476 research outputs found

    Performanse bežičnog telekomunikacionog sistema u prisustvu n-m fedinga

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    In this thesis characteristics of wireless communication system operating over η-μ fading channel are considered together with diversity reception techniques which reduce the influence of η-μ fading on the system’s outage probability, average bit error rate, channel capacity, level crossing rate and average fade duration. Performance improvement is very significant within radio systems operating into cell network configuration. Cell network configuration realization could be used for increasing capacity of wireless communication system. With the increase of number of cells, i.e. with reducing the surface area of each cell, channel capacity increases. With the increase of number of cells, co-channel interference level increase, which degrades system performance values. In this work the compromise between the system capacity and reception quality is inquired. By applying diversity reception techniques, system performance values, degraded by the influences of slow fading, multipath fading and co-channel interference, are improved, so it is possible to reduce the cell area and to increase system capacity. In the second part of Phd thesis, various distributions for modeling the envelope variations in fading channels have been presented, cases in which these models are used have been pointed out, and advantages and imperfections of corresponding models for corresponding propagation scenarios have been presented. In third chapter, statistical characteristics of the first order of η-μ random variable, α-η-μ random variable and squared η-μ random variable are considered. For each mentioned variables, expressions for probability density function, cumulative distributive function, characteristic function and moments have been derived. Also for each observed case sum of two random variables, product of two random variables, ratio of two random variables, maximal value of two random variables and minimum value of two random variables have been determined. Obtained results are used for determining performances of wirelles reception with applied diversity technique for mitigation fading influence on system performances. Based on obtained expressions, graphs are depicted for probability density functions and cumulative distribution functions for the various values of propagation environment parameters. Probability density function and cumulative distribution function values are also graphically presented for α-η-μ random variable in the function of α and μ parameter change. For the purpose of performance analysis in η-μ fading environment, in the fourth chapter have been considered transformations of three η-μ random variables. Based on presented transformations of η-μ random variables, transmission performances estimation has been conducted, for the η-μ fading channel. Estimation of signal performances for the cases when diversity techniques are applied are carried out based on standard signal performance measures, i.e. outage probability (OP), average bit error probability (ABER), for observed modulation format and channel capacity. Graphically are presented ABER values for various values of system parameters when transmission is carried out with different modulation formats. By comparing obtained values it can be seen received signal performance improvement for the cases when diversity techniques are apliied over the reception case when there is no diversity technique applied. In the fifth chapter statistical characteristics of the second order of η-μ radnom proccess, and random proccesses which represent various variations of η-μ radnom proccess, are considered. Brand new random proccesses, for describing fading in special channel conditions are fromed. For all this cases level crossing rates are determined. In the sixth chapter of this Phd thesis are considered wireless communication systems with reception with applied diversity techniques for mitigating the influence of η-μ fading on system performances. Space diveristy technique has been used. Useful signals are accepted at the antennas, envelopes of these signals are combined and decision is made based on the signal values at the combiner outputs. System performances are determined for the cases of SC and MRC combining. For bouth cases probability density function and cumulative distribution function of the signal at the combiners outouts are derived, as well as the average bit error rate for the various used modualtion formats and level crossing rate. Results for ABER for various modulation formats are graphically presented as well as the improvement of the outage probability at the reception obtained by applying SC with two reception branches. In this part it has also been considered the case when bouth desired and interferring signal are described with η-μ distribution, as well as the case when desired signal has been described with η-μ distribution while interference has been described with κ-μ distribution. In the seventh chapter macrodiversity sistem with SC reception and two MRC microdiversity combiners has been considered. At the inputs at the microdiversity combiners η-μ fading is present, while at the inputs as macrodiversity combiners slow Gamma fading is present. For this model of system it has been calculated probability density function, cumulative distribution function, characteristic function, moments, variance, outage probability and level crossing rate for the signal at the macrodiversity combiner output. Results obtained for level croosing rate at the macrodiversity combiner output are graphically presented

    Application of diverse techniques to reduce the impact of α-k-μ-g and k-μ-g feding on wireless performance

