• Journal of Computing Science and Engineering
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• 제7권3호
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• pp.187-197
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• 2013

Security has long been a challenging problem in wireless networks, mainly due to its broadcast nature of communication. This opens up simple yet effective measures to thwart useful communications between legitimate radios. Spread spectrum technologies, such as direct sequence spread spectrum (DSSS), have been developed as effective countermeasures against, for example, jamming attacks. This paper surveys previous research on securing a DSSS channel even further, using physical layer attributes-keyless DSSS mechanisms, and watermarked DSSS (WDSSS) schemes. The former has been motivated by the fact that it is still an open question to establish and share the secret spread sequence between the transmitter and the receiver without being noticed by adversaries. The basic idea of the latter is to exploit the redundancy inherent in DSSS's spreading process to embed watermark information. It can be considered a counter measure (authentication) for an intelligent attacker who obtains the spread sequence to generate fake messages. This paper also presents and evaluates an adaptive DSSS scheme that takes both jam resistance and communication efficiency into account.

• Journal of Communications and Networks
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• 제14권3호
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• pp.230-236
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• 2012

Based on the known binary sequence sets and Gray mapping, a new method for constructing quaternary sequence sets is presented and the resulting sequence sets' properties are investigated. As three direct applications of the proposed method, when we choose the binary aperiodic, periodic, and Z-complementary sequence sets as the known binary sequence sets, the resultant quaternary sequence sets are the quaternary aperiodic, periodic, and Z-complementary sequence sets, respectively. In comparison with themethod proposed by Jang et al., the new method can cope with either both the aperiodic and periodic cases or both even and odd lengths of sub-sequences, whereas the former is only fit for the periodic case with even length of sub-sequences. As a consequence, by both our and Jang et al.'s methods, an arbitrary binary aperiodic, periodic, or Z-complementary sequence set can be transformed into a quaternary one no matter its length of sub-sequences is odd or even. Finally, a table on the existing quaternary periodic complementary sequence sets is given as well.

• Journal of applied mathematics & informatics
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• 제4권1호
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• pp.147-166
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• 1997

The convergence of the power sequence of an $n{\times}n$ fuzzy matrix has been studied. Some theoretical necessary and sufficient con-ditions have been established for the power sequence to be convergent generally. Furthermore as one of our main concerns the convergence index was studied in detail especially for some special types of Boolean matrices. Also it has been established that the convergence index is bounded by $(n-1)^2+1$ from above for an arbitrary $n{\times}n$ fuzzy matrix if its power sequence converges. Our method is concentrated on the limit behavior of the power se-quence. It helped us to make our proofs be simpler and more direct that those in pure algebraic methods.

• 한국음향학회지
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• 제40권4호
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• pp.370-381
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• 2021

본 논문에서는 수중 통신에서 은밀성과 성능 향상을 위해 직접 수열 확산 방식 기반 다중 밴드 기법을 사용한 부 대역 Frequency Shift Keying(FSK) 신호의 효율적인 송수신 구조를 제시하였다. 은밀성적인 측면에서는 Pseudo Noise(PN) 부호의 chip을 직접 곱하는 직접 수열 대역 확산 방식을 적용하였으며, 성능적인 측면에서는 다중 경로 특성, 도플러 확산 등으로 인한 성능 감쇠를 극복하기 위해 다중 밴드, 터보 등화, 각 밴드별 가중치 알고리즘을 적용하였다. 시뮬레이션 결과를 바탕으로, 송수신기 사이의 거리가 약 300 m ~ 500 m인 호수에서 기동 실험을 하여 대역확산 신호의 chip 수를 8개, 32개로, 다중 밴드 수는 4개 일 때의 성능을 분석하였으며, chip 수가 증가할수록, 터보 등화 기법 적용 시 반복횟수가 증가할수록 성능이 향상되었고, 다중 밴드에서 프리엠블 오류율을 분석하여 밴드 별 가중치를 적용 시 더 많은 패킷 전송 성공률을 나타냈다.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2319-2328
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• 2018

This paper introduces a control method for a transformerless MMC-HVDC system. The proposed method can effectively control the grid currents of the MMC-HVDC system under unbalanced grid conditions such as a single line-to-ground fault. The proposed method controls the currents of the positive sequence component and the negative sequence component without separating algorithms. Therefore, complicated calculations for extracting the positive sequence and the negative sequence component are not required. In addition, a control method to regulate a zero sequence component current under unbalanced grid conditions in the transformerless MMC-HVDC system is also proposed. The validity of the proposed method is verified through PSCAD/EMTDC simulation.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1241-1250
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• 2018

Parallel three-phase voltage source inverters in a direct connection configuration are widely used to increase system power ratings. A zero-sequence circulating current can be generated according to the switching method; however, the zero-sequence circulating current not only distorts current, but also reduces the system reliability and efficiency. In this paper, a model predictive control scheme is proposed for parallel inverters to drive an interior permanent magnet synchronous motor with zero-sequence circulating current suppression. The voltage vector of the parallel inverters is derived to predict and control the torque and stator flux components. In addition, the zero-sequence circulating current is suppressed by designing the cost function without an additional current sensor and high-impedance inductor. Simulation and experimental results are presented to verify the proposed control scheme.

