• Proceedings of the KSR Conference
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• 2008.06a
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• pp.339-342
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• 2008

In this paper, the lessons and learns are introduced from the result of the trial project which is the first CBTC(Communication Based Train Control System) at Korail Bundang Line. This project has started end of 2002 and finished recently by Samsung SDS. The main purpose of this project was that new technology was seek for next generation of railway signal control system adapted in Korea. In 2002, there was no any revenue service system using Radio Frequency CBTC in the world at that time. Just a few trial project was on going in USA and EU. In well developed cities, the metro system have been built and old enough therefore they have to be considering re-signalling their existing system with advanced system for increasing availabilities of line usage and safety. This Bundang Line Trial Project was the first Korean CBTC project for above reasons. Most sub systems have been developed using local technology such as Electronics Controlled Interlocking System and Track Circuit Systems etc. Specially, in this project the RF-Communication devices are developed by local technology using DSSS(Direct Sequency Spread Spectrum) instead of FHSS(Frequency Hopping Spread Spectrum). This project has lasted for more than five years originally planned for three years because it was only accessible only night time in the main line from Ori to Suseo about 20km long. Each night only 2 and half hours are available to use the main line. Now the trial project has been done successfully with meet the customer's requirement, therefore the upgrade the mainline of Bundang line and another extension area up to Wangsipli to make revenue service using this new technology. This paper shows this result of the trial project and the strategy of upgrade and extension project as well.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.407-412
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• 2014

In this paper, we propose an underwater acoustic communication of FH-MFSK(Frequency-Hopped Multiple Frequency Shift Keying) system with multiple orthogonal property. Generally, the processing of FSK(Frequency Shift Keying) method is simple, but it is vulnerable to ISI (Inter-Symbol Interference) caused by multipath transmission. In this paper, the orthogonal codes are generated with the same number of transmitting symbols, and these codes are corresponding to multiple frequencies. We used m-sequence to generate multiple orthogonal codes. We compared the performance of proposed method with conventional MFSK method via the experiment. As a result, we confirmed that the proposed method shows 6~10 % lower error rate at 100 bps than conventional method.

• Journal of Adhesion and Interface
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• v.20 no.4
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• pp.155-161
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• 2019

Understanding charge transport anisotropy at the interface of conjugated nanostructures basically gives insight into structure-property relationship in organic field-effect transistors (OFET). Here, the anisotropy of the field-effect mobility at the interface between 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) single crystal with cofacial molecular stacks in a-b basal plane and SiO gate dielectric was investigated. A solvent exchange method has been used in order for TIPS-pentacene single crystals to be grown on the surface of SiO₂ thin film, corresponding to the charge accumulation at the interface in OFET structure. In TIPS-pentacene OFET, the anisotropy ratio between the highest and lowest measured mobility is revealed to be 5.2. By analyzing the interaction of a conjugated unit in TIPS-pentacene with the nearest neighbor units, the mobility anisotropy can be rationalized by differences in HOMO-level coupling and hopping routes of charge carriers. The theoretical estimation of anisotropy based on HOMO-level coupling is also consistent with the experimental result.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4C
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• pp.485-493
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• 2004

The system performance of 2-Dimensional wavelength hopping/time spreading optical CDMA systems is found to be limited by the occurrence of the beat noise between the components of the signal and the multiple user interference. This paper shows that the performance is analyzed under the beat noise and no beat noise to blow impact of the beat noise. To overcome this problem, the OHL(Optical Hard-Limiter) is used in the receiver. The performance is calculated for a optical CDMA system employing asymmetric and symmetric prime-hop 2-Dimensional codes, respectively The analysis results show that the performance improved 3.5 times of simultaneous users of before and after inserting OHL in the case of no beat noise. In the case of beat noise the performance improved 1.5 times of simultaneous users of before and after inserting OHL. The performance marked use of symmetric prime-hop code.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5C
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• pp.443-451
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• 2003

We propose an appropriate approach of defining the linear complexities (LC) of sequences over unknown symbol set. We are able to characterize those p-ary sequences whose R-tuple versions now eve. GF($p^{R}$ ) have the same characteristic polynomial as the original with respect to any basis. This leads to a construction of $p^{R}$ -ary sequences whose characteristic polynomial is essentially over GF(p). In addition, we can characterize those $p^{R}$ -ary sequences whose characteristic polynomials are uniquely determined when symbols are represented as R-tuples over GF(p) with respect to any basis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.901-911
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• 1994