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    U ovoj tezi izvršena je analiza performansi bežičnog prenosa_signala_u_prisustvu α-k-μ-g i k-μ-g fedinga_u_kanalu. Izvedeni_su_izrazi u zatvorenom obliku za funkcije_gustine verovatnoće_raspodele i kumulativnu_funkciju_raspodele odnosa signal-šum (SNR) na prijemu kada se bežični prenos vrši kroz kanale sa fedingom. Primenjene_su_standardne_mere_kvaliteta odnosno_performansi_primljenog_signala, kao što su verovatnoća otkaza (OP - Outage probability) i srednji broj osnih preseka (LCR- Level Crossing Rate), koje su_dobijene za_slučajeve_prenosa u funkciji različitih vrednosti parametara sistema. Poboljšanje ovih mera performansi analizirano je za slučaj kada su kada su na prijemnoj_strani_korišćene_prostorne diverziti tehnike_kombinovanja. U tezi je razmatrano nekoliko tehnika_kombinovanja_signala na prijemu. Korišćene_su_tehnika selektivnog_kombinovanja_signala (SC-Selection Combining) i tehnika_kombinacija_signala_sa_maksimalnim_odnosom (MRC-Maximal Ratio Combining), u cilju_procene_mogućnosti_slabljenja_uticaja fedinga pri prenosu signala u kanalu. Izvršena je i analiza_istovremenog_uticaja pojavljive_fedinga i efekta_senke pri bežičnom_prenosu_signala, a razmatrane su mogućnosti_istovremene_primene tehnika makro-diverziti_kombinovanja gore navedenih prostornih diverziti tehnika, kako_bi_se_smanjili ovi štetni efekti uticaja smetnji i poboljšao_kvalitet_signala_na_prijemnoj_strani. Rezultati_dobijeni u_ovoj_tezi, pokazuju da se primenom_pristupa_predloženih u disertaciji_može postići smanjenje štetnih efekata α-k-μ-g i k-μ-g fedinga u kanalu pri_različitim_scenarijima_bežičnog prenosa

    Performanse kooperativnih bežičnih telekomunikacionih sistema i mogućnosti povećanja kapaciteta kanala u prisustvu fedinga i međukanalne interferencije

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    In order to improve the performance of the wireless signal transmission system in the presence of various types of interference, new methods of combining diversion techniques in the relay and on the receiving side have been proposed. When using diversi, the combining technique has shown a significant improvement in the performance of wireless relay signal transmission, and thus a lower probability of system failure. Increasing the capacity of wireless telecommunications systems is feasible in terms of fixed bandwidth and specified modulation format by using the cooperative concept to increase the signal strength to noise and interference ratio. By using mobile stations as a relay, performance improvement can be achieved in M2M communication, which can be rationally used to increase channel information capacity and transmission reliability. A more detailed analysis has been conducted and can answer questions about quantitative measures of improvement in the conditions of fading and inter-channel interference. The cases of relay transmission are discussed, as well as the possibility of applying a diversion technique to improve performance in conditions of simultaneous reception of a signal through a direct connection and through a relay. For the above cases, standard performance measures will be determined using statistical telecommunications theory

    Statističke karakteristike prvog i drugog reda signala u bežičnom telekomunikacionom sistemu sa selekcionim kombinovanjem

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    In doctoral dissertation, first and second order system performances of wireless communication system in the presence of fading and interference are considered. Theoretically, four cases are taken into consideration, and obtained numerical results are graphically presented and analyzed. Firstly, wireless mobile communication system with the receiver that contains automatic frequency control (AFC) loop operating over fading channel in the presence of single interference is considered. Performance measures, such as average switching rate (ASR) and mean time lose of lock (MTTL), are defined. In this doctoral dissertation, ASR and MTTL, for three different fading channels: Kg, α-μ and k-μ are obtained. In the next chapter, wireless relay communication system with two sections in the presence of multipath fading is considered. Signal envelope at the input of the receiver can be expressed as product of the first section signal envelope and the second section signal envelope. For such system model, average level crossing rate (LCR) for the case when radio relay system of the first section operates over Nakagami-m fading environment and second section operates over k-μ fading environment is obtained. Wireless relay system with two sections in the presence of non-linear α-μ fading channel is than taken into consideration. Moreover, radio relay system with two sections in the presence of multipath fading and interference is also considered. LCR of the ratio of the product of two k-μ random processes and k-μ random process is calculated. Finally, LCR of the ratio of Rician random process and product of two Rician random processes is obtained. Wireless communication system with two inputs SSC diversity receiver operating over correlated multipath η-μ fading in the presence of interference is than considered. Joint probability density function and joint distribution cumulative function of the ratios of signal to interference at inputs of SSC receivers are calculated. By using obtained expressions for probability density function (PDF), average bit error probability (ABER) for different coherent and non-coherent modulation schemes is obtained while by using derived cumulative distribution function (CDF), outage probability (OP) is obtained. At the end of doctoral dissertation, macrodiversity system with macrodiversity SSC receiver and two microdiversity SC receivers operating over Gamma shadowed multipath fading channel is proposed. In one case Nakagami-m multipath fading channel is considered while in the second case k-μ multipath fading is considered. System performances of the proposed system are derived and numerical results are graphically presented and discusse

