RF MEMS/NEMS RESONATORS FOR WIRELESS COMMUNICATION SYSTEMS AND ADSORPTION-DESORPTION PHASE NOISE

During the past two decades a considerable effort has been made to develop radio-frequency (RF) resonators which are fabricated using the micro/nanoelectro-mechanical systems (MEMS/NEMS) technologies, in order to replace conventional large off-chip components in wireless transceivers and other high-speed electronic systems.The first part of the paper presents an overview of RF MEMS and NEMS resonators, including those based on two-dimensional crystals (e.g. graphene). The frequency tuning in MEMS/NEMS resonators is then analyzed. Improvements that would be necessary in order for MEMS/NEMS resonators to meet the requirements of wireless systems are also discussed.The analysis of noise of RF MEMS/NEMS resonators and oscillators is especially important in modern wireless communication systems due to increasingly stringent requirements regarding the acceptable noise level in every next generation. The second part of the paper presents the analysis of adsorption-desorption (AD) noise in RF MEMS/NEMS resonators, which becomes pronounced with the decrease of components' dimensions, and is not sufficiently elaborated in the existing literature about such components. Finally, a theoretical model of phase noise in RF MEMS/NEMS oscillators will be presented, with a special emphasize on the influence of the resonator AD noise on the oscillator phase noise

Uloga savremenih komercijalnih telekomunikacionih sistema u procesu planiranja, organizacije i izvođenja vojnih operacija / Role of contemporary communications systems in the process of planning, organizing and realization of military operations

Ubrzani razvoj komercijalnih telekomunikacionih sistema stvorio je mogućnost da se deo vojnih telekomunikacionih potreba, posebno u mirnodopskim uslovima može u potpunosti zadovoljiti upotrebom komercijalne tehnologije. Izviđački sistem, zasnovan na specifičnoj vojnoj tehnologiji koja eksploatiše komercijalne resurse, poput pasivnih radarskih sistema i akustičkih senzora dostupnih na komercijalnom tržištu, može predstavljati primer jednostavnog i vrlo efikasnog sistema. Potrebna komunikacija sa pretpostavljenom komandom kao i akcije koje se sprovode na osnovu dobijenih rezultata, mogu biti podržane komercijalnim sistemima zasnovanim na savremenim tehnološkim rešenjima, poput adaptivnih modulacionih postupaka i prenosa signala u proširenom spektru sa direktnom sekvencom i/ili frekvencijskim skakanjem i višestrukim pristupom na bazi kodnog multipleksa. Ovako organizovani sistemi u potpunosti zadovoljavaju mirnodopske potrebe Vojske SCG, dok se primena delimično ili potpuno, širi i na slučajeve sukoba ograničenog intenziteta antiteroristička dejstva i slučajeve elementarnih nepogoda. / Fast progress in commercial communications systems development has made possibilities to fulfill communications needs in military organizations especially during the periods of peace. A reconnaissance system, based on specific military technology such as passive radar systems and acoustic sensors, available in commercial market, represents a possible realization of a simple and highly efficient system. Necessary communication with a higher command, also as actions that are made based on gathered information, could supported through use of commercial communications systems employing adaptive modulation processes, direct sequence and frequency hopping spread spectrum communications and code division multiple access. In this way organized systems completely fulfill communication needs of the Army of Serbia and Montenegro during peacetime, but the applicability of such systems expends partially or fully on cases of limited military interventions antiterrorist actions and nature disasters

Decision Feedback Blind Equalizer with Tap-Leaky Whitening for Stable Structure-Criterion Switching