The error performance of M-ary differential phase shift keying (MDPSK) through m-distribution fading channel in hybrid direct sequence/slow frequency hopped spread spectrum multiple access (DS/SFH-SSMA) systems has been evaluated, and also the error probability has been evaluate when adopting diversity technique and coding technique. From the results, we know that the error performance more deteriorates as depth of fading becomes deeper. In Rayleigh fading environment (m=1), increasing of the number of frequency hopping (q) reduces the effect of multiple access interference, because it decreases the probability a hit. When q is much larger than the number of user (K), the probability of error in high E/N region is dominated by the multipath interference while the multiple access interference is negligible. In lower E/N region, the probability of error is independent of q because the effect of gaussian noise becomes dominat.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1177-1188
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• 2004

This paper describes and analyzes the performance of MB-OFDM UWB system that is suggested as one of standards in IEEE 802.15 TG3a for UWB application. UMBchannel model that has been contributed in IEEE 802.15 SG3a is a wideband channel model of 6Ghz bandwidth, so we modify it to have 3 subband channels that are obtained by filtering conventional U Channel, considering center frequency hopping and system bandwidth. From simulations, we compare performances of MB-OFDM system in AWGN and WB channel and verify the frequency and time domain diversity gains from time End frequency spreading technique. We also compare and analyze the performance of proposed SFBC MB-OFDM with that of conventional MB-OFDM system. Simulation results show SFBC MB-OFDM system outperforms conventional MB-OFDM system about 1.5dB of Eb/No at target BER of 10$^{-m4}$./.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4A
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• pp.250-258
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• 2005

An initial carrier frequency offset estimation algorithm is proposed for a multi-user frequency bowing orthogonal frequency division modulation-frequency division multiple access (FH-OFDMA) system with a single preamble symbol. To mitigate the effect of the frequency offset, every mobile station needs to accurately and rapidly acquire synchronization. The proposed algorithm uses only one preamble symbol in which two kinds of subcarriers are designed for coarse and fine frequency offset estimation. The non-data aided estimation using the energy spectrum is exploited for fine offset estimation, and maximum likelihood estimation using correlation for coarse offset estimation. By combining the two estimation results, an accurate frequency offset can be estimated with a single symbol. Through simulations, the performance of the proposed algorithm is evaluated by comparing estimation error variance with a conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.168-180
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• 1992

Commumication technology has been continuously developed to overcome the distance and time for the transmission of information to the human society. Wireless mobile communication, which had been used mostly in the military and police is widely used these days for enterprise and individuals. Therefore the domestic usage of the advanced mobile phone service are progressively gaining wide popularity. The modulation techniques used usually in mobile communications were the analog techniques such as AM and FM, but they are getting replaced by the digital techniques, However, the major disadvantage of the digital communications is the increase of the transmission bandwidth. Therefore, it is very important to use efficiently the limited frequency bandwidth. The domestic research and development on the subject seems quite limited and in order to establish the technology of the digital mobile communications. This thesis presents the design of the frequency hopping synthesizer providing 124 channels with a channel spcing of 200KHz. VCD used in the synthesizer employs a semi-rigid cable for higher purity of signal spectrum, and a hybrid pgase detector is realized with a sample hold phase detector in conjuction with a tri-state phase detedctor.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.12
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• pp.1315-1320
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• 2015

In this paper Communication data link equipment on a high speed-hopping method to use the frequency resources efficiently for the frequency environment is introduced such as sensing techniques, using the same frequency band by using the received two-channel technique and the receive filter bank unit applied to be shared with other equipment such as radar and so on. The real-time measurement and analysis were operated for measurement the frequency environment of the operating band in advance. and primarily equipment to develop is analyzed how the interference effect to the radar minimize the operation of radar equipment. In reverse, to use the same frequency band the methods such as frequency sharing techniques are presented in this paper. Finally, by design of the main items of the RF transceiver NF, transmission output, and a simulation of the IMD, such as whether the key is verified prior to meet specifications.