• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.5
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• pp.547-554
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• 2010

RFID is core technology to lead ubiquitous computing, and attract the notice of the world. It also improves social transparency, creates employment, and invigorates the allied industries. However, The technical characteristic with RFID has some problems with security and privacy. The commercialization of RFID is delayed due to these problems. This paper introduces the technical method to find solutions about an invasion of privacy to be due to introduce RFID system. First, this method applies Hash-Chain proposed by M. Ohkubo and some other researchers. The more tags increase, the more it demands lots of computation time. We divide SPs equally to solve these problems. And then, We'll suggest solutions to shorten the identification time of tag by implementing SPs with multi nodes of Grid environment at the same time. This makes it possible to keep the privacy protection of RFID tag, and process RFID tag in real time at the same time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.3
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• pp.681-686
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• 1999

In this study, the gain characteristics of the strained structures for SOA were calculated numerically and the optimized strained quantum well for the polarization-insensitive SOA was obtained. The structures used in this calculation were consisted of one, two, and three GaAs Delta layers respectively in the GaInAs(160 $\AA$) well. Moreover the third one was calculated by changing from one mono-layer to three mono-layers in the thichless of GaAs delta layers. This structure enhances the TM mode gain coefficient with good efficiency because the light-hole band is lifted up whereas the heavy-hole band is lowered down. Additionally, The structure of the 3 GaAs delta layers(1 mono layer thickness) shows 3dB gain bandwidth of 85nm in 1.55um wavelength system. This study is expected to be used in making a wide band and polarization-independent semiconductor optical amplifier practically.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.54-56
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• 2013

A subcarrier allocation scheme for base station (BS), relay station (RS) and mobile station (MS) can affect the performance of orthogonal frequency division multiple access (OFDMA) relay systems. In this paper, we propose a subcarrier allocation scheme with inter-cell interference and network coding in OFDMA relay systems. In the network coding zone, we consider an environment where RS can transmit a frame to BS and MS simultaneously. We divide an OFDMA frame into downlink zone, uplink zone, and network coding zone. The proposed scheme allocates subcarriers to BS, RS, and MS for each zone with consideration of inter-cell interference in OFDMA relay systems. We evaluate the performance of the proposed subcarrier allocation scheme through simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.378-383
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• 2004

Orthogonal Frequency Division Multiplexing (OFDM) transmits high-speed data by splitting the transmission bandwidth into a number of subcarriers. The bandwidth of each subcarrier is ensured to be smaller than the coherence bandwidth. This paper presents an OFDM system incorporated with the Carrier Interferometry (CI) codes to improve the performance by enhancing frequency diversity effect. The performances of CI-OFDM with multilevel modulations are investigated in highly dispersive fading channels. For the investigation of performance improvement of CI-OFDM, a simulator has been developed using a well-known SPW simulation platform. The simulation results show that the CI-OFDM provides both performance improvement and robustness against dispersive fading channel behavior. The performance of CI-OFBM with multilevel modulations demonstrates that CI-OFDM outperforms a traditional OFDM system, particularly in highly dispersive channels. With a relatively large delay spread of 151㎱ compared to the guard interval of 800㎱, CI-OFDM provides a BER of 10$^{-3}$ if sufficient signal power is present.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1A
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• pp.80-88
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• 2002

Visual media(image, graphic, and video) processing poses challenge from several perpectives, specifically from the point of view of real-time implementation and scalability. There have been several approaches to obtain speedups to meet the computing demands in multimedia processing ranging from media processors to special purpose implementations. A variety of parallel processing strategies are adopted in these implementations in order to achieve the required speedups. We have investigated a parallel processing system for improving the processing speed o f visual media related applications. The parallel processing system we proposed is similar to a pipelined memory stystem(MAMS). The multi-access memory system is made up of m memory modules and a memory controller to perform parallel memory access with a variety of combinations of 1${\times}$pq, pq${\times}$1, and p${\times}$q subarray, which improves both cost and complexity of control. Facial recognition, Phong shading, and automatic segmentation of moving object in image sequences are some that have been applied to the parallel processing system and resulted in faithful processing speed. This paper describes the parallel processing systems for the speedup and its utilization to three time-consuming applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.1933-1940
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• 1997