The research presented in this paper improves the structure-criterion switching performance of the blind decision feedback equalizer (DFE) which eliminates error propagation effects by optimizing both the structure and the cost criterion. To conquer the complexity of the 64-QAM (quadrature amplitude modulated) signal constellation, the stochastic entropy-gradient algorithm is additionally regularized by the coefficient leaky term to avoid a coefficients norm overgrowth of the received signal whitener. Effectively, the leak of coefficients is employed to ensure a stable structure-criterion switching of DFE between blind and decision-directed operation modes. The optimization of the resulting whitening algorithm is achieved by means of two free, leaky and entropic, parameters which act in opposition to each other. Both, the influence of the 64-QAM signal on the feedback filter behavior and the parametric optimization of the whitening algorithm are analyzed through simulations

Blind DFE with Parametric Entropy-Based Feedback

Abstract -This paper considers the blind decision feedback equalizer for quadrature amplitude modulation (QAM) systems and proposes the optimization method of parametric stochastic gradient algorithms particularly derived for its entropy-based feedback filter. The optimization method is based on the fact that the "slope" of applied parametric complex-valued nonlinearity can be adjusted to the unknown probability distribution of an input intersymbol interference to respond with a maximum entropy output. The parametric optimization is achieved for 16-, 32-and 64-QAM signals

Primena metode MUSIC za određivanje smera dolaska radio-signala korišćenjem antenskih nizova ADCOCK / Application of the MUSIC method for direction of arrival estimation using the ADCOCK antenna arrays

Analiziran je problem procene smera dolaska radio-signala metodom MUSIC korišćenjem antenskih nizova ADCOCK. Formulisan je matematički model signala na antenskom nizu ADCOCK. Izvedene su relacije između vektora prostiranja ADCOCK i vektora prostiranja ukupnog antenskog niza (niza od koga se ADCOCK-ov niz formira). Definisana je kriterijumska funkcija algoritma MUSIC i funkcija neodređenosti antenskog niza ADCOCK. Prikazani su rezultati simulacije, kao i rezultati praktične verifikacije mogućnosti primene metode MUSIC na antenske nizove ADCOCK. / The MUSIC based Direction of Arrival estimation using the ADCOCK antenna arrays is considered. Starting from signal model formulation, the cost function of the MUSIC algorithm and the ambiguity functions for the ADCOCK antenna array have been formulated. Some simulation results and some preliminary results of the verification in practice are presented

Analiza korelacionih osobina pseudoslučajnih sekvenci dužine 255 za zaštitu upravljačkog signala bespilotne letelice / Analysis of correlation properties of pseudorandom sequences of length 255 for the UAV control signal protection

Tehnike prenosa signala u proširenom spektru sa direktnom sekvencom predstavlja efikasan metod zaštite upravljačkog signala bespilotne letelice (BL). Zaštita signala se ostvaruje primenom pseudoslučajnih (PS) sekvenci u predajniku, koje su poznate prijemniku, ali ne i neovlašćenom korisniku. Da bi se ostvario pouzdan prenos signala, PS sekvence treba da imaju dobre autokorelacione osobine. Ukoliko je prenos signala realizovan primenom nekoliko PS sekvenci, tada su od velike važnosti i njihove međukorelacione karakteristike. U radu su analizirane autokorelacione i međukorelacione osobine PS sekvenci dužine 255. Razmatrane su tri najčešće korišćene klase PS sekvenci: linearne sekvence maksimalne dužine, Goldove sekvence i Kasamijeve sekvence. Predložen je optimalan skup PS sekvenci za zaštitu upravljačkog signala BL. / The Direct Sequence Spread Spectrum technique represents an effective method for unmanned aerial vehicle (UAV) control signal protection. Signal protection is obtained by applying pseudorandom (PR) sequences within a transmitter, known by a receiver, but unknown to an unauthorized user. In order to achieve reliable signal transmission, PR sequences ought to have good autocorrelation properties. If the signal transmission is realized by using several PR sequences, their crosscorrelation properties are of high importance as well. In this paper autocorrelation and crosscorrelation properties of PR sequences of length 255 are analyzed. Three most frequently used classes of PR sequences: linear maximum length, Gold and Kasami sequences are considered. An optimal set of PR sequences for UAV control signal protection is recommended