• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.917-920
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• 2006

In mobile environments, their is more than one propagation path between each transceiver and Receiver have two or more delayed multipath signals. Delayed multipath signals can cause ISI and Receiver needs a adaptive algorithm to estimate a channel periodically. Also adaptive antenna using adaptive algorithm provide a significant increase in capacity, performance and coverage. This paper describes various LMS algorithm and evaluate the performance of array antenna Base station by using LMS algorithm in the presence of multipath signals and multiple users. As a result of simulation, Adaptive array antenna systems are able to adjust their antenna pattern to select desired signals, and reduce interference.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.1034-1041
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• 2007

In this paper, we propose a FD USE (frequency domain minimum mean square error) equalizer algorithm for MBOK DS-UWB (M-ary bi-orthogonal keying direct sequence UWB) systems considered as a PHY proposal for high-speed wireless communication in IEEE 802.15.TG3a. The conventional FD MMSE equalization scheme has a structural limit due to insertion of the cyclic prefix (CP) in all transmit packets, but the proposed scheme is able to equalize the channel effect without CP. In order to overcome channel estimation error by multipath delay, we introduce a moving FFT and a moving average scheme. Compared with conventional FD MMSE equalizer and the traditional TD (time domain) MMSE-RAKE receiver, the proposed FD MMSE equalizer has better BER performance and we demonstrate this result by computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.703-715
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• 2017

In this paper, we analyze the channel characteristics of the long distance air-ground wideband common data link and we propose a mathematical method to analyze the effect of narrowband and wideband interference of air-ground channel on the received signal of wideband data link. In this paper, we analyze the reception performance according to the communication distance using the proposed performance analysis method, and found out that the communication distance is limited by the narrowband and wideband interference of ground reflection wave. As a result of the performance analysis of the method of controlling the receiving antenna upward, not only the narrow band but also the wideband interference is effectively reduced, so that the communication distance is increased even in the existing wideband data link not including the equalizer.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.184-190
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• 2006

Using COMS which provides multi-beam switching function, the optimal transmission channel environments which provides the high data rate communication are proposed in this paper. Also the link budget for communication transponder of COMSAT is designed. Bsaed on the channel modeling for group delay, non-linear and gain flatness characteristics, the system performances which provide high data rate (HDR) service were analyzed in Ka-band satellite channel. As the transmission data rate is increased, the degradation due to these channel characteristics is severely affect the system performance. To efficiently provide the various service via the same transmission system it is necessary to equlize the primary impairment factors. The optimum operating points of HDR satellite transmission system are implemeted and operated by considering the analyzed results on channel characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.7
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• pp.1734-1745
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• 1996

In this paper, a modified fixed-delay tree search with decision feedback(FDTS/DF) for compensation of non-linear distortion in digital magnetic recording channels is discussed. Since the nonlinear distortion, which becomes significant as recording density increases, is generally well modeled by the discrete Volterra series, the proposed equlizer is composed of a nolinear feedforward filter, a linear feedback filter, and a nonlinear distorton table, the values of which are determined by considering the effect of nonlinear distortion due to future data as well as the previous and current one. At the decision stage of FDTS, a path minimizing the branch metric is chosen by using the previously detected values, current predicted value, and future predicted value. We compare the performance of the linear FDTS/DF, the previous nonlinear FDTS/DF, and the proposed nonlinear FDTS/DF by computer simulation, and confirm that the proposed one chieves the best performance at high-density recording.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.1113-1116
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• 2005

Using COMSAT which provides multi-beam switching function, the optimal transmission channel environment which provides the high data rate communication are proposed in this paper. Also the link budget for communication transponder of COMSAT is designed. Based on the channel modeling for group delay, non-linear and gain flatness characteristics, the system performances which provide various data rate services were analyzed in Ka-band satellite channel. As the transmission data rate is increased, the degradation due to these channel characteristics is severely increased. The linear component of group delay and the AM-AM component of non-linear characteristics severely affect the system performance. To efficiently provide the various service via the same transmission system it is necessary to equalize the primary impairment factors. The optimum operating points of HDR satellite transmission system are implemented and operated by considering the analyzed results on channel characteristics.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.5
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• pp.895-901
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• 2016

The next generation wireless and satellite communications require high transmission efficiency and high reliability to provide various services with subscribers. To satisfied these requirements, incorporated MIMO (Multiple Input Multiple Output) system with FTN (Faster Than Nyquist) techniques based on layered space time coded method are considered in the paper. To improve performance, STTC (Space Time Trellis Code) was employed as an inner code. As the same as SISO (Single Input Single Output) system, the outer codes are turbo codes. In receiver side, BCJR algorithm is used for STTC decoding in order to eliminate interferences induced by FTN transmission. They can yield significantly increased the data rates and improved link reliability without additional bandwidth. Therefore, we proposed a new decoding model for MIMO FTN model and confirmed that performance was improved compared to conventional SISO model according to amount of interference for FTN.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.10
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• pp.15-23
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• 2016

To support the telematics and infotainment services, vehicle-to-everything (V2X) communication requires a robust and reliable network. To do this, the 3rd Generation Partnership Project (3GPP) has recently developed V2X communication. For reliable communication, accurate channel estimation should be done. However, because vehicle speed is very fast, radio channel is rapidly changed with time. Therefore, it is difficult to accurately estimate the channel. In this paper, we propose the new linear minimum mean square error (LMMSE) channel interpolation scheme based on the Long Term Evolution (LTE) sidelink system in vehicle-to-vehicle (V2V) environments. In our proposed reduced decision error (RDE) channel estimation scheme, LMMSE channel estimation is applied in the pilot symbol, and then in the data symbol, smoothing and LMMSE channel interpolation scheme is applied. After that, time and frequency domain averaging are applied to obtain the whole channel frequency response. In addition, the LMMSE equalizer of the receiver side can reduce the error propagation due to the decision error. Therefore, it is possible to detect the reliable data. Analysis and simulation results demonstrate that the proposed scheme outperforms currently conventional schemes in normalized mean square error (NMSE) and bit error rate (BER).

