Václav Valenta

Survey on spectrum utilization in Europe: Measurements, analyses and observations

This paper presents major results and comparisons of radio spectrum utilization measurements that have been carried out in three different locations in Europe, namely in the suburb of the city of Brno in the Czech Republic and in the suburb and the city of Paris in France during years 2008 and 2009 respectively. The analyzed radio bandwidth extends from 400 MHz to 3 GHz. The measurement method is based on the energy detection principle. Utilization performance and behaviors of major wireless communication systems and primary wireless system within different regions and different environments are investigated here. Our analyses pick out correlations between spectrum utilization within different regions and summarize common observations and physical aspects that will have to be considered in the future radio spectrum management to assure efficient spectrum utilization.

Towards cognitive radio networks: Spectrum utilization measurements in suburb environment

This paper deals with spectrum utilization measurements in the frequency band from 100 MHz up to 3 GHz. The measurement is based on the energy detection principle using wideband logarithmically periodic antenna. The results point out the fact, that the frequency spectrum is not utilized in an optimal manner and that there do exist less or more utilized licensed frequency bands that could be possibly used by cognitive radios in an opportunistic way. Cognitive radio concept for better spectrum utilization is introduced here along with an overall approach regarding spectrum utilization in the next generation wireless networks.

Analysis of a PLL based frequency synthesizer using switched loop bandwidth for Mobile WiMAX

This paper is focused on design aspects of a fractional-N PLL (phase locked loop) based frequency synthesizer proposed for the mobile WiMAX (worldwide interoperability for mobile access) standard. Requirements in terms of phase noise, settling time, frequency resolution and frequency of operation for WiMAX frequency synthesizer are presented. Furthermore, a high-speed CP (Charge Pump) PLL based synthesizer with a switched loop bandwidth is proposed and simulated. It has a 32 MHz reference frequency and a 50 kHz loop bandwidth with frequency raster of 125 kHz and 14 mus settling time.

Phase Noise Analysis of PLL Based Frequency Synthesizers for Multi-Radio Mobile Terminals

This paper deals with phase noise analysis and design aspects of PLL based frequency synthesizers for cognitive multi-radio mobile terminals. Principal features of PLL based frequency synthesizers are presented and simulated. This document describes various issues of the loop filter design and the overall impact on the frequency synthesizer performance in terms of the phase noise, settling time and the spurious suppression capability. Phase noise requirements for main communication standards in the frequency band 800 MHz to 6 GHz are investigated as well.

Analysis of spectrum utilization in suburb environment—evaluation of potentials for cognitive radio

This paper deals with spectrum utilization measurements in the frequency band from 100 MHz up to 3 GHz. The measurement method is based on the energy detection principle using wideband log-periodic antenna. Our results show that the radio spectrum is not utilized in an optimal manner and that there do exist sporadically utilized licensed frequency bands that could be possibly used by cognitive radios in an opportunistic way. Cognitive radio concept for better spectrum utilization is introduced here along with an overall approach regarding spectrum utilization in the next generation wireless networks.

Mobile WiMAX Handset Front-end: Design Aspects and Challenges

Mobile WiMAX standard targets worldwide telecommunication market with different regulatory policy requirements. Beside the multiple radio frequency allocation, this standard proposes multiple specifications in terms of the wideband channel bandwidth and therefore, calls for very high performance front-end. Solutions for different RF system blocks have to be flexible and in a certain manner reconfigurable in order to satisfy different modes of operation and various regulations worldwide. The chapter proposed by authors covers various RF requirements of the Mobile WiMAX standard along with its implications on the radio front-end architecture with respect to common performance metrics such as linearity, power output, gain variation, Adjacent Channel Power Rejection (ACPR) Ratio, wideband spurious spectral performance, linearity, noise figure and phase noise. Three main topics will be analyzed in a detail, namely the frequency synthesis, power amplifier design and filter design aspects. These sub-chapters will cover requirements imposed on relevant RF stages and moreover, solutions and analysis of particular approaches will be given as well.

Adaptive Solution of the Wave Equation

The paper focuses on the adaptive solution of two-dimensional wave equation using an adaptive triangulation update based on a posteriori error estimation. The a posteriori error estimation is based on the Gradient super-approximation method which is based on works of J. Dalik et al that is briefly explained. The Modern Taylor Series Method (MTSM) used for solving a set of ordinary differential equations is also explained. The MTSM adapts to the required accuracy by using a variable number of Taylor Series terms. It possible to use the MTSM to solve wave equation in conjunction with Finite Difference Method (FDM).

Flexibility of class E HPA for cognitive multi-radio architecture

This paper consists in the analysis and simulation of two topologies of high efficiency power amplifier (HPA) in the context of the cognitive multi-radio architecture. More precisely, the goal is to study the possibility of front-end radio standards flexibility using a class E HPA. Two main topologies are studied, serial and parallel, and simulations under ADS software are performed in order to validate the proposed tuning of the HPA. Results encourage possibilities of providing efficient and constant power amplification from almost 1 to 5 GHz.

Averaging of gradient in the space of linear triangular and bilinear rectangular finite elements

An averaging method for the second-order approximation of the values of the gradient of an arbitrary smooth function u = u(x1, x2) at the vertices of a regular triangulation Th composed both of rectangles and triangles is presented. The method assumes that only the interpolant Πh[u] of u in the finite element space of the linear triangular and bilinear rectangular finite elements from Th is known. A complete analysis of this method is an extension of the complete analysis concerning the finite element spaces of linear triangular elements from [Dalík J., Averaging of directional derivatives in vertices of nonobtuse regular triangulations, Numer. Math., 2010, 116(4), 619–644]. The second-order approximation of the gradient is extended from the vertices to the whole domain and applied to the a posteriori error estimates of the finite element solutions of the planar elliptic boundary-value problems of second order. Numerical illustrations of the accuracy of the averaging method and of the quality of the a posteriori error estimates are also presented.

Adaptive solution of Laplace equation

The paper is a part of student cooperation in AKTION project (Austria-Czech). Method of aposteriori error estimation based on weighted averaging to improve initial triangulation to get better solution of the planar elliptic boundary-value problem of second order and numerical illustrations of the method are presented in the paper.