• 한국정보통신학회논문지
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• 제7권6호
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• pp.1153-1160
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• 2003

이 논문에서 협대역 간섭 잡음이 존재하는 환경에서 UWB(Ultra-Wide Bandwidth) 통신 시스템의 성능을 분석한다. UWB 통신 시스템은 일반적으로 사용되는 펄스시간위치변조 (Pulse Position Modulation)를 사용하며, 이때 전송 펄스는 가우시안 모노사이클이다. 또한, 다중접근간섭 (Multiple Access Interference)의 영향도 고려한다. 협대역 간섭은 특정 대역에서 일정한 전력 스펙트럼을 갖는 평균이 영인 랜덤 과정으로 모델링 하였다. 이 해석을 통하여, PPM 변조시 사용되는 시간 편이를 적절히 조절하고, 수신기에서 template 신호를 조정함으로써 협대역 간섭을 효과적으로 제거할 수 있음을 알 수 있다.

• Journal of Communications and Networks
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• 제16권3호
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• pp.270-279
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• 2014

The Viterbi decoding algorithm, which provides maximum - likelihood decoding, is currently considered the most widely used technique for the decoding of codes having a state description, including the class of linear error-correcting convolutional codes. Two classes of nonbinary convolutional codes are presented. Distance preserving mapping convolutional codes and M-ary convolutional codes are designed, respectively, from the distance-preserving mappings technique and the implementation of the conventional convolutional codes in Galois fields of order higher than two. We also investigated the performance of these codes when combined with a multiple frequency-shift keying (M-FSK) modulation scheme to correct narrowband interference (NBI) in power-line communications channel. Themodification of certain detectors of the M-FSK demodulator to refine the selection and the detection at the decoder is also presented. M-FSK detectors used in our simulations are discussed, and their chosen values are justified. Interesting and promising obtained results have shown a very strong link between the designed codes and the selected detector for M-FSK modulation. An important improvement in gain for certain values of the modified detectors was also observed. The paper also shows that the newly designed codes outperform the conventional convolutional codes in a NBI environment.

• 대한전자공학회논문지
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• 제26권6호
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• pp.1-6
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• 1989

인덕티브 포스트 장애물을 이용한 구형 도타관형 협대역 대역통과 필터에 관한 연구의 일환으로 중심 주파수 9GHz, 균일 리플 대역폭 50MHz(0.56%의 대역폭)인 chebyshev 대역통과 필터를 단일포스트 및 삼중포스트를 이용해 각각 설계, 제작하고 두 필터간의 특징을 비교하여 보았다. 단일포스트필터와 삼중포스트 필터를 제작해 측정한 중심 주파수, 대역폭, 그리고 손실특성은 이론치와 잘 일치 하였으며 삽입손실면에서 두 필터를 비교해 볼 때 산중포스트를 이용한 필터가 단일포스트를 이용한 필터에 비해 통과대역 특성이 0.8 dB 우수함을 알 수 있었다.

• 비파괴검사학회지
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• 제33권3호
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• pp.257-263
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• 2013

Acoustic nonlinearity of surface waves is an effective method to evaluate the micro damage on the surface of materials. In this method, the $A_1$ (magnitude of the fundamental wave) and $A_2$ (magnitude of the second-order harmonic wave) are measured for evaluation of acoustic nonlinearity. However, if there is another source of second-order harmonic wave other than the material itself, the linear relationship between $A_1{^2}$ and $A_2$ will not be guaranteed. Therefore, the second-order harmonic generation by another source should be fully suppressed. In this paper, we investigated the initial second-order harmonic generation in narrowband surface waves by multi-line laser beams. The spatial profile of laser beam was considered in the cases of Gaussian and square-like. The temporal profile was assumed to be Gaussian. In case of Gaussian spatial profile, the generation of the initial second-order harmonic wave was inevitable. However, when the spatial profile was square-like, the generation of the initial second-order harmonic wave was able to be fully suppressed at specific duty ratio. These results mean that the multi-line laser beams of square-like profile with a proper duty ratio are useful to evaluate the acoustic nonlinearity of the generated surface waves.

• 한국소음진동공학회논문집
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• 제26권5호
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• pp.501-510
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• 2016

Capabilities of several beamforming techniques are compared for estimating the position of a moving source. Beamforming has enabled to widen our perspective of aeroacoustics in wind tunnel experiments and has provided useful approach in array measurements. Meanwhile beamforming techniques have been developed in a way to improve estimation accuracy and to save ing effort at the same time. In order to achieve reasonable outcome from aeroacoustic measurement, it is important to identify the spectral characteristics of source and to select an appropriate beamformer. Though aeroacoustic sources normally generates broadband noises, many array signal processing have been focused on narrowband processing which makes calculation numerically efficient. However, calculation in frequency-domain requires selection of single frequency of interest which affects spatial resolution and sidelobe level as a consequence. To be able to localize broadband noise source, it is proposed to use broadband beamforming. The formulas implements the deletion of diagonal term from cross spectral matrix. In this study, trajectory of flying source emitting broadband noise was simulated and several beamformers are applied.

