• Journal of Applied Reliability
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• v.16 no.2
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• pp.110-117
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• 2016

Purpose: Biswas and Sarkar [11] found the availability of a system maintained through several imperfect repairs before a replacement is allowed. However they missed a part of coefficients in the integration. This paper corrects the erratum of Biswas and Sarkar [11] and performs the reliability analysis incorporating the optimal number of imperfect repairs. Methods: To find the singularities and residues of the suitable complex-valued function for the availability, the computer package Matlab is used. Also the performance measures are calculated by defining and assigning costs. Results: The accurate availability functions with respect to the numbers of imperfect repairs and the optimal number of imperfect repairs before a replacement are obtained. Conclusion: The reliability for a system under imperfect repair before a replacement is analyzed using Fourier transform technique.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.87-90
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• 2003

In this paper, A feedforward linear power amplifier is analyzed for imperfect signal cancellation and negative feedback for basestaion of IMT2000 band. the distortion generatied by the error amplifier is reduced using an imperfect signal cancellation for a 1-carrier WCDMA source by 4.3dB at 2.5MHz offset and 6dB at 5MHz offset of IMSR(intermodulation signal power ratio) compared to a perfect signal cancellation system. additionally, An imperfect signal cancellation using negative feedback improved 1.3dB and 8.2dB at 2.5MHz and 5MHz offset of IMSR compared to an imperfect signal cancellation.

• Journal of applied mathematics & informatics
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• v.6 no.2
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• pp.589-598
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• 1999

Classification errors are included in sampling -with -re-placement model where items are sampled from a Bernoulli process. Bayesian imperfect inspection model is considered. In addition con-jugate prior and predctive densities for imperfect inspection model are obtained.

• Management Science and Financial Engineering
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• v.1 no.1
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• pp.1-19
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• 1995

In this paper, we analyze an M / M / 1 queueing system where there are incentive conflicts among customers. Self-interested customers' decisions whether to join the system or not may not necessarily induce a socially optimal congestion level. As a way to alleviate the over-congestion, toll imposition was used in Naor's paper [3]. Instead of using a toll mechanism, we study the usefulness of imperfect information on system state (queue size, for example) as a way to reduce the over-congestion by self-interested customers. The main conclusion of this paper is that by purposefully giving fuzzy or imperfect information on the current queue size we can improve the congestion in the system. This result might look contradictory to rough intuition since perfect information should give better performance than imperfect information. We show how this idea is verified. In deriving this result, we use the concept of Nash equilibrium (pure and mixed strategy) as introduced in game theory. In some real situations, using imperfect information is easier to apply than imposing a toll, and thus the result of this paper has practical implications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.12
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• pp.3196-3204
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• 1996

We analyze the capacity of the imperfect power controlled DS/CDMA system with the Nakagami faded AMPS interferers by means of the analytical approach. Unlike the theoretical aassumption, the power control of the DS/CDMA system is not perfect. Therefore in this analysis we consider various parameters which cause the capacityreduction of the DS/CDMA system, the imperfect power control, the Nakagami fading index, he processing gain, and the number of AMPS interferers. The analytical results are compared with the Prasad's results which are considered only the imperfect power control of the DS/CDMA system. It is shown that the DS/CDMA capacity is decreased according to the increase of the deviation of the imperfect power control, to icrease the number pf the analog interfering users, and to decrease the processing gain.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.5
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• pp.735-740
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• 2008

Recently, the research of PM (Preventive Maintenance) method on the RCM(Reliability-Centered Maintenance) of the system equipment is being actively advanced for a few years. For the most of the current power equipment maintenance, the state of the equipment after maintenance is assumed to be becoming 'as good as new ones' state. However, the state of the power equipment is maintained like the states of the between 'as good as new ones' and 'as bad as old ones' by imperfect maintenance that implies the life decrease of the equipment by frequent breakdown, the error of maintenance process, and so on. So, the Maintenance method considering the real case has to reflect Imperfect maintenance than perfect maintenance. This paper suggests the Preventive Maintenance method by using Quasi - Renewal Theory for the gas turbine equipment as deliberating the imperfect maintenance for the real cases.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.4
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• pp.989-1005
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• 2012

In this paper, throughput of IEEE 802.11 carrier-sense multiple access (CSMA) with collision-avoidance (CA) protocols in non-saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the utilization of IEEE 802.11 analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the choice of the best probability detection while maintaining probability of false alarm is less than 0.5 is a key factor for maximizing utilization of IEEE 802.11.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.2
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• pp.471-482
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• 1996

In this paper, we analyze the effect of imperfect power control on the capacity of the reverse channel in CDMA cellular system with antenna arrays in the base station. For imperfect power control, we assume that the received power at the base station from the users within each cell has log-normal distribution, and we also consider the effect of imperfect power control of co-channel interferences which arise from both its own cell and outer cells. From the result of numerical analysis, we show that the degree of power control gives a great influence on the capacity of CDMA celluar system with antenna arrays, and also that antenna arrays at the base station can improve greatly the system capacity even when the power control is imperfect.

• International Journal of Reliability and Applications
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• v.15 no.1
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• pp.51-64
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• 2014

This paper develops a warranty cost model for complex systems with imperfect repair within a warranty period by addressing a practical case that the first inter-failure interval is longer than any other inter-failure intervals. The product is in its best condition before the first failure if repair is imperfect. After the imperfect repair, other inter-failure intervals which are explained by renewal processes, are stochastically smaller than the first inter-failure interval. Based on this idea, we suggest the failure-interval-failure-criterion model. In this model, we consider two random variables, X and Y where X represents failure intervals and Y represents failure criterion. We also obtain the distribution of the number of failures and conduct the warranty cost analysis. We investigate different types of warranty cost models, reliabilities and other measures for various systems including series-parallel configurations. Several numerical examples are discussed to demonstrate the applicability of the methodologies derived in the paper.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.253-271
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• 2017

In this paper, considering that perfect channel state information (CSI) is hard to achieve in practice, the downlink capacity of distributed antenna systems (DAS) with imperfect CSI and multiple receive antennas is investigated over composite Rayleigh fading channel. According to the performance analysis, using the numerical calculation, the probability density function (PDF) of the effective output SNR is derived. With this PDF, accurate closed-form expressions of ergodic capacity and outage probability of DAS with imperfect CSI are, respectively, obtained, and they include the ones under perfect CSI as special cases. Besides, the outage capacity of DAS in the presence of imperfect CSI is also derived, and a Newton's method based practical iterative algorithm is proposed to find the accurate outage capacity. By utilizing the Gaussian distribution approximation, another approximate closed-form expression of outage capacity is also derived, and it may simplify the calculation of accurate outage capacity. These theoretical expressions can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI. Simulation results verify the effectiveness of the theoretical analysis, and the system capacity can be improved by increasing the receive antennas, and decreasing the estimation error or path loss. Moreover, the system can tolerate the estimation error variance up to about 0.01 with a slight degradation in the capacity.