• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.6C
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• pp.561-569
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• 2003

In this paper, for my linear orthogonal space-time block including the orthogonal space-time codes introduced by Alamouti［1］, Tarokh［14］, and Xia［11］, the exact expression for the pairwise error probability in the slow Rayleigh fading channel is derived in terms of the message symbol distance between two message vectors rather than the codeword symbol distance between two transmitted codeword matrices. Using the one-dimensional component symbol error probability, the exact closed form expressions for the symbol error probability of linear orthogonal space-time codes are derived for QPSK, 16-QAM, 64-QAM, and 256-QAM.

• Journal of Communications and Networks
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• v.6 no.3
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• pp.258-268
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• 2004

We demonstrate rotationally invariant space-time (ST) trellis codes with a 4-D rectangular signal constellation for data transmission over fading channels using two transmit antennas. The rotational invariance is a good property to have that may alleviate the task of the carrier phase tracking circuit in the receiver. The transmitted data stream is segmented into eight bit blocks and quadrature amplitude modulated using a 256 point 4-D signal constellation whose 2-D constituent constellation is a 16 point square constellation doubly partitioned. The 4-D signal constellation is simply the Cartesian product of the 2-D signal constellation with it-self and has 32 subsets. The partition is performed on one side into four subsets A, B, C, and D with increased minimum-squared Euclidian distance, and on the other side into four rings, where each ring includes four points of equal energy. We propose both linear and nonlinear ST trellis codes and perform simulations using an appropriate multiple-input multiple-output (MIMO) channel model. The 4-D ST codes constructed here demonstrate about the same frame error rate (FER) performance as their 2-D counterparts, having however the added value of rotational invariance.

• Information and Communications Magazine
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• v.16 no.10
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• pp.112-124
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• 1999

본 논문에서는 FTTC/VDSL (Fiber-to-the-Curb/Very High-speed Digital Subscriber Line) 전송시스템의 개발동향과 ANSI, ETSI, ITU등의 표준화 위원회에서 현재 진행중인 VDSL 시스템의 표준화 작업에 대해 기술하였다. 특히, POTS (Plain Old Telephone Service), BA-ISDA(Basic Access Integrated Services Digital Network), HDSL(High-rate Digital Subscriber Line), SDSL (Single-pair HDSL), ADSL(Asymmetric Digital Subscriber Line) 등의 다양한 xDSL (Digital Subscriber Line) 서비스들에서 발생하는 NEXT (Near-end Crosstalk)/FEXT (Far-end Crosstalk)와 같은 crosstalk를 최소화하기 위해 제안된 VDSL시스템의 주파수 대역과 PSD (Power Spectral Density) mask에 관해 설명하고, 순방향(down-stream) 채널과 역방향(upstream) 채널의 데이터 전송률이 대칭적인 VDSL전송시스템과 비대칭적인 VDSL 전송시스템 간의 주파수대역의 호환성 문제, RFI(Radio Frequency Interference) ingress/egress 문제의 해결 방안에 관해 기술하였다. 또한, 현재 VDSL Coalition과 VDSL Alliance 간에 논의 중인 VDSL 전송시스템의 변복조 방식에 관한 표준화 작업과정 및 순방향과 역방향에 할당될 band 개수에 따른 시스템 성능의 장단점 등에 관해 살펴보았다. 끝으로 현재 국내에서 개발되고 있는 FTTC/VDSL 전송시스템의 전체구조를 요약하고, 네트워크에서 가입자쪽으로 순방향 데이터 전송에 사용된 51.84 Mb/s 19-CAP (Carrierless Amplitude/Phase Modulation) 전송시스템과 가입자 댁내에서 네트워크 방향으로 역방향 데이터 전송에 사용된 1.62 Mb/s QPSK (Quadrature Phase Shift Keying) burst-mode TDMA (Time Division Multiple Access) 전송시스템 등의 동작 원리 및 구조를 기술하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.11C
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• pp.1070-1076
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• 2003

This paper presents and analyses the exact and general closed-form expression for the average bit error probability of M-ary square quadrature amplitude modulation (QAM) for maximal ratio combining (MRC) diversity reception in frequency-nonselective Nakagami-m fading. An L-branch Maximal ratio combining diversity technique with independent or correlated fading cases is considered. Numerical results demonstrate the error performance improvement by employing with the use of MRC diversity reception. The new expressions presented here can offer a convenient way to evaluate the performance of an arbitrary square M-W square QAM with an MRC diversity combiner for various cases of practical interest.

