• Journal of Satellite, Information and Communications
• /
• v.12 no.2
• /
• pp.46-50
• /
• 2017

In this paper, we propose an artificial intelligence based spectrum allocation scheme for power line communication system. The frequency band of the transmitted signal can be adjusted through the spectrum allocation technique, thereby avoiding interference. This improves the performance of the transmission signal and the spectral efficiency. Through the simulation results, we show that the proposed spectrum allocation technique improves the spectral efficiency and improve the communication performance.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.4A
• /
• pp.344-350
• /
• 2007

Start after striking space key 2 times. Lately, a lot of researches have been done on the resource allocation for multiuser OFDM(Orthogonal Frequency Division Multiplexing) systems due to its spectral efficiency for high-rate multimedia data services. For multimedia services in which every user is guaranteed to have minimum required bit rate and bit error probability, it is critical to utilize the limited resources efficiently to improve the performance of the system. The introduced allocation method improves spectral efficiency to use the left subcarriers in Zhang's algorithm. By using this method, the system can provide services to more users constantly, except for a bit increasing complexity and memory for deciding the left subcarriers and reallocating the subcarriers.

• Korean Journal of Remote Sensing
• /
• v.19 no.4
• /
• pp.291-305
• /
• 2003

The cost of deploying Geological and Environmental information gathering systems, especially when such systems obtain remote sensing and photographic data through the use of commercial satellites and aircraft. Besides the high cost equipment required, adverse weather conditions can further restrict a researcher's ability to collect data anywhere and anytime. To mitigate this problem, we have developed a compact, multi-spectral automatic Aerial photographic system. This system's Multi-spectral camera is capable of the visible (RGB) and infrared (NIR) bands (3032*2008 pixel). It consists of a thermal infrared camera and automatic balance control, and can be managed by a palm-top computer. Other features includes a camera gimbal system, GPS receiver, weather sensor among others. We have evaluated the efficiency of this system in several field tests at the following locations: Kyongsang-bukdo beach, Nakdong river (at each site of mulkeum-namji and koryung-gumi), and Kyungahn River. Its tested ability in aerial photography, weather data, as well as GPS data acquisition demonstrates its flexibility as a tool for environmental data monitoring.

• 한국공간정보시스템학회:학술대회논문집
• /
• 2007.06a
• /
• pp.139-144
• /
• 2007

Recording data in hundreds of narrow contiguous spectral intervals, hyperspectral images have provided the opportunity to detect small differences in material composition. But a limitation of a hyperspectral image is the signal to noise ratio (SNR) lower than that of a multispectral image. This paper presents the efficiency of Spectral Similarity Scale (SSS) in change detection of hyperspectral image and the experiment was performed with Hyperion data. SSS is an algorithm that objectively quantifies differences between reflectance spectra in both magnitude and direction dimensions. The thresholds for detecting the change area were determined through Expectation-Maximization (EM) algorithm. The experimental result shows that the SSS algorithm and EM algorithm are efficient enough to be applied to the unsupervised change detection of hyperspectral images.

• Journal of Astronomy and Space Sciences
• /
• v.11 no.2
• /
• pp.232-249
• /
• 1994

Since we finished the purchase of the cooled Schottky diode mixer receiver made by Radiometer Physics Co. for the 120-170GHz range in October 1991, we have not prepared the PPL hardware and software for this receiver and the ellipsolidal mirror for beam guiding. After these problems were solved, this receiver was installed at the 14m telescope in late December 1993, and used for the confirmation of a spectral line detection and the measurement of the beam efficiency. The beam efficiency is about 36% at 146 GHz.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.16 no.6
• /
• pp.517-532
• /
• 1991

This paper shows performance analysis for FH/MF나 systems over the cellular mobile communication channel. The Channel capacity over FH/MF나 system is represented as a function of deletion probalblity (Po) and insertion probalbility(Pt). The spectral efficiency of the system serves as a per formance of cellular system is inferior to that of non cellular system. In the case of frequency reuse, we get the best performance when the reuse pattern(N) is 3.

• The Journal of the Acoustical Society of Korea
• /
• v.24 no.7
• /
• pp.402-409
• /
• 2005

In this paper. we propose a coding method using a matching pursuit algorithm in a strongly periodic highband signal. Also. we propose an efficient quantizer for the estimated parameters : spectral magnitude and phase. Based on the error concealment principle and sinusoidal model. the MP algorithm requires the high-precision pitch period estimation. To estimate more accurate pitch period. the refined pitch obtained from lowband speech is used. which increases the efficiency of bit allocation. The spectral magnitude parameters are quantized by the method which is combined with MDCT (Modified Discrete Cosine Transform) and multi-stage structure. The spectral phase quantizer uses the $2{\pi}$ modular characteristic of phases and the weighted function by spectral magnitudes. To evaluate the efficiency of the proposed method. we applied it to analysis-by-synthesis system. Furthermore we suggest the possibillity of scalable wideband speech codecs based on band-split structure.

• Journal of IKEEE
• /
• v.20 no.4
• /
• pp.385-391
• /
• 2016

We demonstrated experimentally a variable optical frequency comb source using a cascaded dual parallel Mach Zehnder modulator (DPMZM) and a phase modulator (PM). With this simple configuration and applying low drive voltages, we generated variable comb source composed of spectral lines 3, 5, 7, 9 and 11 with 10-GHz frequency spacing, also generated 2 and 3 spectral lines with 20 GHz frequency spacing. The generated comb source maintains high spectral coherence across the entire bandwidth with good spectral flatness (within 1-dB for 2, 3, 5, 7 comb lines, within 2-dB for 9-comb lines and within 3-dB for 11 comb lines). The flat and variable comb source is mainly achieved by manipulating 6 operating parameters of DPMZM, setting RF amplifier gain, connected at phase modulator and phase shifters. Hence the method is simple and offers great flexibility in achieving flat and variable comb spectrum, which is experimentally demonstrated. This brings advantages of power efficiency due to low driving voltages, simplicity and cost effectiveness to the system.

• The Journal of the Acoustical Society of Korea
• /
• v.16 no.5
• /
• pp.83-91
• /
• 1997

A reactor vibration monitoring has been performed using neutron noise obtained from excore detectors for the safety operation, Traditionally, the spectral estimator based on Fourier analysis has been widely used in the noise analysis of the reactor system. If the bias is too severe, the resolution would not be adequate for a given application. One major motivation for the current interests in the parametric approach to spectral estimation is the apparent higher resolution achievable with these modern techniques. In considering an unbias, a consistency, an efficency, and a minimum lower bound of the statictic estimation, an AR model is appropriate for noise spectral estimation with sharp peaks but not deep valley. In order to select an appropriate model order, the lag value of autocorrleaton function is applied. Burg method to trace the vibration mode of RPV internal is the most sucuessful.

• Korean Journal of Optics and Photonics
• /
• v.31 no.4
• /
• pp.169-175
• /
• 2020

We design a polarization-independent dielectric multilayer thin-film diffraction grating for a spectral-beam-combining (SBC) system with a simple grating structure and low aspect ratio. To maintain the high quality of the SBC beam, we propose a multilayer mirror structure in which the wavefront distortion due to stress accumulation is minimized. Moreover, to prevent light absorption from contamination, an optimized design to minimize the grating thickness was performed. The optimally designed diffraction grating has 99.36% diffraction efficiency for -1st-order polarization-independent light, for incidence at the Littrow angle and 1055-nm wavelength. It is confirmed that the designed diffraction grating has sufficient process margin to secure a polarization-independent diffraction efficiency of 96% or greater.