• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.4
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• pp.461-469
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• 2008

This paper proposes a hybrid symbol offset estimation algorithm for MIMO(Multiple Input Multiple Output) OFDM system. As MIMO OFDM systems are multiple transmitter and receiver antenna systems, apart from SISO(Single Input Single Output) system, it is possible to use several combining techniques which are used in multiple receive antenna system. In this paper, we propose hybrid symbol offset estimation algorithms using combining techniques in multiple receive antenna systems, simulate and show the performances in MIMO system environments. The proposed equal gain combining correlation algorithm has better performance 1.8 times in searching the ideal symbol offset rather than the conventional early symbol offset algorithm in severe ISI channel.

• Journal of Advanced Navigation Technology
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• v.9 no.2
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• pp.140-146
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• 2005

In this paper, we proposed the frequency offset compensation algorithm and tracking algorithm which could improve the accumulated phase error for HDR-WPAN system. The proposed frequency offset compensation technique estimated each sample phase error by autocorrelation characteristics of CAZAC sequence, estimated phase error multiple each sample in a symbol, and finally compensated for the frequency offset. After frequency offset compensation using two steps, coarse and fine frequency offset, tracking algorithm have to use to compensate for the accumulated phase error. Because there is no pilot symbol in payload, more phase rotation occurred in received signal constellations due to the accumulated phase error as the payload length increase. Tracking algorithm compensates for a cumulative phase error ${\theta}$ between payload data.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.182-187
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• 2012

Since PV PCS uses output current sensor for ac output current control, the sensor's sensing value includes unnecessary offset inevitably. If PV inverter is controlled by the included offset value, it's output current will generate DC offset. The DC offset of output current for trans-less PV inverter is fatal to grid, which results in saturating grid side transformer. Usually DSP controller of PV inverter reads several times sensing value during initial operation and, finally, it's average value is used for offset calibration. However, if temperature changes, the offset changes, too. Therefore, output current sensor measures sensing value that includes offset again. In this paper we propose new algorithm where two identical forward and reverse sensors are used to calculate the offset in real time. As a result the offset is not correlated with temperature change. The proposed algorithm is verified through PSIM simulation for validity.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.319-320
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• 2008

In this paper, we propose a new frequency offset estimation algorithm for DBO-CSS which is a standard for wireless personal area network (WPAN). In DBO-CSS, there can be several integer multiples of $2{\pi}$ in the phase rotation caused by the frequency offset because of the long time difference between the samples of differential relation and the high permissible frequency offset of the crystal oscillators between the transmitter and the receiver. In this paper, we propose an estimation algorithm by using the relationships of each sub-chirp signals to find the integer part without phase ambiguity.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.118-120
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• 2001

This paper presents a distance relaying algorithm based on the Discrete Fourier Transform(DFT) for elimination of DC-Offset. When the DFT is applied to current signal. the real and imaginary parts of fundamental component consist of fundamental component itself and DC-Offset. The DC-Offset is calculated by four consecutive values of the imaginary components, so that the fundamental component can be accurately estimated. Performance evaluation is presented for A-phase ground faults on 154kV 80km overhead transmission line. The proposed algorithm is inspected by software simulation and hardware simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.809-814
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• 2012

We propose an adaptive threshold detector algorithm for multi-level holographic data storage based on the expectation-maximization (EM) method. In this paper, the signal intensities that are passed through the four-level holographic channel are modeled as a four Gaussian mixture with unknown DC offsets and the threshold levels are estimated based on the maximum likelihood criterion. We compare the bit error rate (BER) performance of the proposed algorithm with the non-adaptive threshold detection algorithm for various levels of DC offset and misalignments. Our proposed algorithm shows consistently acceptable performance when the DC offset variance is fixed or the misalignments are lower than 20%. When the DC offset varies with each page, the BER of the proposed method is acceptable when the misalignments are lower than 10% and DC offset variance is 0.001.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.3
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• pp.1-8
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• 2017

Tool path generation is a part of process planning in 3D printing. This is done before actual printing by a computer rather than an AM machine. The mesh geometry of the 3D model is sliced layer-by-layer along the Z-axis and tool paths are generated from the sliced layers. Each 2-dimensional layer can have two types of printing paths: (i) shell and (ii) infill. Shell paths are made of offset loops. During shell generation, twists can be produced in offset loops which will cause twisted tool paths. As a twisted tool path cannot be printed, it is necessary to remove these twists during process planning. In this research, An algorithm is presented to remove twists from the offset loops. To do so the path segments are traversed to identify twisted points. Outer offset loops are represented in the counter-clockwise segment order and clockwise rotation for the inner offset loop to decide which twisted loop should be removed. After testing practical 3D models, the proposed algorithm is verified to use in tool path generation for 3D printing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1832-1843
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• 1995

Tool interference is one of the most critical problems in sculptured surface machining. When machining cavities and concaves, the tool frequently overcuts the portions of the surface, which cause inaccuracy in machining. So tool interference-free paths must be generated for rough cutting more efficiently. In this paper a software using SSI(Surface/Surface intersection) algorithm is developed for eliminating tool interference which occurs in an offset surface in 3-dimensional free form surface modeling. this work consists of two stages : using the offset data, the intersection curves are rapidly checked by this algorithm at the first stage. CL(cutter location) data are obtained by deleting the loop section of intersected offset patches at the second stage. This algorithm can reduce the amount of memory required to store machining data and also easily check region which have the possibility of intersection. Also, This software is verified to be useful in machining a curved object on a DNC milling machine.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.188-196
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• 2007

In this paper we propose an efficient offset curve generation algorithm for open and closed 2D point sequence curve(PS curve) with line segments in the plane. One of the most difficult problems of offset generation is the loop intersection problem caused by the interference of offset curve segments. We propose an algorithm which removes global as well as local intersection loop without making an intermediate offset curve by forward tracing of tangential circle. Experiment in computer sewing machine shows that proposed method is very useful and simple.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1593-1600
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• 2015

This paper proposes a novel compensation algorithm of current offset error for single-phase linear compressor in home appliances. In a half-bridge inverter, current offset error may cause unbalanced DC-link voltage when the DC-link is comprised of two serially connected capacitors. To compensate the current measurement error, the synchronous reference frame transformation is used for detecting the measurement error. When an offset error occurs in the output current of the half-bridge inverter, the d-axis current has a ripple with frequency equal to the fundamental frequency. With the use of a proportional-resonant controller, the ripple component can be removed, and offset error can be compensated. The proposed compensation method can easily be implemented without much computation and additional hardware circuit. The validity of the proposed algorithm is verified through experimental results.