• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.6
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• pp.81-91
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• 2008

In this study, data collection delay time generated in bus information system is analysed and improvement on system reliability by minimizing the delay time is suggested. To minimize the data collection delay time (call setup time), factors on data collection phase are analyzed. Each connecting time that it occurs from wireless communication during data collection phase, is selected as a main effective variable and a model for selecting an optimum communication point to minimize the effect of data delay time by each connecting time is suggested. In this model, minimization of the point between the time carrying out wireless communication and vehicle moving time, is calculated and the difference between the bus arrival time and information delivered time to the passenger is reduced. The test results for the proposed model in BIS using a CDMA (Code Division Multiple Access) communication show that delay time in real system operation has been improved. The minimum data collection delay time based on optimal communication position leads to the better reliability for Bus Information System. This study can be applied to the selection of optimal communication position and detection position instead of empirical methods.

• Journal of the Korean Operations Research and Management Science Society
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• v.18 no.2
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• pp.175-182
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• 1993

The probabilistic order level inventory model is developed when a supplier allows some credit period T for settling the accounts for purchase quantity. The credit period T is known constant. Mathematical models are derived for both the cases i) T'.leq. T and ii) T'>T. Expressions are derived for average expected total cost of the system, the optimum cycle time and for obtaining optimum order level S = S$_{0}$ in each case. The exmaples are given to illustrate the model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.261-270
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• 2007

The Delay Threshold-based Priority Queueing (DTPQ) scheme has been shown useful for scheduling both real-time (RT) and non-real-time (NRT) service traffic in mobile broadband wireless access (MBWA) systems. The overall system capacity can be maximized subject to their QoS requirement by the DTPQ scheme, which takes the urgency of the RT service into account only when their head-of-line (HOL) packet delays exceed a given delay threshold. In practice, the optimum delay threshold must be configured under the varying service scenarios and a corresponding traffic load, e.g., the number of RT and NRTusers in the system. In this paper, we propose an adaptive version of DTPQ scheme, which updates the delay threshold by taking the urgency and channel conditions of RT service users into account. By evaluating the proposed approach in an orthogonal frequency division multiple access/time division duplex (OFDM/TDD)-based broadband mobile access system, it has been found that our adaptive scheme significantly improves the system capacity as compared to the existing DTPQ scheme with a fixed delay threshold.

• Proceedings of the KIEE Conference
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• 1987.07b
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• pp.1174-1177
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• 1987

The design of flow control protocols for integrared networks with complete voice traffic on the data link level is investigated. The class of admissible flow control policies analyzed maximized the average data link throughput subject to an average system time delay constraints a finite intervals (O,s). In particular, it is shown that the optimum control law is bang-bang (window flow mechanism). The window size L can be analytically derived from maximum tolerated time delay T, the input arrival C of the queueing system, the duration of the time interval S, the initial number of packets in the queue.

• ETRI Journal
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• v.22 no.4
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• pp.40-50
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• 2000

We apply a "sliding-window" Maximum Likelihood(ML) estimator to estimate traffic parameters On-Off source and develop a method for estimating stochastic predicted individual cell arrival rates. Based on these results, we propose a simple Connection Admission Control(CAC)scheme for delay sensitive services in broadband onboard packet switching satellite systems. The algorithms are motivated by the limited onboard satellite buffer, the large propagation delay, and low computational capabilities inherent in satellite communication systems. We develop an algorithm using the predicted individual cell loss ratio instead of using steady state cell loss ratios. We demonstrate the CAC benefits of this approach over using steady state cell loss ratios as well as predicted total cell loss ratios. We also derive the predictive saturation probability and the predictive cell loss ratio and use them to control the total number of connections. Predictive congestion control mechanisms allow a satellite network to operate in the optimum region of low delay and high throughput. This is different from the traditional reactive congestion control mechanism that allows the network to recover from the congested state. Numerical and simulation results obtained suggest that the proposed predictive scheme is a promising approach for real time CAC.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.3
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• pp.60-65
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• 1988