    Određivanje preostalog životnog veka i strategije zamene malouljnih prekidača na osnovu dinamičke analize rizika: doktorske disertacije

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    The main goal of this dissertation is to estimate the remaining useful life of minimum oil circuit breakers (CB) based on data collected during their regular inspection. Using the proposed approach, CB’s with the highest risk can be identified, whose failure can cause the greatest economic consequences, but also consequences for the stability of the power system. By determining the reliability and risk of minimum oil CB’s, it is possible to see what influence has the place of installation on the aging process. In this way, a correlation is established between the values of voltage drops and other categories such as: feeder type, voltage level, year of production, number of disconnected short-circuit currents. The end result of the CB’s analysis is the possibility of knowing its aging process, classification of the state of all CB’s based on the risk of failure, knowledge of the impact of CB’s replacement on the availability of the power station, without additional investment in new equipment or labor

    α-Q fading model: Statistical analisis of the first order

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    Radiation resistance of flash memory manufactured in deep-submicron technology

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    U radu radijaciona otpornost fleš memorija izrañenih u duboko-submikronskoj tehnologiji, razmatra se aktuelan problem pouzdanosti rada elektronskih memorija u uslovima dejstva jonizujućeg zračenja. Rad je aktuelan pošto visoki stepen minijaturizacije komponenata integrisanih u fleš memorije prouzrokovao izuzetnu osetljivost ovog tipa memorija na efekte jonizujućeg zračenja. Efekti jonizujućeg zračenja mogu biti takvi da dovedu do promene memorisanih podataka ili čak do fizičkog uništenja samih komponenata. Rad je teoretskog, eksperimentalnog i numeričkog karaktera. U uvodnim poglavljima se navode osnovni podacio interakciji zračenja sa materijalom, definiše doza zračenja, ukratko prikazuje metoda Monte - Karlo za simulaciju nuklearnih interakcija, daju podaci o tipovima i konstruktivnim rešenjima ispitivanih fleš memorija. U poglavlju u kome se govori o eksperimentu, ukratko su prikazana polja zračenja Instituta za nuklearne nauke Vinča, gde je eksperimentalni deo rada rañen, i definisane energije i doze primenjivanog zračenja. U poglavlju koje sledi dati su rezultati brojnih autora, meñu kojima je bio i autor teze, o radijacionoj otpornosti MOSFETA sa izolovanim gejtom, na kome se u osnovi, bazira funkcionisanje fleš memorija. Nakon toga je data teorija radijacionih efekata na fleš memorije na kojima se nalaze i originalna tumačenja ovih efekata. Na kraju rada su prikazani i prodiskutovani eksperimentalno i numerički dobijeni efekti zračenja na konkretnim fleš memorijama. Rezultati dobijeni realnim i numeričkim eksperimentom su pokazali dobro slaganje, kako meñusobno, tako i sa teoretski očekivanim rezultatima.Dissertation "Radiation Hardness of Flash Memories Fabricated in Deep Submicron Technology" investigates the relevant problem of electronic memory reliability under exposure to ionizing radiation. The dissertation is up-to-date because the high degree of miniaturization of components integrated into flash memories makes this type of memory very sensitive to ionizing radiation. Ionizing radiation effects can cause changes in the stored content or even physical destruction of memory components. The dissertation is theoretical, experimental, and numerical in character. Introductory chapters provide basic information about the interaction of radiation with materials, state the definition of the absorbed dose, describe concisely the Monte Carlo methods for simulating nuclear interactions, and provide data about the types and construction details of the investigated flash memories. The chapter concerned with the experiment gives a short depiction of radiation fields at the Vinča Institute of Nuclear Sciences, where the experimental part was conducted, and defines the energies and doses of utilized radiation. The next chapter provides results by several authors, including the author of the dissertation, on the radiation hardness of MOSFETs with insulated gates, which form the basis of flash memories. The next part of the dissertation deals with the theory of radiation effects in flash memories, including original explanations of these effects. The final part presents and discusses the effects observed experimentally and numerically in specific flash memories. Results from real and numerical experiments are in good agreement, both with one another and with the theoretically anticipated value

