• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.10
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• pp.97-102
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• 2004

In this paper, a new predistorter controlling modified individual order jntermodulation distortion signals is proposed. The proposed predistorter generates and controls predistorted third and high order IM signals independently. Using predistorted signals, jntermodulation distortion signals of power amplifier are suppressed effectively. The predistortion linearizer has been implemented to operate in Korean PCS basestation transmitting band (1840～1870MHz). The test results show that IMD3 and IMD5 (C/I) of power amplifier are improved more than 40dB and 23dB for CW two tone signals, respectively. The predistorter improves the adjacent channel power ratio (ACPR) more than 10dB at 885KHz offset point for CDMA (IS-95) signals.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.193-196
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• 2000

In this paper, the performance of DS-CDMA system with smart antenna is analyzed for different bandwidths (1.25MHz, 5MHz) and different channel environments (rural, urban). For the analysis of smart antenna system, the vector channel model having the spatio-temporal correlation is needed. Hence, the channel is modeled as a time-variant linear filter in time, and each multipath is assumed as a reflective wave from only one direction (only one cluster) in space. A simulation is carried out by dividing several multipaths within one chip into each one and searching the strongest signal. DS-CDMA system with smart antenna using wider bandwidth present better performance than that using narrow bandwidth. It is shown that the smart antenna is more effective in urban area when using 2D-RAKE receiver.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11B
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• pp.1534-1539
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• 2001

In this paper, effects of soft handoff region on the reverse link capacity of a DS-CDMA cellular system are investigated. The reverse link capacity of a CDMA cellular system is calculated at a given soft handoff region ratio (SHRR) and path loss model. The results show that the reverse link capacity increases by 1 ∼ 4 channels according to the soft handoff region ratio and the path loss model. However, in the case of the path loss model having a large attenuation exponent ($\mu$ = 5) and a small shadowing standard deviation ( $\sigma$ = 6 dB), the reverse link capacity is no more increased by increasing SHRR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.421-428
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• 2009

Inter-cell coordination has been an emerging issue for mitigating inter-cell interference in broadband wireless access networks such as IEEE802.16 and 3GPP LTE (Long Term Evolution). This paper proposes uplink/downlink hybrid inter-cell coordination patterns for a TDD (Time Division Duplex)/MC-CDMA (Multi-Carrier Code Division Multiple Access) system. For the performance analysis, closed forms of inter-cell interferences are derived when uplink and downlink transmissions coexist over a multi-cell environment. In the analysis, we find an optimal ratio of downlink transmit powers of BSs (Base Stations) based on the target outage probability and the performance according to ratios of uplink/downlink transmit powers of MSs (Mobile Stations)/BSs is explored. Our numerical results show that interference mitigation utilizing the characteristics of the uplink and downlink power ratio is very effective in improving system performance in terms of QoS.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.311-314
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• 2001

본 논문에서는 다중 경로 레일리 페이딩 채널에서 MC (Multi-Carrier) CDMA 시스템의 BER 성능을 분석하였고, 최근에 가장 강력한 부호화 기법으로 급부상하고 있는 터보 코드를 MC CDMA 시스템에 적용하여 성능 개선 정도를 평가하였다. 성능 해석 결과, 레일리 페이딩 채널에서는 강력한 성능 개선 기법을 적용하지 않는 한 사용자수와 E$_{b}$/N$_{o}$ 값에 관계없이 음성 서비스를 지원하지 못함을 알 수 있었다. 한편, 터보 코드를 성능 개선 기법으로 적용하면 BER 성능이 매우 개선되고, 사용자 수와 E$_{b}$/N$_{o}$ 값에 관계없이 음성 서비스를 충분히 지원할 수 있음을 알 수 있었다. 예를 들어 E$_{b}$/N$_{o}$ 가 10 dB이고 사용자 수가 10명인 경우, 터보 코드를 적용함에 의해 BER 성능이 약 5$\times$$10^{-3}$ 정도 개선됨을 알 수 있었다.

