• Korean Journal of Optics and Photonics
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• v.13 no.5
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• pp.435-441
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• 2002

In this paper, we propose an optimal 2-dimensional construction algorithm of a code family for a high-speed optical code division multiple access network. The optimal 2-D code family generated by search algorithm has better spectrum efficiency than previous codes, having relatively many code sets with short code length and the same or lower BER. Using the optimal 2-D code, OCDMA systems make it possible to utilize the spectrum more efficiently than WDM systems. The probability of bit error for high-speed OCDMA transmissions is calculated as a function of the number of users in the presence of receiver and shot noise(additive white Gaussian noise).

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.1
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• pp.29-34
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• 2004

We present the first demonstration of waveguide-type depleted optical thyristor laser diode with InGaAs/InGaAsP multiple quantum well structure. The measured switching voltage and current are 4.63 V and 10uA respectively. The holding voltage and current are respectively 0.59 V, 20uA. The lasing threshold current at the temperature of $25^{\circ}C$ and $10^{\circ}C$ are 111 mAA and 72.5 mA, respectively. The lasing wavelength is centered at 1.561um at a bias current equal to 1.41 times threshold.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3239-3241
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• 1999

Two-dimensional optical code-division multiple access is a system to transmit a two- dimensional data via parallel transmission line. The probability density function (pdf) of interference noise from other users is calculated and the pdf of asynchronous interference noise is newly calculated to present lower bounds of probability of error. The corresponding bit error rate is evaluated from this results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1216-1221
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• 2011

We propose a multiplexed fiber Bragg grating (FBG) sensor network for vessel monitoring to measure the variation of strain and temperature by environmental perturbation based on code division multiple access (CDMA). The center wavelength of FBG was linearly changed by environmental perturbation such as strain and temperature variation so that we could be monitoring the state of sensors. A RSOA was used as optical broadband source and which was modulated by using pseudo random binary sequence (PRBS) signal. The correlation peak of reflected signal from sensor networks was measured. In this paper, we used the sliding correlation techniques for high speed response and dynamic rage of sensors.

• Korean Journal of Optics and Photonics
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• v.13 no.2
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• pp.146-150
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• 2002

1.55${\mu}{\textrm}{m}$ PnpN optical thyristor as a smart optical switch has potential applications in advanced optical communication systems. PnpP optical thyristors operating at 1.55${\mu}{\textrm}{m}$ are proposed and fabricated for the first time. In the optical thyristors, we employ InGaAs/InP multiple quantum well (MQW) for the active n- and p-layers. The thyristors show sufficiently nonlinear s-shape I-V characteristics and spontaneous emission. In the OFF-state, the device has a high-impedance up to switching voltage of 4.03(V). On the other hand, it has low-impedance and emits spontaneous light as a light-emitting diode in the ON-state voltage of 1.77(V), and switching voltage is changed under several light input conditions. It can be used as a header processor in optical asynchronous transfer mode (ATM), as a hard limiter in optical code division multiple access (CDMA) and as a wavelength converter in optical WDM systems.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.1
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• pp.117-123
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• 2013

By calculating the spectral efficiency of symmetric balance incomplete block design(BIBD) codes satisfying BER=$10^{-9}$, it can be found that ideal BIBD code design with m=2 and various q's is effective when effective power is high($P_{sr}=-10$ dBm). But BIBD code design with q > 2 and various m's can be effective when effective power is low($P_{sr}=-25$ dBm).

• Journal of Positioning, Navigation, and Timing
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• v.12 no.3
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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.

• Journal of information and communication convergence engineering
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• v.7 no.2
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• pp.176-181
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• 2009

This study is part of a project to develop and improve mooring systems for oceanographic use that include an electro-optical sensor, 1MHz Nortek Aquadopp Doppler Profiler and AIRMAR multipurpose Sensor. The adaption of Doppler current profilers to measure directional wave spectra has provided a new instrumentation approach to coastal and nearshore oceanographic studies. The HEIOB is developed are light weight and of a compact design, and can be easily installed in marine environment. Since there are no base station and gateways in marine environments, we selected CDMA and Orbcomm to send the data information. Therefore, the data can be sent by either e-mail service or Short Message Service (SMS). This paper will present some of scientific sensor results regarding real-time oceanographic and meteorological parameters such as wind spend, wind direction, wave direction, and etc. The modeling and test results highlight the engineering challenges associated with designing these systems for long lifetimes. It can also be used in future application to build wave observation buoy network in real-time using multiple ubiquitous buoys that share wave data and allow analysis of multipoint, multi-layer wave profiler.