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

Uncoded space-time labeling diversity with three transmit antennas: symbol mapping designs and error performance analysis.

Doctoral Degrees. University of KwaZulu-Natal, Durban.Abstract available in PDF.Publications on page iii

Povećanje informacionog kapaciteta i pouzdanosti u bežičnim optičkim komunikacijama primenom algoritama adaptivnog prenosa

This dissertation considers adaptive transmission algorithms and their influence towards increasing information capacity and system reliability. Theses algorithms are applied to optical wireless communications, as well as to radio-frequency system with diversity receiver. System of adaptive transmission is described in detail, and different algorithms of adaptation are applied: ORA, OPRA, CIFR, and TIFR. Derived probability density function combines influence of atmospheric turbulence, atmospheric losses and positioning errors that consist of laser pointing precision and jitter. FSO system without adaptation is also considered. For this case, bit-error rate and outage probability are determined when signal is exposed to different strengths of atmospheric turbulence, when there is atmospheric attenuation and positioning errors due to both main causes, when IM/DD and heterodyne detection are used. Power penalty is also determined for such system. Bit-error rate is also determined for the case when SIM is used in combination with binary modulation and quadrature amplitude modulation. Capacity analysis is given for the use of ORA, OPRA, CIFR and TIFR adaptive transmission algorithms, and for IM/DD and heterodyne detection cases. Algorithms used for transmitter power adaptation are additionally analyzed and improved with an aim to obtain realistic and functional systems. Based on analytical expression, simulation model is developed for adaptive transmission systems, which is used to validate numerical results. Approximate expressions are also given for used adaptive algorithms. Finally, adaptive transmission is considered also for a class of wireless RF systems. Fading model used is based on α-κ-μ distribution. Outage probability and amount of fading are given as representative performance measures. Besides adaptive transmission algorithms used in FSO systems, analysis of space diversity reception is also presented for the general case of using L antennas

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

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