    Quality control by monitoring central tendency of nongaussian random variables

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    Razmatran je dizajn kontrolnih grafika za pracenje centralne tendencije negausovih slucajnih velicina sa simetricnim ili pozitivno asimetricnim raspodelama. U slucaju negausovih simetricnih raspodela, u ovoj disertaciji je predložen modifikovani kontrolni grafik uzoracke sredine. Za odabranu Studentovu, Laplasovu, logisticku i uniformnu raspodelu izracunata je teorijska raspodela standardizovane uzoracke sredine i aproksimirana je Pirsonovom raspodelom II tipa ili Pirsonovom raspodelom VII tipa. Izracunate su širina kontrolnih granica i moc kontrolnog grafika uzoracke sredine, za datu verovatnocu greške prve vrste. Dobijeni rezultati ukazuju da odgovarajuca Pirsonova raspodela može poslužiti kao veoma dobra aproksimacija raspodele standardizovane uzoracke sredine. Za primenu kontrolnog grafika uzoracke sredine u praksi, pore ene su mere koeficijenta spljoštenosti i upotreba predloženog grafika ilustrovana je na podacima. U slucaju pozitivno asimetricnih raspodela, u ovoj disertaciji je predložen jednostrani kontrolni grafik medijane za pracenje centralne tendencije karakteristike kvaliteta. Za odabranu eksponencijalnu, gama i Vejbulovu raspodelu izvedena je teorijska raspodela uzoracke medijane i aproksimirana je Pirsonovom raspodelom I tipa ili Pirsonovom raspodelom VI tipa. Dobijene vrednosti za gornju kontrolnu granicu i moc kontrolnog grafika medijane za teorijsku raspodelu medijane i odgovarajucu Pirsonovu raspodelu su vrlo bliske. Za primenu predloženog kontrolnog grafika medijane, upore ene su mere koeficijenata asimetrije i spljoštenosti i zatim je konstruisan kontrolni grafik medijane za date podatke. Pored statistickog dizajna kontrolnih grafika za pracenje centralne tendencije negausovih slucajnih velicina, razmatran je i njihov optimalni ekonomsko-statisticki dizajn. U ovoj disertaciji je predložena upotreba genetskog algoritma za minimizaciju funkcije ocekivanog gubitka pod ogranicenjima. Odabrane su iste simetricne raspodele kao u slucaju statistickog dizajna kontrolnog grafika uzoracke sredine, odnosno iste pozitivno asimetricne raspodele kao u slucaju statistickog dizajna kontrolnog grafika medijane. Za sve odabrane raspodele karakteristike kvaliteta, odgovarajuca Pirsonova raspodela daje rezultate vrlo bliske rezultatima za teorijsku raspodelu standardizovane uzoracke sredine (uzoracke medijane).Design of control chart for monitoring central tendency of nongaussian random variables with symmetric or positively skewed distributions is considered. In the case of nongaussian symmetric distributions, modified X bar control chart is proposed in this dissertation. For chosen Student, Laplace, logistic and uniform distributions, theoretical distribution of the standardized sample mean is calculated and approximated with Pearson type II or Pearson type VII distributions. Width of control limits and power of X bar control chart are established, for a given probability of type I error. The results imply that the corresponding Pearson distribution represents very good approximation of the distribution of the standardized sample mean. For implementation of X bar control chart in practice, measures of sample kurtosis are compared and the usage of proposed chart is illustrated on given data. In the case of positively skewed distributions, one sided median control chart for monitoring central tendency of quality characteristics is proposed in this dissertation. For chosen exponential, gamma and Weibull distributions, theoretical distribution of sample median is calculated and approximated with Pearson type I or Pearson type VI distributions. Calculated values of upper control limits and power of median control chart for theoretical distribution of sample median and corresponding Pearson distribution are very close. For implementation of median control chart in practice, measures of sample skewness and sample kurtosis are compared and then proposed median chart is constructed for given data. Besides the statistical design of control charts for monitoring central tendency of nongaussian random variables, their optimal economic statistical design is also considered. Use of genetic algorithms for constrained minimization of expected loss function is proposed in this dissertation. Same symmetric distributions as in the case of statistical design of the X bar control chart and positively skewed distributions as in the case of statistical design of median control chart are chosen. For all chosen distributions of quality characteristic, a corresponding Pearson distribution gives results very close to results based on the theoretical distribution of the standardized sample mean (sample median)

    New algorithms for improving the probability of strong barrier coverage using mobile nodes

