• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.74-84
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• 2008

UWB radio systems have drawn attention during the last few years. These systems are the core technique for ubiquitous home and enable to co-exist with other narrow band systems over the same frequency without interfering them. But UWB signals have a very low power per pulse, so they are affected by strong narrow band interferences. Specially, IEEE 802.11a systems which operate around 5GHz overlap the band of UWB signals and they will interfere with UWB systems significantly. In this paper, we propose a novel narrow band interference suppression method based on singular value decomposition(SVD) algorithm for DS-UWB in IEEE 802.15.4a channel model. The proposed method is very effective and robust for both a single user DS-UWB system and a multiuser DS-UWB system to reduce the narrow band interference.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1209-1215
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• 2014

The Uniform Geometrical Theory of Diffraction(UTD) is an effective technique to analyze the radio wave by ray-based calculation of the diffraction coefficient and the reflection coefficient. In this paper, user body shadowing based on the UTD is investigated when the user is close to the mobile device. Two cases are introduced. One is that the user is calling with the mobile attached to the ear(Head Model). The other is that the mobile is located about 15cm away from the user's chest(Chest Model) Radiation Model and Scattering Model are applied to these cases presenting which model is applicable.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5A
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• pp.479-486
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• 2008

In this paper, an efficient training symbol design with m-sequence is proposed for the MIMO-OFDM based next generation wireless transmission system which supports gigabits per second data rate. In the traditional blute force method, the preamble design is based on the case by case comparison with the system requirements. This paper discusses a training symbol design methodology for the MIMO-OFDM system based on the m-sequence which has been widely used in the spread spectrum communication areas due to its good correlation characteristics. Also the step-by-step design and performance verification method within the limited search space is discussed. The proposed method targets the design of the training symbol which satisfies system requirements for the packet based MIMO-OFDM wireless communication system including automatic gain control(AGC), timing synchronization, frequency and sampling offset estimation, and MIMO channel estimation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.4
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• pp.325-336
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• 2013

FlashLinQ, one of the typical D2D communication systems developed by Qualcomm, considers a single-tone communication based distributed channel-aware link scheduling method to realize the link scheduling process with low control overheads. However, considering the frequency selective fading effect of practical multi-path channel, the single-tone based SIR estimation causes a critical scheduling error problem because the received single-tone signal has quite different channel gain at each sub-carrier location. In order to overcome this problem, we propose a novel link scheduling method based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence for D2D communication system. In the proposed method, each link has a unique offset value set for the generation of CAZAC sequences. CAZAC sequences with the cyclic offsets are transmitted using multiple sub-blocks in the entire bandwidth, and then each device can obtain nearly full-band SIR using a good cyclic cross-correlation property of CAZAC sequence.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.1 s.116
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• pp.15-23
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• 2007

A simple six-port direct conversion QPSK receiver which is made up of a six-port phase correlator, a signal power detector, and I/Q channel signal de-modulator is designed and implemented in this paper. The output phase signals of six-port phase correlator are also analysed. On the basis of $90^{\circ}C$ phase relation among the six-port phase correlator output signals, the QPSK de-modulation circuit is designed by a simple circuit. The six-port phase correlator is made up of $90^{\circ}$ hybrid branch line and power detector. The six-port phase correlator, which is designed in frequency range of 11.7 to 12.0 GHz, gets the phase error characteristics less than $5^{\circ}$. By considering matching network and amplitude balance in the designed fiequency range, the designed six-port direct conversion QPSK receiver demodulates the I and Q signals with performance less than $5^{\circ}$ phase error.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.1 s.116
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• pp.53-61
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• 2007

This paper researches on the scheme superimposing the rotation phases over the pilot and data symbols in order to reduce the peak-to-average power ratio(PAPR) of the orthogonal frequency division multiplexing(OFDM) communication. The bandwidth and power efficiency are the main consideration. The phases of rotation vector are added to those of both pilot symbols and data symbols interlaying between any two pilot symbols in an OFDM block. Owing to this scheme the transmitter reduces the PAPR using the partial transmit sequences(PTS) and the receiver restores the data symbol utilizing the channel estimation of pilot symbols. Therefore, the bandwidth efficiency is accomplished by not using the further subcarriers for the reduction of PAPR and the enormous increase of bit error rate according to the receiving error of the side information, i.e. the phases of rotation vector, is prevented. In other words, both bandwidth-and power-efficiency and quality of communication performance can be improved.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.2
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• pp.139-146
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• 2017

A ground moving target's velocity estimation algorithm applicable for a SAR-GMTI system using 2 channel displaced phase center antenna(DPCA) is proposed. In this algorithm, we assume target's across-track velocity can be estimated by along-track interferometry (ATI) and present a method to estimate target's along-track velocity. To accomplish this method, we first transform a radar-target geometry in which a moving target has zero velocity via altering a radar velocity such that target's velocity is reflected into it and next manipulate the spectral centers of the subapertures within the synthetic aperture. The validity of the proposed algorithm is demonstrated through simulation results showing the performance of the target's velocity estimation and the enhancement of reconstructed target image quality in terms of resolution and SINR.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.390-394
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• 1999

In this paper, we have evaluated BER performance of digital subscriber line(DSL) using the twisted-pair channel model by means of Semi-analytic simulation technique. As a result, it was known that the Semi-analytic simulation was proved to be a good technique because of the attenuation of 0.5dB. To keep the BER=10$\^$-7/, 4dB of E$\^$b//N$\^$0/ is needed more when the DSL length extends to 5000m, while 2dB increase of E$\^$b//N$\^$0/ is required when Nyquist frequency goes to 512kb/s with the keeping same distance. In addition, the effect by FEXT noise is serious, when the FEXT noise damping constant, k is over 10/sup-10/ in DSL length and 10$\^$-14/ in the aspect of Nyquist frequency. As the basic, results of this analysis can be used in setting in internal and external standardization of DSL system in the future.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.380-385
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• 2006

In this paper, a program that can be utilized to measure and analyze radio propagation characteristics is developed. This program is able to control the measurement instruments including spectrum analyzer through GPIB interface and analyze the measured data to yield mean excess delay and RMS delay spread. The measured path loss can be compared with theoretical value in free space or inside a tunnel. The measured and analyzed results can also be presented in the forms of graphs. As these tasks can be conducted on the spot of the measurements, this program is very helpful in performing and verifying the measurements immediately. In this thesis radio propagation characteristics with frequency bands of 2.45 and 5.8GHz in subway tunnels are measured by using the program. Path loss and delay spread in subway tunnel is measured and compared according to the form of antenna beam and LOS(Line of Sight) and N-LOS(Non-Line of Sight).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.7
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• pp.993-1000
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• 2018

This paper proposes a low-dropout voltage regulator(LDO) using self-cascode structure. The self-cascode structure was optimized by adjusting the channel length of the source-side MOSFET and applying a forward voltage to the body of the drain-side MOSFET. The self-cascode of the input differential stage of the error amplifier is optimized to give higher transconductance, but the self-cascode of the output stage is optimized to give higher output resistance, The proposed LDO using self-cascode structure was designed by a $0.18{\mu}m$ CMOS technology and simulated using SPECTRE. The load regulation of the proposed LDO regulator was 0.03V/A, whereas that of the conventional LDO was 0.29V/A. The line regulation of the proposed LDO regulator was 2.23mV/V, which is approximately three times improvement compared to that of the conventional LDO. The transient response of the proposed LDO regulator was 625ns, which is 346ns faster than that of the conventional LDO.