• Korean Journal of Optics and Photonics
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• v.30 no.6
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• pp.230-236
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• 2019

We propose and demonstrate a searching and autoalignment method for indoor optical wireless communication, using a cost-effective retroreflective sheet and a microelectromechanical system (MEMS) mirror. We use an extremum-seeking method for a single axis and beam steering with a MEMS mirror to maintain a line of sight (LOS) with the optical link. This autoalignment method shows a receiver sensitivity of -31.87 dBm for a bit rate of 2.5 Gb/s over a 7 m communication link.

• Journal of Korean Society of Forest Science
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• v.94 no.5 s.162
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• pp.307-312
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• 2005

This study aimed to develop an agroforestry technology through the participation of local people. The study was conducted in the Makiling Forest Reserve (MFR) of the University of the Philippines Los Banos (UPLB). Diagnosis and Design (D&D) methodology was employed to plan and implement effective research and development projects. Diagnostic interview and direct field observation were conducted to identify the significance of the land-use system and to understand how the system works. As a result of the diagnostic interview and direct field observation in San Vicente, old coconut-based land-use system is shifting to mahogany-based agroforestry system. One of the reasons is due to the very complicated socio-economic and silvicultural factors including lower price of coconut farm products, industry development, lack of labor force, and pest and diseases. Change in land use brought about by the shifting to mahogany-based farming system is slow. Also, mahogany trees are observed to be not well-maintained. However, mahogany based land use system gives farmers' a bigger income as well as environmental benefit. Farmer's cooperation and local forestry policy for CDM were proposed to encourage people's self-restoration effort.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.1
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• pp.65-74
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• 2002

A three dimension(3D) link analysis is peformed considering multipath effects caused by a reflected signal and the difference angle between the antenna bore-sight and Line-Of-Sight(LOS). In addition, a direction of a receive antenna is determined for a receiver to get maximum signal strength in a telemetry situation. For a fixed receive antenna, the angle is determined to maximize the average Carrier to Noise Ratio(CNR) over the interested part of a trajectory. For a tracking antenna, the angle at every position is selected to give maximum CNR or to direct the boresight to the flying projectile.

• Journal of Advanced Navigation Technology
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• v.5 no.1
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• pp.62-73
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• 2001

In this paper, performance of DSRC systems is analyzed with considering the real roads and height of vehicles. The channels are modeled as 2-Ray and 4-Ray with a direct wave and reflected waves by a road and buildings in a physical layer because DSRC keeps LOS propagation characteristics, and the pass loss for each model is calculated respectively. Rician factor is obtained through the calculated path loss on two models for DSRC, and the performance of the systems is analyzed in AWGN and Rician fading channels, Impulsive noise and Rician fading channels respectively. As a result, in Rician fading channels with impulsive noise(A=0.2, ${\Gamma}^{\prime}=0.22$), BER is below $10^{-6}$ when the distance is farther than 80[m] and 40[m] in 2-Ray model and 4-Ray model respectively. For performance improvement, BCH coding scheme and MRC diversity scheme are adopted.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.2A
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• pp.119-127
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• 2012

In this paper a super-resolution time delay estimation algorithm is developed for real-time locating systems (RTLSs) that employ a direct-sequence spread spectrum technique, along with its performance analysis in multipath environments. The classical correlation method provides relatively good performance in line-of-sight (LOS) environments but its performance seriously degrades in multipath environments, especially when signals are spaced closer than a PN chip. Therefore we shall develop a super-resolution time delay estimation algorithm that may estimate the time delays of multipath signals even in closely spaced multipath environments using the MUSIC algorithm for direction-of-arrival estimation and analyze its performance by applying the algorithm to the ISO/IEC 24730-2.1 RTLS system. 

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2A
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• pp.128-133
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• 2010

We investigate the optimal chip rate of power or rate adapted direct-sequence code division multiple access (DS/CDMA) communication systems in Nakagami fading channels. We find that the optimal chip rate that maximizes the spectral efficiency depends upon both the channel parameters, such as multipath intensity profile (MIP) and line-of-sight (LOS) component, and the adaptation scheme itself. With the rate adaptation, the optimal chip rate is less than $1/T_m$, irrespective of the channel parameters, where $1/T_m$ is multipath delay spread. This indicates that with the rate adaptation, correlation receiver achieves higher spectral efficiency than RAKE receiver. With the power adaptation, however, the optimal chip rate and the corresponding number of tabs in RAKE receiver are sensitive to MIP and LOS component.

