• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.35.3-36
• /
• 2020

The Time Domain Field is one of the future GTO program fields of JWST(JWST/GTO TDS), surveying about 14' diameter field at the North Eliptical Pole(NEP) with NIRCam/NIRISS. As a part of the multi-wavelength study of the field, we have obtained SCUBA-2 850㎛ mapping which reaches a depth of σrms = 0.9mJy/beam and detect 93 sources at S/N > 3.5 ― which are expected to be highly star-forming (SFR>400M◉/yr) galaxies at z ≳ 1.5-4 and pinpoint the location at <0. " 1 accuracy of 68 sub-mm sources by identifying VLA 3GHz radio counterparts. In this talk, we will introduce the SCUBA-2 JWST/GTO TDS project and the newly discovered sub-mm sources in this field.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.4
• /
• pp.475-483
• /
• 2012

This paper presents new type of the hybrid supply modulator for the next reconfigurable transmitters. The efficiency of the hybrid supply modulator is one of the most important performance. For enhancement the efficiency, multi-switching structure in the hybrid supply modulator is employed. Additionally, input envelope signal sensing stage is employed for implementation multi-mode operation. To compare the performance of the proposed hybrid supply modulator, the conventional hybrid supply modulator is also designed. The measured efficiency of the proposed hybrid supply modulator is 85 %/84 %/79 % for EDGE/WCDMA/LTE signals which have 384 kHz/3.84 MHz/5 MHz bandwidth, respectively. The efficiency of the proposed hybrid supply modulator is higher than the conventional hybrid supply modulator. Therefore, this structure shows good candidate for the reconfigurable transmitters.

• Journal of Satellite, Information and Communications
• /
• v.2 no.2
• /
• pp.1-9
• /
• 2007

In this paper, we describe the performance degradation of satellite Wibro system and compensation method in the high-speed railroad channel environment. High-speed railroad channel environment is divided into LOS channel and tunnel. In the LOS channel, signal blocking caused by railroad power feeder structures can be a critical problem which is can be solved with antenna diversity. On the other hand, multi path interference phenomenon, representable by propagation model of Optic Fiber, occurred in the tunnel may be another obstacle. These satellite Wibro system performance degradations in railroad channel environment are addressed and adequate compensation methods are proposed and verified through computer simulation. In addition, the ICI caused by Doppler shift in OFDM system is analyzed with its compensation method.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.43 no.1 s.343
• /
• pp.133-142
• /
• 2006

This paper suggests an efficient method of protection ratio(PR) calculation and shows some results of point-to-point radio relay system for frequency coordination. The proposed PR can be expressed as a function of C/N of modulation scheme, noise-to-interference ratio(N/I), multiple interference allowance, fade margins of multi-Path and rain attenuation and net filter discrimination. And PR calculation is performed in view of fade margin, modulation scheme, distance, and interference for actual point-to-point radio relay frequency. According to results for 6.2 GHz, 64-QAM and 60 km at BER 10-6, fade margin and co-channel Protection ratio reveal 41.1dB and 74.9 dB, respectively The merit of presented method provides a systematic and easy calculation by means of PR correction factor related with various parameters and can apply the same concept to frequency coordination of millimeter wave radio relay system.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.8
• /
• pp.1901-1907
• /
• 2015

Today's smartphones and user devices are equipped with multiple radio interfaces increasingly. Aggregating theses multiple radio interfaces and using them concurrently will increase a user's communication speed immediately, but at the expense of increased power consumption. In this paper, we develop a mathematical performance model of an adaptive radio activation scheme by which a radio interface is activated only when needed for performance increase and deactivated otherwise. The developed model shows that the adaptive scheme reduces delay significantly and almost halves power consumption below a certain level of traffic input.

