The N∗ Fisher-Snedecor F Cascaded Fading Model

The Fisher-Snedecor F distribution was recently proposed as an accurate and tractable composite fading model in the context of device-to-device communications. The present work derives the product of the Fisher-Snedecor F composite fading model, which is useful in characterizing fading effects in numerous realistic communication scenarios. To this end, novel analytic expressions are first derived for the probability density function, the cumulative distribution function and the moment of the product of N statistically independent, but not necessarily identically distributed, Fisher-Snedecor F random variables. Capitalizing on these expressions, we derive tractable closed-form expressions for channel quality estimation of the proposed model as well as the corresponding outage probability and average bit error probability for binary modulations. The offered results are corroborated by extensive Monte-Carlo simulation results, which verify the validity of the derived expressions. It is shown that the number of cascaded channels affects considerably the corresponding performance, as a variation of over an order of magnitude is observed across all signal-to-noise ratio regimes

Second Order Statistics of -Fisher-Snedecor Distribution and Their Application to Burst Error Rate Analysis of Multi-Hop Communications

An advantage of using the composite fading models (CFMs) is their ability to concurrently address the impact of multi-path and shadowing phenomena on the system performance in wireless communications. A Fisher-Snedecor (FS) F CFM has been recently proposed as an experimentally verified and tractable fading model that can be efficiently applied for 5G and beyond 5G wireless communication systems. This paper provides second-order (s-order) performance analysis of the product of N independent but not identically distributed (i.n.i.d) FS F random variables (RVs). In particular, accurate and closedform approximations for level crossing rate (LCR) and average fade duration (AFD) of the product of N i.n.i.d FS F(N-FS F) RVs are successfully derived by exploiting a general property of a Laplace approximation method for evaluation of the N -folded integral-form LCR expression. Based on the obtained s-order statistical results, the burst error rate and maximum symbol rate of the N -FS F distribution are addressed and thoroughly examined. The numerical results of the considered performance measures are discussed in relation to the N-FS F multi-path and shadowing severity parameters. Moreover, the impact of the number of hops (N) of the N -FS F CFM on the s-order metrics, the burst error rate and maximum symbol rate are numerically evaluated and investigated. The derived s-order statistical results can be used to address the cooperative relay-assisted (RA) communications for vehicular systems. Monte-Carlo (M - C) simulations for the addressed statistical measures are developed in order to confirm the provided theoretical results.This work was supported in part by UC3M and the European Union's Horizon 2020 Programme under the Marie Sklodowska-Curie Grant through the CONEX-Plus Project under Agreement 801538; in part by the IRENE-EARTH Project under Grant PID2020-115323RB-C33/AEI/10.13039/501100011033; in part by ERDF and the Spanish Government Projects under Grant PID2019-106808RA-I00 AEI/FEDER, UE; in part by CDTI Cervera Project INTEGRA under Grant CER-20211031; in part by the Secretaria d'Universitats i Recerca de la Generalitat de Catalunya under Project 2017-SGR-00376 and Project Fem IoT under Grant 001-P-001662; in part by the European Commission Project CPSoSaware; and in part by the Cost Actions under Grant CA19111, Grant CA20120, and Grant CA16220.Publicad

Wireless networks physical layer security : modeling and performance characterization

