• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.97-100
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• 2005

우리는 페이딩 환경에서 비동기 블록 수신 CPFSK에 적용되는 TCM의 성능을 분석하였다. 여기서 비동기 블록 수신기는 N개의 심볼을 하나의 블록으로 취급하여 비동기 복조를 수행한다. 일반적으로 이러한 블록 수신 방식은 관찰 블록의 길이가 길어질수록 더 좋은 성능을 나타낸다. 그러나 페이딩의 응집 시간이 수신기의 관찰 블록 길이 보다 작아지면, 블록 수신기의 오류 성능은 매우 나빠지게 된다. 본 논문에서는 페이딩의 응집 시간이 수신기의 관찰 블록 시간 NT(여기서, T는 심볼 시간)보다 큰 환경을 저속 페이딩 환경 이라고 하고, 그렇지 않은 환경을 고속 페이딩 환경이라고 정의하여, 각각의 환경에서 시스템의 성능을 분석하였다. 그 결과 고속 페이딩 환경에서 비동기 블록 수신기의 사용은 오류 층(error floor) 현상을 초래한다는 사실을 알 수 있었다. 따라서 고속 페이딩 환경에서는 수신기의 관찰 블록 길이를 짧게 하는 것이 더 좋다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.5
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• pp.980-987
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• 2009

A timing synchronization method is presented for IEEE 802.11a wireless OFDM system. First the signal detection is achieved by measuring the moving energy of the received OFDM signal in two consecutive windows. By measuring the correlation between the short training signal and received envelope signal, fine OFDM symbol synchronization can be acquired. The variance and average value of the correlation value is acquired. And the theoretical values are compared with computer simulation results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.3 s.94
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• pp.286-292
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• 2005

We design and analyze the bit interleaved coded modulation(BICM) for noncoherent N-symbol continuous phase frequency shift keying(CPFSK) on the interleaved Rayleigh fading channel. In this paper, we use the equivalent normalized squared distance(ENSD) of noncoherent N-symbol CPFSK to design and analyze the BICM system. Specially, we design the BICM system for noncoherent 2-symbol 4-ary CPFSK, and analyze the performance of the system by using the ENSD. Simulation results are also provided to verify the theoretical performance analysis.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.1277-1280
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• 2009

본 논문은 ITU-T 권고안 J-38 부록 B에 명시된 전송방식의 분석 및 시뮬레이션을 토대로 성능을 분석 하였으며 FPGA 구현시 야기되는 문제점을 나타내고, 해결방안을 제시하였다. 구현상의 문제점으로는 크게 두 가지로 분류되는데, 첫째로 다양한 부호화 방식과 변조방식 그리고 심볼 단위 및 비트 단위의 처리로 인해 많은 클럭수를 요구하는데 본 논문에서는 읽기/쓰기 메모리를 이용하여 필요한 클럭수를 줄였다. 둘째로는 펑쳐링 부호화된 TCM 복호기에 펑처링 패턴에 정확한 동기를 얻지 못하면 프레임 동기 심볼인 UW(Unique sync-Word)를 획득하지 못하여 모든 데이터가 에러 처리되기 때문에 본 논문에서는 펑처링 패턴과 UW 심볼의 동기를 맞추는 알고리즘을 제시하였다. 이러한 알고리즘 분석 및 구현상의 문제점 해결을 토대로 본 논문에서는 ITU-T J38 annex B의 하향 스트림 채널 부호화 시스템을 VHDL 언어를 사용하여 FPGA 칩에 직접 구현하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.8A
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• pp.1367-1377
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• 2001

고전력 증폭기의 비선형성, 수신 주파수 편차 및 심볼 타이밍 편차가 모두 존재하는 실제 IEEE 802.11a 무선 LNA 시스템의 성능을 분석하였다. 이러한 시스템에서 데이터가 OFDM 변조된 후 주파수 선택적 Rayleigh 페이딩 채널을 통하여 전송될 때의 비트 오류율을 구하였다. 증폭기의 최대 출력 전력 대 평균 출력 전력비가 6dB이며 주파수 편차가 0.01이고 심볼 타이밍 편차가 2 샘플링 주기 시간인 경우에, 이 무선 LAN 시스템에서 10-5의 비트 오류율을 얻기 위하여 필요한 $E_{b}$ /$N_{o}$ 의 크기는 대략 20~24dB로 분석되었다. 이와 같은 실제 시스템과 정확한 채널 추정, 선형 증폭기, 정확한 주파수 동기 및 심볼 동기 가정의 이상적인 시스템간의 성능을 비교한 결과, 같은 크기의 비트 오류율을 얻기 위하여 이 실제 시스템에서 대략 1~3dB 정도의 $E_{b}$ /$N_{o}$ 가 더 소요된다.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.7
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• pp.3-9
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• 2013

