• Journal of KIISE:Information Networking
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• v.35 no.3
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• pp.227-234
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• 2008

The development of wireless network technology allows high data rate seamless communication irrespective of the place and time in various emerging mobile service environment. Unlike wired networks, however, wireless networks utilize expensive limited bandwidth. MBS(Multicast Broadcast Service), which is supported by mobile WiMAX system based on IEEE802.16e, overcomes this problem using a shared downlink channel for efficiently supporting a number of users. However. the coverage and throughput of the system are significantly affected by the channel condition. In this paper we propose on MBS system employing Mobile Multi-Hop Relay(MMR) and adaptive modulation and coding(AMC) scheme. The result of NS-2 computer simulation shows that the throughput and transmission time are substantially improved by the proposed approach compared to the existing MBS system.

• Journal of KIISE:Information Networking
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• v.32 no.5
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• pp.633-640
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• 2005

This paper proposes and analyzes a message scheduling scheme and corresponding bandwidth allocation method for the hard real-time communication on dual standard 802.11 Wireless LANs. By making the superframeof one network precede that of the other by half, the dual network architecture can minimize the effect of deferred beacon and reduce the worst case waiting timeby half. The effect of deferred beacon is formalized and directly considered to decide the polling schedule of PCF phase. Simulation results executed via ns-2 show that the proposed scheme can improve the schedulability by 3$36\%$ for real-time messages and give $9\%$ more bandwidth to non-real-time messages for the given stream sets, compared with the network whose bandwidth is just doubled with the same MAC.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.3 s.333
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• pp.43-50
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• 2005

In this paper, quaternary logic gates using Down literal circuit(DLC) has been designed, and then synchronous Quaternary un/down counter using those gates has been proposed The proposed counter consists of T-type quaternary flip flop and 1-of-2 threshold-t MUX, and T-type quaternary flip flop consists of D-type quaternary flip flop and quaternary logic gates(modulo-4 addition gates, Quaternary inverter, identity cell, 1-of-4 MUX). The simulation result of this counter show delay time of 10[ns] and power consumption of 8.48[mW]. Also, assigning the designed counter to MVL(Multiple-valued Logic) circuit, it has advantages of the reduced interconnection and chip area as well as easy expansion of digit.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3B
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• pp.255-263
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• 2009

In this paper, we propose an adaptive beacon scheduling algorithm to control a reception period of actual data according to variation of amount of traffic in IEEE 802.15.4 LR-WPAN(Low Rate-Wireless Personal Area Network) with the cluster-tree topology. If a beacon interval is shortened, the amount of the traffic a node receives can be increased while consumption of the energy can be also increased. In this sense, we can achieve optimal on orgy consumption by controlling the beacon interval when the amount of data to be received is being decreased. The result of simulation using NS-2 shows that the proposed algorithm improves performances in terms of packet loss rate and end-to-end delay compared with algorithm using a fixed beacon interval. For a design of cluster-tree based LR-WPAN managing delay-sensitive services, the proposed algorithm and the associated results can be applied usefully.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.3
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• pp.68-74
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• 2008

Ethernet is the very successful technology in private local area network. Therefore, we can obtain the advantage to reduce network overhead due to such as protocol translation when to apply Ethernet to the public backbone network. However, in order to do that, it is required to restore the network within 50msec when link failure occurs, in order to provide seamless connections to end users. Currently, ITU-T standardized the automatic protection switching (APS) based Ethernet protection switching system. In this paper, we propose the improved Ethernet protection switching system to minimize the number of Ethernet frames lost when the network is restored from the failure. The proposed mechanism is analyzed by using simulation based on ns-2 and numerical results show that the proposed one provides superior performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.221-231
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• 2006

TCP is needed as a transport protocol to provide reliable end-to-end message delivery for MANETs in order to achieve a smooth integration with the fixed Internet. Particularly, TCP has its variants, namely TCP-Reno and TCP-Vegas. However, there has been no research work on extensive performance comparison of TCP-Reno and TCP-Vegas over AODV and OLSR. This paper is the first trial to perform the research by using ns-2 simulator. Through the extensive simulations, we found that which to select among routing protocols is more important than which to select among TCP variants, because the performance difference between TCP-Reno and TCP-Vegas over uy selected routing protocol is not so much outstanding. Particularly, TCP-Vegas relies on an accurate BaseRTT estimation in order to decide the sending rate of a TCP Sender. However, it cannot be directly applied to MANET because a route change makes the Base an used over a Previous Path obsolete. Therefore, we propose a technique for improving the performance of TCP-Vegas by considering the route change, and show the performance improvement through simulation study.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.7
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• pp.669-676
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• 2015