• 한국통신학회논문지
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• 제19권8호
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• pp.1536-1547
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• 1994

본 논문은 패킷전송을 위한 협대역 무선모뎀의 구현과 설계에 대해 다루었다. 모뎀은 송신부, 수신부 그리고 제어부로 구성되어 있다. 송신부는 협대역 필터링과 함께 BP나 변조를 사용하였다. 수신부는 반송파 복구, 비트동기, lock 검출부 등의 기능적인 모듈로 구성되어 있다. 분산 패킷 무선망을 위해 3개의 모뎀을 구현하여 패킷 데이터의 전송을 평가하였다. PC의 RC-232C 포트를 통해 패킷화된 데이터의 전송을 확인하였으며 측정장비를 이용하여 실험 결과 데이타를 그림으로 나타내었다. 본 논문에서 구현된 모뎀은 무선 LAN을 제작하는데 유용하리라 기대된다.

• 기술사
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• 제27권2호
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• pp.42-54
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• 1994

Nowadays communication network is steadily changing from a main body of telephone to a network which is creating new services such as multimedia etc. Jhis article introduces a bud of new service and new network which are able to sustain the above service. Including Korea, world advanced countries have been digitatizing their network with N-ISDN (narrowband ISDN) by e.g. 64K b/s and 1.5M b/s. New service by N-ISDN are extraordinary, though it can not solve all kinds of services. To solve these problems, a solving platform should be constituted. B-ISDN(broadband ISDN), as a platform has to be built to deal with almost all uinds of services, whatever the communication speed, communication mode or communication quality may be. Korea Telecommunication Authority(KTA) opened the narrowband ISDN(N-ISDN) at the end of 1993. This was one step previous opening of the broadband ISDN(B-ISDN) service scheduled to be rendered in 2001. B-ISDN, receiving and transmitting by far more information with high speed than the N-NSDN does, is one of G-7 Progects which the Korean government is driving foreward to raise the national scientific power to seven advan ced countries. This is also linked with an extremely high speed information network scheduled to be built by the Ministry of Communications in 2015.

• 한국통신학회논문지
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• 제19권12호
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• pp.2303-2312
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• 1994

등간격 선형 어레이로 입사하는 다중 협대역 신호를 분리 추정하기 위한 고해상도 알고리즘을 제안한다. 코히어런트 신호로 인한 여러가지 문제점을 해결하기 위하여 잡음 고유벡터를 기본으로 한 방법들이 제안되어 왔다. 그러나, 여러가지 이유로 인하여 이러한 방법들은 뛰어난 분해능을 보여 주지 못한다. 그리하여, 제안된 알고리즘은 공분간 행렬의 큰 고유치에 대응하는 신호 고유벡터가 가지고 있는 근본적인 성질을 이용하여 등간격 선형 어레이로 입사하는 평면파의 도래각 추정 문제를 해결한다. 시뮬레이션을 통하여 비교 분석한 결과 제안된 방법이 MUSIC 및 spatial smoothed MUSIC 방법 보다 높은 분해성능을 보여 주었다.

• ETRI Journal
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• 제37권3호
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• pp.460-470
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• 2015

Orthogonal frequency-division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM-based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify-and-Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF-relay, and incremental relaying modes. The outage performance of the proposed AF relay-based CR network is proven to be better than that of direct mode.

• 천문학회보
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• 제46권2호
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• pp.76.1-76.1
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• 2021

Maemi Dual Field Telescope System (MDFTS) is a dual telescope system located at Kyung Hee University. The system consists of 0.4 m telescope and 0.1 m telescope for wide-field observation. The 0.4 m telescope provides photometric observation which covers a field of view of 21'×16'. It has been used for various purposes with Johnson-Cousins UBVRI broadband filter system, e.g., SomangNet and Intensive Monitoring Survey of Nearby Galaxies. In this poster, we present the standard calibration result for our broadband filter system. Also, we suggest a new usage of the KHAO 0.4m telescope which is narrowband photometry by demonstrating the standard calibration of H-alpha filter. For flux calibration, not only R filter but also V filter is used for compensating the central wavelength discrepancy between R filter and H-alpha filter.