• Journal of Communications and Networks
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• v.11 no.1
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• pp.11-19
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• 2009

Multicarrier direct sequence code division multiple access (MC DS-CDMA) is an attractive technique for achieving high data rate transmission. This is valid regardless of whether or not the potentially large peak-to-average power ratio (PAPR) is an important factor for its application. On the other hand, code select CDMA (CS-CDMA) is an attractive technique with constant amplitude transmission of multicode signal regardless of subchannels. This is achieved by introducing a code select method. In this paper, we propose a new multiple access scheme based on the combination of MC DS-CDMA and CS-CDMA. The proposed scheme, which we call MC CS-CDMA, includes as special cases the subclasses of MC DS-CDMA and CS-CDMA. This paper investigates the performance of these systems over a multipath frequency selective fading channel using a RAKE receiver with maximal ratio combiner. In addition, the PAPR of the proposed system is compared with that of both MC DS-CDMA and CS-CDMA. Simulation results demonstrate that the proposed system provides better PAPR reduction than MC DS-CDMA, at the expense of the complexity of the receiver and the number of available users. The numerical result demonstrates that the proposed system has better performance than MC DS-CDMA due to the increased processing gain and time diversity gain.

• The korean journal of orthodontics
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• v.45 no.4
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• pp.171-179
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• 2015

Objective: To compare dentoalveolar and skeletal changes produced by the pendulum appliance (PA) and the distal screw appliance (DS) in Class II patients. Methods: Forty-three patients (19 men, 24 women) with Class II malocclusion were retrospectively selected for the study. Twenty-four patients (mean age, $12.2{\pm}1.5years$) were treated with the PA, and 19 patients (mean age, $11.3{\pm}1.9years$) were treated with the DS. The mean distalization time was 7 months for the PA group and 9 months for the DS group. Lateral cephalograms were obtained at T1, before treatment, and at T2, the end of distalization. A Mann-Whitney U test was used for statistical comparisons of the two groups between T1 and T2. Results: PA and DS were equally effective in distalizing maxillary molars (4.7 mm and 4.2 mm, respectively) between T1 and T2; however, the maxillary first molars showed less distal tipping in the DS group than in the PA group ($3.2^{\circ}$ vs. $9.0^{\circ}$, respectively). Moreover, significant premolar anchorage loss (2.7 mm) and incisor proclination ($5.0^{\circ}$) were noted in the PA group, whereas premolar distal movement (1.9 mm) and no significant changes at the incisor ($0.1^{\circ}$) were observed in the DS group. No significant sagittal or vertical skeletal changes were detected between the two groups during the distalization phase. Conclusions: PA and DS seem to be equally effective in distalizing maxillary molars; however, greater distal molar tipping and premolar anchorage loss can be expected using PA.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.12
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• pp.69-75
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• 2004

In the paper, system is combined multiband system with DS-UWB techniques with properties including low peak-to-average power ratio, robustness to multiuser interference and excellent security. Because each sub-band is not satisfied with coherence bandwidth, rake receiver in each sub-band is applied to the Proposed system receiver. Output of rake receiver is combined by using Maximal Ratio combining technology. In this paper we mathematically analyse the BER of the DS-UWB system with singleband and multiband systems in the narrow interference channel condition and multi user interference channel condition, the simulation results show that proposed scheme is getting robuster with increasing of the number of subbands.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.9
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• pp.11-23
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• 2000

Multicarrier DS-CDMA is an effective approach to realize wideband CDMA system in a multipath fading channel. In this paper, we propose a convolutionally-coded overlapped multicarrier DS-CDMA system, and analyze the performance with subband overlapping variation to determine the overlapping percentage showing best performance. Given a total number of subcarriers M*R, we will show that the BER variation is highly dependent on the rolloff factor P of raised-cosine chip wave-shaping filter irrespective of convolutional encoding rate I/M and repetition coding rate 1/R. We also analyze the possibility of reduction in total MUI by considering both variation of a rolloff factor (0 ($\beta$ :1) and variation of subband overlapping factor (0 ( A :2), and show that the proposed system may outperform the multicarrier DS-CDMA system in [1, 12].

• Journal of the Korean Society of Food Science and Nutrition
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• v.35 no.4
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• pp.487-492
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• 2006

Acetylated rice starches were prepared by reaction of rice starch with acetic anhydride, and their physicochemical properties as a function of degree of substitution (DS) were evaluated. The percentage of acetyl group and DS were $0{\sim}2.71%\;and\;0{\sim}0.104$, respectively. DS increased with increase in acetic anhydride content. DS increased swelling power and solubility of rice starch. Light transmittance (%) values of acetylated rice starches were much higher than that of native rice starch and increased with increase in DS. Rapid Visco Analyzer initial pasting temperature of acetylated rice starches decreased with increase in DS, while peak viscosity and breakdown values increased. Starch gets showed a significant decrease in syneresis (%) with the increase in DS.

