• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8C
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• pp.782-791
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• 2002

This paper discusses a far-end crosstalk (FEXT) canceller for twisted-pair transmission. Many twisted-pair systems such as fiber-to-the-curb (FTTC), very high-speed digital subscriber line (VDSL), and high-speed LAN systems, use frequency-division duplexing (FDD) for duplex transmission. It is shown that the maximum reach of FDD twisted-pair system is limited by the performance of its upstream channel, which is located at higher frequencies than the downstream channel. In order to improve the performance of such FDD transceiver, FEXT cancellation is introduced for the channel at higher frequencies. A system arrangement and its blind start-up procedure are studied when the FEXT canceller and equalizer are jointly adapted to combat channel intersymbol interference (ISI), FEXT, and other additive noise. The initial convergence and the steady-state behavior of the proposed twisted-pair system without requiring transmission of an ideal training sequence are investigated. Measured characteristics as well as analytical model of the FEXT channel are used to estimate the time span needed for the FEXT canceller. It is also shown that the memory span for the FEXT canceller is almost independent of the channel, thus making our results useful for the twisted-pair system over all different channels.

• Journal of Plant Biotechnology
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• v.30 no.4
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• pp.307-313
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• 2003

Fluorescent differential display (FDD) is a method for identifying differentially expressed genes in eukaryotic cells. The mRNA FDD technology works by systematic amplification of the 3' terminal regions of mRNAs. This method involve the reverse transcription using anchored primers designed to bind 5'boundary of the poly A tails, followed by polymerase chain reaction (PCR) amplification with additional upstream primers of arbitrary sequences. The amplified cDNA subpopulations are separated by denaturing polyacrylamide electrophoresis. To identify the genes involved in the development of first trap leaf, we applied a FDD method using mRNAs from leaf base, first trap leaf and flower tissue, respectively. We screened several genes that expressed specifically in first trap leaf. Nucleotide sequence analysis of these genes revealed that these were protease inhibitor (PI), myo-inositol-1-phosphate synthase and lipocalin-type prostaglandin D synthase. Northern blot analysis showed that these genes were expressed specifically in first trap leaf (in vivo and in vitro). FDD could prove to be useful for simultaneous scanning of transcripts from multiple cDNA samples and faster selection of differentially expressed transcripts of interest.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.113-122
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• 2010

In this paper, we propose a CP (Cyclic Prefix) detection based SSS (Secondary Synchronization Signal) detection method for initial cell search in 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) FDD/TDD (Frequency Division Duplex/Time Division Duplex) dual mode downlink receiver. In general, a blind coherent SSS detection method which can detect SSS without CP detection is applied. However, coherent detection method caused performance degradation by channel compensation error at high speed environment because it uses estimated CFR (Channel Frequency Response) at PSS (Primary Synchronization Signal), and it can be more serious problem in TDD mode due to increased distance between PSS and SSS. Also blind detectionhas the drawback of high computational complexity. Therefore, we proposed a CP type pre-decision structure with non-coherent SSS detection which has stable operation in high speed channel environments for 3GPP LTE TDD mode as well as FDD mode, and can reduce computational complexity by applying CP detection before SSS detection. Simulation results show that the proposed method has stable operation for 3GPP LTE TDD/FDD dual mode downlink receiver in various channel environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.103-112
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• 2010

In this paper, we propose a coarse and fine frequency synchronization method which is suitable for the 3GPP(3rd Generation Partnership Project) LTE(Long Term Evolution) FDD(Frequency Division Duplexing) / TDD(Time Division Duplexing) dual mode system. In general, PSS(Primary Synchronization Signal) correlation based estimation method and CP(Cyclic Prefix) correlation based tracking loop are applied for coarse and fine frequency synchronization in 3GPP LTE OFDMA(Orthogonal Frequency Division Multiple Access) system, respectively. However, the conventional coarse frequency synchronization method has performance degradation caused by fading channel and squaring loss. Also, the conventional fine frequency synchronization method cannot guarantee stable operation in TDD mode because of signal power difference between uplink and downlink subframe. Therefore, in this paper, we propose enhanced coarse and fine frequency synchronization methods which can estimate more accurately in multi-path fading channel and high speed channel environments and has stable operation for TDD frame structure, respectively. By computer simulation, we show that the proposed methods outperform the conventional methods, and verify that the proposed frequency synchronization method can guarantee stable operation in 3GPP LTE FDD/TDD dual mode downlink receiver.

