• Journal of Satellite, Information and Communications
• /
• v.10 no.1
• /
• pp.12-16
• /
• 2015

In this paper, we introduce a wireless package system based on the amateur radio HR(HAM Radio) and satellite communication as a novel wireless disaster communication system and have configured a interference scenario receiving interference from adjacent base stations and D2D groups in the disaster network. In such interference scenarios, we propose a frequency re-allocation method to avoid interference and communicate with disaster networks by securing the channel capacity required between D2D terminals. As a result of computer simulation, we can find the proposed method has improved BED performance of a gain of 1.5dB and overall system throughput than conventional methods.

• Journal of information and communication convergence engineering
• /
• v.18 no.3
• /
• pp.155-161
• /
• 2020

The fifth generation (5G) is a state-of-the-art mobile communication access technology that uses sub 6 GHz bands and mmWave. Presently, the 5G network is partially deployed along with 4G in areas with dense traffic. In the future, the demand for the 5G bandwidth may increase. Thus, it is necessary to study the coexistence between the 5G and radio systems using adjacent or same channels to eliminate the interference between radio systems and efficiently utilize the frequency. This paper analyzed the impact of 5G new radio downlink on the fixed-satellite service earth station operating at the co-channel and adjacent channel in the upper 3.7 GHz band using the Spectrum Engineering Advanced Monte Carlo Analysis Tool, which is based on the Monte Carlo method. The results of this paper can be utilized for planning the frequency allocation of 5G networks; they can also be used as a guideline for deploying 5G base stations around a fixed-satellite service earth station.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.7A
• /
• pp.587-596
• /
• 2005

In this paper, we propose an OFDMA/CDM-based cellular system, which accommodates multiple users in frequency-domain and multiplexes user data with frequency-domain spreading. The proposed system utilizes random codes to discriminate cells and adopts the pre-equalization to enhance the performance. For cellular applications, a number of pre-equalization techniques are compared and an efficient power allocation scheme is suggested with a transmit power constraint. Especially, the validity of OFDMA/CDM based cellular system is investigated, by comparing the performance for varying the number of multiplexed data symbols at different locations. Finally the pre/post-equalization is proposed to reduce the performance degradation caused by time delay.

• Korean Journal of Optics and Photonics
• /
• v.8 no.1
• /
• pp.68-72
• /
• 1997

Using one of the absorption lines of $^{13}C_2H_2$ molecules near the zero dispersion wavelength(1549.49nm) of dispersion shifted fiber, we stabilized center frequency of an optical fiber Fabry-Perot filter. The free spectral range of the filter is 100 GHz for 100 GHz channel allocation. For equi-spaced three channel multiplexing, channel locking of three DFB-LDs to transmission peaks of the fiber Fabry-Perot filter was tried. To investigate the effect of dithering current applied to each DFB-LD, the change of DFB-LD linewidth was measured.

• The Journal of Korean Medicine
• /
• v.21 no.2
• /
• pp.3-13
• /
• 2000

Objectives : In oriental medicine, Daeseungki-tang is one of the most useful prescriptions for the therapy of constipation. And we also frequently use this prescription for constipated stroke patients. Methods : In order to identify the effects of Daeseungki-tang on constipated stroke patients, we administrated the extract of Daeseungki-tang(code number, HH264) to constipated stroke patients. We gave the medicine in two ways, one-pack group and two-pack group by random allocation and investigated the amount of stool, the frequency of defecation, the stool-form and the changes of blood pressure and body temperature before and after defecation. We also tried to examine the difference of symptoms between defecation-group and non-defecation group. Results : 1. There were no distinct symptoms between defecation-group and non-defecation-group in one-pack group. 2. After defecation, body temperature decreased significantly(P<0.05) in one-pack group and blood pressure decreased significantly(P<0.05) in two-pack group. 3. As for the stool-form, watery-soft was 41.9% in the firstt defecation and 47.1 % in the second defecation. 4. In one-pack group(23 cases), 13 cases(57%) defecated and 10 cases(43%) didn't defecate. And in two-pack group(24 cases), 19 cases(80%) defecated and 5 cases(20%) didn't defecate. These results meant that the effect of Daeseungki-tang was dose dependent. The amount of stool and the frequency of defecation were also dose dependent.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.46 no.2
• /
• pp.11-17
• /
• 2009

