• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.133-136
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• 2003

UWB(Ultra-Wide Band) system is transmitted using Gaussian monocycle pulse of very short pulse duration less than 1 nsec. Therefore, transmission signal has ultra-wide band spectrum to GHz band of very low power and not interfere with the existing communication system. A collision of multipath waves in UWB system with tarrier frequency very different with general wireless communication system. In this paper, the BER(Bit Error Rate) performance of UWB system applying Binary Phase Shift Keying, Quadrature Phase Shift Keying, 16-Quadrature Amplitude Modulation method under multipath channel using computer simulation is compared and analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7A
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• pp.682-687
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• 2010

The IEEE 802.15.4a specification targets the low-rate (LR) Impulse-radio (IR) ultra-wideband (UWB) system which is now widely applied in the WPANs considering rather short distance communications with low complexity and power consumption. The physical (PHY) layer uses concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM), and direct sequence spreading with time hopping in order that both coherent and non-coherent receiver architectures are supported. In this paper, the performances of multiple access schemes compliant with IEEE 802.15.4a specification are investigated with energy detection receiver, which allow avoiding the complex channel estimation needed by a coherent receiver. However, the performance of energy detection receiver is severely degraded by multi-user interference (MUI), which largely diminishes one of the most fascinating advantages of UWB, namely robustness to MUI as well as the possibility to allow parallel transmissions. So as to improve the performance of multiple access schemes, we propose to apply the novel TH sequences as well as to increase the number of TH positions. The simulation results show that our novel multiple access schemes significantly improve the performance against MUI.

• ETRI Journal
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• v.27 no.5
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• pp.579-584
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• 2005

A CMOS direct-conversion mixer with a single transistor-level topology is proposed in this paper. Since the single transistor-level topology needs smaller supply voltage than the conventional Gilbert-cell topology, the proposed mixer structure is suitable for a low power and highly integrated RF system-on-a-chip (SoC). The proposed direct-conversion mixer is designed for the multi-band ultra-wideband (UWB) system covering from 3 to 7 GHz. The conversion gain and input P1dB of the mixer are about 3 dB and -10 dBm, respectively, with multi-band RF signals. The mixer consumes 4.3 mA under a 1.8 V supply voltage.

• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1584-1602
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• 2024

It is vital to output the required electrical power following various task requirements when the space reactor power supply is operating in orbit. The dynamic performance of the closed Brayton cycle thermoelectric conversion system is initially studied and analyzed. Based on this, a load tracking power regulation method is developed for the liquid metal cooled space reactor power system, which takes into account the inlet temperature of the lithium on the hot side of the intermediate heat exchanger, the filling quantity of helium and xenon, and the input amount of the heat pipe radiator module. After comparing several methods, a power regulation method with fast response speed and strong system stability is obtained. Under various changes in power output, the dynamic response characteristics of the ultra-small liquid metal lithium-cooled space reactor concept scheme are analyzed. The transient operation process of 70 % load power shows that core power variation is within 30 % and core coolant temperature can operate at the set safety temperature. The second loop's helium-xenon working fluid has a 65K temperature change range and a 25 % filling quantity. The lithium at the radiator loop outlet changes by less than ±7 K, and the system's main key parameters change as expected, indicating safety. The core system uses less power during 30 % load power transient operation. According to the response characteristics of various system parameters, under low power operation conditions, the lithium working fluid temperature of the radiator circuit and the high-temperature heat pipe operation temperature are limiting conditions for low-power operation, and multiple system parameters must be coordinated to ensure that the radiator system does not condense the lithium working fluid and the heat pipe.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.3-32
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• 2016

High power impulse magnetron sputtering (HiPIMS) technique has been developed for more than 15 years. It is characterized by its ultra-high peak current and peak power density to obtain unique thin film properties, such as high hardness, good adhesion and tribological performance. However, its low deposition rate makes it hard to be applied in industries. In this work, the development of HiPIMS system and integration of radio frequency (RF) or mid-frequency (MF) power supplies were introduced. Effects of duty cycle and repetition frequency on the microstructure, mechanical property, optical and electrical properties of some binary, ternary and quarternary nitride coatings and oxide thin films were discussed. It can be observed that the deposition rate was effectively increased by the superimposed HiPIMS with RF or MF power. High hardness, good adhesion and sufficient wear resistance can be obtained through a proper adjustment of processing parameters of HiPIMS power system.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.361-365
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• 2005