The ignition characteristics of repetitive electric sparks into a quiescent acetylene-air premixture and LPG-argon-air premixture was investigated by using a home-made Repetitive-Spark-Generator(RSG) to elucidate the effect of fuel burning velocity to ignition ability of RSG. Results show that the optimum spark delay time interval is strongly related with fuel burning velocity, or implicitly with characteristic reaction time scale of each fuel.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.3 no.3
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• pp.35-39
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• 1980

Although the product line produces a large volume of goods in a relatively short time, once the product line is established there are numerous problems that arise in connection with this product line. One of these problems is the problem of balancing operations or stations in terms of equal times and in terms of the times required to meet the desered rate of production. The objective of line balancing is minimizing the idle time on the line for all combinations of work stations subject to certain restrictions. In general, there are two types of line-balancing situations : (1) assembly line balancing and (2) fabrication line balancing. Two approaches to the assembly line balancing problem have been used. The first assumes a filed cycle time and find the optimum number of work stations. The second approach to the assembly line balancing problem assumes the number of work stations to be fixed and systematically coverages on a solution which minimizes the total delay time by minimizing the cycle time. Here the cycle time is determined by the longest station time. In this paper, by using the second approach method, a general mathematical model, problem solutions, and computer program for the assembly line balancing problem is presented. Data used is obtained from the company which has been confronted with many problems arising in connection with their assembly line.

• Journal of Welding and Joining
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• v.21 no.1
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• pp.48-53
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• 2003

The object of this study is to examine the effect of short circuit time ratio (SCTR) and current rise delay time (Td) on the spatter generation at low and medium current range in $CO_2$ welding. The spatter was evaluated by the weight generated in the welding of bead-on-plate for 30 seconds (3 times). Td was varied by order of 0, 0.4, 0.8 and 1.2 msec. At each Td, the short circuit time ratio was varied by the output voltage of the welding power source. In the low current range, it was found that the optimum SCTR was 20~25%, and the minimum spatter generation weight was obtained in the case of Td=0.4msec and SCTR=22% even though the remarkable difference was not showed by the application of Td. In the medium current range, it was confirmed that the arc was stable though the SCTR was increased from 20% to 40% by the control of current wave. Spatter generation weight depended on the variation of Td, and the lowest value of spatter generation weight occurred at Td=0.8~1.2msec.

• Journal of the Korean Institute of Telematics and Electronics
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• v.18 no.1
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• pp.16-24
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• 1981

The delay-lock loop (DLL) is a statistically optimum device for tracking the de]ay difference between two correlated waveforms. In this paper an extended n - $\Delta$ (n=1,2,3‥‥) DLL is described, and its baseband performance including the frequency to lose lock is analyzed. The present DLL system employs a correlator and a pseudonoise sequence synthesizer that has been improved from the previously used ones The shape of the correlator characterigtic has the form of expanded S-curve. Despite of increase noise, this extended DLL has desirable characteristics in tracking range and initial synchronization time. Comparing a 3 - $\Delta$ DLL with a 1 - A DLL, the former Bives three times faster initial synchronization time with the serial synchronization method, and gives two times immunity against doppler shift.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.11
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• pp.1929-1945
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• 2011

RFID technologies have attracted a lot of attention in recent years because of their cost/time-effectiveness in large-scale logistics, supply chain management (SCM) and other various potential applications. One of the most important issues of the RFID-based systems is how quickly tags can be identified. Tag collision arbitration plays a more critical role in determining the system performance especially for passive tag-based ones where tag collisions are dealt with rather than prevented. We present a novel tag collision arbitration protocol called Optimum Frame-Slotted Aloha (OFSA). The protocol has been designed to achieve time-optimal efficiency in tag identification through an analytic study of tag identification delay and tag number estimation. Results from our analysis and extensive simulations demonstrate that OFSA outperforms other collision arbitration protocols. Also, unlike most prior anti-collision protocols, it does not require any modification to the current standards and architectures facilitating the rollout of RFID systems.