• 생명과학회지
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• 제8권1호
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• pp.102-108
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• 1998

Gltcosylphosphatidylinositol (GPI)에 의해 고정된 단백질의 초기 형태는 골지체에서의 직접적인 processing을 수행하기 위한 아미노와 카르 복시 말단의 hydrophobic signal sequence를 소유하고 있다. 앞서, mouse 임파구로부터 NAD;arginine ADP-ribosyltransferase (Yac-1)가 클로닝되었으며 Yac-1 transferase의 아미노산 배열을 추정해 본 결과, hydrophobic 아미노와 카르복시 말단을 포함하고 있었으며 이는 GPI-anchroed 단백질들의 알려진 signal sequence와 일치하였다. 미 transferase는 야생형의 cDNA로 transfection된 NMU (rat mammary adenocarcinoma) cell의 표면에 존재하였으며 phosphoatidylinosotol-specific phospholipase C에 의해 방출되어졌다. 카르복시 말단의 hydrophobic sequence가 없는 돌연변이체는 수용성이며 분비성인 transferase를 생산하였다. 이러한 사실은 카르복시 말단의 sequence가 없는 돌연변이체는 수용성이며 분비성인 transferase를 생산하였다. 이러한 사실은 카르복시 말단의 sequence가 GPI의 부착에 중요함을 나타내준다.

• Journal of Ginseng Research
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• 제33권1호
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• pp.55-58
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• 2009

Generally, the direct sequencing through PCR is faster, easier, cheaper, and more practical than clone sequencing. Frequently, standard PCR amplification is usually interpreted by mispriming internal or external regions of the target template. Normally, DNA fragments were eluted from the gel using Gel extraction kit and subjected to direct sequencing or cloning sequencing. Cloning sequencing has often troublesome and needs more time to analyze for many samples. Since touchdown (TD) PCR can generate sufficient and highly specific amplification, it reduces unwanted amplicon generation. Accordingly, TD PCR is a good method for direct sequencing due to amplifying wanted fragment. In plants the 5S-rRNA gene is separated by simple spacers. The 5S-rRNA gene sequence is very well-conserved between plant species while the spacer is species-specific. Therefore, the sequence has been used for phylogenetic studies and species identification. But frequent occurrences of spurious bands caused by complex genomes are encountered in the product spectrum of standard PCR amplification. In conclusion, the TD PCR method can be applied easily to amplify main 5S-rRNA and direct sequencing of panax ginseng cultivars.

• ETRI Journal
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• 제19권1호
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• pp.1-12
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• 1997

In this paper, we present an improved multicarrier direct sequence (DS) code division multiple access (CDMA) scheme by modifying the system originally proposed by Kondo and Milstein [13]. In this modified system, different spreading sequences multiplied by a data sequence modulate different carriers. This is to prevent the multiple access capability from reducing when the fading characteristics of different carrier frequencies are highly correlated. We have derived a formula which determines the mean values of the relative received signal strength in a single carrier DS CDMA rake system and in a multicarrier DS-CDMA system. We present results on the comparison of the bit error rate (BER) performance of the two systems including the effect of correlation between fading characteristics of different frequencies under various multipath fading conditions. The results indicate that with 50 users the modified multicarrier DS CDMA system can achieve an uncoded irreducible BER of $1.7{\times}10^{-3}$ with an average received signal-to-noise ratio per bit of 10dB, which is better that $3.0{\times}10^{-3}$ achieved by the single carrier DS CDMA rake system, and also show that if multicarrier CDMA system is used with respect to single carrier CDMA system, the SNR gain is up to 4.5 dB for the uncode BER of $10^{-3}$ being achieved.

• Journal of Communications and Networks
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• 제7권3호
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• pp.243-247
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• 2005

We propose an efficient block least-mean-square (BLMS) adaptive algorithm, in conjunction with error control coding, for direct-sequence code division multiple access (DS-CDMA) systems. The proposed adaptive receiver incorporates decision feedback detection and channel encoding in order to improve the performance of the standard LMS algorithm in convolutionally coded systems. The BLMS algorithm involves two modes of operation: (i) The training mode where an uncoded training sequence is used for initial filter tap-weights adaptation, and (ii) the decision-directed where the filter weights are adapted, using the BLMS algorithm, after decoding/encoding operation. It is shown that the proposed adaptive receiver structure is able to compensate for the signal-to­noise ratio (SNR) loss incurred due to the switching from uncoded training mode to coded decision-directed mode. Our results show that by using the proposed adaptive receiver (with decision feed­back block adaptation) one can achieve a much better performance than both the coded LMS with no decision feedback employed. The convergence behavior of the proposed BLMS receiver is simulated and compared to the standard LMS with and without channel coding. We also examine the steady-state bit-error rate (BER) performance of the proposed adaptive BLMS and standard LMS, both with convolutional coding, where we show that the former is more superior than the latter especially at large SNRs ($SNR\;\geq\;9\;dB$).