Intrigued by the rapid growth and expand of wireless devices, data security is increasingly playing a significant role in our daily transactions and interactions with different entities. Possible examples, including e-healthcare information and online shopping, are becoming vulnerable due to the intrinsic nature of wireless transmission medium and the widespread open access of wireless links. Traditionally, the communication security is mainly regarded as the tasks at the upper layers of layered protocol stack, security techniques, including personal access control, password protection, and end-to-end encryption, have been widely studied in the open literature. More recently, plenty of research interests have been drawn to the physical layer forms of secrecy. As a new but appealing paradigm at physical layer, physical layer security is based on two pioneering works: (i) Shannon’s information-theoretic formulation and (ii) Wyner’s wiretap formulation. On account of the fundamental of physical layer security and the different nature of various wireless network, this dissertation is supposed to further fill the lacking of the existing research outcomes. To be specific, the contributions of this dissertation can be summarized as three-fold:(i) exploration of secrecy metrics to more general fading channels; (ii) characterization a new fading channel model and its reliability and security analysis in digital communication systems; and (iii) investigation of physical layer security over the random multiple-input multiple-output (MIMO) α −μ fading channels. Taking into account the classic Alice-Bob-Eve wiretap model, the first contribution can be divided into four aspects: (i) we have investigated the secrecy performance over single-input single-output (SISO) α −μ fading channels. The probability of non-zero (PNZ) secrecy capacity and the lower bound of secrecy outage probability (SOP) are derived for the special case when the main channel and wiretap channel undergo the same non-linearity fading parameter, i.e., α. Later on, for the purpose of filling the gap of lacking closed-form expression of SOP in the open literature and extending the obtained results in chapter 2 to the single-input multiple-output (SIMO) α − μ wiretap fading channels, utilizing the fact that the received signal-tonoise ratios (SNRs) at the legitimate receiver and eavesdropper can be approximated as new α −μ distributed random variables (RVs), the SOP metric is therefore derived, and given in terms of the bivariate Fox’s H-function; (ii) the secrecy performance over the Fisher-Snedecor F wiretap fading channels is initially considered. The SOP, PNZ, and ASC are finalized in terms of Meijer’s G-function; (iii) in order to generalize the obtained results over α −μ and Fisher-Snedecor F wiretap fading channels, a more flexible and general fading channel, i.e., Fox’s H-function fading model, are taken into consideration. Both the exact and asymptotic analysis of SOP, PNZ, and average secrecy capacity (ASC), are developed with closed-form expressions; and (iv) finally, motivated by the fact that the mixture gamma (MG) distribution is an appealing tool, which can be used to model the received instantaneous SNRs over wireless fading channels, the secrecy metrics over wiretap fading channels are derived based on the MG approach. Due to the limited transmission power and communication range, cooperative relays or multi-hop wireless networks are usually regarded as two promising means to address these concerns. Inspired by the obtained results in Chapters 2 and 3, the second main contribution is to propose a novel but simple fading channel model, namely, the cascaded α −μ. This new distribution is advantageous since it encompasses the existing cascaded Rayleigh, cascaded Nakagami-m, and cascaded Weibull with ease. Based on this, both the reliability and secrecy performance of a digital system over cascaded α −μ fading channels are further evaluated. Closed-form expressions of reliability metrics (including amount of fading (AF), outage probability, average channel capacity, and average symbol error probability (ABEP).) and secrecy metrics (including SOP, PNZ, and ASC) are respectively provided. Besides, their asymptotic behaviors are also performed and compared with the exact results. Considering the impacts of users’ densities, spatial distribution, and the path-loss exponent on secrecy issue, the third aspect of this thesis is detailed in Chapter 8 as the secrecy investigation of stochastic MIMO system over α −μ wiretap fading channels. Both the stochastic geometry and conventional space-time transmission (STT) scheme are used in the system configuration. The secrecy issue is mathematically evaluated by three metrics, i.e., connection outage, the probability of non-zero secrecy capacity and the ergodic secrecy capacity. Those three metrics are later on derived regarding two ordering scheme, and further compared with Monte-Carlo simulations

Energy Detection Based Spectrum Sensing Over k-μ and k-μ Extreme Fading Channels

Energy detection (ED) is a simple and popular method of spectrum sensing in cognitive radio systems. It is also widely known that the performance of sensing techniques is largely affected when users experience fading effects. This paper investigates the performance of an energy detector over generalized κ-μ and κ- μ extreme fading channels, which have been shown to provide remarkably accurate fading characterization. Novel analytic expressions are firstly derived for the corresponding average probability of detection for the case of single-user detection. These results are subsequently extended to the case of square-law selection (SLS) diversity and for collaborative detection scenarios. As expected, the performance of the detector is highly dependent upon the severity of fading since even small variations of the fading conditions affect significantly the value of the average probability of detection. Furthermore, the performance of the detector improves substantially as the number of branches or collaborating users increase in both severe and moderate fading conditions, whereas it is shown that the κ- μ extreme model is capable of accounting for fading variations even at low signal-to-noise values. The offered results are particularly useful in assessing the effect of fading in ED-based cognitive radio communication systems; therefore, they can be used in quantifying the associated tradeoffs between sensing performance and energy efficiency in cognitive radio networks.

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

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

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