• 한국멀티미디어학회논문지
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• 제9권6호
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• pp.728-734
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• 2006

Carrier interferometry code is considered as a promising scheme that provides significant performance improvement via frequency diversity effect. Space-time coding is commonly employed to achieve a performance gain through space diversity. The combination of these techniques and forward error correction coding will lead to enhanced system capacity and performance. This paper presents a low-density parity check (LDPC) coded space-time orthogonal frequency division multiplexing (OFDM) transmission scheme with carrier interferometry code for high-capacity and high-performance mobile multimedia communications. Computer simulations demonstrate that the proposed mobile multimedia transmission system offers a considerable performance improvement of approximately 9dB in terms of Eb/No in the Rayleigh fading channel with relatively low delay spread, in comparison with space-time OFDM. Performance gains are further increased, comparing with traditional OFDM systems.

• 한국위성정보통신학회논문지
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• 제5권1호
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• pp.6-16
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• 2010

Since OFDM system suffers from high peak-to average power ratio(PAPR) drawbacks, more energy has been converted to seek for a new substitutable system which can maintain OFDM system's inherent virtues while avoid its defects. Consequently, a new multicarrier system called as CI/OFDM system has been proposed which applied carrier interferometry(CI) code to OFDM system. Due to its low PAPR advantage and orthogonal property, it has received more and more attention. Simultaneously, an old technique called single carrier(SC) system has retaken its attractions for the same purposes. This paper analyzes two cyclic prefixed transmission schemes variants of OFDM system: 1.carrier interferometry-Orthogonal Frequency-Division Multiplexing (CI/OFDM); 2. Cyclic prefixed single carrie(CP-SC) with frequency domain equalization. We compare the achievable bit rate transmission of the two systems in terms of signal to noise ratio(SNR) by mathematical derivation. We demonstrated that CI/OFDM achieves a bit higher transmission bit rate to that of the CP-SC with frequency domain equalizer.

• Journal of information and communication convergence engineering
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• 제2권1호
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• pp.5-8
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• 2004

DS-COMA is now a matured multiple access technology that utilizes spreading codes for user separation. In this paper, we attempt to improve the performance of a multiuser DS-COMA system with a unique chip shaping code called Carrier Interferometry (CI) code. The CI codes exhibit an excellent correlation property that can be used in many applications. In DS-COMA with CI codes (CI/DS-COMA), the symbols are spread by a spreading code and then the chip signals are shaped using a CI code. Due to the correlation property of the CI code, a diversity gain from the shaped chip signals is achieved and the performance of DS-COMA is significantly improved. Comparison study demonstrates that the DS-COMA with CI outperforms the conventional DS-COMA system in multiuser environments.

• 한국정보통신학회논문지
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• 제9권8호
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• pp.1643-1648
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• 2005

MIMO (Multiple put Multiple Output) 시스템은 공간적으로 분리된 안테나를 이용하여 공간 다이버시티 이득을 제공하는 고성능, 고용량의 광대역 무선 접속 기술이다. 본 논문에서는 주파수 다이버시티의 이득을 제공하는 다중 반송파 부호 기술인 반송파 간섭 부호 (Carrier Interferometry Code)를 MIMO-OFDM 시스템에 적용하여 성능을 추가적으로 개선하는 반송파 간섭 부호 기반의 MIMO-OFDM 시스템을 제안한다. SPW 시뮬레이션 플랫폼을 이용한 시뮬레이션 분석 결과에 의하면 주파수 선택적 페이딩 채널 환경에서 기존의 MIMO-OFDM 시스템 보다 반송파 간섭 부호를 적용한 MIMO-OFDM 시스템의 성능이 높은 채널 지연 환경에서도 약 4dB까지 개선됨을 알 수 있었다.

• 한국전자파학회논문지
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• 제20권4호
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• pp.381-389
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• 2009

높은 데이터 전송 속도를 갖는 OFDM(Orthogonal Frequency Division Multiplexing) 통신 시스템은 시간 영역에서 높은 PAPR(Peak-to-Average Power Ratio)이 발생되는 중요한 단점이 있다. 이 때문에 송신 신호의 비선형 왜곡을 일으켜 통신 성능을 매우 나쁘게 된다. CI(Carrier Interferometry) - OFDM 시스템은 각각 병렬 데이터를 N개의 모든 부반송파와 서로 직교하는 위상 성분에 실어 전송함으로써 첨두값이 낮추는 효과를 얻는다. 또한, 한 데이터를 N개의 부반송파에 나누어 전송하기 때문에 주파수 다이버시티(FD: Frequency Diversity) 효과를 얻는다. 그러므로 CI-OFDM은 PAPR 저감과 BER 개선에 우수한 성능을 보인다. 그러나 CI-OFDM을 실제로 구현할 때, 송신기에서 모든 데이터마다 각각 다른 위상 성분들과 반송파에 실려 동시에 전송되기 때문에 수신기에서 독립적인 위상 성분들을 차례로 보상할 수 있는가가 매우 중요한 문제점이 된다. 이 논문에서는 Walsh Hadamard 시퀀스를 사용하여 각 병렬 데이터를 구분하고, 동시에 기존 CI-OFDM의 특성을 갖는 개선된 CI-OFDM, 즉 FD-CI-OFDM 시스템을 제안하고 성능을 평가한다 컴퓨터 시뮬레이션을 통하여 그 성능이 기존 OFDM이나 CI-OFDM보다 개선됨을 보인다.

• Journal of Positioning, Navigation, and Timing
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• 제12권3호
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• pp.245-255
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• 2023

Time comparison techniques are necessary for generating and keeping Coordinated Universal Time (UTC) and distributing standard time clocks. Global Navigation Satellite System (GNSS) Common View, GNSS All-in-View, Two-Way Satellite Time and Frequency Transfer (TWSTFT), Very Long Baseline Interferometry (VLBI), optical fiber, and Network Time Protocol (NTP) based methods have been used for time comparison. In these methods, GNSS based time comparison techniques are widely used for time synchronization in critical national infrastructures and in common areas of application such as finance, military, and wireless communication. However, GNSS-based time comparison techniques are vulnerable to jamming or interference environments and it is difficult to respond to GNSS signal disconnection according to the international situation. In response, in this paper, Code-Division Multiple Access (CDMA) based All-to-All TWSTFT operation method is proposed. A software-based simulation platform also was designed for performance analysis in multi-TWSTFT signal environments. Furthermore, code and carrier measurement jitters were calculated in multi-signal environments using the designed simulation platform. By using the technique proposed in this paper, it is anticipated that the TWSTFT-based time comparison method will be used in various fields and satisfy high-performance requirements such as those of a GNSS master station and power plant network reference station.