• Journal of Information Processing Systems
• /
• v.17 no.3
• /
• pp.615-629
• /
• 2021

With the development of mobile edge computing, how to utilize the computing power of edge computing to effectively and efficiently offload data and to compute offloading is of great research value. This paper studies the computation offloading problem of multi-user and multi-server in mobile edge computing. Firstly, in order to minimize system energy consumption, the problem is modeled by considering the joint optimization of the offloading strategy and the wireless and computing resource allocation in a multi-user and multi-server scenario. Additionally, this paper explores the computation offloading scheme to optimize the overall cost. As the centralized optimization method is an NP problem, the game method is used to achieve effective computation offloading in a distributed manner. The decision problem of distributed computation offloading between the mobile equipment is modeled as a multi-user computation offloading game. There is a Nash equilibrium in this game, and it can be achieved by a limited number of iterations. Then, we propose a distributed computation offloading algorithm, which first calculates offloading weights, and then distributedly iterates by the time slot to update the computation offloading decision. Finally, the algorithm is verified by simulation experiments. Simulation results show that our proposed algorithm can achieve the balance by a limited number of iterations. At the same time, the algorithm outperforms several other advanced computation offloading algorithms in terms of the number of users and overall overheads for beneficial decision-making.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.7B
• /
• pp.1098-1104
• /
• 2010

Recently, a variety of research of multi-hop routing protocol have been done to balance the sensor node energy consumption of WSN(wireless sensor network) and to improve the node efficiency for extending the life of the entire network. Especially in multi-hop protocol, a variety of models have been concerned to improve energy efficiency and apply in the reality. In multi-hop protocol, we assumption that energy consumption can be adjusted based on the distance between the sensor nodes. However, according to the physical property of the actual WSN, it's hard to establish this assumption. In this dissertation, we propose low-power sub-cluster protocol to improve the energy efficiency based on the spread of distance. Compared with the previous protocols, this proposed protocol can be effectively used in the wireless sensing networks.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.48 no.5
• /
• pp.129-136
• /
• 2011

This paper presents the coding method that have multi-mode and efficiency of audio codecs using the feature of audio signal. Recently, the developed extension super-wideband codec based on G.718 wideband divides two mode between Generic and Sinusiodal. So codec efficently encode audio signal exist in super-wideband. But the codec is not as efficent coding for harmonic component of wind instrument and string instrument and individual-Line component of percussion instrument. The proposed method are modeling and encoding multiple pitch and individual-line feature using multi mode coding. For the performance evaluation, we used SNR in MDCT domain for objective test and MUSHRA test for subjective test. As a result, the performance of SNR and MUSHRA test of the proposed method have better performance than the G.718 super-wideband codec.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39A no.2
• /
• pp.77-85
• /
• 2014

Recently, utilization of MIMO(Multi-Input Multi-Output) system using array antennas is evaluated significantly according to the extension of high-capacity and high-speed communication services. However, MIMO system has disadvantages such as high-complexity and high-power-consumption, because RF(Radio Frequency) chain is required as antenna number, and several array antenna is used in conventional MIMO system. In order to solve these problems, research about beamspace MIMO system using ESPAR(Electronically Steerable Parasitic Array Radiator) antenna that has single RF chain by using one active antenna and several parasitic elements has been studied actively. Beamspace MIMO system using ESPAR antenna is possible to solve the problems of conventional MIMO system, because this system is composed by single RF chain. In this paper, in order to improve the system security, chaos communication algorithm that has characteristics such as non-periodic, non-predictability, easy implementation and initial condition is applied to QPSK (Quadrature Phase Shift Keying) modulated beamspace MIMO system. We design the chaos QPSK modulated beamspace MIMO system, and evaluate SER performance of this system.

• Journal of Navigation and Port Research
• /
• v.34 no.10
• /
• pp.769-774
• /
• 2010

The performance of underwater communication system is influenced on channel characteristic. Delay spread cause by reverberation and multi-path happen the ISI (Inter Symbol Interference) and reduces the communication performance. In this paper, we analyze the performance of acoustic communication experiment in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for overcome the reverberation and multi-path. As a result, we acquired the BER of modulation techniques. The BER of 2kbps data rate is $1.22{\times}10^{-1}$ and BER of 4 kbps data rate is $2.47{\times}10^{-2}$.