University of Dubrovnik

About: University of Dubrovnik is a education organization based out in Dubrovnik, Croatia. It is known for research contribution in the topics: Population & Tourism. The organization has 351 authors who have published 954 publications receiving 7126 citations. The organization is also known as: University Durbrovnik.

Analysis of OFDM error floor in indoor channels by stochastic modeling

Abstract: In this paper, we propose a model for estimating the error floor in a small-time-dispersion environment - typically indoor, where both channel and overall OFDM symbol are represented stochastically. The developed novel model for the error floor prediction involves modified common channel time dispersion parameters as well as the ones characterizing the OFDM signal. The validity of the model was confirmed by the results of the corresponding Monte-Carlo simulations.

BER-Based Estimation of OFDM CFO-Caused Symbol Phase Deviation

Abstract: Carrier Frequency Offset (CFO) and (high) Peak-to-Average Power Ratio (PAPR) are well-known major drawbacks of the Orthogonal Frequency-Division Multiplexing (OFDM) signal. So, in many practical situations, specifically with LTE-Advanced downlink introducing carrier aggregation, estimation of PAPR and CFO-induced OFDM symbol phase deviation is of interest. However, this demands complex test equipment, such as e.g. Vector Signal Analyzer (VSA), which might not be always and everywhere available. Therefore, we applied the link abstraction principle on the residual BER that is considered to be determined just by the CFO-caused phase deviation, i.e. as if the channel is noiseless and time-dispersion-free (so that evident errors occur just due to actual CFO). Moreover, as recently it has been shown that the phase deviation is linear with the instantaneous (per-OFDM-symbol) PAPR, we develop a simple model for analytical estimating of BER-based CFO, considering the easy-to-measure BER degradation as resulting just from the according additive white Gaussian noise (AWGN) power level, which abstracts the CFO distortion. The proposed analytical model is validated by according Monte-Carlo simulations.

Changes in the non-crustacean zooplankton community in the middle Adriatic Sea during the Eastern Mediterranean Transient

Abstract: Background and Purpose: Here we presented changes in the non-crustacean zooplankton community in the years characterized by the large scale changes in the thermohaline circulation in the East Mediterranean known as the Eastern Mediterranean transient (EMT) and stronger inflow of colder and less saline Modified Atlantic Water (MAW) into the Adriatic Sea. Material and Method: Monthly samplings from February 1995 to February 1996, were performed at fixed station Stoncica near the Island of Vis in the open oligotrophic Middle Adriatic waters. Zooplankton samples, taken vertically from 100 m to the surface using a Nansen net with 125-µm mesh size were analyzed in detail for the following zooplankton taxa: Hydromedusae, Calycophorae, Ctenophora, Pteropoda, Heteropoda, Polychaeta and Chaetognatha. Results and Conclusions: Among the investigated non-crustacean zooplankton three species were registered for the first time, while one species reappeared after years of absence. Compared with earlier data there was a dramatic change in dominant species of calycophoran medusae, pteropods and polychaetes. Data presented herein provide baseline information that is essential for the evaluation of impact of hydroclimatic changes on the zooplankton community, which started in the East Mediterranean in the 1990s and are still on going. Keywords : zooplankton, hydroclimatic changes, Middle Adriatic

Samoorganiziranje neizrazitog analitičkog regulatora pri vođenju mobilnog robota

Abstract: In this work new analitycal form of membership function of input fuzzy sets and a new form of analytical function for mapping of input fuzzy sets on positions of centres of output fuzzy sets is suggested. By changing of basic structure, fuzzy domain of fuzzy analitical controller is increasing, thus resulting in a fact that possibilities in process of interference were improving. In the phase plane of condition, impact analysis of free parameters on forming of space of fuzzy action is realised, and proposition by which „Sufficient number of free parameters of fuzzy logic controllers can aproximate any unknown analytical function“ is founded. The method of the starting adjustment of fuzzy logic controllers without a fuzzy rule base which showed good emulation of classic PD and PI controller is suggested. With regard to gradient of tracking error of nominal trajectory in space of inner coordinates in OFF-line mode, method of selforganising which include adaptations of free parameters of contemporary fuzzy logic controllers is suggested. In respect of convergence speed and stability of nonlinear algorithm of adaptation, restriction on coefficient of training are made, and also restrictions, which, according Lyapunov, should be satisfied to ensure stability of control algorithm. By improved fuzzy analytical controller nonlinear structure are realised, with integral action in scope of which algorithm of integral strenghtening is suggested. To assure ON-line leading of autonomous mobile robot in real time, change of analytical structure of fuzzy controller with discrete data written in memory card of fuzzy control action is suggested. On basis of position error in conditions of stationar and nonstationar measurment disturbance of „white noise“ type, fuzzy mechanism for adjusting of free parameters of improved fuzzy analytical controller and strengthening of classic PI-controller to make compromise between lowering of influences of measurment disturbance and increasing of speed estimation of controlled variables, is suggested. Correctness of all suggested methods is verified by simulation of autonomous mobile robot through specified nominal trajectory of complex shape.

The Necessity of Adoption of New National Regulations to Prevent the Pollution of Croatian Coastal Sea by Sewage from Various Vessels

Abstract: This paper addresses international, Croatian and EU legislation on the prevention of sea water pollution by sewage from vessels. The paper also highlights the disadvantages of international legislation on the protection of coastal sea against pollution by vessel sewage. International legislation is enacted at the global level rather than for each individual coastal sea due to each sea having different exposure to pollution. Either the insufficiently comprehensive national legislation needs to be amended or, more suitably and effectively in the case of the Republic of Croatia, new rules regulating the prevention of coastal sea pollution at the national level and the prevention of negative influence on the marine eco-system, human health and economy established.