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    U ovoj tezi se razmatra problem pokrivenosti bežičnim senzorskim mrežama u slučaju stohastičkog razmeštaja čvorova u određenom regionu od interesa. Stohastički razmeštaj čvorova je jedini način instalacije mreže u situacijama kada je pristup terenu otežan ili nemoguć. Tipični primeri ovog načina instalacije nalaze se u oblasti vojnih primena. U vojnim aplikacijama, najčešće je potrebno obezbediti dobru pokrivenost regiona od interesa senzorskim poljem, bez obzira na činjenicu što se senzori ne mogu manuelno smestiti u optimalnim pozicijama gde je pokrivenost maksimalna pri minimalnom broju senzorskih čvorova i pri određenom nivou robusnosti i redundatnosti mreže. Štaviše, ovakav vid instalacije se može realizovati uglavnom samo upotrebom artiljerije ili avijacije te je, u ovim uslovima, pre nego što se pristupi optimizaciji mreže po pitanju potrošnje energije, sigurnosti i pouzdanosti, potrebno odrediti fundamentalne parametre pri kojima se može postići osnovna funkcionalnost mreže, odnosno određeni stepen pokrivenosti područja od interesa i potrebna konektivnost. Područje od interesa može biti region bilo kojeg oblika. U vojnim aplikacijama, to je najčešće geografsko područje površine od 5 do 20 . Ako je cilj očitavanje veličina iz čitavog regiona, govorimo o pokrivenosti regiona. Drugi čest slučaj primene senzorskih mreža u vojnim aplikacijama, odnosi se na obezbeđivanje određene linije između dva regiona po pitanju prelaska neprijateljskih vojnih trupa sa jednog regiona na drugi. U ovom slučaju se govori o pokrivenosti barijere.This thesis treats the problem of the network coverage in randomly deployed wireless sensor networks. Placing the nodes quasi-randomly is often the only way of deploying the network in geographically inaccessible regions. This way of deployment is often present in military applications. In military applications, high quality of the network coverage is usually a primary goal, despite the fact that the nodes cannot be placed manually in the optimal positions where they would all together provide the highest coverage, a certain degree of robustness, and redundancy, by using the minimum number of nodes. Bearing in mind that this kind of installation is usually realized by using artillery or the aircrafts, before approaching the energy, security, and reliability optimization, it is important for the application to meet the basic functionality, i. e., it is important for the values of the basic parameters that provide a certain degree of the network coverage and connectivity for a given area of interest to be assessed. The area of interest can be a region of any shape. In military applications, it is usually the region of size 5-20 . If the aim is for the whole area to be covered, we deal with the area coverage. Another usual example of the appliance of the wireless sensor networks in military applications is related to the detection of intruders while attempting to cross the line between two regions. In this case, we deal with the barrier coverage

    Unapređenje metoda merenja fedinga u RF telemetrijskim sistemima srednje naponskih distributivnih mreža

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    In this paper, the estimation of Nakagami-m short term fading severity parameter and signal envelope average power are considered. Two methods enabling calculation severity parameter of Nakagami-m fading and are average power of signal envelope propagation in Nakagami-m fading channel by using measured values samples of Nakagami-m random process is considered in this work. By using measured values moments of Nakagami-m random process can be calculated. Nakagami-m fading parameters can be evaluated from moments. In this paper is considered the case when fading parameters are calculated from the second moment and the forth moment. Also, the case when Nakagami-m parameters are calculated by using the first, the second and the three moment is studied. In this paper diversity technique is applied for evaluation Nakagami-m fading parameters by using method of moments. Used diversity technique has MRC (maximal ratio combining) receiver with two and three inputs operating over independent and identical multipath fading channel. Moments of MRC receiver output signal enable Nakagami-m fading parameters evaluation. The accuracy of obtained results increases as the number of samples increases, the order of diversity increases and when the number of realizations increases. The second method studied in this paper, for estimating the Nakagami-m fading severity parameter and average power of Nakagami-m fading signal envelope is level crossing method. Level crossing rate is calculated for three values of signal envelope and from these three equations evaluated Nakagami-m parameters. Obtained expressions for level crossing rate are simple and Nakagami-m parameters can be determined. MRC diversity technique is applied for the estimation of Nakagami-m fading severity parameter and Nakagami-m signal envelope average power. The accurately of calculated values for Nakagami-m parameters increases as the number of samples increases, the number of realization increases and MRC diversity order increases. Also the accurately of obtained reports is higher for lower values of Nakagami-m fading severity parameter. *Application diversity technique for estimation of Nakagami-m fading parameters by using the method moments is not considered in open technical literature. *Level crossing rate method for estimation of Nakagami-m fading parameters is not considered in open technical literature
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