Spare Parts Forecasting Based on Reliability

Stochastic models for spare parts forecasting have not been widely researched in scientific literature from the aspect of their reliability. In this chapter, the authors present models which analyze standard reliability parameters of technical systems’ parts/components. By analyzing system reliability and failure rate, we estimate the required number of spare parts in the moment of expected failure or when reliability falls below the predefined level. Two different approaches based on data availability are presented herewith

Average Bit Error Rate at Signal Transmission with OOK Modulation Scheme in Different FSO Channels

In this paper, the Average Bit Error Rate of the signal in the Free Space Optical system modulated with On-Off keying scheme is calculated and analysed. The Average Bit Error Rate is determined in the case of an atmospheric channel modelled with Gamma-Gamma distribution, Log-Normal distribution, K distribution and I-K distribution. The results are presented both analytically and graphically for different lengths of the Free Space Optical link and the strength of the atmospheric turbulence. The quality of the received signal based on the Average Bit Error Rate for weak, moderate and strong atmospheric turbulences, different lengths of the transmission section and different Signal-to-Noise Ratio values was analysed. The operation of the Free Space Optical system in the observed environment was simulated and the transmission quality was analysed based on Bit Error Rate and Q factor

On the macrodiversity reception in the correlated Gamma shadowed Nakagami-m fading

U ovom radu je izložena analiza makrovišestrukog prijama za slučaj uporabe tehnike prostornog raščlanjenja sa selektivnim kombiniranjem (SC – selection combining) u prisustvu korelacijske Gamma sjene. Na mikrorazinama razmatrane su tehnike prostornog raščlanjenja kombiniranja s maksimalnim odnosom (MRC – maximal ratio combining) za ulazne korelirane grane, kako bi se sprječio utjecaj brzog Nakagami-m fedinga. Prvo su izvedeni izrazi u zatvorenom obliku za statističke karakteristike sustava drugog reda: srednji broj osnih presjeka (LCR – level crossing rate) i srednje vrijeme trajanja slabljenja (AFD – average fade duration). Na osnovu ovih izraza, kroz njihove priraštaje analiziran je utjecaj korelacije na makrorazini (korelacije zasjenjenja) na karakteristike sustava. Analiza prezentirana u ovom radu, može biti od značaja u procesu projektiranja makroraščlanjenih sustava.In this paper an analysis of selection combining (SC) macrodiversity reception performed in correlated Gamma shadowing environment will be presented. At each microlevel maximal ratio combining (MRC) with correlated branches is observed, for mitigating effects of Nakagami-m short-time fading. First, novel closed form expressions are derived for second order statistical measures, level crossing rate (LCR) and average fade duration (AFD). Capitalizing on these expressions, the influence of correlation at macrolevel (shadowing correlation) will be analysed through their derivatives. Provided analysis could find application in current macrodiversity system design

Relative measurement error analysis in the process of the Nakagami-m fading parameter estimation

An approach to the relative measurement error analysis in the process of the Nakagami-m fading signal moments estimation will be presented in this paper. Relative error expressions will be also derived for the cases when MRC (Maximal Ratio Combining) diversity technique is performed at the receiver. Capitalizing on them, results will be graphically presented and discussed to show the influence of various parameters, such as diversity order and fading severity on the relative measurement error bounds

Level crossing rate of macrodiversity with three microdiversity SC receivers over gamma shadowed Nakagami-m channel

Macrodiversity system with macrodiversity selection combining (SC) receiver and three microdiversity SC receivers operating over Gamma shadowed Nakagami-m multipath fading environment is considered in this work. Level crossing arte of signals at outputs microdiversity SC receivers are calculated and by using these formulas, closed form expression for average level crossing rate of macrodiversity SC receiver output signal is evaluated. Average fade duration of proposed macrodiversity system can be calculated as ratio of outage probability and level crossing rate. By using obtained results the influence of Nakagami-m multipath fading severity parameter, Gamma shadowing severity parameter and shadowing correlation parameter on average level crossing rate is analyzed and discussed

Vjerojatnost ispada koreliranih SIR prijemnika sa SSC raznolikosti putem kanala s kompozitnim K_G slabljenjem/zasjenjivanjem signala

In this paper, the effects of multipath fading and shadowing over the propagation channel are observed through the performance analysis of switch and stay selection combining (SSC) technique. The short term fading (multipath fading) in conjunction with the long term fading (shadowing) are both modeled by Generalized-K (K_G) distribution. The proposed system is considered as interference-limited system in correlated fading environment. The probability density function (PDF) of signal-to-interference ratio (SIR) at the output of SSC receiver is derived in form of Meijer G functions. According to this new expression, the outage probability is considered and the effects of fading and shadowing parameters and correlation coefficients on the performance gain are analyzed.U radu su razmatrana djelovanja višeputnog slabljenja i zasjenjivanja signala u propagacijskom kanalu pomoću analize SSC prijemnika raznolikosti (prekidački prostorni kombinator raznolikosti). Kompozitni utjecaj brzog (višeputnog) i sporog slabljenja signala (zasjenjivanja) modeliran je poopćenom-K (K_G) razdiobom. Predloženi sustav razmatran je kao sustav s ko-kanalnom interferencijom kao dominantnom smetnjom i koreliranim slabljenjem signala. Funkcija gustoće razdiobe (PDF) odnosa signal/smetnja (SIR) SSC izlaza prijemnika izvedena je u obliku Meijer G funkcija. Na osnovu ovog izraza, razmatra se vjerojatnost ispada te analiziraju učinci parametara i korelacijskih koeficijenata slabljenja i zasjenjivanja signala na unaprijeđenje performansi sustava

LCR OF SC RECEIVER OUTPUT SIGNAL OVER α-κ-µ MULTIPATH FADING CHANNELS

Wireless mobile communication system with selection combining (SC) diversity receiver is analyzed. Received signal envelope experiences α-κ-µ short term fading resulting in system performance degradation. Level crossing rate (LCR) and average fade duration (AFD) of SC receiver output signal envelope is obtained as rapidly converging infinite series expressions. Numerical resulting are presented graphically to show the influence of transmission parameters, such are multipath fading severity, dominant component power and nonlinearity propagation parameter on observed LCR performance of dual SC

A Stochastic Model for Achieving Required Level of Availability Based on the Repair Rate Analysis

The aim of this paper is to set framework for the repair rate in order to achieve required availability of a repairable system with alternating renewal process where the failure rate is Weibull distributed. In order to accomplish this goal, this paper proposes a novel model for a complete stochastic analysis of the repair rate. The resulting equation for probability density function of the repair rate enables precise modelling of the repair rate process for related values of availability and failure rate. The obtained results can be used for dynamic forecasting of system’s characteristics, planning of maintenance activities, inventory and servicing capacities