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Pitanje izloženosti elektromagnetskom polju koje potiče od mobilnih komunikacionih sistema pažnju javnosti privuklo je sa širenjem ovih sistema i sa sve dužim vremenom korišćenja, a posebno sa uvođenjem 5G tehnologije u višim frekvencijskim opsezima, sa naprednim tehnikama prenosa i velikim brojem malih ćelija i korisničkih uređaja. Regulativa u ovoj oblasti definiše bazična ograničenja i referentne granične nivoe, pri čemu se usklađenost sa normama za korisničke uređaje i za bazne stanice proverava na različit način. Na ovaj način se ne može odrediti stvarna izloženost u toku korišćenja mobilnog uređaja niti izvršiti poređenja komponenata izloženosti. U ovoj disertaciji definisana je metoda za određivanje srednje stvarne izloženosti stanovništva koja potiče od korisničkih uređaja i baznih stanica, na način da se u najvećoj meri koriste podaci iz same mobilne mreže. Utvrđeni su osnovni činioci koji utiču na izloženost. Izvršena je analiza uticaja korišćenih servisa odnosno ponašanja korisnika. Uticaj arhitekture mreže razmatran je u dva testna slučaja, dodavanjem malih ćelija na dve lokacije, na otvorenom i u zatvorenom, sa dve antenske konfiguracije. U prvom slučaju je uvođenje malih ćelija u GSM i UMTS tehnologiji smanjilo ukupnu izloženost više od 84%, a u drugom više od 58% u oblasti pokrivanja malih ćelija, dominantno kao posledica smanjenja zračenja korisničkih uređaja preko GSM-a. U drugom slučaju se ukupna izloženost od UMTS-a povećala usled blizine antena male ćelije. Rezultati pokazuju da male ćelije u opštem slučaju smanjuju izloženost usled smanjenja predajne snage korisničkih uređaja, ali i da je potrebno pažljivo planiranje arhitekture jer se u nekim slučajevima izloženost može i povećati. Definisana metoda predstavlja statistički proračun stvarne izloženosti u složenom okruženju i može se primeniti za bilo koji bežični sistem uz odgovarajuće prikupljanje podataka. Predloženi su napredni alati u mreži za precizniji proračun i date su smernice za smanjenje izloženosti, koje bi se uz alate za samo-evaluaciju moglo postaviti kao još jedan cilj samo-optimizacije mreže. Exposure to electromagnetic fields induced by mobile communication systems has gained public attention with the expansion of these systems and longer usage times, and specially with the introduction of 5G technology in higher frequency bands, with advanced transmission techniques and huge number of small cells and user devices. Regulations in the area define basic restrictions and reference levels, whereby the compliance is verified using different procedures for user devices and for base stations. This way the actual exposure during real usage of mobile device cannot be determined, nor can the exposure components be compared. This research defined a method for determining the average actual exposure of population originated from user devices and base stations, using data from the mobile network to the maximum extent. Basic factors that affect exposure are determined. The impact of services used i.e. user behaviour on exposure was analyzed. The impact of mobile network architecture was evaluated through two test cases, adding small cells at two sites, outdoors and indoors, with two antenna configurations. In the first case, the introduction of small cells in GSM and UMTS technologies reduced the total exposure by more than 84%, and in the second case by more than 58%, in the coverage area of small cells, predominantly as the result of decreased radiation of user devices over GSM. However, in the second case the total exposure originated from UMTS increased due to vicinity of small cell antennas. Results indicate that small cells generally reduce exposure due to decrease of user device transmit power, but also point out that careful planning of the architecture is needed as in some cases the exposure might rise. The defined method represents a statistical calculus of actual exposure in complex environment and it may be applied to any wireless system with the appropriate data collection. Usage of advanced network tools is proposed for more precise calculation and guidelines are given for exposure reduction, which could be set as another target for network self-optimization based on self-evaluation.

Tokom prethodnih godina, potreba za podrškom sve većeg broja LBS (Location Based Services) servisa dovela je do intezivnog razvoja tehnika za pozicioniranje mobilnih korisnika (objekata) u radio sistemima. Pri tom, zahtevi koje sistemi za pozicioniranje treba da ispune, prvenstveno po pitanju tačnosti, ali i po pitanju kašnjenja, dostupnosti servisa, kompleksnosti i cene implementacije, postaju sve strožiji... Over the last years, the necessity of providing the support for various Location Based Services (LBS) has led to the intensive development of the techniques for mobile user (objects) positioning in radio systems. At the same time, the requirements that need to be fulfilled by the positioning technique in terms of accuracy, latency, availability, complexity and implementation costs, are getting higher...