The development of CMOS IC chip and external system with optical transmission sytem is proposed in this paper, which deal with 4 subject 4 channel biological signals, receive and transmit biological signals to the external system using LED and infrared light of photodiode. This system decreases the dependency of power supply voltage to the COMS IC chip. A newenforce synchronization technique using infrared bi-directional communication has ben proposed. The telemetner IC with the size of $5.1{\times}5.1mm^2$ has the followingfunctions:receiving of command signal, initialization of internal state of all functional blocks, decoding of subject selection signal, time division multiplexing of 4-channel modulated biological signals, transmission of modulated signals to external system, and auto power down control. To confirm the total telemetry system, electrocardogram is transmitted and received to the external system using optical link.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.370-377
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• 2004

In this paper, we present an adaptive modulation technique for orthogonal frequency division multiplexing (OFDM) for broadband wireless communications. Also, using improved channel prediction, we enhance the performance of adaptive OFDM in high mobility environments. Adaptive modulation technique has been shown to achieve reliable high-rate data transmission over frequency-selective fading channel when OFDM is employed. This scheme requires the accurate channel information between two stations for a better performance. In an outdoor high mobility environment, most of adaptive OFDM systems have to be given the channel information transmitted from the receiver. Even if it is possible, there is some delay. Moreover, the channel impulse response between two stations is very rapidly varied. If the channel information is obsolete at the time of transmission, then poor system performance will result. In order to solve this problem, we propose adaptive OFDM with improved channel predictor. The proposed bit allocation algorithm has a lower complexity and the proposed scheme mitigates the effect of channel delay. Robust approach is less sensitive to outdated channel information. Performance results show that the proposed scheme can achieve considerable performance enhancement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1200-1209
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• 2011

In this paper, we propose a novel energy efficient MAC protocol which is based on orthogonal frequency division multiple access (OFDMA) and exploits the physical characteristic that propagation loss of acoustic wave depends on the distance. In the proposed scheme, sensor nodes are grouped according to the distance to sink node. Then, each group uses a different frequency band. The proposed scheme not only enables all sensor nodes to maintain the signal-to-noise ratio above a certain required level (Accepted Minimum SNR, AMS), but also reduces overall transmission power consumption. In addition, the dynamic sub-channel allocation is employed in order to improve data transmission rate. Simulations show that proposed MAC protocol has better performance in a delay-tolerant underwater acoustic sensor networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2C
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• pp.105-111
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• 2011

In this paper, we propose a novel Alamouti space-time transmission scheme for orthogonal frequency division multiplexing (OFDM) based asynchronous cooperative communication systems with low relay complexity. The conventional scheme requires an additional operation likes time-reversal at the relay nodes besides the simple multiplications at the relay nodes, which result in increasing the complexity of relay nodes. Unlike the conventional scheme, exploiting the simple combination of the symbols at the source node and the simple multiplications at the relay nodes, the proposed scheme achieves the second order diversity gain by obtaining the Alamouti code structure at the destination node. Simulation results show that the proposed scheme achieves the second order diversity gain and has the same bit error rate performance as the conventional scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.450-457
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• 2012

For orthogonal frequency-division multiplexing (OFDM) systems, we propose a blind channel estimation scheme based on non-redundant precoding. In the proposed scheme, a modified covariance matrix is first obtained by dividing the covariance matrix of the received signal vector by the precoding matrix element-by-element. Then, the channel vector is estimated as an eigenvector corresponding to the largest eigenvalue of the modified covariance matrix. The eigenvector can be obtained by power method with low computational complexity instead of the complicated eigenvalue decomposition. We analytically derive a mean square error (MSE) of the proposed channel estimation scheme and show that the analysis result coincides well with the simulation result. Also, simulation results show that the proposed scheme has better MSE and bit error rate (BER) performance than conventional channel estimation schemes.