Primena tehnika kombinovanja kod bežičnih telekomunikacionih sistema u prisustvu smetnje

Research results shown in this thesis consider selection combining space diversity systems. Weibull fading model is used to describe a desired signal and interference in a wireless telecommunication channel. In an interference-limited environment, like a cellular communication system, the level of cochannel interference is sufficiently high compared to noise so that it can be neglected. In that case, a selection combining receiver can employ different combining algorithms, that can be used to forward the chosen signal to the output of the receiver. After the theoretical basis, which is given at the beginning of the thesis, a detailed analysis of space diversity systems that use different selection algorithms is presented. The system performance is analyzed using one of the proposed criteria: maximal signal-tointerference ratio, maximal desired signal, maximal total signal, and minimal interference. For a system employing each of these algorithms, a detailed analysis of statistical characteristics of first and second order is given using the expressions derived in this thesis. The first focus is on deriving the expressions for probability density function of instantaneous signal-to-interference ratio at the output of selection combining receiver employing each of the previously mentioned algorithms. Based on the derived expressions, numerical results are presented for statistical characteristics of the first order, namely outage probability, average bit error probability, average signal-to-interference ratio and channel capacity. Additionally, for the statistical characteristics of the second order, which are level crossing rate and average fade duration, expressions for joint probability density function of instantaneous signal-tointerference ratio and its time derivative are derived. A new mathematical approach for obtaining analytical expression for probability density function of instantaneous signal-to-interference ratio at the output of selection combining receiver with two branches that uses maximal signal-to-noise ratio algorithm is presented. Considering that mobile terminals are relatively small, the distance between receiving antennas is not large enough to be neglected. Therefore, the correlation between the branches is included in the analysis of statistical characteristics of the first order. Due to easier mathematical manipulation, statistical characteristics of second order do not consider correlation between receiving branches. Numerical results obtained using the expressions derived in this thesis for different decision algorithms are presented graphically. The illustrations show the influence of fading severity, correlation between the desired signals, as well as the interfering ones and balanced and unbalanced inputs for each of mentioned algorithms on outage probability, average bit error probability, average signal-to-interference ratio and channel capacity. The results for second order statistics for dual branch selection diversity system operating in Weibull fading environment were compared for a system that employs two selection algorithms, algorithm based on maximal signal-to-interference ratio, as most frequently used one, and algorithm based on minimal interference, the algorithm that was not exploited in literature. The main contribution of this thesis lies in obtained results for statistical characteristics and performance of the system that uses four proposed algorithms at receiver side. The presented analysis of selection diversity system for given channel conditions can be applied to achieve optimized solutions of wireless system design

Performanse bežičnog telekomunikacionog sistema u prisustvu n-m fedinga

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

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

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

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

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

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

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

Actual maintenance management tendencies: Risk based maintenance

U radu su prikazani savremeni koncepti u upravljanju održavanjem tehničkih uređaja, opreme, instalacije i fabričkih postrojenja. Izložene su ukratko karakteristike pojedinih metoda i strategija održavanja. Poseban akcenat stavljen je na upravljanje održavanjem zasnovano na riziku i analizirana je mogućnost uvođenja ovog koncepta u druge industrijske segmente osim u procesnu, hemijsku, energetsku industriju što je i primarna oblast primene RBIM koncepta.Actual management concepts for maintenance technical devices, parts installation and facilities are presented in this paper. Characteristics of certain methods and strategies are presents. Focus of the paper is on maintenance management based on risk. Also, application of maintenance management based on risk in other industrial sector (beside petroleum chemical, power plant industries as primary RBIM application domain) are discussed

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

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

Actual maintenance management tendencies: Risk based maintenance

U radu su prikazani savremeni koncepti u upravljanju održavanjem tehničkih uređaja, opreme, instalacije i fabričkih postrojenja. Izložene su ukratko karakteristike pojedinih metoda i strategija održavanja. Poseban akcenat stavljen je na upravljanje održavanjem zasnovano na riziku i analizirana je mogućnost uvođenja ovog koncepta u druge industrijske segmente osim u procesnu, hemijsku, energetsku industriju što je i primarna oblast primene RBIM koncepta.Actual management concepts for maintenance technical devices, parts installation and facilities are presented in this paper. Characteristics of certain methods and strategies are presents. Focus of the paper is on maintenance management based on risk. Also, application of maintenance management based on risk in other industrial sector (beside petroleum chemical, power plant industries as primary RBIM application domain) are discussed

