• Journal of Biomedical Engineering Research
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• v.28 no.3
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• pp.429-440
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• 2007

A coded excitation has been studied to improve the performance for ultrasound imaging in term of SNR, imaging frame rate, contrast to tissue ratio, and so forth. However, it requires a complicated arbitrary waveform transmitter for each active channel that is typically composed of a multi-bit Digital-to-Analog Converter (DAC) and a linear power amplifier (LPA). Not only does the LPA increase the cost and size of a transmitter block, but it consumes much power, increasing the system complexity further and causing a heating-up problem. This paper proposes an optimized 1.5bit fourth order sigma-delta modulation technique applicable to design an efficient arbitrary waveform generator with greatly reduced power dissipation and hardware. The proposed SDM can provide a required SQNR with a low over-sampling ratio of 4. To this end, the loop coefficients are optimized to minimize the quantization noise power in signal band while maintaining system stability. In addition, the decision level for the 1.5 bit quantizer is optimized for a given input waveform, which results in the SQNR improvement of more than 5dB. Computer simulation results show that the SQNR of a FM(frequency modulated) signal generated by using the proposed method is about 26dB, and the peak side-lobe level (PSL) of its compressed waveform on receive is -48dB.

• Journal of Satellite, Information and Communications
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• v.11 no.3
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• pp.104-109
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• 2016

A technology of GEO satellite communications starts from Koreasat program in Korea. Payload equipment of EQM Ku and Ka band transponders had been developed and space-qualified Ka band payload in COMS was successfully launched in June, 2010. For the purpose of military communications, Dehop-Rehop transponder was developed in Koreasat5 as ANASIS system and DAT(Digital Active Transponder) and DCAMP(Digital Channel AMPlifier) transponders are now under development. In this paper, from the study of military satellite communications trend, a direction of military communication satellite is suggested based on the current GEO SATCOM technologies in Korea. Considering the limit of frequency resources, a technology of battlefield adaptive transponder with medium capacity against high moveable jamming tactics would be efficient for the future military SATCOM system. Mid-sized military satellites with frequency hopping and mid-capacity transponders can be a solution of vitalizing the GEO satellite programs.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.1-12
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• 1999

This paper illustrates and analyzes system structure, link budget and cell coverage to accommodate Korea environment about LMDS systems that are expected to play an important role as the future wireless infrastructure of the information superhighway. In the mean time, many parameters used for the analysis apply to the allocated frequency bandwidth (Up-stream : 24.25GHz-24.75GHz, Down-stream : 25.5GHz-27.5GHz) of Ministry of Information and Communication. The modem and channel coding must be developed to accommodate specifications of DAVIC protocol. The materials about atmospheric phenomena refer to apply specifications of ITU-R. This paper will be need to disign the network structure and system configuration of LMDS system.

• Composites Research
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• v.31 no.4
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• pp.145-150
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• 2018

Various structural health monitoring (SHM) systems have been suggested for aerospace industry in order to increase its life-cycle and economic efficiency. In the case of aircraft structure madden with metal, a major concern was hot spots, such as notches, bolts holes, and where corrosion or stress concentration occurs due to moisture or salinity. However, with the increasing use of composites in the aerospace industry, further advanced SHM systems have been being required to be applied to composite structures, which have much complex damage mechanism. In this paper, a method of acoustic emission localization for composite structures using Q-switched laser and multiple Amplifier-integrated PZTs have been proposed. The presented technique aims at localization of the AE with an error in distance of less than 10 mm. Acoustic emission simulation and the localization attempt were conducted in the composite structure to validate the suggested method. Localization results, which are coordinates of detected regions, grid plots and color intensity map have been presented together to show reliability of the method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.705-711
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• 2004

We propose novel OCDMA system with the structure of reconfigurable may encoder/decoder(RAE/ RAD), which are able to reallocate the 2-D optical codes to each subscriber and recover the transmitted data at all the receiving nodes. We have first implemented the double hard limiters composed of limiting amplifier(first hard limiter) that maintain a level of the encoded data from receiving node and AND detector(second hard limiter) for detecting the position of the encoded data and recovering the data. With the proposed system, it was successfully implemented to recover a specific channel data out of 16 code-multiplxed channels using FPGA and 4 DFB-LDs having distinct wavelengths. From experimental results, the code length resulted from increasing the number of the simultaneously connected channels has been reduced by using 2-D OCDMA multiplexed in time and wavelength instead of 1-D OCDMA. In addition, bit errors phenomenon on account of deterioration of autocorrelation peak-to-side lobe ratio is enhanced by using the double hard limiters composed of AND detector and limiting amplifiers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.1
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• pp.72-78
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• 2015