• Journal of Korean Neurosurgical Society
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• v.64 no.6
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• pp.891-900
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• 2021

Objective : Vertebral artery dissecting aneurysm (VADA) is a very rare subtype of intracranial aneurysms; when ruptured, it is associated with significantly high rates of morbidity and mortality. Despite several discussions and debates, the optimal treatment for VADA has not yet been established. In the last 10 years, flow diverter devices (FDD) have emerged as a challenging and new treatment method, and various clinical and radiological results have been reported about their safety and effectiveness. The aim of our study was to evaluate the clinical and radiological results with the use of FDD in the treatment of unruptured VADA. Methods : We retrospectively evaluated the data of all patients with unruptured VADA treated with FDD between January 2018 and February 2021 at our hybrid operating room. Nine patients with unruptured VADA, deemed hemodynamically unstable, were treated with FDD. Among other parameters, the technical feasibility of the procedure, procedure-related complications, angiographic results, and clinical outcomes were evaluated. Results : Successful FDD deployment was achieved in all cases, and the immediate follow-up angiography showed intra-aneurysmal contrast stasis with parent artery preservation. A temporary episode of facial numbness and palsy was noted in one patient; however, the symptoms had completely disappeared when followed up at the outpatient clinic 2 weeks after the procedure. The 3-6 months follow-up angiography (n=9) demonstrated complete/near-complete obliteration of the aneurysm in seven patients, and partial obliteration and segmental occlusion in one patient each. In the patient who achieved only partial obliteration, there was a sac 13 mm in size, and there was no change in the 1-year follow-up angiography. In the patient with segmental occlusion, the cause could not be determined. The clinical outcome was modified Rankin Scale 0 in all patients. Conclusion : Our preliminary study using FDD to treat hemodynamically unstable unruptured VADA showed that FDD is safe and effective. Our study has limitations in that the number of cases is small, and it is not a prospective study. However, we believe that the study contributes to evidence regarding the safety and effectiveness of FDD in the treatment of unruptured VADA.

• Proceedings of the SAREK Conference
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• 2006.11a
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• pp.92-92
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• 2006

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8A
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• pp.745-751
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• 2006

The transmitter requires knowledge of the channel status information in order to adopt the adaptive modulation and coding scheme(AMC) for OFDM system. But in the outdoor environment which the users have high mobility, the channel status information from the users is outdated, so that it induces the degradation of system throughput and packet error rate(PER) performance. To solve this problem, researches about applying channel prediction technique to the AMC scheme have been proceeded. Most channel prediction techniques assume that there is no channel variation in the predefined time duration, e.g., a slot. As a result, those techniques cannot compensate the degradation of PER performance resulting from the rapid variation of channel during the slot duration. This paper introduces a novel channel prediction technique for OFDM/FDD system to support adaptive modulation and coding scheme over rapidly time-varying multipath fading channel. The proposed channel prediction technique considers the time-varying nature of channel during the slot duration. Simulation results show that the AMC scheme of OFDM/FDD system utilizing the proposed channel prediction technique can guarantee the target PER of 1% without any loss of system throughput compared with the case supported by the conventional channel prediction under ITU-R Veh A 30km/h.

• Journal of Advanced Navigation Technology
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• v.11 no.4
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• pp.430-436
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• 2007

In this paper, we assume the uplink multiuser MIMO system based on FDD. Considering the implementation of practical system, Antenna selection and Transmit Beamforming scheme are suggested. System model of both two schemes are introduced and the scheduling algorithm which approaches the optimal performance with affordable computational complexity is proposed for each transmission scheme. Simulation results show that the sum-rate of the proposed low complexity scheduler approaches the performance of brute-force scheduler which is believed to be the optimal scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.9
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• pp.497-507
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• 2014

This paper investigates the standard features of Carrier aggregation (CA), the related UE RF requirements in 3GPP release 12 and estimated CA evolution in future. The main CA feature of 3GPP release 12 in WG4 perspectives includes 2Uplink(UL) CA, 3Downlink(DL) CA and TDD-FDD CA. To support these features in UE, UE-to-UE coexistence problem and RF requirements generated by unwanted emissions such as inter-modulation and harmonics are analyzed. Also, future CA technology such as LTE in unlicensed bands is described.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.140-146
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• 2004

In this paper we proposed the reducing method of feedback information for transmitting of adaptable data rate in multi-user OFDMA/FDD systems. In order to transmit downlink channel information to Base-Station(BS) through the limited uplink control channel, the proposed algorithm exploits the channel variation level which describes the similarity among the adjacent clusters and uses just one modulation and coding scheme(MCS) level representing channel information of all clusters'. We investigated the performance in single cell environment. It has a similar overhead for feedback information with conventional algorithm and has better performance in that bandwidth efficiency and outage probability than the conventional algorithms.