• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4A
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• pp.302-308
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• 2009

In this paper, two receive diversity combining techniques are proposed for single-carrier Sequency division multiple access (SC-FDMA)-based cooperative relay systems when DFT spreading sizes for mobile station (MS) and relay station (RS) are different. A simplified-MRC (5-MRC) technique performs diversity combining in the time domain using the estimated channel weight and initial values obtained by SC-FDMA signal detection. An interference rejection-MRC (IR-MRC) technique performs diversity combining in the frequency domain by adjusting DFT spreading size in the receiver. It is shown by computer simulation that the proposed receive diversity combining techniques achieve a significant performance gain over the conventional MRC technique with zero forcing (ZF) detector.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.307-314
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• 2010

In this paper, a receive diversity combining technique is proposed for single-carrier frequency division multiple access (SC-FDMA)-based cooperative relay systems when discrete Fourier transform (DFT) spreading sizes for mobile station (MS) and relay station (RS) are different. The proposed technique is composed of a DFT spreading size adjustment block, a phase rotation compensation block, a channel phase compensation block, and a receive diversity combining block. The proposed technique is robust to multipath channels and can be operated with a relatively small computational complexity because receive diversity combining is performed with scalar operations in the frequency-domain. It is shown by computer simulation that the proposed receive diversity combining techniques achieve a performance gain over the conventional maximal ratio combining (MRC) techniques for SC-FDMA-based cooperative relay systems.

• Journal of Convergence Society for SMB
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• v.6 no.3
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• pp.49-55
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• 2016

This paper proposes an adaptive video signal transmission scheme in order to ensure the QoS (Quality of Service) of user requirements. SVC (Scalable Video Coding) is an effective transmission scheme, because that can transmit video signal according to the video layer's weight. However, in previous works, those adaptive transmission systems which are considered about the various channel environments and user requirements have not been insufficiently studied. So, we propose the SVC signal transmission using inter-layer differential OVSF code allocation scheme in MC-CDMA. The proposed scheme is able to obtain each layer signal's protection order and control the sub-block of MC-CDMA by feedback information from receiver. Therefore, our proposed scheme is possible to provide the video quality for each users according to variable channel environments. The simulation results demonstrate the enhancement of proposed system in terms of BER performance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2623-2631
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• 2010

In this paper, we propose a new interference cancellation(IC) receiver for multirate Multicarrier DS/CDMA(MC DS/CDMA) system based on orthogonal variable spreading factor(OVSF) code. The users are assigned different lengths of OVSF codes as a spreading code according to their data rates and the active users having same representative code split into a group for effective cancellation. The code grouping interference cancellation(IC) receiver performs cancellation between the groups first and cancellation within group. This proposed IC receiver can cancel the interferences using desired user's code information and then desired signals are detected. The results show that the large improvement in performance can be attained by group-wise IC scheme and we can make the effective systems compare to conventional ones. The bit error rate of the system is analytically derived in frequency selective Rayleigh fading channel and we also compare the system performance with that of multirate DS/CDMA system. We also analyze the performance of the proposed system with same bandwidth and processing gain. The results show the large improvement in performance that can be attained by cancellation scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.4 s.119
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• pp.351-357
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• 2007

In this paper, we propose a new cooperative signaling structure based on CDMA to overcome both 2/3 spectrum efficiency and low diversity gain of conventional cooperative signaling through continuous overlapping of signal that each user wants to transmit. Proposed signal structure can achieve the spectrum efficiency nearly "1" by receiving additional data for next time as well as maximum diversity gain to detect data continuously at both base station and each user. The orthogonality of CDMA's spreading codes can improve performance of optimal detector by reducing inter-user channel environment and distinguishing each user. We perform the computer simulation to verify the proposed system through comparing cooperative mode and non-cooperative mode under Rayleigh fading channel plus AWGN (Additive White Gaussian Noise).

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.3
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• pp.213-224
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• 2010

An optically controlled silicon MESFET (OPFET) was fabricated by diffusion process to enhance the quantum efficiency, which is the most important optoelectronic device performance usually affected by ion implantation process due to large number of process induced defects. The desired impurity distribution profile and the junction depth were obtained solely with diffusion, and etching processes monitored by atomic force microscope, spreading resistance profiling and C-V measurements. With this approach fabrication induced defects are reduced, leading to significantly improved performance. The fabricated OPFET devices showed proper I-V characteristics with desired pinch-off voltage and threshold voltage for normally-on devices. The peak photoresponsivity was obtained at 620 nm wavelength and the extracted external quantum efficiency from the photoresponse plot was found to be approximately 87.9%. This result is evidence of enhancement of device quantum efficiency fabricated by the diffusion process. It also supports the fact that the diffusion process is an extremely suitable process for fabrication of high performance optoelectronic devices. The maximum gain of OPFET at optical modulated signal was obtained at the frequency of 1 MHz with rise time and fall time approximately of 480 nS. The extracted transconductance shows the possible potential of device speed performance improvements for shorter gate length. The results support the use of a diffusion process for fabrication of high performance optoelectronic devices.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.85-90
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• 2008

In this paper, we studied on dual reflector adjusted to monopulse antenna system. As a result, when the efficiency of main reflector is more than 70%, The size of reflector is 30 wavelength of maximum frequency and minimum frequency gain is 37.9dBi, and Maximum frequency gain is 38.6dBi. Also, when a radius is D and Focus-distance is $F_e$, a scheme for efficiency improvement of Sub Reflector is to increase the Focus-distance to Diameter Ratio. In this case, Cross polarization in Far field improved and spherical spreading loss in circumference of reflector reduced. The influence of Radiation pattern followed by the side displacement of feed antenna(at $x_sy_s$) is decreased, it is confirmed that performance of scanning is improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.680-687
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• 2013

We investigate a generalized combined power and rate adaptation scheme in direct-sequence (DS) code-division multiple-access (CDMA) communications over Nakagami fading channels. The transmission power allocated to user i is proportional to $G^p_i$, where $G_i$ is the channel gain of user i and p is a real number, and the data rate (i.e., spreading gain) is jointly adapted so that a desired QoS is maintained. We analyze the average data rate of the proposed adaptation scheme subject to fixed average and peak transmission power constraints. Our results show that the proposed joint adaptation scheme provides a significant performance improvement over power-only and rate-only adaptation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.9
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• pp.757-766
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• 2014

To compensate signal loss due to the channel blockage in satellite communication link, we propose a cooperative communication scheme for OTM(On-The-Move) terminal in next generation satellite communication systems. The proposed scheme configures cooperation subnet with adjacent OTM terminal with the help of ground communication equipment. Shared data is spread by orthogonal spreading code, then the spread sequences are transmitted simultaneously. The receiver combines the power of received signals by EGC(Equal gain combining). The OTM terminal blockage channel is modeled by 2-state Markov chain. We evaluate the bit error rate according to the blockage channel of the channel state for the performance analysis of the proposed scheme. As a result, the proposed scheme shows better BER performance than traditional scheme with the help of subset members. In particular, the proposed scheme shows superior performance as the channel block probability is higher. However, as the number of subset members is increasing, there is a constraint because of the higher multiple access interference.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.8
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• pp.1-9
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• 2009

In this paper, we describe DSSS transceiver development robust to jamming signals as an investigation of ECCM transceiver for UAV uplink. The jamming margin is 15dB or greater with the development target of transceiver because the jamming margin is more important than the transmission rate of data and the spreading code can be changeable. The rake receiver is applied to combine multipath components and turbo code which the coding gain is 7.2dB as a FEC. In this paper, the whole structure, design method and functional test result about the designed modem are described and a conclusion is made.