Predmet ove disertacije jeste razvoj detaljnih i efikasnih numeričkih i analitičkih modela poluprovodničkih optičkih pojačivača, za primrnu u pristupnim optičkim mrežeme... The object of the dissertation is the development of various detailed and efficient numerical and analytical models of semiconductor optical amplifiers, employed in access optical networks. Starting from the optical properties of active regions based on the bulk semiconductor and the multiple quantum wells, the theoretical model of the two most commonly used amplier types traveling-wave and reective, is developed, such that the ampliers are optimized to be polarization insensitive. The models are based on a system of integro-dierential equations, written with respect to carrier densities, spectral photon densities of the signals and noise, and signals' phases for both propagation directions. First o, a wideband steady-state amplier model is developed, together with the accompanying numerical algorithm, further used for a detailed amplier analysis. It has been shown that the reective amplier exhibits pronounced resonances and antiresonances in the spectrum of the output amplied spontaneous emission noise. The transmission gain of the reective ampliers proves to be higher in comparison to the traveling-wave ones. Results show that spectrally dependent connement factor and refractive index variation signicantly inuence the transmission gain. Relying on a set of appropriately chosen approximations, a new, semi-analytical model is developed, together with the algorithm for its implementation. Semianalytical model provides reliable results within the time that is up to two orders of magnitude shorter in comparison with the wideband steady-state model, which makes it an attractive choice for software solutions intended for modeling of complex optical communication systems. Dynamic analysis starts with the large signal numerical model, implemented using the ½up-wind scheme for equation solving. It has been shown that both amplier types can be successfully used in electro-optic signal (re)modulation. Dynamic characteristics are further studied using a detailed small-signal model with the current modeled as a traveling microwave. Results reveal that reective ampliers exhibit two maxima in −3dB bandwidth dependence on input optical power, which is not the case with their traveling-wave counterparts. Finally, analytical formulae for −3dB bandwidth of both amplier types are developed, for a commonly chosen transparency operating regime, which show excellent qualitative agreement with the results obtained using the numerical model. Based on the obtained results, guidelines are provided for the choice of operating regime, geometrical and structural amplier parameters, for increasing the transmission gain and the modulation bandwidth.

Дисертација се бави унапређењем телекомуникационих система и у њој су предложена решења која се могу искористити у садашњим и будућим телекомуникационим системима. Након кратког увода у основне класе рада појачавача на микроталасним фреквенцијама, представљена су три појачавача снаге. Сва три појачавача су намењена модерним телекомуникационим системима. Ближе речено, сва три појачавача су конципирана и направљена да раде у више фреквенцијских опсега. У дизајнирању појачавача, акценат је био стављен на ефикасност појачавача. Стога су прва два појачавача дизајнирана и реализована да раде у класи АБ. Код првог, реконфигурабилног, појачавача једна од две могуће радне фреквенције бира се помоћу укључења/искључења PIN диоде у улазном колу за прилагођење. Други, подесиви (тјунабилни), појачавач је дизајниран и реализован тако да може континуално да мења фреквенцију рада, између две удаљене фреквенције, адекватном поларизацијом варикап диоде смештене у улазно коло за прилагођење. Трећи појачавач је дизајниран и реализован да ради у класи Ј. У вези с њим је најпре представљена теорија која се до сада није могла наћи у литератури. Та теорија представља допуну постојеће теорије везане за појачаваче у класи Ј. У оквиру новоразвијене теорије предложен је начин дизајнирања појачавача, где се на почетку одређују параметри појачавача за унапред задату ефикасност. Пратећи предложену теорију, дизајниран је и реализован појачавач у класи Ј. Резултати добијени симулацијом и мерени резултати су се одлично поклопили, што је верификовало ваљаност предложене теорије. На крају су дати резултати симулација нелинераности пројектованог појачавача у случају да му се на улаз доведу неки од сигнала који се користе у модерним телекомуникационим системима... This dissertation addresses the improvement of telecommunication systems. The proposed solutions can be implemented in both present and future telecommunication systems. After a brief introduction regarding the classes of amplifiers operating at microwave frequencies, three power amplifiers are presented. All three amplifiers are designed for modern telecommunication systems. More precisely, they are able to operate in several frequency bands. In the process of the amplifier design, the focus was set on the amplifier efficiency. Hence, the first two amplifiers are designed and fabricated to operate in class AB. In the first, reconfigurable amplifier, one of two possible operating frequencies can be chosen by