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디지털 마이크로웨이브 수신기에서의 선형 증폭기와 ADC 접속 해석 및 고해상도 스펙트럼 추정
이민혁,최희주,박지언,변건식 東亞大學校 附設 情報通信硏究所 1998 情報通信硏究所論文誌 Vol.6 No.1
An analysis of the relationship between a linear amplifier chain and an analog-to-digital converter(ADC) in a digital microwave wideband receiver, with respect to sensitivity and dynamic range issues, is presented. The effects of gain, third-order intermodulation products and ADC characteristics on the performance of teh receiver are illustrated and design criteria for the linear amplifier chain are developed. Simulated results are also presented and compared with theoretical values. If there are two signals with frequencies very close, an FFT operation may generate one peak containing both signals. Therefore, high resolution spectrum estimation may need ot separate the two signals.
초광대역 시간 호핑 PPM UWB 통신 시스템의 성능 평가
이민혁,전제훈,이성신,변건식 동아대학교 정보기술연구소 2003 情報技術硏究所論文誌 Vol.11 No.1
Ultra-wideband(UWB) communication applications is a recent innovation due to high transmission rate and low power emission. Therefore, it is important to research UWB singal's characteristics and modulation methods to apply to various UWB communication technologies. In this paper the characteristics of Gaussian monopulse which is capable of using UWB communication was analyzed and we compared the performance of PPM and PAM modulation method. Also we simulated the interference effect of QPSK system with different center frequencies in the present of various UWB noises and simply modeled UWB system.
MIMO-PFDM 시스템에서 적응비트로딩 알고리즘의 성능평가
이민혁,변건석 동아대학교 정보기술연구소 2006 情報技術硏究所論文誌 Vol.14 No.1
Combined with multiple antennas at the transmitter and the receiver as well as adaptive modulation, OFDM proved to be robust against channel delay spread, in this paper. Futhermore, the optimal adaptive bitloading algorithm is proposed and the analysis was considered to involve the application of a variable-bit allocation and variable-power MQAM technique for a Single-Input Single-Output (SISO) OFDM system. This is compared with the performance of fixed OFDM transmission where a constant rate is applied to each subcarrier. The applied adaptive bitloading algorithm was in use as an inherent assumption in subchannel gain. Given this knowledge, the proposed system was designed to allocate the bit and power according to each subchannel. To prove the performance of adaptive bitloading algorithm, the simulation of SISO-OFDM system was conducted. It was concluded that the decision of bit numbers and power optimization algorithm served well to improve performance. Also, adaptive modulation was applied to a general MIMO system by making use of the singular value decomposition(SVD) to separate the MIMO channel into parallel subchannels. We can decompose the MIMO channel on each tone into parallel non-interfering SISO channels using the SVD. Namely, every matrix channel can be decomposed into a set of parallel subchannels over which data can be transmitted independently, given appropriate precoding and shaping transformations at the transmitter and the receiver, respectively. Finally, adaptive modulation combined with MIMO-OFDM system using an adaptive bitloading algorithm was applied to improve system performance. For a two-input antenna, two-output antenna system, the performance is compared with the performance of a system with a four-input antenna and a four-output antenna. Through MIMO-OFDM system simulation, we found that using more transmitter antenna and receiver antenna progress system performance because of increment of channel capacity, finally. Further, we concluded that the MIMO-OFDM system appling bitloading algorithm in general leads to better BER performance, as well as outperforming a common MIMO-OFDM system. A very useful extension of this paper would be in MIMO-OFDM systems with channel estimation technique. Throughout it, the performance analysis of more practical system is expected from now on.
오정근,박미선,이성신,이민혁,변건식 동아대학교 정보기술연구소 2002 情報技術硏究所論文誌 Vol.10 No.1
In the design of mobile wireless communication system, Base station location is one of the most important parameters. Designing base station location, the cost of equipment makes low by combining various, complex parameters. We can solve this problem by combining optimization algorithm, such as Simulated Annealing, Tabu Search, Genetic Algorithm, Random Walk Algorithm that have been used extensively for global optimization. This paper shows the 4 kinds of algorithm to be applied to the base station location optimization of mobile communication system and then compares, analyzes the results and shows optimization process of algorithm.
디지털 마이크로파 수신기에서의 선형 증폭기와 ADC 접속 해석
이민혁,김성곤,최희주,변건식 한국항행학회 1999 韓國航行學會論文誌 Vol.3 No.1
선형 증폭단. ADC 그리고 디지털 신호 처리기로 이루어진 디지털 광대역 마이크로파 수신기는 시스템의 감도와 동적 범위로 성능 평가를 해석할 수 있다. 시스템의 감도와 동적 범위는 시스템의 이득, 3차 상호변조적과 ADC 특성으로 결정되어지며 선형 증폭단의 설계 방법 또한 중요한 영향을 미친다. 그리고 수신기로 입력되는 두 신호의 주파수가 인접한 경우 디지털 신호 처리기는 두 신호를 분리할 수 있어야 한다. 본 논문에서는 증폭단의 이득을 변화시켜 동적 범위를 측정한 다음, 가장 적절한 감도와 동적 범위를 선택할 수 있는 이득 값을 결정하고, 인접한 두 신호의 분리를 위해 고해상도 스펙트럼 추정법을 사용하였다. Digital microwave wideband receiver including linear amplifier, analog-to-digital converter(ADC) and digital signal processor is able to analyze its performance using sensitivity and dynamic range of system. Determination of gain, third-order intermodulation products and ADC characteristics and design criteria for the linear amplifier chain is essential problem for sensitive and dynamic range. Also, if there are two signals with frequencies very close, digital signal processor must be able to separate the two signals. In this paper, we measured dynamic range as gain was changed and determined gain value for the proper sensitivity and dynamic range and high resolution spectrum estimation was used to separate two close signals.
정민영 ( Min Young Jeong ),김영환 ( Young Hwan Kim ),경규혁 ( Kyu Hyouck Kyoung ),이성구 ( Sung Koo Lee ),홍석경 ( Suk Kyung Hong ) 대한외상학회 2011 大韓外傷學會誌 Vol.24 No.2
Purpose: Blunt pancreatic injury has a high mortality rate, especially if adequate management is delayed. Although many guidelines exist for diagnosis and treatment, there is no consensus to date. Therefore, we analyzed the role of endoscopic retrograde cholangiopancreatography (ERCP) as a diagnostic and therapeutic tool for the treatment of traumatic pancreatic injury. Methods: We retrospectively reviewed the electronic medical records (EMR) database at Asan Medical Center (Seoul, South Korea) to identify all patients diagnosed with trauma to the pancreas between June 2003 and December 2010. Clinical and operative findings, CT (computed tomography) images, and ERCP findings were assessed. Results: A total of 40 patients were evaluated in this study. Of these, 14 patients underwent diagnostic ERCP, and 26 did not. Of the 14 patients who underwent diagnostic ERCP, 5 were found to have normal pancreatic ducts, thereby preventing a needless laparotomy in these patients. Of the patients diagnosed with ductal injury, four were treated with endoscopic intervention, and four underwent an exploratory laparotomy. The remaining patient was treated with radiologic intervention (percutaneous drainage) to manage pancreatic pseudocyst formation. Conclusion: Our findings suggest that ERCP is a beneficial diagnostic and therapeutic modality for the treatment of traumatic pancreatic injury.