• Journal of Korean Neurosurgical Society
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• v.50 no.5
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• pp.415-419
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• 2011

Objective : The purpose of this study was to investigate the possible association of estrogen receptor alpha ($ER{\alpha}$) gene polymorphisms in a cohort of degenerative spondylolisthesis (DS) patients. Methods : Accordingly, the authors examined the association between DS and $ER{\alpha}$ gene polymorphisms in 174 patients diagnosed with DS. The $Pvu$ $II$ and $Xba$ $I$ polymorphisms, bone mineral density at the lumbar spine and femoral neck, and biochemical markers were analyzed and compared in the 174 patients with DS and 214 patients with spinal stenosis (SS). Results : A comparison of genotype frequencies in DS and SS patients revealed a significant difference for the $Pvu$ $II$ polymorphism only ($p$=0.0452). No significant difference was found between these two groups with respect to the $Xba$ $I$ polymorphism, BMD or biochemical markers. No significant association was found between the$Pvu$ $II$ polymorphism of $ER{\alpha}$ and BMD, vertebral slip or biochemical markers in patients with DS. Conclusion : These results suggest that the $ER{\alpha}$ gene polymorphism using $Pvu$ $II$ restriction enzyme influences the prevalence of DS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8B
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• pp.745-751
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• 2002

The performance of existing CDMA-type multiple access data transmission systems is limited by interferences due to adverse mobile communication channel characteristics. Among them, the multi-user interference becomes one of the major performance degradation factors because the signal-to-signal orthogonality can be easily perturbed when numerous user signals are distorted by multipath fading channels and mixed together. In order to enhance the performance of CDMA-type systems by suppressing the multi-user interference, we have adopted chip-based cyclic prefix insertion along with adaptive one-tap DFE equalization into MC-DS-CDMA, which is known for its robustness in the frequency selective multipath fading channel environment. In order to assess the performance of the proposed system, a set of computer simulations is performed in the reverse link in which each user signal undergoes different multipath Rayleigh fading. The results show us a superior performance of our system over other CDMA systems in terms of SNR to BER measurements.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.627-633
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• 2006

In spite of many advantages of Meteor Burst Communications(MBC) on its transmission channel, the fact that its duty rate is less than 10 percents is a considerable deficiency of MBC. To overcome with this deficiency without paying large cost, we use a direct sequence(DS) simple reception system. This method doesn't need to add the components for acquisition or tracking the signal so that it keeps the cost efficiency of the MBC. But it has a disadvantage that its duty rate shows a large decline by noise. For this problem we adopt the proposed system applying a transversal filter circuit. The improvement by this method is more significant when the received signal is weak Simulation results show as t1 is 100ms, then the burst length would be increased by 35% when the initial value of the received signal power increases by 3 dB, t2 is 135ms. If the power increases by 6dB the burst length would be 170ms thus increased by 70%, which shows a great enhancement. Suppose now that t1 is 50ms and the power is increased by 3dB, then t2 would be increased by 70% to 85ms, and increasing the power by 6dB it would be increased by 130% to 115ms.

• Clean Technology
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• v.10 no.3
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• pp.169-176
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• 2004

Sulfonated ionomer membranes, sulfonated poly(ether ether)ketone (SPEEK)-$AgNO_3$, were prepared and tested for separation of the isoprene/n-pentane mixtures. The facilitated transport membranes showed good selectivity and permeance of isoprene over n-pentane and long-term stability. Depending on various reaction conditions, the degree of sulfonation (DS) of SPEEK was measured by 1H NMR spectroscopy and the performance of the membranes was affected by the DS of SPEEK as a whole. As the DS of SPEEK was increased, the selectivity of isoprene over n-pentane increased and eventually reached a maximum selectivity of 850 ~ 900 and the stability of that was continued more than 100 h.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.74-84
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• 2008

UWB radio systems have drawn attention during the last few years. These systems are the core technique for ubiquitous home and enable to co-exist with other narrow band systems over the same frequency without interfering them. But UWB signals have a very low power per pulse, so they are affected by strong narrow band interferences. Specially, IEEE 802.11a systems which operate around 5GHz overlap the band of UWB signals and they will interfere with UWB systems significantly. In this paper, we propose a novel narrow band interference suppression method based on singular value decomposition(SVD) algorithm for DS-UWB in IEEE 802.15.4a channel model. The proposed method is very effective and robust for both a single user DS-UWB system and a multiuser DS-UWB system to reduce the narrow band interference.