Since the fuel cell uses the hydrogen for its fuel. it has no emission and higher efficiency than an internal combustion engine. Also fuel cell is much quieter than engine generator and generates heat much less than engine generator. So it has advantage of Army's 'si lent watch' capability and the ability to operate undetected by the enemy. The fuel cell hybrid system combines a fuel cell power system with an ESS. The ESS (e.g., batteries or ultracapacitors) reduces the fuel cell's peak power and transient response requirements. It allows the fuel cell to operate more efficiently and recovery of vehicle energy during deceleration. The battery has high energy density, so it has the advantage regarding driving distance. However, it has a disadvantage considering dynamic characteristic because of low power density. One other hand. the ultracapacitor has higher power density, so it can handle sudden change or discharge of required power. Yet. it has lower energy density. so it will be bigger and heavier than the battery when it has the same energy. This paper proposes the power management strategy for multi-power source fuel cell hybrid system. which is applied with the merits of both battery and ultra capacitor by using both of them simultaneous.

• Journal of Electrical Engineering and Technology
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• v.11 no.2
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• pp.353-360
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• 2016

Series hybrid electric vehicles (SHEVs) having multiple power sources such as an engine- generator (EnGen), a battery, and an ultra-capacitor require a power control unit with high power density and reliable control operation. However, manufacturing using separate individual power converters has the disadvantage of low power density and requires a large number of power and signal cable wires. It is also difficult to implement the optimal power distribution and fault management algorithm because of the communication delay between the units. In order to address these concerns, this approach presents a design methodology and a power control algorithm of an integrated power converter for the SHEVs powered by multiple power sources. In this work, the design methodology of the integrated power control unit (IPCU) is firstly elaborately described, and then efficient and reliable power distribution algorithms are proposed. The design works are verified with product-level and vehicle-level performance experiments on a 10-ton SHEV.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.11
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• pp.1495-1504
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• 2021

An ultra-compact binary power generation plant converts thermal energy into electric power using temperature difference between heat source and cooling source. In the actual power generation environment, the characteristic value of the plant changes due to any negative effects such as environmental condition or corrosion of related equipment. If the characteristic value of the plant changes, it may lead to unstable output of the turbine in a conventional PID control system with fixed PID parameters. A Neuro PID control system based on Neural Network adaptively to adjust the PID parameters according to the change in the characteristic value of the plant is proposed in this paper. Discrete-time transfer function models to represent the dynamic characteristics near the operating point of the investigated plant are deduced, and a design strategy of the proposed control system is described. The proposed Neuro PID control system is compared with the conventional PID control system, and its effectiveness is demonstrated through the simulation results.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.3
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• pp.15-26
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• 1997

In this study, the theoretical investigation of the electrically heated catalyst(EHC) for vehicle application has been carried out using the thermal equivalence of EHC system and the data of vehicle tests to meet ultra low emission vehicle(ULEV) standard. To improve the efficiency of EHC system, it is necessary to understand relation between the power, the operating time and the conversion efficiency of EHC system. The relation was found with thermal equivalence of EHC system which considers the power supply to EHC, heat loss, chemical exothermic energy generated by oxidation reaction and net energy coming in via the exhaust gas. From this relation, the limits of needful power and operating time to meet the ULEV standard can be suggested, when the conversion efficiency of catalyst was known.

• Journal of Advanced Navigation Technology
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• v.9 no.1
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• pp.1-8
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• 2005

In this paper, an impulse generator for UWB(Ultra Wide-band) technique with great possibility to be adopted as a next generation indoor WLAN(Wireless Local Area Network) has been designed by using SRD(Step Recovery Diode). Design goal is to design an impulse generator with simple structure, low cost, small size, and high performance. The impulse generator satisfied by FCC's regulation ( frequency range: 3.1~10.6 GHz, limit of power level: -41.25 dBm ) has been simulated by using ADS(Advanced Design System) which is the trade name of the Agilent Technologies. The output power of the impulse generator has been explained separately for single and multi band purposes, respectively.