In this paper, we described the simulation results of the phase offset performance of a clock in holdover mode which was normally operated in GPS Disciplined Oscillator (GPSDO). In the TIE model, we included the time error term caused by environmental temperature variation because one of the most important parameters of clock phase error is the frequency offset and drift caused by the variation of temperature. For the simulation, we employed Maximum Time Interval Error (MTIE) for the performance evaluation when the frequency offset and drift are estimated by using an Unbiased Finite Impulse Response (UFIR) filter with ladder algorithm. We assumed that the noise in the GPS measurement is white Gaussian with zero mean and 1 ns standard deviation, and temperature linearly varies with a slope of $1{^{\circ}C}$ per hour. From the simulation results, the followings were observed. First, with the estimation error of temperature of less than 3 % and the temperature compensation period of less than 900 seconds, the requirement of CDMA2000 phase synchronization under 10 us could be achieved for more than 40,000 seconds holdover time if we employ an OCXO (Oven Controlled Crystal Oscillator) clock. Second, in order to achieve the requirement of LTE-TDD under 1.5 us for more than 10,000 seconds holdover time, below 3 % estimation error and 500 seconds should be retained if a Rubidium clock is adopted.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.3
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• pp.295-305
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• 2018

We present a passively Q-switched monolithic Er:Yb:glass microchip laser developed in our lab. The microchip laser can produce pulses at 1535 nm of the 'eye-safe' wavelengths with the pulse energy of 50 uJ and the pulse width of 4-6 ns. Using the laser we also designed and developed a pulsed Er:Yb:glass microchip laser rangefinder. Expressions for background and signal power, noise, and signal-to-noise ratio are reviewed. A computer simulation was used to optimize laser power, receiver aperture, and preamplifier bandwidth for the efficient system design of the laser rangefinder. Experimental results are presented to compare with the theory.

• Journal of information and communication convergence engineering
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• v.11 no.3
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• pp.147-152
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• 2013

A novel balun being the structure of a Wilkinson power divider is suggested and fabricated. One of the power dividing paths in the suggested balun uses a conventional ${\lambda}/4$ transmission line for $-90^{\circ}$ phase shifting, and the other path uses a composite right/left-handed -${\lambda}/4$ transmission line for $+90^{\circ}$ phase shifting with four series capacitors and three parallel inductors. In addition, the suggested balun uses two $50-{\Omega}$ resistors and a conventional $50-{\Omega}$ transmission line of ${\lambda}/2$ electrical length between the two output ports, achieving good isolation and reflection values of two balanced ports. The suggested balun is simulated by the advanced design system simulation program and fabricated on TLX-9 20-mil substrate. The fabricated balun has a very good values of $S_{11}$ = -27.46 dB, $S_{21}$ = -3.40 dB, and $S_{31}$ = -3.28 dB, a phase difference of $-179.5^{\circ}$, a magnitude difference of 0.12 dB, and a delay difference of 0.1 ns, with $S_{22}$ = -36.28 dB, $S_{33}$ = -27.19 dB, and $S_{32}$ = -25.2 dB at 1 GHz, respectively.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.14 no.4
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• pp.40-51
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• 2015

This study analysis traffic phase order alternatives to maximize throughput. According to theoretical analysis alternative2(EW: left turn after through, NS: through after left turn) and alternative5(EW: through after left turn, NS: left turn after through) can minimize the maximum delay. Both alternatives split the phase that have the same destination link under the whole cycle length. This shows that phase order alternative can effect to the fully saturated intersection. In side of simulation analysis by microscopic traffic simulator PTV VISSIM F 7.0, each phase order alternatives can't effect throughput under the non saturated condition. However under the saturated condition, the average controlled delay of the intersection has been changed by phase order alternatives. The simulation analysis shows that alternative2 and alternative5 increase throughput 3.8% to 5.1% under the saturated condition.