• Journal of information and communication convergence engineering
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• v.14 no.3
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• pp.163-170
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• 2016

Because of rapid technological advancements, increased data rate support has become the key criterion for future communication medium selection. Multimode optical fibers and multicore optical fibers are well matched to high data rate throughput requirements because of their tendency to support multiple modes through one core at a time, which results in higher data rates. Using the numerical mode solver OptiFiber, we have designed a concentric core fiber by investigating certain design parameters, namely core diameter (µm), wavelength (nm), and refractive index profile, and as a result, the number of channels, material losses, bending losses, polarization mode dispersion, and the effective nonlinear refractive index have been determined. Space division multiplexing is a promising future technology that uses few-mode fibers in parallel to form a multicore fiber. The experimental tests are conducted using the standard second window wavelength of 1,550 nm and simulated results are presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1251-1259
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• 2007

A scheme for selecting the mode with the maximum system capacity is proposed for cooperative relaying. Three possible modes are presented based on decode-and-forward relaying, and the time required by each mode is evaluated. Based on these results, a method is then developed for selecting the optimal mode with the minimum time duration (or maximum channel capacity). Computer simulations confirm that the optimal mode outperforms the other modes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.1
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• pp.39-45
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• 2009

OFDM is used for achieving a high-speed data transmission in mobile wireless communication systems. Conventionally, fast Fourier transform that is the main signal processing of OFDM is implemented using digital signal processing. The DSP FFT LSI requires large power consumption. Current-mode FFT LSI with analog signal processing is one of the best solutions for high speed and low power consumption. However, for the operation of current-mode FFT LSI that has the structure of parallel-input and parallel-output, current-mode serial-to-parallel and parallel-to-serial converter are indispensable. We propose a novel current-mode SPC and PSC and full chip simulation results agree with experimental data. The proposed current-mode SPC and PSC promise the wide application of the current-mode analog signal processing in the field of low power wireless communication LSI.

• The Journal of the Korea institute of electronic communication sciences
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• v.3 no.2
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• pp.86-92
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• 2008

Othogonal Frequency Division Multiplexing(OFDM) has been taken notice of 4th generation communication method because it has a merit of high data rate(HDR). To realize HDR communication, The OFDM a s high efficient Fast-Fourier-Transform (FFT)/Inversion FFT (IFFT) processor. Currently OFDM is realized by Digital Signal Processor(DSP) but it consumes a lot of Power. Therefore, current-mode FFT LSI has been proposed for compensation of this demerit. In this paper, we propose IVC for current-mode FFT LSI. From the simulation result, the output value of IVC is more than 3V when the value of FFT Block output is more than $7.35{\mu}A$. The output value of IVC is lower than 0.5V when the value of FFT Block output is lower than $0.97{\mu}A$. Designed IVC Low-power Current mode FFT LSI will contribute to the operation of current-mode FFT LSI and the development of next generation wireless communication systems.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.1
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• pp.69-75
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• 2011

As part of its space development program, Korea has a plan for the launch of a lunar orbiter and a lunar lander. To enable the transmission of lunar information based on multimedia, it is necessary to construct a communication system that is capable of transmitting large-volume telemetry data. The CCSDS standard recommends the deferred NAK mode as ARQ scheme for reliable long-distance deep-space communication systems. In this paper, we implement a space communication system simulator in the deferred NAK mode using models of the lunar orbiter, the earth station, and the space environment. The simulator employs modulation techniques and turbo coding schemes for transmitting large-volume telemetry data. We analyze the transmission performance of telemetry data through the simulation.

• Journal of Advanced Navigation Technology
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• v.15 no.4
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• pp.571-577
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• 2011

This paper presents a novel balanced filter design based on a metamaterial structure applicable to differential-mode excitation. The metamaterial structure is based on a unit-cell which under a differential-mode excitation behaves like composite right/left-handed(CRLH) metamaterial with filter characteristics. In contrast, the metamaterial unit-cell is below cut-off under a common-mode excitation. Experimental results are used to verify the proposed metamaterial's differential-mode characteristics. The metamaterial is fabricated with a balanced filter design resulting in an operating frequency range of 960~1000 MHz with a insertion loss of 4.1 dB.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.3
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• pp.950-975
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• 2016

Device-to-Device (D2D) communication underlaying cellular networks is a promising add-on component for future radio communication systems. It provides more access opportunities for local device pairs and enhances system throughput (ST), especially when mobile relays (MR) are further enabled to facilitate D2D links when the channel condition of their desired links is unfavorable. However, mutual interference is inevitable due to spectral reuse, and moreover, selecting a suitable transmission mode to benefit the correlated resource allocation (RA) is another difficult problem. We aim to optimize ST of the hybrid system via joint consideration of mode selection (MS) and RA, which includes admission control (AC), power control (PC), channel assignment (CA) and relay selection (RS). However, the original problem is generally NP-hard; therefore, we decompose it into two parts where a hierarchical structure exists: (i) PC is mode-dependent, but its optimality can be perfectly addressed for any given mode with additional AC design to achieve individual quality-of-service requirements. (ii) Based on that optimality, the joint design of MS, CA and RS can be viewed from the graph perspective and transferred into the maximum weighted independent set problem, which is then approximated by our greedy algorithm in polynomial-time. Thanks to the numerical results, we elucidate the efficacy of our mechanism and observe a resulting gain in MR-aided D2D communication.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.747-750
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• 2002

A circuit building block for realizing a continuous-time active-only current-mode integrator is presented. The proposed integrator is composed only of internally compensated type operational amplifier (OA) and operational transconductance amplifiers (OTAs). The integrator is suitable for integrated circuit implementation in either bipolar or CMOS technologies, since it does not require any external passive elements. Moreover, the integrator gain can be tuned through the transconductance gains of the OTAs. Some application examples in the realization of current-mode network functions using the proposed current-mode integrator as an active element are also given.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.6
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• pp.810-817
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• 2014

An on-chip current sensor with fast response time for the peak-current-mode buck regulator is proposed. The initial operating points of the peak current sensor are determined in advance by the valley current level, which is sensed by a valley current sensor. As a result, the proposed current sensor achieves a fast response time of less than 20 ns, and a sensing accuracy of over 90%. Applying the proposed current sensor, the peak-current-mode buck regulator for the mobile application is realized with an operating frequency of 2 MHz, an output voltage of 0.8 V, a maximum load current of 500 mA, and a peak efficiency of over 83%.

• Journal of Power Electronics
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• v.9 no.1
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• pp.26-35
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• 2009

A high efficiency active clamp sepic-flyback converter is presented for fuel cell generation systems. The proposed converter is a superposition of a sepic converter mode and. flyback converter mode. The output voltages of the sepic converter mode and flyback converter mode can be regulated by the same PWM technique with constant frequency. By merging the sepic and flyback topologies, they can share the transformer, power MOSFET and active clamp circuit. The result has outstanding advantages over conventional active clamp DC-DC converters: high efficiency, high power density, and component utilization. Simulation results and experimental results are presented to verify the principles of operation for the proposed converter.