Martin Pospisil

On the New Control Functions for Linear Discrete Delay Systems

New control functions are derived for linear difference equations with delay, which can be used to construct a nontrivial solution of a boundary value problem with zero boundary conditions. Later, a special case of invariant linear subspace is considered and corresponding control functions are constructed. Results for weakly nonlinear problems are also discussed.

On exponential stability of nonlinear fractional multidelay integro-differential equations defined by pairwise permutable matrices

In this paper, systems of nonlinear differential equations with Caputo fractional derivative and multiple delays are considered. Using representation of a solution of differential equation with multiple delays in the form of matrix polynomial and stability results such as Gronwalls and Pintos inequality, sufficient conditions for the exponential stability of a trivial solution of nonlinear multidelay fractional differential equations are proved.

Nonexistence of periodic solutions and S-asymptotically periodic solutions in fractional difference equations

Nonexistence of periodic solution is proved for periodic right-hand side.Existence of S-asymptotically periodic solutions is discussed.Existence and uniqueness results are obtained for S-asymptotically periodic solution.Nontrivial estimations of a ratio of gamma functions are used. In this paper, it is shown that a fractional difference equation with a periodic right-hand side can not possess a periodic solution but it can have an S-asymptotically periodic solution. Sufficient conditions are proved for the existence of a unique S-asymptotically periodic solution. An example is also given illustrating the obtained results.

Wireless device authentication through transmitter imperfections — measurement and classification

This paper is oriented in the area of wireless device identification through the analysis of emitted signals corrupted by radio frequency transmitter impairments. These impairments (such as power amplifier nonlinearity, IQ modulator imbalance, DC offset, phase noise, carrier frequency offset, shaping filter length and its shape) represent a unique characterization of any radio wireless transmitting device. We have performed a set of measurements on a sample of nine different transmitters (three baseboards plus three different front-ends) based on USRP software defined radio family in order to verify the potential of real applications of this authentication principle. After performing measurements in ideal conditions, we further proceeded in simulating a simple classifier based on gaussian mixture models and we briefly evaluated its performance in a real situation of a radio transmitting through air to the vector signal analyzer serving as the receiver. We also analyzed the influence of number of measurements on the classifier performance.

CLEAN algorithms for intra-vehicular time-domain UWB channel sounding

A comparison of two variants of CLEAN, a time-domain serial subtractive deconvolution algorithm, is presented. Appropriate statistical metrics for assessing the relative merit of the deconvolution technique are identified in the context of intra vehicle ultra wide band transmission, and the better variant was selected based on its performance over a standard IEEE channel simulation testbed. The chosen method is then applied to extract important channel characteristics for a real-world channel sounding experiment performed inside a passenger car.

Experimental verification and comparison of polynomials and LUTs predistortion techniques

In order to compensate for nonlinearities and memory effects introduced by power amplifiers, the digital predistortion is a widely used technique. Commonly the digital predistortion is based on polynomials derived from Volterra series or on lookup tables. Both approaches require time to find the the solution that can be applied to digital predistorter. Nevertheless, for predistorters to be actually implemented in real-time scenarios, fast convergence and low complexity is highly required. Unfortunately there does not exist a general rule for simple choice in therms of performance, convergence time and complexity. Thus in this paper a brief comparison of Volterra based series (orthogonal polynomials and simplified dynamic deviation reduction of second order) and lookup tables with cubic interpolation which are widely used schematic is provided.

Experimental evaluation of the impact of receiver front-end on spectrum sensing

This paper investigates the evaluation of a spectrum sensing technique from the point of view of detection degradation caused by the real receiver front-end imperfections. Two spectrum sensing detectors (energy detector and goodness of fit - based detector) have been tested with various modulation formats for four different types of front-ends in form of daughter-boards for widely used radio device USRP. After analysis of front-end architectures and their noise parameters, the real detection performance has been confirmed by the real experimental measurements and receiver operational characteristics evaluation.

Evaluation of digital predistortion using the USRP N200 software defined radio transceiver

This paper is oriented into domain of digital predistortion for power amplifier linearization. Its main contribution is a description of experimental evaluation of predistortion techniques using the commercial low-cost software defined transceiver USRP N200. The low-complexity predistorter based on the Look-Up-Table approach is used for verification. This type of predistorter has been chosen for the reason that although it cannot linearize the amplifier perfectly, its low complexity makes it suitable to be used in the transceivers based on the small FPGAs with limited free resources, e.g. in the low-end terminals.

Wireless device classification through transmitter imperfections — Evaluation of performance degradation due to the chip heating

The wireless devices classification based on the transmitter imperfections is one of the promising ways to provide additional security to future wireless communication networks. Although several aspects, both theoretical and practical, have been studied recently, there are no studies investigating the degradation of such authentication due to the environmental changes, such as the device temperature. We present the initial results of measurements of RF-classification method based on the Gaussian mixture model classifier under the influence of temperature variations. With the use of the widely used USRP devices, we also try to estimate which of the RF impairments is sensitive to such changes.

Time-domain nonstationary intra-car channel measurement in 60 GHz band

The paper deals with a time varying intra-vehicle channel measurement in the 60 GHz millimeter wave (MMW) band using a unique time-domain channel sounder built from off-the-shelf components and standard measurement devices. The aim of the presented work is to describe the sounder architecture, the primary data processing technique, and preliminary results of measurements aimed at the effect of vehicle vibrations and twisting, and passengers moving in a car cabin. As the amplitude of the car cabin vibration and twisting had been supposed to be comparable with the MMW wavelength, some effect on the channel impulse response (CIR) and consequently on the delay-Doppler spread (DDS) was expected. Preliminary results confirm the correctness of this assumption and allow us to assess the effect of different above-mentioned phenomena. We tested the effect of driving the car on different types of road (bumpy road, flat road, highway, etc.). For comparison purposes we use DDS and statistics of CIR amplitudes calculated using the correlative technique applied to the pseudorandom binary sequence.