• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1246-1252
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• 2006

In this paper, a collision probability, processing time and traffic capacity analysis algorithm for RFID system using random FHSS and synchronous FHSS is proposed. Service time, duty cycle, traffic intensity and additional delay time required for re-transmission due to collision are considered and the processing delay and frequency channel capacity are analyzed for the steady state operation of the system. The simulation results which show maximum capacity of the system and explain the accuracy of the algorithm are provided.

• Journal of KIISE
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• v.42 no.8
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• pp.972-978
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• 2015

Non-volatile memory (NVM) supports both byte addressability and non-volatility. These characteristics make it feasible for NVM to be employed at any layer of the memory hierarchy such as cache, memory and disk. An interesting characteristic of NVM is that, even though it supports non-volatility, its retention capability is limited. Furthermore NVM has tradeoff between its retention capability and write latency. In this paper, we propose a novel NVM-based file cache management scheme that makes use of the limited retention capability to improve the cache performance. Experimental results with real-workloads show that our scheme can reduce access latency by up to 31% (24.4% average) compared with the conventional LRU based cache management scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.05a
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• pp.469-472
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• 2014

S-MAC is hybrids of CSMA and TDMA approaches that use local sleep-wake schedules to coordinate packet exchanges and reduce idle listening. In this method, all the nodes are considered with equal priority which may lead to increased delay during heavy traffic. The method introduced in this paper provides high throughput and small end-to-end delay suitable for applications such as real-time voice streaming and its functionality is independent of underlying synchronization protocol. The novel idea behind our scheme is that it uses the priority concept with (m,k)-firm scheduling in order to achieve its objectives. The performance of our scheme is obtained through simulations for various packet sizes, traffic loads which show significant improvements in packet delivery ratio, and delay compared to existing protocols.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.10
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• pp.2237-2246
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• 2010

In this paper, the performance of a RCO-MAC protocol is evaluated using a different traffic model. Data frames are assumed to generate based on an exponential distribution from one source node and then directly to be stored into the input buffer in the source node. System throughput, average access delay and average system delay are used as a performance measure. Performance evaluation is carried out by the computer simulation. Numerical results show that the RCO-MAC scheme offers 18% higher system throughput than the rDCF scheme. In addition, the numerical results show that the RCO-MAC protocol also offers the better average system delay under any traffic load than that by the rDCF scheme, which was not obtained in the previous research due to the saturated traffic model.

• Journal of Korean Society of Transportation
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• v.20 no.5
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• pp.175-181
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• 2002

BIS(Bus arrival Information System) is a system that informs Passengers waiting at bus stops of the bus arrival time of next buses. However, when operating this system, it is not exactly known what type of bus arrival information should be provided. The purpose of this paper is to develop a model of the optimal bus arrival time to be informed for BIS. Analyzing Efficiency in the Seoul's Urban Bus Industry Using Data Envelopment Analysis. Two basic types of bus arrival information can be considered. One is Bus Locations : Where next buses are located and under what situation they are, such as the next bus departed from the previous stop, The other is Expected Arrival Time. Time to the arrivals of next buses. Characteristics of these two types of bus arrival time information provided for passengers waiting at bus stops for BIS are examined. The waiting time of passengers at bus stops is derived as a function of the bus arrival time to be informed. Some basic principles about the optimal bus arrival time to be informed are found. Finally, a case study assuming several simplifications is performed. One of the key findings is that there exists optimal arrival time to be informed other than the average arrival time. The optimal arrival time to be informed should be closer to the average arrival time for small and very large standard deviations and be earlier for certain amounts of standard deviations.

• The Journal of the Korea Contents Association
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• v.18 no.3
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• pp.34-40
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• 2018

In this study, the optimal buffer size is calculated for seamless video playback on a mobile device. Buffer means the memory space for multimedia packet which arrives in mobile device for video play such as VOD service. If the buffer size is too large, latency time before video playback can be longer. However, if it is too short, playback service can be paused because of shortage of packets arrived. Hence, the optimal buffer size insures QoS of video playback on mobile devices. We model the process of buffering into a discret-time queueing model. Mean busy period length and mean waiting time of Geo/G/1 queue with N-policy is analyzed. After then, we uses the main performance measures to present numerical examples to decide the optimal buffer size on mobile devices. Our results enhance the user satisfaction by insuring the seamless playback and minimizing the initial delay time in VOD streaming process.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.3
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• pp.479-491
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• 1994

In this paper, we proposed cell priority control with 2-level thresholds, which was considered cell loss and cell delay requirement, in ATM switch with output buffer. Priority control mechanism presented in this paper improved cell loss rate for cell loss censitive cell and cell delay for delay censitive cell. In this mechanism cell loss rate and mean cell delay of cell priority control mechanism were obtained theoretically. The results show that cell loss rate and mean cell delay improvement become better by adjusting two thresholds according to QOS characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.2
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• pp.97-104
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• 2013

This paper introduces waiting time based periodic packet discard policy for frame based scheduler. This policy can be used with conventional packet discard policy or buffer management schemes, such as drop-tail or random early detection. Proposed discard policy discards packets, which are stayed in the buffer longer than threshold, at every period of scheduling. This decision of discard is based on waiting time of packet. In this paper, mathematical analysis is performed with situation of network congestion. Also, the simulation is performed to evaluate the performance of proposed discard policy. In the result, proposed discard policy can limit queuing delay by threshold. Also, if the packet discard is performed before scheduling and threshold is set with smaller value than frame length, it can limit the throughput of traffic.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.7
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• pp.50-57
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• 2000

We propose a logic synthesis algorithm for the design of FPGAs operating at high speed. FPGA is a novel technology that provides programmability in the field. Because of short turnaround time and low manufacturing cost, FPGA has been noticed as an ideal device for system prototyping. Despite these merits, FPGA has drawbacks, namely low integration and long delay time comparing to ASIC. The proposed algorithm partitions a given circuit into subcircuits utilizing a kernel divisor such that the subcircuits can be performed at the same time, hence reducing the delay of the circuit. Experimental results on the MCNC benchmark show that the proposed algorithm is effective by generating circuits having 19.1% les delay on average, when compared to the FlowMap algorithm.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.510-514
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• 2002

A simple method for a time delay measurement of a chirped fiber grating by using bidirectional modulation of a Mach-Zehnder modulator has been proposed. The bidirectionally modulated light with time difference makes an interference fringe in the RF domain. The time delay of a chirped fiber grating can be obtained by measuring the period of the RF interference fringe for different wavelengths. We have measured the time delay of a chirped fiber grating with a chirped length of 5 cm and a bandwidth of 3.16 nm. The average slope of the time delay has been measured to be 183 ps/nm and its uncertainty has been less than $\pm$1.7%.