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.450-453
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• 2003

본 논문에서는 그룹별 가변 길이 직교코드 다중화를 이용한 OFDM (orthogonal frequency division multiplexing) 전송방식의 제안하고, 그룹별로 동일한 부반송파 개수를 가정하여 코드 길이에 따른 시스템 성능과 복잡도를 분석함으로써 최적의 시스템 파라미터들을 결정한다. 제안된 방식에서는 상호 상관성이 낮은 부반송파들로 동일 반송파 그룹으로 구분함으로써 부반송파 전체를 다수의 부반송파 그룹으로 나누고, 그룹마다 부반송파 개수와 동일한 길이의 직교코드들을 사용하여 다중화하여 전송한다. 따라서, 제안된 시스템을 사용하면 적절한 시스템 파라미터의 선정을 통하여 부반송파 전체를 하나의 그룹으로 하는 기존의 직교코드 다중화 방식에[2] 비하여 다이버시티 이득은 유지하면서 시스템 복잡도를 크게 줄일 수 있다. 또한, 제안된 직교코드 다중화 전송방식에서는 수신기에서 직교코드들간의 직교성 복원이 필수적이며, 수신기에서 불완전한 채널등화는 인접한 직교코드들 간에 상호 간섭을 유발하는 요인이 된다. 따라서, 채널추정 오류의 정도가 증가함에 따라 직교코드들 간의 상호 간섭으로 인하여 증가하는 비트오류를 줄이기 위하여 채널추정 오류의 정도에 따라 블록길이와 블록 인터리버 구조를 조절하여 시스템을 최적화 한다. 가변 길이 직교코드로는 길이에 상관 없이 직교성을 유지하며 에너지의 균등 분배가 가능한 DFT (discrete Fourier transform) 코드를 사용한다. 최적 시스템 파라미터를 결정하기 위하여 모의실험을 통하여 코드 길이에 따른 시스템 성능을 분석한다. 또한, 채널추정 오류가 존재하는 경우에 시스템 성능을 분석한다. 마지막으로, 채널 부호화를 적용하는 경우에 시스템 파라미터들을 최적화함으로써 부호화 이득이 시스템 성능과 시스템 복잡도 감소, 채널추정 오류의 극복에 미치는 영향을 분석한다. nature, in contrast to physical theories that are of a geometrical nature. An application to the interpretation of intelligence is proposed, based on the "intelligence"of movement. Co layer from 1.4 to 1.6 nm was measured to be ranged from 0.004 to 0.021 ${\AA}$$\^$-1/.문에 기업간 관계를 연구하는 측면에서는 탐험적 연구성격이 강하다. 더 나아가 본 산업의 주된 연구가 질적이고 기업내부만을 연구했던 것에 비교하면 시초적이라고 할 수 있다. 또한 관계마케팅, CRM 등의 이론적 배경이 되고 있는 신뢰와 결속의 중요성이 재확인하는 결과도 의의라고 할 수 있다. 그리고 신뢰는 양사 간의 상호관계에서 조성될 수 있는 특성을 가진 반면, 결속은 계약관계 초기단계에서 성문화하고 규정화 할 수 있는 변수의 성격이 강하다고 할 수가 있다. 본 연구는 복잡한 기업간 관계를 지나치게 협력적 측면에서만 규명했기 때문에 많은 측면을 간과할 가능성이 있다. 또한 방법론적으로 일방향의 시각만을 고려했고, 횡단적 조사를 통하고 국내의 한 서비스제공업체와 관련이 있는 컨텐츠 공급파트너만의 시각을 검증했기 때문에 해석에서 유의할 필요가 있다. 또한 타당성확보 노력을 기하였지만 측정도구 면에서 엄격한 개발과정을 준수하지는 못했다. 향후에는 모바일 컨텐츠 파트너의 기업의 특성을 조사하여 관계성 변수와의 상호관련연구를 진행할 필요가 있다. 관계기간, 의존성, 거래처의 단/복수여부, 서비스 범주 등의 제반 변수를 고려하여 이러한 변수가 양사와의 관계성 변수에 어떤 영향이 있는가를 검증할 필요가 있다. 또한 신뢰,

• The Journal of the Acoustical Society of Korea
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• v.31 no.6
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• pp.373-383
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• 2012

The performance of underwater acoustic communication system is sensitive to the Doppler shift and ISI(Inter-Symbol Interference). Therefore, the simulation algorithm needs to consider time-spread due to multipath arrivals which cause the ISI, and time-varying Doppler shift along with moving source and receiver. For this purpose, VirTEX(Virtual Time series EXperiment) based on Ray model has been developed. In this paper, VirTEX is used to compare the characteristics of ocean waveguide from the experimental data and illustrate the performance. The CIR(Channel Impulse Response) that characterizes the multipath arrivals with representative time-spread due to multipath arrivals is compared between numerically simulated and experimental probe signal. Also, the communication performance analysis for BER(Bit Error Rate) is compared between numerically simulated and experimental data signal. As a result, VirTEX can be useful as a simulation tool for evaluating the performance of underwater acoustic communication system.