• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1C
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• pp.81-89
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• 2009

We propose a D-ATR UWB (Differential-Average Transmitted Reference Ultra Wide Band) system based on impulse radio. The TR-UWB systems including traditional TR (Transmitted Reference) and ATR (Average TR), exhibit a problem of reduced data rate, since reference signals are additionally transmitted. To tackle this issue, the transmitter of the proposed D-ATR system employs a differential coding like the conventional D-TR system. In addition, the receiver of the proposed system has the structure that can improve signal-to-noise ratio of the reference template used in the correlation process, by recursively averaging the received reference signals like the conventional ATR system. The simulation results in the IEEE 802.15.4a UWB multipath channel models reveal that the proposed D-ATR system achieves much better bit error rate performance as compared to the conventional D- TR system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.77-86
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• 2010

In this paper, we present a noncoherent IR-UWB (Impulse Radio-Ultra Wide Band) ranging system with an AFE (Analog Front End) composed of a simple integrator and an 1-bit ADC (Analog-to-Digital Converter), and define AFE characteristics affecting the ranging performance. This system is realistic and easy to implement, since the integrator simply accumulates signal energies and the simple 1-bit ADC is applied instead of the multi-bit ADCs for coherent IR-UWB systems. On the other hand, its ranging accuracy is largely affected channel environments such as noise, multipath fading and so on, since the noncoherent receiver simply squares and integrates the received signals. However, despite these practical importances, there are few conventional researches on the performance analysis according to AFE characteristics in IR-UWB ranging systems. To this end, we analyze in this paper ranging performance according to AFE characteristics for the noncoherent IR-UWB ranging system in various wireless channel environments, and through these results we also present system parameters to be considered in UWB hardware designs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.632-639
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• 2012

Ad-hoc networks can be used various environment, which it is difficult to construct infrastructures, such as shadowing areas, disaster areas, war area, and so on. In order to support to considerable and various wireless services, more spectrum resources are needed. However, efficient utilization of the frequency resource is difficult because of spectrum scarcity and the conventional frequency regulation. Ad-hoc networks employing cognitive radio(CR) system that guarantee high spectrum utilization provide effective way to increase the network capacity. In conventional CR based ad-hoc network, it uses constant threshold value to detect primary user signal, so the results become not reliable. In this paper, to solve this problem, we apply adaptive threshold value to the CR based ad-hoc network, and adaptive threshold is immediately changed by SNR(Signal to Noise Ratio). From the simulation results, we confirmed that proposed algorithm has the greatly better detection probabilities than conventional CR based ad-hoc network.

• Journal of Navigation and Port Research
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• v.35 no.10
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• pp.811-816
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• 2011

In this paper, we analysis to consider the performance of PSPM (Phase Shift Pulse-position Modulation), the one of the low power communication technique, in near-field underwater sound channel by sea trial. PSPM is a QPSK(Quadrature Phase Shift Keying) modulation combined with PPM(Pulse Position Modulation) for low power communication in WBAN(Wireless Body Area Network). It is known that the bandwidth efficiency of PSPM is lower than conventional PSK but the power efficiency increases. In this paper, we will analyze the BER performance of PSPM using data acquired from the sea trials. The BER of QPSK was $6.04{\times}10^{-2}$, PSPM was $3.5{\times}10^{-1}$. Also, PSNR of QPSK was 9.37 dB and in case of PSPM was 9.11 dB.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.4
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• pp.808-814
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• 2007

In this paper, the measurement system of crane moving range is concerned with range recognition technology using phase and magnitude of radio wave. By the proposed technology, we design the radio transmitter and receiver and realize the measurement system, and save the data in disk that is earned from 900Mhz RF signal, middle frequency 450khz of analog signal. As a result of RF measurement, we got 9.3 dBm of RF output and 96 dBc@10khz of phase noise. Range information is earned the data through digital signal processing of IF signal. For the estimation of range measured, we analyze the difference between real range and measurement range, and also suggest the method to remove the measurement error using average processing and amplitude properties. A result is 0.12 and 0.00422 deviation in l0mn-30m and within 5m respectively, and then 2.4E-04 deviation in 4m by using compensation of level characteristics lately.

• KSCI Review
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• v.2 no.1
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• pp.55-67
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• 1995

Recently, it is possible to high speed transmission of the non-voiced data, including voice, data, moving image instead of voice only in the past by changing the communication method to digital form from analog owing to the development of semiconductor and computer technology which for information transmission of the remote point. By doing so, we can get the improvement of the noise effect and low cost but the loss of transmission bandwidth. It is necessary to take some method in oreder to reducing the fading which is propotional to transmission bandwidth during the transmission of radio communication channel, especially. When we design the digital communication system, we must considered to the fading effect in order to determination of the transmitting power, modulation /demodulation method, transmission speed, bit error rate. This paper mainly concerns to the method to the channel simulator which descrives the fading effect during the transmission by computer model and digital filter modeling of the radio fading channel by unsing the transmitting and received signal. By taking the inverse of the characteristic of the modeled filter, it is possible to improvement of the communication system by reducing the distortion and inter-symbol interference which occurs in the channel.