switching on or off a PIN diode in the input matching network. The second, tunable, amplifier is designed and fabricated in such a way that the operating frequency can be continuously changed, between the lower and upper frequency boundaries. This is achieved by controlling the bias of the varicap diode, positioned in the input matching network. The third amplifier is designed and fabricated to operate in class J. Firstly, a novel theory describing the operation and design procedure of a class-J power amplifier is presented as an extension of the existing theory given in the literature. In the process, novel simple formulas are derived which govern the amplifier efficiency. An amplifier in class J is designed and fabricated following the proposed theory. Results obtained by numerical simulations and measurements on fabricated prototypes are in excellent agreement, thus verifying the proposed theory. Finally, simulation results are presented that characterize the amplifier performance when it is excited by some of the wideband signals used in modern telecommunication systems. The obtained results, which give insight in the linearity of the designed amplifier, are comparable with other results published in the literature, thus they additionally validate the applicability of the newly proposed theory...

Rastući zahtevi korisnika za pristupačnim i visokokvalitetnim telekomunikacionim servisima doveli su do intenzivnog razvoja sistema i uređaja za bežične komunikacije. Zbog prostorne rasprostranjenosti naročito se ističu javni mobilni sistemi (GSM - Global System for Mobile Communications, DCS - Digital Communication System, UMTS - Universal Mobile Telecommunication System, LTE - Long-Term Evolution). Sa obzirom da ovi sistemi kao osnov za međusobnu komunikaciju koriste elektromagnetne talase, javlja se potreba za objektivnim sagledavanjem nivoa elektromagnetnog zračenja u životnom okruženju. Da bi se uticaj elektromagntetnog zračenja na ljude kontrolisao, usvojene su norme kojima se ograničava izlaganje, iskazane kroz bazična ograničenja i izvedene referentne granične nivoe. U okviru ove disertacije dat je pregled bazičnih ograničenja i referentnih graničnih nivoa definisanih Pravilnikom o granicama izlaganja nejonizujućim zračenjima, ICNIRP (International Commission on Non-Ionizing Radiation Protection) preporukom, FCC (Federal Communications Commission) preporukom, IEEE (Institute of Electrical and Electronics Engineers) standardom i ARPANSA (Australian Radiation Protection and Nuclear Safety Agency) standardom. Da bi se ispitala usklađenost instalacije bazne stanice sa referentnim graničnim nivoima, sprovode se merenja intenziteta elektromagnetnog polja u okolini baznih stanica, korišćenjem metoda definisanih međunarodnim standardima. Ove metode se razvijaju i nadograđuju u skladu sa razvojem telekomunikacih sistema, kao i poboljšanjima mernih uređaja. Važan segment u razvoju ovih metoda, koji je posebno aktuelan u poslednje vreme, je određivanje merne nesigurnosti rezultata merenja. U ovoj disertaciji, predložena je praktična metoda za procenu merne nesigurnosti rezultata merenja intenziteta električnog polja, za slučajeve širokopojasnog mernog sistema i frekvencijski selektivnog mernog sistema. Ova metoda bazirana je na zakonu propagacije... Increasing user demand for accessible and high quality telecommunication services has led to intensive development of systems and devices for wireless communications. Because of their wide distribution, public mobile systems (GSM - Global System for Mobile Communications, DCS - Digital Communication System, UMTS - Universal Mobile Telecommunication System, LTE - Long-Term Evolution) are the most important. Having in mind that these systems use electromagnetic waves as basis for the communication, there is a need for an objective assessment of the electromagnetic radiation level in the living environment. To control the influence of electromagnetic radiation on people, norms that limit human exposure were adopted and stated as basic restrictions and reference levels. In this dissertation, an overview of basic restrictions and reference levels defined with Regulation on the limits of exposure to non-ionizing radiation, ICNIRP (International Commission on Non-Ionizing Radiation Protection) guidelines, FCC (Federal Communications Commission) recommendation, IEEE (Institute of Electrical and Electronics Engineers) standard and ARPANSA (Australian Radiation Protection and Nuclear Safety Agency) standard, is given. In order to evaluate compliance of base station with reference levels, measurement of electromagnetic field in the vicinity of base station should be conducted, using methods defined by the international standards. These methods are developed and upgraded in line with the development of telecommunication systems as well as with the improvements to the measuring devices. An important part in the development of these methods, which is especially important in recent time, is evaluation of measurement result uncertainty. In the dissertation, practical procedure for evaluation of uncertainty of electric field strength measurements, for the cases of broadband and frequency selective measurement system, is developed. This procedure is based on the low of propagation of uncertainty, and...