• Information and Communications Magazine
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• v.17 no.5
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• pp.66-76
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• 2000

본 논문은 IS-95 CDMA 환경에서 수신 안테나 어레이로 입사되는 신호를 처리하여 최적의 빔패턴을 단말기로 제공해주는 새로운 적응 알고리즘인 그래디언트 온-오프(gradient on-off) 알고리즘을 제안한다. 본 제안 알고리즘의 수신 신호처리 계산량은 O(3N)으로 IS-95 CDMA 환경에서 범용 DSP(Digital Signal Processor)를 이용한 알고리즘 계산결과 수신신호의 실시간 처리가 가능한 것이 판명되었다. 제안한 그래디언트 온-오프 알고리즘을 이용하여 IS-95 CDMA 이동통신 환경하에서 시뮬레이션을 수행한 결과 8개의 안테나를 사용한 경우 단일 안테나보다 약 3-4배 정도 용량이 증가하였다. 또한 사용자간의 최대 파워치를 ${\pm}$2dB로한 불환전한(imperfect) power control 시에도 본 제안 알고리즘에 대한 성능에는 영향이 거의 없음을 확인하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.479-486
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• 1999

In this paper the system performance degradation resulting from nonlinear transmitter power amplifier which is essential to increase the efficiency is analyzed in a forward link CDMA system. The power amplifier is modeled by power series model which includes only odd-order terms. The effects of power amplifier's nonlinearity such as intersymbol interference, phase distortion on the RF system performance were visualized by examining the distorted time domain waveforms, signal vector constellation. And through the investigation of the power spectrum density of the transmitted signal, spectral regrowth or sideband regrowth which is result from amplitude distortion can be seen. All these characteristics result in BER performance degradation due to other user interferences and intersymbol interference. The analysis technique described here applies not only to power amplifier but also to any other nonlinear components such as mixers and switches. Also the effects of adjacent channel interference and supurious emission can be analysed between different systems.

• Journal of IKEEE
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• v.4 no.2 s.7
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• pp.241-248
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• 2000

A linear power amplifier is particular emphasized on the CDMA system using a linear modulation scheme, because intermodulation distortion which cause adjacent channel interference and co channel interference is mostly generated in a nonlinear power amplifier. In this paper, a new type of linearization technique proposed. It is presented that balanced MESFET predistortion linearizer added. Experimental result are present for Korea PCS(Personal Communication Service) frequency band. The implemented linearizer is applied to a 30dBm class A power amplifier for simulation Performance. The predistortion linearizer improves the 1dB compression point of the HPA about 2dBm, and intermoudulation distortion about 12.5dBc.

• The Journal of the Acoustical Society of Korea
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• v.18 no.1
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• pp.10-15
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• 1999

We have studied a method to design and fabricate the Intermediate Frequency(IF) band pass filter with low shape factor which is used for CDMA base station on the 35°Y-cut X-propagation Quartz substrate. In order to fabricate a device of the low shape factor for the IF SAW filter on this substrate, we employed apodization weighted type interdigital transducer(IDT) as an input and withdrawal weighted type IDT as an output by using impulse modelling method. Also, using the Kaiser-Bessel window function, we have adopted 2200pairs and 1000pairs of input and oueut IDT respectively to minimize the effect of ripple. Furthermore, the width and the space of IDT finger are 3.6 ㎛ and 3.5 ㎛ respectively. Thus, we can have optimal results when the IDT thickness is 6000Å in consideration of the ratio of SAW's wavelength while it's aperture is 2mm for impedance matching. The fabricated SAW filter for CDMA had the property of almost 115.2MHz of a center frequency, less then 1.27MHz of bandwidth, less than 1.3 of shape factor, - l5dB of out band attenuation insertion loss and -45dB of rejection band.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.9 s.339
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• pp.73-80
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• 2005

The Turbo decoders based on Log-MAP decoding algorithm inherently requires large amount of memory and intensive complexity of hardware due to iterative decoding, despite of excellent decoding efficiency. To decrease the large amount of memory and reduce hardware complexity, the result of previous research. And this paper design the Turbo decoder applicable to the 3G W-CDMA systems. Through the result of previous research, we decided 5-bits for the received data 6-bits for a priori information, and 7-bits for the quantization state metrics. The error correction term for $MAX^{*}$ operation which is the main function of Log-MAP decoding algorithm is implemented with very small hardware overhead. The proposed Turbo decoder is synthesized in $0.35\mu$m Hynix CMOS technology. The synthesized result for the Turbo decoder shows that it supports a maximum 9Mbps data rate, and a BER of $10^{-6}$ is achieved(Eb/No=1.0dB, 5 iterations, and the interleaver size $\geq$ 2000).