This paper presents a new adaptive relay selection scheme for a regenerative orthogonal frequency division multiplexing access(OFDMA) relay network with fairness constrains. In the Proposed scheme, we select the best M relays out of a set of K potential relays to maximize system capacity. Among these selected relays, subcarriers are reallocated to satisfy fairness constraints as well as to minimize the degradation of the system performance. Afterwards, power allocation is performed for each subcarrier based on the water-filling method to enhance the performance improvement. By using the trade-off relationship between the system capacity and the fairness, the modified version of proposed scheme is also investigated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.11
• /
• pp.1323-1326
• /
• 2012

In military applications, many radar systems are simultaneously operated at a close range. In particular, the frequency allocation must be executed for operating the homogeneous radar systems at the same time. As many radar systems are simultaneously operated with overlapping frequency bands, interference between systems inevitably occurs. Because interference can degrade radar performance, suppression of interference is a critical issue in radar systems. In this letter, we analyze the interference between two FMCW radars. In addition, time synchronization method between radars using mutual interference is proposed. Experiments are carried out to validate the proposed method. The results demonstrate that the proposed method is suitable for real radar systems.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.6
• /
• pp.13-19
• /
• 2008

In this paper, the new cooperative communication techniques is proposed for multi-input multi-output(MIMO)-orthogonal frequency division multiplexing (OFDM) system using the relay with multiple antenna. As the MIMO channel is formed by space time coding at the MS(mobile station)-RS(relay station) and RS-BS(base station), we can get the cooperative diversity and MIMO diversity gain simultaneously. Therefore, the performance of MIMO-OFDM system using the relay with multiple-antennas is very improved. And the simple power allocation technique is Proposed for the transmitting power of the mobile station and the relay.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.1A
• /
• pp.1-11
• /
• 2009

In OFDMA or SC-FDMA systems one can generate time varying channels or frequency selective channels using multiple transmit antennas to achieve diversity without special space-time processing at the receivers. While low channel coding rate needs to be used for distributed-allocation SC-FDMA systems with a phase rolling technique to produce time fluctuation, relatively high channel coding rate can be used when cyclic delay diversity is used to increase frequency selectivity assuming quasi-static channel. On the other hand, for block-hopping SC-FDMA systems there is no significant difference between two diversity techniques in terms of optimal channel coding rates.

• International Journal of Contents
• /
• v.14 no.2
• /
• pp.1-6
• /
• 2018

In a wireless mobile communication system, a pilot signal has been considered to be a necessary signal for estimating a changing channel between a base station and a terminal. All mobile communication systems developed so far have a specification for transmitting pilot signals. However, although the pilot signal transmission is easy to estimate the channel,(Ed: unclear wording: it is easy to use the pilot signal transmission to estimate the channel?) it should be minimized because it uses radio resources for data transmission. In this paper, we propose a pilotless channel estimation scheme (PCE) by introducing the clustering method of unsupervised learning used in our deep learning into channel estimation.(Ed: highlight- unclear) The PCE estimates the channel using only the data symbols without using the pilot signal at all. Also, to apply PCE to a real system, we evaluated the performance of PCE based on the resource block (RB), which is a resource allocation unit used in LTE. According to the results of this study, the PCE always provides a better mean square error (MSE) performance than the least square estimator using pilots, although it does not use the pilot signal at all. The MSE performance of the PCE is affected by the number of data symbols used and the frequency selectivity of the channel. In this paper, we provide simulation results considering various effects(Ed: unclear, clarify).