresponding current loops control. The results obtained with simulations are compared to experimental data obtained from voltage sags provoked to real wind turbines.     

Empirical studies on programming language stimuli

Comprehending and debugging computer programs are inherently difficult tasks. The current approach to building program execution and debugging environments is to use exclusively visual stimuli on programming languages whose syntax and semantics has often been designed without empirical guidance. We present an alternative: Sodbeans, an open-source integrated development environment designed to output carefully chosen spoken auditory cues to supplement empirically evaluated visual stimuli. Originally designed for the blind, earlier work suggested that Sodbeans may benefit sighted programmers as well. We evaluate Sodbeans in two experiments. First, we report on a formal debugging experiment comparing (1) a visual debugger, (2) an auditory debugger, and (3) a multimedia debugger, which includes both visual and auditory stimuli. The results from this study indicate that while auditory debuggers on their own are significantly less effective for sighted users when compared with visual and multimedia debuggers, multimedia debuggers might benefit sighted programmers under certain circumstances. Specifically, we found that while multimedia debuggers do not provide instant usability, once programmers have some practice, their performance in answering comprehension questions improves. Second, we created and evaluated a pilot survey analyzing individual elements in a custom programming language (called HOP) to garner empirical metrics on their comprehensibility. Results showed that some of the most widely used syntax and semantics choices in commercial programming languages are extraordinarily unintuitive for novices. For example, at an aggregate level, the word for , as in a for loop, was rated reliably worse than repeat by more than 673% by novices. After completing our studies, we implemented the HOP programming language and integrated it into Sodbeans.     

Adaptive neural dynamic surface control for servo systems with unknown dead-zone

An adaptive neural controller is proposed for nonlinear systems with a nonlinear dead-zone and multiple time-delays. The often used inverse model compensation approach is avoided by representing the dead-zone as a time-varying system. The “explosion of complexity” in the backstepping synthesis is eliminated in terms of the dynamic surface control (DSC) technique. A novel high-order neural network (HONN) with only a scalar weight parameter is developed to account for unknown nonlinearities. The control singularity and some restrictive requirements on the system are circumvented. Simulations and experiments for a turntable servo system with permanent-magnet synchronous motor (PMSM) are provided to verify the reliability and effectiveness.     

A novel HMM-based learning framework for improving dynamic wireless push system performance

A new machine learning framework is introduced in this paper, based on the hidden Markov model (HMM), designed to provide scheduling in dynamic wireless push systems. In realistic wireless systems, the clients’ intentions change dynamically; hence a cognitive scheduling scheme is needed to estimate the desirability of the connected clients. The proposed scheduling scheme is enhanced with self-organized HMMs, supporting the network with an estimated expectation of the clients’ intentions, since the system’s environment characteristics alter dynamically and the base station (server side) has no a priori knowledge of such changes. Compared to the original pure scheme, the proposed machine learning framework succeeds in predicting the clients’ information desires and overcomes the limitation of the original static scheme, in terms of mean delay and system efficiency.     

Safety,Security, and Rescue Missions with an Unmanned Aerial Vehicle (UAV)

Several missions with an Unmanned Aerial Vehicle (UAV) in different realistic safety, security, and rescue field tests are presented. First, results from two safety and security missions at the 2009 European Land Robot Trials (ELROB) are presented. A UAV in form of an Airrobot AR100-B is used in a reconnaissance and in a camp security scenario. The UAV is capable of autonomous waypoint navigation using onboard GPS processing. A digital video stream from the vehicle is used to create photo maps—also known as mosaicking—in real time at the operator station. This mapping is done using an enhanced version of Fourier Mellin based registration, which turns out to be very fast and robust. Furthermore, results from a rescue oriented scenario at the 2010 Response Robot Evaluation Exercises (RREE) at Disaster City, Texas are presented. The registration for the aerial mosaicking is supplemented by an uncertainty metric and embedded into Simultaneous Localization and Mapping (SLAM), which further enhances the photo maps as main mission deliveries.     

Spectral registration of noisy sonar data for underwater 3D mapping

3D mapping is very challenging in the underwater domain, especially due to the lack of high resolution, low noise sensors. A new spectral registration method is presented that can determine the spatial 6 DOF transformation between pairs of very noisy 3D scans with only partial overlap. The approach is hence suited to cope with sonar as the predominant underwater sensor. The spectral registration method is based on Phase Only Matched Filtering (POMF) on non-trivially resampled spectra of the 3D data.     

Tracking control for boundary controlled parabolic PDEs with varying parameters: Combining backstepping and differential flatness

The combination of backstepping-based state-feedback control and flatness-based trajectory planning and feedforward control is considered for the design of an exponentially stabilizing tracking controller for a linear diffusion-convection-reaction system with spatially and temporally varying parameters and nonlinear boundary input. For this, in a first step the backstepping transformation is utilized to determine a state-feedback controller, which transforms the original distributed-parameter system into an appropriately chosen exponentially stable distributed-parameter target system of a significantly simpler structure. In a second step, the flatness property of the target system is exploited in order to determine the feedforward controller, which allows us to realize the tracking of suitably prescribed trajectories for the system output. This results in a systematic procedure for the design of an exponentially stabilizing tracking controller for the considered general linear diffusion-convection-reaction system with varying parameters, whose applicability and tracking performance is evaluated in simulation studies.