Recently, the usage of the satellite is increased more and more in the areas that are communication, weather, marine, optical, radar etc. The functions of the Satellite are evolving from passive transponder to active transponder by the developing of a technology. Advanced countries in satellites install the DCAMP for increase of bandwidth efficiency, improvement of QoS by interference rejection. DCAMP includes many digital components in order to implement functions. Thus, these kinds of active transponders consume much more power compared to passive transponder and then increase the heat. In this paper, we discuss the TVAC test result of DCAMP in EQM(Engineering Qualification Model) level. The paper shows the test results of digital gain control in order to verify DCAMP status under the TVAC test. In addition, the temperature and heat condition of main components from viewpoint of derating will be treated through the official environment test for qualification.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8A
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• pp.785-793
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• 2007

This paper presents the digital signal processing submodule of a 100Base-TX Ethernet receiver to support 100Mbps at TP cable channel. The proposed submodule consists of programmable gain controller, timing recovery, adaptive equalizer and baseline wander compensator. The measured Bit Error Rate is less than $10^{-12}BER$ when continuously receiving data up to 150m. The proposed signal processing submodule is implemented in digital circuits except for PLL and amplifier. The performance improvement of the proposed equalizer and BLW compensator is measured about 1dB compared with the existing architecture that removes BLW using errors of an adaptive equalizer. The architecture has been modeled using Verilog-HDL and synthesized using samsung $0.18{\mu}m$ cell library. The implemented digital signal processing submodule operates at 142.7 MHz and the total number of gates are about 128,528.

• Journal of the Korea Society of Computer and Information
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• v.13 no.4
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• pp.133-140
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• 2008

The cable TV network has delivered downward broadcasting signals from distribution centers to subscribers. Since the traditional coaxial cable has been upgraded by the Hybrid Fiber Coaxial(HFC) cable, the upward channels has expanded broadband services such as Internet. This upward channel is vulnerable to ingress noises. When the noises from the children nodes accumulated in an amplifier exceeds a certain level, that node has to be cut off to prevent the noise propagation. The node selection problem(NSP) is defined to select nodes so that the noise in each node does not exceed the given threshold value and the sum of Profits of selected nodes can be maximized. The NSP has shown to be NP-hard. In this paper, we have proposed heuristics to find the near-optimal solution for NSP. The experimental results show that interval partitioning is better than greedy approach. Our heuristics can be used by the HFC network management system to provide privileged services to the premium subscribers on HFC networks.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.12
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• pp.66-71
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• 2014

This paper presents an analog front-end integrated circuit (IC) for medical ultrasound imaging systems using standard $0.18-{\mu}m$ CMOS process. The proposed front-end circuit includes the transmit part which consists of 15-V high-voltage pulser operating at 2.6 MHz, and the receive part which consists of switch and a low-power low-noise preamplifier. Depending on the operation mode, the output driver in the transmit pulser can be reconfigured as the switch in the receive path and thus the area of the overall front-end IC is reduced by over 70% in comparison to previous work. The designed single-channel front-end prototype consumes less than $0.045mm^2$ of core area and can be utilized as a key building block in highly-integrated multi-array ultrasound medical imaging systems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1757-1763
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• 2014

Optical wavelength division multiplexing signals of eight non-return-to-zero 10 Gb/s channels were transmitted on the long-haul link up to 720 km. The link span was composed of 80 km single mode fiber, dispersion compensation fiber for complete compensation, and EDFAs. A circulating loop method was applied to the link experiment and the loop was optimized for the transmission link. Wavelength-dependent gain variation of EDFA was compensated using EDFAs of opposite gain slopes without expensive gain flattening filters. Average OSNR was aggravated to 22 dB and the worst OSNR channel variation was 9.7 dB after the transmission. It was confirmed by analyzing optical spectra that this OSNR variation was mainly caused by the hole burning effect of EDFA.