• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.9A
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• pp.1459-1464
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• 2001

본 논문에서는 나카가미 페이딩에서 STTD(Space Time Transmitter Diversity)기법을 적용한 셀룰러 무선 시스템의 오수신확률을 유도한다. 라플라스 변환을 이용하여 L개의 독립적이고 동일분포의 다중간섭신호에 대한 새로운 확률밀도함수를 유도하고, 동일채널 나카가미 간섭신호속에서 나카가미 페이딩을 겪는 신호에 대한 오수신확률을 나타내며, 주파수 재사용거리의 함수로 오수신확률을 표현한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.1-7
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• 2010

A new frequency offset estimation algorithm for chirp spread spectrum based on matched filter is proposed. Generally, the differential phase between successive symbols is used for the conventional frequency offset estimation algorithm. However, if the conventional frequency offset estimation algorithm is used for CSS, phase ambiguity arises because of long symbol duration and guard time. The phase ambiguity causes performance degradation of matched filter since the received signal is corrupted by the integer frequency offset. In this paper, we propose a new frequency offset estimation algorithm which separates integer and fractional frequency offset estimation for removing the phase ambiguity. The proposed algorithm estimates the integer frequency offset by using differential phase between matched filtering results of sub-chirps and successive symbols. Then, the fractional frequency offset is estimated by using the differential phase between successive symbols Simulation results show that the proposed algorithm well removes the phase ambiguity, and have almost same estimation performance compared with conventional one when there is not the phase ambiguity.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.183-184
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• 2012

동일 주파수를 이용하여 방송신호를 송출하는 동일채널중계기의 신호 송출 타이밍과 파워를 조절함으로써 신호 중첩지역에 위치한 수신기의 성능 열화를 최소화 할 수 있다. 이를 위해 방송망을 구성하는 각각의 동일채널중계기에 고유의 TxID를 부여하여 DTV 신호에 낮은 파워로 삽입하여 송출한다. 본 논문에서는 동일채널중계기에 삽입된 TxID 신호의 검출 성능을 향상시키기 위한 방법을 제안하고 모의실험을 통해 제안된 방법의 효과를 검증한다.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.397-398
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• 2014

Phase Shifted PWM은 각각의 셀이 동일한 스위칭 주파수로 PWM을 수행하므로 전압지령의 크기와 관계없이 셀 간의 전력은 동일하나, 각 셀 출력 전압의 위상이 다르므로 무부하 운전이나 부하의 급변동 시 발생하는 회생이 특정 셀에 집중되고 전압지령과 실제 출력전압 사이의 위상 차이가 존재하는 단점을 가지고 있다. 반면 기존 Level Shifted PWM은 전압지령의 크기에 따라 각 셀 간의 스위칭 조건이 다르고 동일 전력 분배가 되지 않는 문제를 가지고 있어 이를 개선하는 Level Shifted PWM 방법에 대해서는 이미 연구가 진행된 상태이다. 본 논문에서는 제어기가 분산화된 H-브릿지 멀티레벨 인버터에 각 셀의 스위칭 조건을 동일하게 유지하는 Level Shifted PWM을 적용하기 위해서 전압지령을 보정하는 방법을 사용하였고 시뮬레이션과 시험을 통해 제어기가 분산화된 H-브릿지 멀티레벨 인버터에 적용 가능함을 증명하였다.

• Korean Journal of Cognitive Science
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• v.23 no.2
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• pp.225-248
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• 2012

The summed-similarity model of visual short-term recognition proposes that the estimated amount of summed similarity between remembered items and a recognition probe determines recognition judgement decision (Kahan & Sekuler, 2002). This study examined the effect of a task-irrelevant location change on the recognition decision against two remembered Gabor gratings differing in their spatial frequencies. On each trial in Experiment, participants reported if two gratings displayed across the visual fields are the same or not as the probe grating displayed after about a second of memory delay. The probe grating would be the same as or different from the memory items (lure) by 1 or 4 JND units. The location of the probe would also vary randomly across the left and right visual field with respect to the location of the corresponding memory item. The participants were instructed to perform their recognition task exclusively to the spatial frequencies of the memory items and the probe while ignoring the potential location change of the probe. The results showed that false-recognition rates of the lure probe increased as the summed similarity between the memory items and the probe increased. The rates also further increased in the condition where the probe location was different from the location of the corresponding memory item compared to the condition where the probe location was the same. The increased false-recognition rates indicate that information stored into visual short-term memory is represented as a form of well-bound visual features rather than independent features.

• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.31-37
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• 2014

In situ investigations and laboratory tests using elastic wave have become popular in geotechnical and geoenvironmental engineering. Propagation velocity of elastic wave is the key index to evaluate the ground characteristics. To evaluate this, various methods were used in both time domain and frequency domain. In time domain, the travel time can be found from the two points that have the same phase such as peaks or first rises. Cross-correlation can also be used in time domain by evaluating the time shift amount that makes the product of signals of input and received waveforms maximum. In frequency domain, wave propagation velocity can be evaluated by computing the phase differences between the source and received waves. In this study, wave propagation velocity evaluated by the methods listed above were compared. Bender element tests were conducted on the specimens cut from the undisturbed hand-cut block samples obtained from Block 37 excavation site in Chicago, IL, US. The evaluation methods in time domain provides relatively wide range of wave propagation velocities due to the noise in signals and the sampling frequency of data logger. Frequency domain approach provides relatively accurate wave propagation velocities and is irrelevant to the sampling frequency of data logger.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.3
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• pp.359-364
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• 2016

As cable TV networks have a media feature that is a broadband wire network, they can provide not only TV broadcasting services but also communication services. Accordingly, the cable TV network is mentioned as the optimal network for convergence of broadcasting and communication services. Recently, Available frequencies of the cable TV network have become insufficient as enhancement of video quality, increment of VoD service, and growth of high-speed internet service. This paper presents a new implementation method of switched digital video (SDV) technology that is introduced for obtaining additional frequency band. In the SDV system, only TV channels requested from viewer are sent and non-requested channels are dropped. The presented SDV uses a sharing method of TV broadcasting and communication service in a same frequency band. This method shows increase of spectrum efficient from switching of TV service channels without building a complex system.

• Journal of Broadcast Engineering
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• v.15 no.1
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• pp.14-28
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• 2010

This paper considers technological requirements to broadcast digital television signals using distributed frequency network (DFN) in the advanced television systems committee (ATSC) transmission system and proposes distributed translator (DTxR) to meet such requirements. In the DFN, DTxR uses different frequency from main transmitter, but same among DTxRs. In addition, this paper introduces digital signal processing (DSP) techniques, which consist of demodulation, equalization, transmitter identification (TxID) generation and insertion, and modulation, to implement DTxR.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.809-815
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• 2003

It is very important to get very high switching speed as well as low phase noise of frequency synthesizer in the OFDM/FH communication system. In this paper we compare the phase noises and switching speeds of the conventional PLL and digital hybrid PLL(DH-PLL) frequency synthesizer, also, we investigate the effect of phase noise on the performance of OFDM/FH communication system. DH-PLL has high switching speed property at the cost of circuit complexity and more power consumption. Unlike the conventional PLL in which the phase noise and switching speed have the trade off relationship in respect of loop filter bandwidth, DH-PLL frequency synthesizer can perform fast switching speed and low phase noise simultaneously. Under the condition of same hopping speed requirement, DH-PLL can achieve faster switching speed and lower SNR penalty compared with conventional PLL in the OFDM/FH communication system.

• Journal of Broadcast Engineering
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• v.9 no.4 s.25
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• pp.371-383
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• 2004

In this paper we consider technological requirements to broadcast digital television signals using single frequency networks (SFN) in the Advanced Television Systems Committee (ATSC) transmission systems and propose equalization digital on-channel repeater (EDOCR) that overcomes the limitations of conventional digital on-channel repeaters (DOCRs). Since there are no forward error correction (FEC) decoder and encoder, the EDOCR does not have an ambiguity problem. In addition, since an adaptive equalizer in the EDOCR removes multi-path signals, additive white Gaussian noise (A WGN), and feedback signal due to low antenna isolation, the EDOCR may have good output signal quality with high power.