• Journal of Korean Society of Transportation
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• v.28 no.3
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• pp.157-167
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• 2010

Density is the most important congestion indicator among the three fundamental flow variables, flow, speed and density. Measuring density in the field has two different ways, direct and indirect. Taking photos with wide views is one of direct ways, which is not widely used because of its cost and lacking of proper positions. Another direct density measuring method using two point detectors has been introduced with the concept of instantaneous density, average density and measurement interval. The relationship between accuracy and measurement interval has been investigated using the SIMULATION data produced by Paramics Application Programming Interface function. We analyze the affect of segment density accuracy by sensing gap each road condition such as sensing segment length, lane and LOS after gathering data by Paramics Application Programming Interface.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.4
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• pp.105-113
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• 2010

In this paper, a 1.485 Gbps video signal transmission system using the carrier frequency of 240 GHz band was designed and simulated. The sub-harmonic mixer based on Schottky barrier diode was simulated in the transmitter and receiver. Both of heterodyne and direct detection receivers were simulated for each performance analysis. The ASK modulation was used in the transmitter and the envelop detection method was used in the receiver. The transmitter simulation results showed that the RF output power was -11.4 dBm($73{\mu}W$), when the IF input power was -3 dBm(0.5 mW) at the LO power of 7 dBm(5 mW) in sub-harmonic mixer, which corresponds to SSB(Single Side Band) conversion loss of 8.4 dB. This value is similar to the conversion loss of 8.0 dB(SSB) of VDI's commercial model WR3.4SHM(220~325 GHz) at 240 GHz. The combined transmitter and receiver simulation results showed that the recovered signal waveforms were in good agreement to the transmitted 1.485 Gbps NRZ signal.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11A
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• pp.1086-1095
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• 2007

This paper proposes a novel non-coherent TOA estimation scheme using multiple correlation process on the existence of multiple simultaneously operating piconets (SOPs). Impulse radio-ultra wideband (IR-UWB) based on direct sequence spread spectrum (DSSS) using Gold sequence is employed in order to discriminate each piconet. In order to enhance the characteristic of correlation, this paper presents the method of multiple mask operation (MMO). The time of arrival (TOA) of direct line of sight (DLOS) path is estimated via two step coarse/fine timing detection. To verify the performance of proposed scheme, two distinct channel models approved by IEEE 802.15.4a Task Group (TG) are considered. According to the simulation results, it could conclude that the proposed scheme have performed better performance than the conventional method well even in densed indoor multi-path environment as well as in the existence of multiple SOPs.

• Proceedings of the Acoustical Society of Korea Conference
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• 1992.06a
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• pp.127-130
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• 1992

한국 근해에서 능동소나 (active sonar) 사용시 사용되는 environmental parameters 가운데 하나인 volume reverberation(REv)을 산출하기 위하여 플랑크톤에 의한 후방산란 강도(backscattering strength)에 대한 연구를 하였다. 이를 위하여 수산진흥원 자료(80-89년)중 부유생물조사표에서 후방산란 강도가 다른 종에 비하여 큰 copepoda의 개체수를 평균한 후, 수심별 개체수를 계산하여 수심별, 주파수별(10, 50kHz), 계절별(2월, 8월) 후방산란 강도와 multipath eigenray model을 이용하여 REv를 산출하였다. 예로 사용한 동남해역(zone:S3), 서해중부해역(zone:W3)에서 주파수별 REv는 일반적인 형태인 포기에는 고주파가 높고, 1.5초 이후에는 저주파가 높게 나타났다. 그러나 여름이 겨울보다 플랑크톤 개체수가 많아 후방산란 강도가 크지만(2-5dB), REv는 겨울이 더 크게 나타났다. 이러한 이유는 SVP profile에 의한 pressure 계산결과, 여름에는 ray가 down-ward이고 겨울에는 duct를 형성하여 ray가 거의 direct로 진행하므로 transmission loss가 여름이 크기 때문이다. 또한 ray tracing결과 여름철에는 ray crossing이 많아 겨울에 비하여 fluctuation이 심하게 나타나는 현상을 보이고 있다. 두 지역 이외에도 한국근해의 정확한 REv을 예측하기 위해서는 플랑크톤의 정확한 측정과, 이론적인 수치와 비교할 수 있는 실측치를 얻는 것이 필요하다고 볼 수 있다.