• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.810-817
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• 2001

Performance of a water-to-water multi-type heat pump system using R22 which has tow indoor units has been investigated experimentally. The refrigerant flow rate of each indoor unit was regulated by an electronic expansion valve and the total refrigerant flow rate of the system was controlled by a variable speed compressor. In the system, evaporator outlet pressure of refrigerant and outlet temperatures of secondary fluid from indoor units were selected as control variables. Experiments were executed for both cooling and heating modes using PID control method with fuzzy logic, and results of the test are compared with a classical PID method. In the case of PID control with fuzzy logic, the fuzzy control rules corrects PID parameters each time. Results show that PID control with fuzzy logic has the merits of quick response and reduced overshoot.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1076-1078
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• 2001

In this paper, we studies PWM control method for 400kVA inverter. This method is compared with the conventional sinusoidal modulation method applying to the power converter with large capacity. The inverter controls a PWM modulation using a DSP processor.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.175-176
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• 2007

In this paper, we introduce Satellite Digital Multimedia Broadcasting(S-DMB) system and show the method increasing the channel capacity. To reduce the burden that has to change the existing system, the system has to be offered the Backward-compatibility. This paper show the method using hierarchical 16APSK modulation. And to obtain the reasonable BER performance between existing path(we call high priority) and additional path(we call low priority).

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.330-335
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• 2012

Brushless doubly-fed machine (BDFM) doesn't use brush and slip ring, and has advantages such as high system reliability, small capacity of its frequency converter, low system cost, adjustable power factor and speed, etc. At the same time, it has good applicable potentials on the variable frequency motors and the variable speed constant frequency generators. However, due to the complicacy and particularity of BDFM in the structure and operating mechanism, the effect of magnetic field modulation directly influences the operating efficiency of BDFM. To study the effect of different cage rotor structures on the magnetic field modulation of BDFM, the rotor magnetomotive force (MMF) of BDFM with cage rotor is studied by the analytical method. The components and features of rotor harmonic MMFs are discussed. At the same time, the method to weaken the higher harmonics is analyzed by the theoretic formulae. Furthermore, the magnetic field modulation mechanism is expounded on in detail and the relationship between the magnetic field modulation effect and the operating efficiency of BDFM is established. And then, a new method for estimating the magnetic field modulation effect is proposed. At last, the magnetic field modulation effects of four BDFM prototypes with different cage rotor structures are compared by the MMF analysis and the efficiency data of electromagnetic design. The results verify the effectiveness of the new method for estimating the magnetic field modulation effect of BDFM with cage rotor.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.10
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• pp.11-20
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• 2014

In this paper, a novel transmission scheme is proposed to improve the data rates of spatial modulation (SM) which has low complexity and improves the spectral efficiency in correlated channel environments. The conventional SM scheme utilizes partial multiple antennas to transmit signal constellations and additional bits using antenna combinations. Therefore the channel capacity of SM is less than that of the conventional multiple input-multiple output (MIMO) scheme which uses all the available antennas. In this paper, an SM transmission scheme is proposed to improve the channel capacity using a tight frame pre-coder. The improvement in channel capacity of the SM scheme will be shown using computer simulations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.484-491
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• 2000

It is necessary to apply SSB modulation method with high bandwidth efficiency to the DS-CDMA mobile communication systems in order to accommodate the increasing number of voice users as well as the broad band and high data rate service in the future. Even though the bandwidth efficiency increases if SSB modulation is applied to BPSK-DS/CDMA, its performance gets degraded because of the increased multiple access interference. Therefore for eliminating the increased multiple access interference, the SSB/BPSK-DS/CDMA with successive interference canceller(SIC) is proposed and its performance and capacity are analyzed. With the limited system bandwidth, it is shown that the SSB/BPSK-DS/CDMA with SIC can accommodate more capacity than the conventional BPSK-DS/CDMA with SIC.

• Journal of Digital Contents Society
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• v.5 no.4
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• pp.306-310
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• 2004

In this paper, we proposed a capacity enhancement method using TCM-128QAM modulation and bandwidth extension of 25MHz in HDR-WPAN (high data rate wireless personal area network) system. In case using TCM-128 QAM modulation scheme, we can obtain maximum 66Mbps transmission rate in bandwidth of 15MHz. If extend bandwidth by 25MHz and roll-off coefficient ${\alpha}=0.35$, we can obtain maximum 110Mbps transmission rate. These results are confirmed through PSD(power spectrum density) analysis and BER (bit error rate) performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.4
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• pp.767-773
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• 2004

An UWB communication system are a promising communication technique suitable for the current trends, which are requesting communication methods with the high throughputs and very high speed. A key feature of UWB communication systems is the very narrow pulse used in transmitting the data and PPM(Pulse Position Modulation) for modulating the data. So, the timing accuracy is very important. It is very important to accurately analyze the effect of the timing jitter on the performance of UWB communication systems. In this paper, the methods of analyzing the timing jitter effects on UWB communication systems are introduced. In particular, the channel capacities with timing jitter are calculated including the multiuser access interference.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.360-369
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• 1992

A heat pump system is constructed to evaluate its performance and heat transfer characteristics with mixtures of R22/R142b as working fluids. The heat transfer in the evaporator and the overall performance are measured and analyzed in terms of the compositions and relevant variables. Possibility of capacity modulation by changing composition is observed without degradation of heat transfer coefficients and coefficient of performance. The cooling capacity is varied continuously within 200 percent based on minimum capacity at constant compressor speed. For similar cooling capacity, COP is improved by mixing two refrigerants and shows maximum value at 60％ mass fraction of R22. Average heat transfer coefficients of mixtures decrease in comparison with pure refrigerants at similar cooling capacity and mass flow rate. However, the overall heat transfer coefficients decrease moderately. A cycle simulation is performed in order to manifest the advantages of using refrigerant mixtures, considering experimentally observed heat transfer characteristics.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.3
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• pp.514-522
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• 2015

In Microwave Radio Link, it is necessary to consider the radio fading to consistently assure the radio link of the high quality as the distance. If the fixed modulation is used for the microwave radio link, it is difficult to keep the high availability of link for the case of the long distance. Adaptive Modulation(AM) provide good quality on microwave link, but the application of the only-AM is not enough to provide the availability assurance due to the fluctuating characteristics of link capacity. Our previous study has proposed the improvement method of transmission in association with the distance, however the previous method needed to make up for the common application. There was no suggestion of a mathematical formula with a variable. In this paper, we propose an optimized Adaptive Transmission Techniques with calculating formula of the priority traffic transmission capacity based on AM in consideration of the fade margin for the availability assurance as the distance and the comparison of the channel bandwidth for Long-distance Radio Link.