• Investigative Magnetic Resonance Imaging
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• v.22 no.4
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• pp.218-228
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• 2018

Purpose: The objective of this study is to determine the effect of physical changes on MR temperature imaging at 7.0T and to examine proton-resonance-frequency related changes of MR phase images and T1 related changes of MR magnitude images, which are obtained for MR thermometry at various magnetic field strengths. Materials and Methods: An MR-compatible capacitive-coupled radio-frequency hyperthermia system was implemented for heating a phantom and swine muscle tissue, which can be used for both 7.0T and 3.0T MRI. To determine the effect of flip angle correction on T1-based MR thermometry, proton resonance frequency, apparent T1, actual flip angle, and T1 images were obtained. For this purpose, three types of imaging sequences are used, namely, T1-weighted fast field echo with variable flip angle method, dual repetition time method, and variable flip angle method with radio-frequency field nonuniformity correction. Results: Signal-to-noise ratio of the proton resonance frequency shift-based temperature images obtained at 7.0T was five-fold higher than that at 3.0T. The T1 value increases with increasing temperature at both 3.0T and 7.0T. However, temperature measurement using apparent T1-based MR thermometry results in bias and error because B1 varies with temperature. After correcting for the effect of B1 changes, our experimental results confirmed that the calculated T1 increases with increasing temperature both at 3.0T and 7.0T. Conclusion: This study suggests that the temperature-induced flip angle variations need to be considered for accurate temperature measurements in T1-based MR thermometry.

• Journal of Advanced Navigation Technology
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• v.26 no.5
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• pp.319-324
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• 2022

If radio interference occurs or there is no navigation device, radio navigation of high-speed moving object becomes impossible. Nevertheless, if there are multiple ground stations and precise range measurement between the high-speed moving object and the ground station can be secured, it is possible to estimate the position of moving object. This paper proposes a position estimation method using high-precision TDOA measurement generated using TLM signal. In the proposed method, a common error of moving object is removed using the TDOA measurements. The measurements is generated based on TLM signal including SOQPSK PN symbol capable of precise timing synchronization. Therefore, since precise timing synchronization of the system has been performed, the timing error between ground stations has a very small value. This improved the position estimation performance by increasing the accuracy of the measured values. The proposed method is verified through software-based simulation, and the performance of estimated position satisfies the target performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.6
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• pp.591-600
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• 2010

In this paper, three kinds of 24 GHz low-power CMOS cross-coupled voltage controlled oscillators are designed and fabricated for a short-range radar applications using TSMC 0.13 ${\mu}m$ CMOS process. The basic CMOS crosscoupled voltage controlled oscillator is designed for oscillating around a center frequency of 24.1 GHz and subthreshold oscillators are developed for low power operation from it. A double resonant circuit is newly applied to the subthreshold oscillator to improve the problem that parasitic capacitance of large transistors in a subthreshold oscillator can push the oscillation frequency toward lower frequencies. The fabricated chips show the phase noise of -101~-103.5 dBc/Hz at 1 MHz offset, the output power of -11.85~-15.33 dBm and the frequency tuning range of 475~852 MHz. In terms of power consumption, the basic oscillator consumes 5.6 mW, while the subthreshold oscillator does 3.3 mW. The subthreshold oscillator with the double resonant circuit shows relatively lower power consumption and improved phase noise performance while maintaining a comparable frequency tuning range. The subthreshold oscillator with double resonances has FOM of -185.2 dBc based on 1 mW DC power reference, which is an about 3 dB improved result compared with the basic oscillator.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.4
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• pp.27-35
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• 2008

This work proposes a 14b 150MS/s 0.13um CMOS ADC for SDR systems requiring simultaneously high resolution, low power, and small size at high speed. The proposed ADC employs a calibration-free four-step pipeline architecture optimizing the scaling factor for the input trans-conductance of amplifiers and the sampling capacitance in each stage to minimize thermal noise effects and power consumption at the target resolution and sampling rate. A signal- insensitive 3-D fully symmetric layout achieves a 14b level resolution by reducing a capacitor mismatch of three MDACs. The proposed supply- and temperature- insensitive current and voltage references with on-chip RC filters minimizing the effect of switching noise are implemented with off-chip C filters. The prototype ADC in a 0.13um 1P8M CMOS technology demonstrates a measured DNL and INL within 0.81LSB and 2.83LSB, at 14b, respectively. The ADC shows a maximum SNDR of 64dB and 61dB and a maximum SFDR of 71dB and 70dB at 120MS/s and 150MS/s, respectively. The ADC with an active die area of $2.0mm^2$ consumes 140mW at 150MS/s and 1.2V.