분산 파일럿 기반의 OFDM 시스템의 채널 추정

김시현,Kim, See-Hyun 한국전기전자학회 2011 전기전자학회논문지 Vol.15 No.3

지상파 DTV 표준인 DVB-T에 채택된 분산 파일럿은 블록 형태와 빗 형태의 파일럿 배치의 장점을 모두 가지며 전송 효율을 증가시킨다. 데이터 부반송파에 대한 채널 추정을 위해 파일럿 부반송파를 이용한 시간 및 주파수 영역 추정이 필요하다. MSE (mean square error) 관점에서 최적인 2D Wiener 추정기는 너무 복잡하여 실현성이 떨어진다. 본 논문에서는 가산 백색 가우스 잡음의 전력을 추정하여 이를 채널 추정치에서 제거하는 새로운 채널 추정 방식을 제안한다. 또한 모의 실험을 통해 제안된 방식이 페이딩 채널에서 2차원 선형 보간 방식보다 채널 추정 성능이 우수함을 보인다. The scattered pilots employed in DVB-T take advantage of the merits of both the block type and comb type pilot arrangement to increase the transmission efficiency. To estimate the channel transfer functions for data subcarriers, it is required to conduct time-frequency domain 2D estimation using the pilots. Though 2D Wiener estimator is optimal in sense of MSE (mean square error), it is too complex to implement in hardware. In this paper a new channel estimation method for the scattered pilot based OFDM system by measuring the power of AWGN and removing the noise in the LS (least square) estimate of the channel is proposed. And the simulation results reveal the proposed method outperforms the 2D linear interpolation in the fading channel.

다중반송파 시스템의 정합추구 기반 희소 다중경로 채널 추정

김시현,Kim, See-Hyun 한국전기전자학회 2012 전기전자학회논문지 Vol.16 No.3

Although linear channel estimation for the frequency selective fading channel has been widely deployed, its accuracy depends on the number of pilots to probe the channel. Thus, it is unavoidable to employ large number of pilots to enhance the channel estimation performance, which essentially leads to the degradation of the transmission efficiency. It even does not utilize the sparseness of the multipath channel. In this paper a sparse channel estimation scheme based on the matching pursuit algorithm and a pilot assignment method, which minimizes the coherence, are proposed. The simulation results reveal that the proposed algorithm shows superior channel estimation performance with fewer pilots to the LS based ones. 주파수 선택적 페이딩 채널을 위한 선형 채널 추정 방식의 성능은 파일럿의 개수에 비례하므로 채널 추정의 정확도를 높이기 위해서 많은 파일럿을 쓰지 않을 수 없으며 필연적으로 전송 효율성이 낮아지는 단점이 있다. 또한 다중경로 채널의 희소(sparse)한 특성을 활용하지 않고 있다. 본 논문에서는 압축센싱 기법을 이용하여 아주 적은 수의 파일럿으로 희소한 채널을 추정하는 정합추구 기반 알고리듬과 간섭도(coherence)를 최소화하기 위한 파일럿 배치 방법을 제안한다. 또한 모의 실험을 통해 LS (least square) 채널 추정 방식보다 적은 수의 파일럿으로 우수한 채널 추정 성능을 보임을 확인한다.

DVB-T2 복조기를 위한 재표본화기 구조

김시현,Kim, See-hyun 한국전기전자학회 2011 전기전자학회논문지 Vol.15 No.4

차세대 DTV 표준인 DVB-T2는 다양한 전송 대역폭을 지원하며, 대역폭에 따라 심볼 주파수가 달라진다. 따라서 다양한 심볼 주파수로 수신 신호를 표본화해야 한다. 또한 수신부 발진기의 주파수 오차로 인한 표본화 주파수 오차의 보상을 위해 미세한 표본화 주파수 보정도 필요하다. 수신 신호를 고정된 표본화 주파수를 갖는 ADC로 표본화 하고, 재표본화기를 이용하여 표본화 주파수를 심볼 주파수에 맞출 수 있다. 본 논문에서는 DVB-T2 복조기를 위한 재표본화기의 구조를 제안한다. 또한 모의실험을 통해 DVB-T2 신호의 각각의 부반송파에 대한 재표본화 결과의 주파수 특성을 보인다. DVB-T2 is a next generation DTV transmission standard, which supports various channel bandwidths. Since the symbol rate of the DVB-T2 signal is changed according to its bandwidth, the received signal needs to be sampled at a different frequency. The sampling frequency should be also adjusted depending on the sampling frequency offset due to the frequency error in the local oscillator. The sampling frequency can be locked into the symbol frequency by resampling the sampled data by ADC running at a fixed frequency. In this paper a resampler architecture for DVB-T2 is proposed. And the simulation results reveal the spectral characteristics of each subcarriers used in DVB-T2 system.

