Roman Marsalek

Bio: Roman Marsalek is an academic researcher from Brno University of Technology. The author has contributed to research in topics: Orthogonal frequency-division multiplexing & Cognitive radio. The author has an hindex of 13, co-authored 111 publications receiving 880 citations. Previous affiliations of Roman Marsalek include ESIEE.

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

Abstract: 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.

From post-distortion to pre-distortion for power amplifiers linearization

Abstract: This letter presents a new method of digital adaptive pre-distortion for linearization of power amplifiers (PA). The method is derived from a post-distortion approach which identifies the PA inverse function. This approach leads to the minimization of a quadratic function of the polynomial coefficients in the case of a polynomial predistorter form and a least square criterion. We have compared our solution to a method previously proposed by Ghaderi (1996) that was also based on the transformation of a post-distortion into a pre-distortion system. We have tested our predistorter (along with a baseband adaptation of Ghaderi's) on OFDM Hiperlan signals. Both methods significantly reduced the signal distortion and the spectral regrowth. Our less complex approach proved to be even better for small peak back off values.

Towards cognitive radio networks: Spectrum utilization measurements in suburb environment

Abstract: 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.

In-Vehicle Channel Measurement, Characterization, and Spatial Consistency Comparison of $\text{30}\hbox{--}\text{11 GHz}$ and $\text{55}\hbox{--}\text{65 GHz}$ Frequency Bands

Abstract: The paper provides real-word wireless measurement data of the intravehicular channel for both the $\text{3}\hbox{--}\text{11 GHz}$ and the $\text{55}\hbox{--}\text{65 GHz}$ frequency bands under similar conditions. By spatially averaging channel impulse response realizations within a $10\times 10$ grid, we obtain the power-delay profile (PDP). The data measured at $\text{3}\hbox{--}\text{11 GHz}$ and $\text{55}\hbox{--}\text{65 GHz}$ exhibit significant differences in terms of root mean square (RMS) delay spread, number of resolvable clusters, and variance of the maximal excess delay. Moreover, we evaluate the spatial stationarity via the Pearson correlation coefficient and via the PDP collinearity, depending on the distance in the grid. The measured and calculated results indicate that a strong reverberation inside the vehicle produces similar PDPs within the range of approximately ten wavelengths. We also provide a linear piecewise model of the PDP in logarithmic scale and a generalized extreme value model of a small-scale signal fading. Our channel model is validated utilizing the Kolmogorov–Smirnov test.

In-Vehicle mm-Wave Channel Model and Measurement

Abstract: This contribution documents and discusses recent wideband radio channel measurements carried out in the intra– vehicle environment. Channels in the millimeter-wave (MMW) frequency band have been measured in 55–65GHz using openended rectangular waveguides. We present a channel modeling approach based on a decomposition of spatially specific Channel Impulse Responses (CIRs) into large and small scale fading. The decomposition is done by the Hodrick-Prescott filter. We parametrize the small scale fading utilizing Maximum-likelihood estimates for the parameters of a generalized extreme value (GEV) distribution. The large scale fading is described by a two dimensional polynomial curve. We also compare simulated results with our measurement exploiting the two-sample Kolmogorov-Smirnov test.

Shape Fluctuations and Random Matrices

Abstract: We study a certain random groeth model in two dimensions closely related to the one-dimensional totally asymmetric exclusion process. The results show that the shape fluctuations, appropriately scaled, converges in distribution to the Tracy-Widom largest eigenvalue distribution for the Gaussian Unitary Ensemble.

A Survey on Security Threats and Detection Techniques in Cognitive Radio Networks

Abstract: With the rapid proliferation of new technologies and services in the wireless domain, spectrum scarcity has become a major concern. The allocation of the Industrial, Medical and Scientific (ISM) band has enabled the explosion of new technologies (e.g. Wi-Fi) due to its licence-exempt characteristic. The widespread adoption of Wi-Fi technology, combined with the rapid penetration of smart phones running popular user services (e.g. social online networks) has overcrowded substantially the ISM band. On the other hand, according to a number of recent reports, several parts of the static allocated licensed bands are under-utilized. This has brought up the idea of the opportunistic use of these bands through the, so-called, cognitive radios and cognitive radio networks. Cognitive radios have enabled the opportunity to transmit in several licensed bands without causing harmful interference to licensed users. Along with the realization of cognitive radios, new security threats have been raised. Adversaries can exploit several vulnerabilities of this new technology and cause severe performance degradation. Security threats are mainly related to two fundamental characteristics of cognitive radios: cognitive capability, and reconfigurability. Threats related to the cognitive capability include attacks launched by adversaries that mimic primary transmitters, and transmission of false observations related to spectrum sensing. Reconfiguration can be exploited by attackers through the use of malicious code installed in cognitive radios. Furthermore, as cognitive radio networks are wireless in nature, they face all classic threats present in the conventional wireless networks. The scope of this work is to give an overview of the security threats and challenges that cognitive radios and cognitive radio networks face, along with the current state-of-the-art to detect the corresponding attacks. In addition, future challenges are addressed.