Application of diversity techniques for solving the problems of the effects impurities in optical fibers on the performance of optical systems

We analyzed the methods for reducing the impact of noise and interference, the performance of digital optical IM-DD system. Performances of digital optical telecommunication systems, as well as their improvement, were analyzed using standard criteria for evaluation: outage probability, average probability, channel capacity, and average fading duration. These performance measures are determined on the basis of statistical characteristics of the first and second rows of signal reception and are part of the technical documentation accompanying each of the realized digital optical communication system. Therefore, the closed form of expressions, derived in this dissertation, which can be used to calculate the statistical characteristics of signal reception, represent a significant contribution, in terms of design of digital optical transmission systems. Our analysis is placed on theoretical consideration on so far untreated cases, and therefore the theoretical basis of physical phenomena that affect the transmission through the digital optical systems, well known from the literature, are not further elaborated. We included a procedure for determining the expression for the multidimensional joint probability density distribution with correlated and uncorrelated random variables. The derived expressions have a wide range of applicability and are an excellent basis for further performance analysis of optical digital transmission systems, in terms of correlated channels, as well as the characteristics of the connection by using multiple-input receiver. Their practical use is demonstrated especially in the section that deals λSK optical systems, as well as the part of that processes - the relay optical systems. Improving the transmission reliability and reducing the impact of noise and interference on the performance of digital optical telecommunication systems, with a reduction in power transmission and increasing the distance between the transmitter and receiver, is analyzed through the applying of techniques using spatial diversity reception. The dissertation discussed the various techniques of spatial combining receiving signals from the receiving branches of optical systems, in terms of reducing impact noise and interference. Ratios were formed and interference signals at the entrance combiner branches and under the terms of the previous chapter are determined by the joint probability density of these relationships for all incoming branches and the corresponding joint cumulative probability. Using this statistical feature of the incoming signal and interference are determined and statistical characteristics of signal-to-interference at the output of given combiner, which represents the next significant contribution to the dissertation. The contribution of these derived expressions can be seen from the aspect of using the results obtained for the case of the proposed statistical modeling of the channel model when considering the reduction of the impact of various types of noise and interference, and examination performance enhancements of digital optical telecommunication systems using diversity reception techniques. Specifically, by assigning appropriate values of parameters in the corresponding expressions, which describe the statistical characteristics of the first order of receipt, an analysis of the value of standard measures of performance of optical telecommunication systems, as well as improve their use of spatial diversity techniques, for cases when the communication channel is exposed to various types of interference and noises. Using the derived expressions can be shown to improve all the standard measure of performance of optical telecommunication systems. Also, when transferred unchanged forces the useful signal and interference, and at the same range of connections, get better system performance (lower values of the probability of cancellation, less the value of average bet error probability, lower average fading duration...). Based on these facts can be concluded that the required the outage probability values (ABEP) for the reception, when we apply the described techniques of receipt, in the same range of connections and the same noise power, can achieve the necessary reduction of the useful signal power in transmission, that is, at the same useful signal power, the same level of interference in the channel, the required the outage probability (ASEP) at the reception, when we apply the described techniques of receipt, can be achieved at larger distances from the transmitting terminal

Diagnostics of maintenance technical indicators of the thermal power plants

Pouzdanost je osnovni tehnički pokazatelj koji utiče na konkurentnost termoelektrana u uslovima deregulisanog tržišta električnom energijom. Da bi se moglo upravljati ovim parametrom tokom eksploatacije, neophodno je odrediti fizičke uzroke promene pouzdanosti tokom radnog veka. U radu je analizirana eksploataciona istorija kondenzacione termoelektrane koja sagoreva mrki ugalj u prahu, na način pogodan za proračun pouzdanosti postrojenja, definisana je pouzdanost tokom eksploatacije i razmotreni su fizički uzroci njene promene tokom radnog veka.Reliability is the basic technical indicator which affects on competitiveness of thermal power plants in the terms of deregulated electricity market. Physical causes of reliability changes are important for evaluation because of it's influence on reliable management during service life. Service history of condensation type thermal power plant with coal powder combustion was analyzed in this article in the manner convenient for reliability calculations. These calculations were made in the first approximation with taking into account the physical causes of reliability exchanges