• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.5
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• pp.899-906
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• 1997

It is known that the Differential Phase Shift Keying (DPSK) modulation scheme in the coherent optical communication system is suitable for design of long-distance transmission system because its receiver performance is 3-5dB better than ASK and FSK. In this paper, we descrive a fundamental understanding of the effects of laser phase noise on the performance of coherent lighwave communication systems. Formulas are derived for the bit error rate in homodyne and heterodyne DPSK. Based on detailed mathematical analysis and estimates, we explain the following finding. DPSK can operates at rates only 300 times greater than the laser linewidth.

• Electronics and Telecommunications Trends
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• v.39 no.1
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• pp.48-61
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• 2024

The integration of high-capacity terrestrial networks with non-terrestrial communication using satellites has become essential to support seamless low-latency services based on artificial intelligence and big data. Tunable light sources have been instrumental in resolving the complexity of channel management in wavelength division multiplexing (WDM) systems, contributing to increased network flexibility and serving as optical sources for long-distance coherent systems. Recently, these light sources have been applied to beam-steering devices in laser communication and sensing applications across ground, aerial, and satellite transport. We examine the utilization and requirements of tunable lasers in WDM networks and describe the relevant development status. In addition, performance requirements and development directions for tunable lasers used in optical interference systems and beam-steering devices are reviewed.

• Journal of the Institute of Convergence Signal Processing
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• v.10 no.1
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• pp.1-6
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• 2009

Propagation of electromagnetic wave in the water or underground is very difficult because of the conductivity of the propagation materials. In this case, we usually use acoustic signal as ultrasonic but, it is not easy to transfer long distance with coherent method because of time varying multipath, doppler effect, and attenuations. So, we use noncoherent method as FSK to communicate between long distances. But, as the propagation speed of acoustic sound is very slow, the BW of the channel is narrow. It is very hard to guaranty the enough speed of communication like digital image data. In this paper, we proposed a new data communication protocol which can transmit multi-bit digital data with every single ping, and improve the data communication speed in the water.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2498-2507
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• 1994

This paper proposes the Doppler frequency tracking system by the optimum synchronization technique which compensates the frequency shifts caused by satellite movement in a coherent digital satellite communication system. A Doppler frequency shift caused by satellite movements and the design theories of the optimum synchronization system are mathematically described. Based on this theory, a Doppler frequency tracking system is implemented via digital signal processing techniques utilizing a DSP chip, RAMs, PROMs, and a 80286 microprocessor. The performance of the designed system was evaluated through the experiments with the INTELSATVA satellite.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.483-486
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• 2004

수중음향채널의 다중경로에 의한 수신신호의 시간확산(Time spread)은 ISI를 유발하여 수중통신시스템의 성능을 저하시킨다. 시간확산에 의한 ISI를 줄이고 전송율이 높은 코히어런트(coherent) 시스템을 적용하기 위해서는 다중경로 영향을 제거해야 한다. 본 연구에서 적용하는 수동 페이저 컨쥬게이션(passive phase conjugation) 기법은 시역전 기술로 프로브 신호에 의한 시역전을 수행하여 다중경로에 의한 ISI가 감소하여 비트 오류율이 적어진다. 아울러 수신신호의 처리가 간단하여 다중경로에 의한 시간확산에 비례하는 탭수의 증가로 수신신호 처리시간이 과다한 적응등화기 기법에 비해 실시간 시스템 구현에 유리한 기법이다. 수치모의 실험으로 제안하는 기법의 성능을 해석하였다.

• Journal of Navigation and Port Research
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• v.29 no.5 s.101
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• pp.403-408
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• 2005

The techniques of estimating angle of arrival(AOA) have played a key role for enhancement of wireless communications using array antennas. Among those techniques, the superresolution algorithms, such as MUSIC and ESPRIT, calculate the covariance matrix of the array output vectors which are observed at the array antennas, and then by using eigen-decomposition of the covariance matrix, they estimate AOAs of the received signals with high accuracy. However, superresolution algorithms based eigenvalue decomposition fails to estimate AOAs under multipath environments. Under multipath environments, it is difficult to estimate AOAs of the received signals due to coherency and high-correlation. To resolve coherent signals, the covariance matrix is calculated by using the conventional spatial smoothing technique, and then the techniques based on eigen-descomposition is applied. The result of the conventional spatial smoothing technique, however, is obtained at the cost of losing effective spatial aperture. Moreover, the conventional technique ignores any information in the cross-correlations of the array outputs the subarrays. As the result, the performance for AOA estimation is degraded. In this paper, we propose a new spatial smoothing technique, which consider the cross-correlation for subarrays. By computer simulation, the AOA estimation performance of the proposed method is compared with the conventional method and evaluated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.2B
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• pp.171-177
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• 2002

As speed and capacity of optical communication system increase dramatically, polarization-mode-dispersion compensation(PMDC) becomes a hot issue in these days. In this paper, we introduce a new state-of-polarization (SOP) tracking algorithm that can be used in a PMDC system. The new SOP tracking algorithm is also based on optical heterodyne coherent detection technique like the previous algorithm that we have reported before. However, unlike the previous algorithm, the new algorithm requires only three times of measurement in any circumstances to find the exact SOP information so that it can effectively be applied to PMDC system where very fast and stable operation is indispensible.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.16-17
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• 2000

코히어런트한 두 기록빔의 간섭에 의해 광굴절 Fe-LiMb $O_3$ 결정 내에 형성된 반사형 부피 격자는 협대역성$^{[l]}$, 고효율, 높은 신호대 잡음비, 역다중성, 재구성성, 다채널화 등과 같은 특성을 갖는다. 본 논문에서는 광굴절 부피격자의 이러한 특성을 이용하여 WDM 광통신 시스템에 응용 가능한 역다중화 기법을 제안하고, 광학적으로 구현하였다. (중략)략)

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12B
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• pp.1244-1250
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• 2010

This paper presents a detection and ranging algorithm for a high-speed targets in the high PRF radar. We show, unlike the conventional methods, it firstly estimates Doppler frequency with a quasi-periodic pulse train prior to range processing. The estimated Doppler frequency can compensate the phase error enbeded in the received signal, which makes the signal integrated coherently in the range direction and localizes the target's signiture in low SNR. We present the derivation of the proposed algorithm and discuss how the system parameters such as the range/Doppler sampling condition, processing time and Doppler estimation error affect the performance of the proposed algorithm, which is verified by simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2303-2312
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• 1994

A high resolution algorithm is presented for resolving multiple narrowband plane waves that are incident on an equispaced linear array. To overcome the deleterious effects due to coherent sources, a number of noise-eigenvector-based approaches have been proposed for narrowband signal processing. For differing reasons, each f these methods provide a less than satisfactory resolution of the coherency problem. The proposed algorithm makes use of fundamental property possessed by those eigenvectors of the spatial covariance matrix that are associated with eigenvalues that are larger than the sensor noise level. This property is then used to solve the incoherent and coherent sources incident on an equispaced linear array. Simulation results are shown to illustrate the high resolution performance achieved with this new approach relative to that obtained with MUSIC and spatial smoothed MUSIC.