This paper proposes a selective-weighted energy detection (S-WED) and a synchronization algorithm appropriate for it in IR-UWB system. Energy detectors that are practical in terms of implementation are employed widely for noncoherent reception in IR-UWB systems. However, they show low performance due to using the energy samples captured at symbol rate. For this reason, weighted energy detectors are developed to improve the performance of EDs. Hence, for WED, not only synchronization but also the weight coefficients are needed to be obtained prior to data detection. Meanwhile, the optimal weighting coefficients of WEDs are known to be energy values. Therefore, synchronization and the weighting coefficients can be obtained simultaneously. This paper proposes an S-WED and a simple synchronization algorithm for it in which sub-intervals having energies under a certain level are excluded in energy accumulation resulting in a simpler WED with a bit performance increase in low SNR region. The proposed algorithm is verified through simulations using the preamble symbol and channel models defined in the IEEE 802.15.4a.

• Journal of Advanced Navigation Technology
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• v.15 no.6
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• pp.1042-1046
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• 2011

In this paper, we analyze the STO (Symbol Timing Offset) problem in conventional ZP-OFDM (Zero Padding-Orthogonal Frequency Division Multiplexing) systems and propose a robust ZP-OFDM system with bi-directional overlap-add scheme to overcome the problem. The proposed ZP-OFDM system is able to preserve the orthogonality between subcarriers and reduce the interference from other ZP-OFDM symbols due to the BOA scheme, which exploits both ZP intervals of the previous and the current ZP-OFDM symbols, even though serious STOs result from inaccurate symbol timing synchronization. Simulation results verify that the proposed ZP-OFDM system is superior to the conventional ZP-OFDM system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.992-1003
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• 2007

In this paper, a channel estimation technique based on pilot tones, which does not degrade channel estimation performance even with the existence of symbol timing offset (STO) in OFDM systems, is proposed. The proposed technique performs channel estimation by interpolating channels with respect to amplitude and phase with a minimum computational complexity, differently from the conventional interpolation techniques. The proposed technique requires neither the estimation of fine STO in advance nor trigonometric operation for phase interpolation, signifying a significant reduction in computational complexity. Since the performance of the proposed technique does not depend on the STO present in OFDM systems. It can be directly applied to the following areas in OFDM-based communication system: elimination of fine STO estimation step in the synchronization procedure, elimination of STO estimation step in multiuser uplink, and channel estimation in multi-hop relay system. It is verified by computer simulation that the proposed technique can improve the performance of channel estimation significantly in the presence of STOs, compared with previous channel estimation techniques based on pilot tones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.7
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• pp.545-551
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• 2013

Timing recovery loop composed of the Timing Error Detector(TED), loop filter and resampler is widely used for the timing synchronization in MQASK receivers. Since TED is sensitive to the delay between the symbol period of the signal and sampling period, the output is averaged out when the symbol rate and sampling rate are quite different the recovery loop cannot work at all. This paper presents a sampling frequency discriminator (SRD), which detects the frequency offset of the sampling clock to the symbol clock of the MQASK data transmitted. Employing the SRD, the closed loop timing recovery scheme performs the frequency-aided timing acquisition and achieve the synchronization at extremely high sampling frequency offset, which can be used in variable symbol rate MQASK receivers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.3
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• pp.266-273
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• 2016

In this paper, we propose the signal processing techniques for the command link receiver mounted to aircrafts flying at a high speed. In order to acquire the various information transmitted from ground through radio frequency links, the wide received signal range must be guaranteed as well as the carrier synchronization and symbol synchronization be performed correctly within short pulse sections. After the synchronization step, we should be able to achieve theoretical performance of the modulation and demodulation scheme applied as deciding bit and symbol at the time appointed. By test results, we make sure that the proposed signal processing techniques can be effectively applied command link receiver mounted to aircrafts.