Razvoj modernog društva se u velikoj meri zasniva na kvalitetnim telekomunikacionim mrežama. U tom smislu, od velike je važnosti da telekomunikacione mreže imaju visoku raspoloživost čime se postiže i visoka raspoloživost servisa koje koriste krajnji korisnici. Danas se okosnice mreža najčešće realizuju sa velikim brojem čvorova (više desetina) zbog čega je problem direktno izračunati raspoloživost takve mreže, jer vremena izvršavanja algoritama za tačno računanje raspoloživosti eksponencijalno rastu sa porastom broja čvorova i linkova. Zbog toga je od velike praktične važnosti korišćenje aproksimativnih algoritama koji tokom procesa projektovanja takvih mreža omogućavaju definisanje početnih uslova za dizajniranje topologije mreže. Cilj ove doktorske disertacije je uvođenje novog metoda za aproksimativno računanje maksimalne all-terminal raspoloživosti složenih telekomunikacionih mreža. U cilju dobijanja vrednosti maksimalne all-terminal raspoloživosti, razvijena je metoda sinteze mreže. Kod metode sinteze mreže početna topologija je lanac. Kod određivanja maksimalne raspoloživosti mreže, u prvom koraku sinteze se formira prsten da bi se dalje dodavao po jedan link u mrežnoj topologiji tako da se svaki put dobije maksimalni priraštaj all-terminal raspoloživosti mreže. Dodavanjem jednog po jednog linka, gde svi linkovi imaju istu raspoloživost, vrši se sinteza mreže koja u svakom koraku ima maksimalnu raspoloživost za dati broj čvorova, linkova i datu raspoloživost linkova. Analizom dobijenih rezultata za maksimalnu all-terminal raspoloživost mreže definisane su funkcije aproksimacije maksimalne all-terminal raspoloživosti mreže za zadati broj čvorova, linkova i raspoloživost linkova. Na osnovu dobijenih aproksimativnih izraza može se izračunati granica raspoloživosti mreže u zavisnosti od topologije za zadate parametre. S druge strane, korišćenjem funkcija aproksimacija može se definisati donja granica za broj linkova da bi se mogla dobiti željena... The development of modern society is largely based on high-quality telecommunications networks. In this regard, it is of great importance to telecommunication networks have high availability which achieves high availability of services used by end users. Today, the backbone networks are usually implemented with a large number of nodes (several dozen) why there is a problem to directly calculate the availability of such networks, since the execution time of algorithms for exact calculation of availability increase exponentially with the number of nodes and links. Therefore, it is of great practical importance of the use of approximation algorithms during the design of such networks to help in the definition of initial conditions for the design of the network topology. The aim of this PhD thesis is the introduction of a new method for approximate calculation of the maximum availability of complex telecommunications networks. In order to obtain the maximum values of the availability, it was developed a method of network synthesis. Starting network topology for this new method is a chain. In determining the maximum network availability, the first step of the synthesis is to form the ring and then continue adding one-by-one links in the network topology so that it delivers a maximum increase of all-terminal availability. By adding one link at a time, where all links have the same availability, perform the synthesis of the network in which each step has a maximum availability for a given number of nodes, links, and the availability of links. The approximation functions of the maximum network availability for a given number of nodes, links and the availability of links are obtained by the analysis of the results of network synthesis method for the networks with maximum availability. Limits of the availability of the network (which depends of the network topology) can be calculated based on the approximation functions. In addition, based on the approximation functions can be defined the boundaries in which they need to move a number of links to be able to get the desired availability of appropriate choice of the network topology. It...