준안정 확산화염에서 레이저 유도 백열법을 이용한 매연 입자 분포에 관한 연구

김시현(See-hyun Kim),김규보(Gyu-bo Kim),조승완(Seung-wan Cho),이종호(Jong-ho Lee),정동수(Dong-soo Jeong),전충환(Chung-hwan Jeon),장영준(Young-june Jang) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6

An experimental study on soot volume fraction measurement using laser induced incandescence (LII) in ethylene diffusion flame has been conducted. LII is a powerful technique to measure soot particle distribution and particle size. This technique is based on the heating of the particles by short laser pulse and the subsequent detection of the thermal radiation. An axisymmetric loud speaker was used to control fuel flow. The fuel flow conditions are made by using different two modes as sine and rectangular wave. The acoustic pulse duration of 10㎐ is selected for observing soot particle distribution in periodic flames. The experimental conditions are 0.045 lpm in the fuel flow rate and 50 lpm in the secondary air flow rate. Strain rate of periodic flame is more increasing than that of unforced flame. In the characteristics of the LII signals, it seems to be same tendency. That is to say, more soot particles are distributed in the periodic flames than unforced flames. This study has led to a better understanding of unsteady flame.

레이저 유도 백열법을 이용한 가진된 확산화염에서의 매연입자에 관한 연구

김시현(See-hyun Kim),김규보(Gyu-bo Kim),조승완(Seung-wan Cho),이종호(Jong-ho Lee),정동수(Dong-soo Jeong),전충환(Chung-hwan Jeon),장영준(Young-june Jang) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

The flames have been investigated with laser diagnostics. Laser extinction has been used to calibrate the experimental soot volume fractions. This technique is based on the heating of the particles by short laser pulse and the subsequent detection of the thermal radiation. An axisymmetric loud speaker was used to control fuel flow. The fuel flow conditions are made by using various frequency. The various acoustic pulse durations of 2,5,10,16,20,100,200,400㎐ are selected for observing soot particle distribution in periodic flames. The experimental conditions are 0.045 lpm in the fuel flow rate and 50 lpm in the secondary air flow rate. Strain rate of periodic flame is increased than that of unforced flame. And soot volume fraction of flickering flames are increased than that of steady flame. The peak soot volume fractions in the 16hz flickering flame is 18% larger than measured in a steady flame burning with the same mean fuel flow rate. Generally, more soot particles are distributed in the periodic flames than unforced flames. However, soot volume fractions within 20hz~200hz flickering flames are smaller than that of steady flame. This study has led to a better understanding of the behavior of more complex flame-flow systems.

테이블 방법을 이용한 절대위치 검출기에 대한 개선된 위상 오차 보상

안기호(Ki-Ho Ahn),김시현(See-Hyun Kim),양윤기(Yoon-Gi Yang),이창수(Chang-Su Lee) 제어로봇시스템학회 2010 제어·로봇·시스템학회 논문지 Vol.16 No.10

Existing error compensation method of industrial electronic absolute displacement detector only depends on skilled engineers. This paper proposes a new table method in order to automatize error compensation. An waveform changes according to the parallel resistance for each pole were tabularized and four waveforms were superimposed to minimize total phase error. These process was verified using simulink. As a result of applying proposed method to the real sensor, peak to peak error was reduced from 3.428° to 0.879°. In this case, compensation resistance is 4.7kΩ in B pole and 20kΩ in C pole. This compensation rate is comparable to skilled engineers, and it takes 0.8 second which is far shorter than 15 minutes when expert does.

불안정 가스 터빈 연소기에서 부분 예혼합이 화염구조와 NOx 배출 특성에 미치는 영향

이재호(Lee Jae Ho),이종호(Lee Jong Ho),김시현(Kim See Hyun),장영준(Chang Young June),전충환(Jeon Chung Hwan) 한국추진공학회 2005 한국추진공학회 학술대회논문집 Vol.2005 No.11

OFDM 복조기의 개발을 위한 동기부 설계

김시현 水原大學校 2016 論文集 Vol.30 No.-

In a variety of wireless applications, such as digital TV, mobile communication, and wireless communication, orthogonal frequency division multiplexing (OFDM) has been accepted. It is crucial to develop a hard-wired OFDM demodulator for the low cost and low power solution. In this paper, the synchronization block of the hard-wired demodulator is developed. Both in the time and frequency domain the synchronizer finds the exact symbol window and compensates the frequency offset by acquiring the fine synchronization. It then tracks the time and frequency residual and maintains the synchronization, which leads to the maximum reception performance. The simulation results show that the designed block shows stable and robust time and frequency synchronization performance in the white gaussian and multipath fading channel.