• Journal of the Semiconductor & Display Technology
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• v.3 no.1
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• pp.21-26
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• 2004

Recently with the development of power switching device and DSP which has peripheral devices to control AC servo system, the servo technology has met a new development opportunity. Those things make it possible to reduce the time of developing a AC servo system. Fixed point DSP such as TMS320F240x, and TMS320F28x series have a disadvantage in calculating floating number where TMS320C32 or TMS320C31 are floating point DSP. However they usually become a complex hardware system to implement the AC servo system and it increases the cost. In this study, a DSP based AC servo system with a 3-phase PMSM is proposed. The newly produced DSP TMX320F28l2-version C which has the performance of fast speed, 150MIPS, and a rich peripheral interface such as a 12bit high speed AD converter, QEP(Quadrature Encoder Pulse) circuit, PDPINT(Power Drive Protect Interrupt), SVPWM module and dead time module are used. This paper presents a method to overcome fixed point calculating using scaling all parameters. Also space vector pulse width modulation (SVPWM) using off-set voltage and a digital PI control are implemented to the servo system.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.770-773
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• 2005

최근 산업 분야에 걸쳐서 고속, 고정밀도의 요구사항에 따라, 회전 모터와 볼 스크류, 벨트를 이용한 직선구동방식보다 빠르고 정확하며, 효율이 높은 직접구동 방식의 리니어모터 및 컨트롤러의 개발이 요구되고 있다. 이런 상황에 고속 연산을 수행할 수 있는 DSP(Digital Signal Processor)의 사용이 불가피하며, 기존의 칩들은 A/D변환기, PWM발생장치 등이 내장되지 않아 제어장치의 부품 수증가 및 복잡성을 피할 수 없었다. 따라서 본 논문에서는 SVPWM(Space Vector Pulse Width Modulation) 및 QEP(Quadrature Encoder Pulse) 회로와 PWM 발생기, 12bit의 고속 A/D변환기, 파워 드라이버보호회로 등을 내장한 TMS320F2812 DSP를 사용하여 반도체장비분야, 자동화분야 등에 사용되는 LBLDCM의 제어를 가능하게 만들었다. 또한, 기존의 DSP 시리즈 보다 연산속도가 고속화되어 고속연산에 의한 시간적 제한을 극복 할 수 있게 되었고, 제어에 필요한 하드웨어적인 기능들을 내장하고 있어서 주변회로가 필요 없게 되었다. 따라서 하드웨어의 간소화와 개발 시간의 단축 및 신뢰도의 향상과 모터 효율의 향상을 가져오도록 하였다. 제안된 제어장치는 제작되어, 실험을 통하여 그 타당성을 입증하였다.

• Journal of Communications and Networks
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• v.17 no.6
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• pp.634-646
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• 2015

Assuming perfect channel state information (CSI) at the transmitter and receiver, the optimization problem of maximizing the minimum Euclidean distance between two received signals by a linear precoder is considered for multiple-input multiple-output (MIMO) systems with arbitrary dimensions and arbitraryary quadrature amplitude modulation (QAM) input. A general precoding framework is first presented based on the Gram matrix, which is shown for 2-dimensional (2-D) and 3-dimensional (3-D) MIMO systems when employing the ellipse expanding method (EEM). An extended precoder for high-dimensional MIMO system is proposed following the precoding framework, where the Gram matrix for high-dimensional precoding matrix can be generated through those chosen from 2-D and 3-D results in association with a permutation matrix. A complexity-reduced maximum likelihood detector is also obtained according to the special structure of the proposed precoder. The analytical and numerical results indicate that the proposed precoder outperforms the other precoding schemes in terms of both minimum distance and bit error rate (BER).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.3
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• pp.517-522
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• 2004

In this paper, we have analyzed the performance enhancement of Orthogonal Frequency Division Multiplexing/Quadrature Phase Shift Keying Modulation-Digital Microwave Radio(OFDM/QPSK-DMR) system using Band Limited-Pulse Shaping Filter(BL-PSF) over microwave channel environments. For performance enhancement, the one-tap adaptive equalizer is adopted in the OFDM/QPSK-DMR system and than both BER and signature curve performance are compared with those of single carrier DMR system. Computer simulations confirm that the OFDM/QPSK-DMR system using 16 sub-carrier increase the fade margin about 2 dB over microwave channel environments and that of performance using one-tap adaptive equalizer is highly increased the fade margin as the number of sub-carriers is larger.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.705-708
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• 2010

Recently, HSRC (Half-Symbol-Rate-Carrier) OQPSK (Offset Quadrature Phase Shift Keying) signaling which reduces the bandwidth of transmitted signal for high-speed data communications has been introduced. Since the signal is based on QPSK modulation, it also has the characteristics of QPSK signal. This paper introduces architectures of the transceiver using differential coding to resolve the 4-phase ambiguity problem of the HSRC-QOPSK signaling for high-speed data communications. In addition, this paper proves the functionality of the transceiver with differential coding and shows the BER (bit-error-rate) performance of the transceiver by simulations.

• Journal of Biomedical Engineering Research
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• v.21 no.4
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• pp.345-351
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• 2000

This study is to dvelop a radiotelemetry system to transmit and receive ECG (electrocardiograph) and event signals by using the frequency division multiplexing(FDM) technique. ECG signal sensed by the electrodes is amplified and added to the event signals acting in different frequency range for lead-off, nurse call and low level battery by using FDM. The sub-carrier oscillator using Colpitts circuits and main carrier frequency which is multiplied is frequency modulated by this superhetrodyne technique, and demodulated from the compose IF signal through the quadrature demodulator. A pulse counter demodulator and filtering circuits extract the original ECG and event signals.