Predmet istraživanja ove doktorske disertacije je projektovanje mikrotalasnih filtara propusnika i nepropusnika opsega učestanosti realizovanih u talasovodnoj tehnici sa štampanim diskontinuitetima. Predložen je novi metod projektovanja talasovodnih filtara, kao naučni doprinos disertacije. Ova tematika svakako pripada aktuelnoj i značajnoj oblasti mikrotalasne tehnike, o čemu svedoče brojne publikacije. Poslednjih godina, ova problematika dobija novi zamah usled sve većih zahteva za minijaturizacijom mikrotalasnih sklopova koji predstavljaju sastavni deo komunikacionih sistema na mikrotalasnim učestanostima. Mikrotalasni filtri u talasovodnoj tehnici imaju značajnu primenu u sistemima gde su potrebne velike snage i mali gubici. Cilj istraživanja je realizacija mikrotalasnih filtara sa više propusnih ili nepropusnih opsega u talasovodnoj tehnici korišćenjem štampanih diskontinuiteta koji imaju bolje karakteristike u odnosu na karakteristike odgovarajućih mikrotalasnih filtara objavljenih u dostupnoj otvorenoj literaturi. Kriterijumi za poređenje karakteristika filtara uključuju veličinu zauzeća strukture, relativnu širinu propusnog odnosno nepropusnog opsega, selektivnost amplitudske karakteristike i uneto slabljenje. Takođe, u postupku projektovanja filtara sa više propusnih ili nepropusnih opsega u talasovodnoj tehnici uvodi se novi način realizacije mikrotalasnih rezonatora, u poređenju sa do sada predloženim realizacijama u dostupnoj literaturi. Novi metod projektovanja filtara u talasovodnoj tehnici polazi od razvoja novih rezonatora u vidu štampanih pregrada koje se postavljaju u unutrašnjost pravougaonog talasovoda. Pri tome, ideja je da se ostvari jedna ili više rezonantnih učestanosti primenom jedne rezonantne pregrade, što se postiže optimalnim rasporedom više rezonatora na njoj. Poželjno je da ovi rezonatori ne budu međusobno spregnuti, jer to omogućava da se modifikacijom parametara svakog pojedinačnog rezonatora nezavisno podešava svaki od propusnih/nepropusnih opsega. Time se stiču uslovi za realizaciju filtara sa više propusnih/nepropusnih opsega primenom ovih rezonatora. U zavisnosti od... The scope of the research presented in this doctoral dissertation is design of microwave bandpass and bandstop waveguide filters using printed-circuit discontinuities. A new method for waveguide filter design is proposed, as a scientific contribution of the dissertation. This topic certainly belongs to the popular and significant field of microwave engineering, as confirmed by numerous publications. In recent years, this topic has gained attention due to more demanding requirements regarding miniaturization of microwave devices, which represent integral parts of communication systems operating at microwave frequencies. Microwave waveguide filters have significant application in the systems where high power and small losses are needed. The object of the research is implementation of microwave waveguide filters, with multiple pass bands or rejection bands, using printed-circuit discontinuities, which have better characteristics compared to the characteristics of corresponding microwave filters already published in the available literature. Comparison criteria regarding filter characteristics include the size of the structure, fractional bandwidth of the pass band or rejection band, selectivity of the amplitude response and insertion loss. Also, as part of the multi-band waveguide filters design procedure, a novel method for implementing microwave resonators is introduced, compared to the previously proposed implementations found in the available literature. Novel method for waveguide filter design starts from the development of novel resonators in a form of printed-circuit inserts, placed inside the rectangular waveguide. Thereby, the idea is to have one or more resonant frequencies by employing only one resonant insert, which can be accomplished by means of optimal distribution of the resonators on the insert. Preferably, these resonators should not be mutually coupled, because in that case it is possible to independently tune each of the pass bands/rejection bands by modifying the parameters of each individual resonator. Thus, conditions for implementing multi-band filters using these resonators are met. Depending on the...

