• Journal of the Korea Convergence Society
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• v.8 no.1
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• pp.1-6
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• 2017

In this paper, we propose a new method for a correlative phase comparison direction finding(DF) which detects the arrival direction of radio waves by data fusing the calculated phase difference and the measured phase difference between the antennas when the radio waves are incident on the circular array antenna composed of 7 antennas respectively. The correlation type phase comparison method uses a uniform circular array(UCA) and a linear array method. The phase difference data calculated formally and the phase difference data measured in the test environment are fused with a correlation function, therefore, it is superior to the currently used phase comparison direction detection method. When the signal-to-noise ratio (SNR) of the received signal is 20dB and the inter-antenna distance to the wavelength of the received signal($L/{\lambda}$) is 0.5, the accuracy of the correlative DF is $1.7^{\circ}$ while measurement phase comparison's is larger than $2.5^{\circ}$, It can be used for electromagnetic signal monitoring and military direction detection.

• Journal of The Korean Astronomical Society
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• v.49 no.6
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• pp.255-259
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• 2016

We estimate the fractal dimension of the ${\rho}$ Ophiuchus Molecular Cloud Complex, associated with star forming regions. We selected a cube (${\upsilon}$, l, b) database, obtained with J = 1-0 transition lines of $^{12}CO$ and $^{13}CO$ at a resolution of 22" using a multibeam receiver system on the 14-m telescope of the Five College Radio Astronomy Observatory. Using a code developed within IRAF, we identified slice-clouds with two threshold temperatures to estimate the fractal dimension. With threshold temperatures of 2.25 K ($3{\sigma}$) and 3.75 K ($5{\sigma}$), the fractal dimension of the target cloud is estimated to be D = 1.52-1.54, where $P{\propto}A^{D/2}$, which is larger than previous results. We suggest that the sampling rate (spatial resolution) of observed data must be an important parameter when estimating the fractal dimension, and that narrower or wider dispersion around an arbitrary fit line and the intercepts at NP = 100 should be checked whether they relate to firms noise level or characteristic structure of the target cloud. This issue could be investigated by analysing several high resolution databases with different quality (low or moderate sensitivity).

• Fire Science and Engineering
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• v.27 no.1
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• pp.60-65
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• 2013

From an accident at 2:00 a.m. in November 2nd, 2012 that one fire-fighter died while suppressing the E land World Inc. Fire in Bupyeong-Gu, Incheon, we concluded the problem and the improvement method of using the wireless communication (the two-way radio) that the fire safety officer and the safety crew use when identifying the safety of the fire scene. And after the investigation, we could find that the communication between the fire safety officer and the safety crew was difficult in the scene of the fire by voice because of much noise, so they could rely solely on the wireless communication. Therefore, we investigated the wireless communication and its frequency now used in Incheon Fire Safety Devision. Also, we compared with those of the military and the police. As a result, by making use of the wireless communication and its frequency currently possessed in Incheon Fire Safety Division, we found that the fire safety officer and the safety crew rescuing people at the risk of their own life in the various fire scene can communicate effectively.

• Journal of Advanced Navigation Technology
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• v.11 no.1
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• pp.17-23
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• 2007

This paper, describes the VDR physical layer design in VDL Mode-2 in order to meet the requirements of International standards. VDR's frequency band is 117.975~137MHz, and CSMA(Carrier Sense Multiple Access), D8PSK(Differential Eight Phase Shift Keyed), 25KHz's channel bandwidth use. The analysis of the isolated channel from near channels, sensitivity of the receiver, dynamic range of the receiver, linear of the transmitter and energy of spurious for linear and non-linear simulation as a requirement condition of performance of VDR and teaches the course of design. The transmitting power level should be lower than 5dB from Po1dB point and the selected IF frequency is 45MHz to suppress the spurious signals. The receiver designed has 4.5dB of Noise figure, 27.52dB of Es/No, Mixer isolation up to 30dB, IIP3 power of LNA up to +10dBm to minimize the intermodulation.

• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.64-71
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• 2017

In this paper, Kalman filter and RRWA algorithm are used to estimate the accurate target in IR-UWB (Impulse-Radio Ultra Wideband) radar system, which enables accurate location recognition of indoors and outdoors with low cost and low power consumption. In the signal reflected by the target, unnecessary signals exist in addition to the target signal. We have tried to remove unnecessary signals and to derive accurate target signals and improve performance. The location of the targets is estimated in real time with one transmitting antenna and one receiving antenna. The Kalman filter was used to remove the background noise and the RRWA algorithm was used to remove the reflected signal. In this paper, we think that it will be useful to study the accurate distance estimation and tracking in future target estimation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.1 s.92
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• pp.49-55
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• 2005

In this paper, the phase locked harmonic oscillator(PLHO) using the analog PLL(Phase Locked Loop) is designed and implemented for a wireless LAN system. The harmonic oscillator is consisted of a ring resonator, a varactor diode and a PLL circuit. Because the fundamental fiequency of 8.5 GHz is used as the feedback signal for the PLL and the 2nd harmonic of 17.0 GHz is used as the output, a analog frequency divider for the phase comparison in the PLL system can be omitted. For the simple PLL circuit, the SPD(Sampling Phase Detector) as a phase comparator is used. The output power of the phase locked harmonic oscillator is 2.23 dBm at 17 GHz. The fundamental and 3rd harmonic suppressions are -31.5 dBc and -29.0 dBc, respectively. The measured phase noise characteristics are -87.6 dBc/Hz and -95.4 dBc/Hz at the of offset frequency of 1 kHz and 10 kHz from the carrier, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.1
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• pp.89-97
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• 2011

We analyze the performance of various techniques to overcome degradation of performance of STAP caused by nonhomogeneous clutter. The performance of NHD that used to eliminate outliers from nonhomogeneous clutter is improved by using the projection statistics(PS) that is robust to multiple outliers. The method of clutter covariance matrix estimation using a median value and the conventional method are also investigated and then compared. From the simulation results of STAP, the method of clutter covariance matrix estimation using a median value shows better performance than the conventional method for the calculation of the SINR loss, and MSMI for the single target and the multiple targets regardless of the NHD methods.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1422-1430
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• 2016

Researches for oceans are limited to military purpose such as underwater sound detection and tracking system. Underwater acoustic communications with low-probability-of-interception (LPI) covert characteristics were received much attention recently. Covert communications are conducted at a low received signal-to-noise ratio to prevent interception or detection by an eavesdropper. This paper proposed optimal covert communication model based on direct sequence spread spectrum for underwater environments. Spread spectrum signals may be used for data transmission on underwater acoustic channels to achieve reliable transmission by suppressing the detrimental effect of interference and self-interference due to jamming and multipath propagation. The characteristics of the underwater acoustic channel present special problems in the design of covert communication systems. To improve performance and probability of interception, we applied BCJR(Bahl, Cocke, Jelinek, Raviv) decoding method and the direct sequence spread spectrum technology in low SNR. Also, we compared the performance between conventional model and proposed model based on turbo equalization by simulation and lake experiment.

• Journal of Broadcast Engineering
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• v.13 no.3
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• pp.328-338
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• 2008

Multi-view video coding (MVC) based on H.264/AVC encodes multiple views efficiently by using a prediction scheme that exploits inter-view correlation among multiple views. However, with the increase of the number of views and use of inter-view prediction among views, total encoding time will be increased in multiview video coding. In this paper, we propose a fast mode decision using both MB(Macroblock)-based region segmentation information corresponding to each view in multiple views and global disparity vector among views in order to reduce encoding time. The proposed method achieves on average 40% reduction of total encoding time with the objective video quality degradation of about 0.04 dB peak signal-to-noise ratio (PSNR) by using joint multi-view video model (JMVM) 4.0 that is the reference software of the multiview video coding standard.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.238-245
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• 2010

For orthogonal frequency division multiplexing (OFDM) systems sharing the spectrum with narrow band primary devices, a fractional bandwidth (FBW) mode has been proposed recently to reduce the interference to the primary users. The FBW mode divides the total OFDM bandwidth into subbands and activates (or deactivates) a subset of the subbands according to the result of spectrum sensing. In this paper, we analyze the detection error probability of FBW mode information which is delivered by the sequence embedded in the preamble and evaluate the performance in wireless regional area network environments. The results show that the detection probability derived analytically estimates the actual value from simulation adequately and that a low detection error probability less than $10^{-3}$ is obtained at a low signal-to-noise power ratio.