Bežične mesh mreže – WMN (Wireless Mesh Network) predstavljaju noviji trend u bežičnim komunikacijama kojim se obezbeđuje veća fleksibilnost, pouzdanost i bolje performanse nego standardnim bežičnim lokalnim mrežama. Imajući u vidu sve veće potrebe korisnika za brzim i efikasnim prenosom podataka, kao i prenosom multimedijalnih (govornih i video) sadržaja, povećanje protoka, ostvareno uvođenjem višekanalnih višeinterfejsnih – MCMI (Multi Channel Multi Interface) WMN, i vođenje računa o kvalitetu servisa, QoS (Quality of Service), predstavljaju glavne izazove u projektovanju WMN. Kako bi se ostvarile što bolje mrežne performanse neophodno je definisati protokole i metrike rutiranja kojima se određuje optimalna putanja između izvorišnog i odredišnog čvora. S obzirom da WMN karakteriše velika dinamika signala, posebno u kompleksnim okruženjima (sa stanovišta radio pokrivanja), kakva su zatvoreni objekti, u okviru doktorske disertacije definisane su metrike rutiranja koje mogu da isprate brze promene uslova propagacije koje se dešavaju na svakom pojedinačnom linku u mreži. Predložene su tri nove metrike: powerETX (Expected Transmission Count), powerWCETT (Weighted Cumulative Expected Transmission Time) i powerMIC (Metric of Interference and Channel-switching), koje u cenu linka, osim parametara definisanih u okviru postojećih metrika ETX, WCETT i MIC, respektivno, uključuju i parametar koji zavisi od nivoa snage signala na prijemu. Nove metrike obezbeđuju veće protoke korisničkih podataka i manje kašnjenje s kraja na kraj u poređenju sa postojećim, a njihova praktična realizacija moguća je bez dodatnih hardverskih ulaganja, i uz minimalne softverske izmene. Imajući u vidu da postojeći algoritmi dodele kanala ne uključuju QoS podršku u MCMI-WMN, i da se prenos multimedijalnih sadržaja obavlja uz neprihvatljiva kašnjenja, predložen je novi protokol za sloj linka, QoS-HMCP (QoS-Hybrid Multi Channel Protocol), koji uvodi podršku QoS kroz EDCA (Enhanced Distributed Channel Access) mehanizam pristupa, i koristi dobre karakteristike hibridnog algoritma dodele kanala definisane HMCP protokolom za sloj linka. Predložene su četiri varijante QoS-HMCP protokola koji u obzir uzimaju različite kriterijume za promenu kanala i... Wireless mesh networks (WMNs) are a new trend in wireless communications which provide greater flexibility, reliability and better network performances than standard wireless local area networks. Having in mind the growing demand for the fast and efficient data transfer as well as multimedia transmission (voice and video), the major challenges in designing WMN are increasing throughput (by introducing multichannel multi-interfaces (MCMI) approach into the WMN), and taking into account the quality of service (QoS). To achieve the best network performances, it is necessary to define protocols and routing metrics that determine the optimal path between the source and the destination node. Since the WMN is characterized by high dynamics of the signal, especially in complex environments (from the radio coverage point of view), such as those found indoors, routing metrics that can track fast changes in propagation conditions at each link in the network, are proposed in this dissertation. The link costs of the three new metrics, powerETX (Expected Transmission Count), powerWCETT (Weighted Cumulative Expected Transmission Time) and powerMIC (Metric of Interference and Channel-switching), besides the parameters defined in the existing ETX, WCETT and MIC metrics, respectively, include the parameter that depends on the received signal level. In comparison with existing metrics, these new metrics not only provide a greater data throughput and less average end-to-end delay, but also can be realized without any additional hardware and with minimal software changes. Keeping in mind that existing channel assignment (CA) algorithms do not include QoS support in MCMI-WMNs and that the multimedia transmission can suffer from unacceptable delays, a new protocol for link layer QoS-HMCP (QoS Hybrid Multi-Channel Protocol) which introduces QoS support through EDCA (Enhanced Distributed Channel Access) mechanism, and uses the good characteristics of the hybrid CA algorithm defined by HMCP protocol for link layer, is proposed in this dissertation. Four versions of the QoS-HMCP protocols, which take into account different criteria for channel switching and procedure for medium competition, are proposed. These versions are compared with basic HMCP protocol with regards to the throughput of user data and...