• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1685-1690
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• 2006

The future mobile communication system should be operated with hierarchical cellular system for providing high quality multimedia services within limited wireless resources. In this paper, we have studied a call admission control scheme applied in hierarchical CDMA cellular system nested with macro, macro, and pico cells. When the proposed call admission control algorithm was applied we got 20% more system capacity than no admission control was applied.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.8 no.4
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• pp.207-215
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• 2009

In recent digital communication systems, the performance of Turbo Code used as the error correction coding method depends on the interleaver size influencing the free distance determination and iterative decoding algorithms of the turbo decoder. However, some iterations are needed to get a better performance, but these processes require large time delay. Recently, methods of reducing the number of iteration have been studied without degrading original performance. In this paper, the new method combining ME (Mean Estimate) stopping criterion with SDR (sign difference ratio) stopping criterion of previous stopping criteria is proposed, and the fact of compensating each method's missed detection is verified Faster decoding realizes that reducing the number of iterative decoding about 1~2 times by adopting our proposed method into serially concatenation of both decoder. System Environments were assumed DS-CDMA forward link system with intense MAI (multiple access interference).

• Journal of Internet Computing and Services
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• v.7 no.1
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• pp.173-178
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• 2006

In this paper, a channel estimation based on the time-domain windowing and its imperfectness in OFDM-based multiple-antenna transmission systems are analyzed with an emphasis on a preamble design for multi-channel separation, From the computer simulation results, the OFDM-CDMA system applying a space-time-frequency diversity with a full-rate full diversity code can give the diversity of D = 4 and D = 8 for both multi-user cases of maximum user and half user capacities, respectively

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11A
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• pp.1021-1026
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• 2005

In this paper, we present a novel predictive CDMA closed-loop power control (CLPC) method with a multi-step least squares (LS) linear predictor for time-varying fading channels. The proposed method effectively compensates multiple power control group delays and provides significant performance gains over nonpredictive CLPCs as well as conventional predictive CLPCs with one-step linear predictor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.5B
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• pp.545-553
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• 2001

다중 사용자 DS-CDMA 시스템에서 더 나은 성능을 얻고자 컨볼루션 코드와 차등 코드의 직렬 연쇄 구조를 제안한다. 시스템은 접속 간섭 (MAI: Multiple-access Interference)를 억제하기 위해 다른 사용자의 확산 코드, 동기, 그리고 전력 정보 등을 필요로 하지 않는 단일 사용자 검파기(SUD: Single User Detection)로 이루어진다. 채널 부호로 사용된 부호화율 1과 메모리 수 1을 가지는 차등 부호는 부호화로 인한 효율 저하를 가져오지 않으며 최소 상태수를 가지게 된다. 이러한 차등 부호와 컨볼루션 부호를 복호함에 있어서 서로간의 정보를 교환하는 반복 복호 처리를 이용한다. AWGN 채널에서의 분석 결과로부터 본 연쇄 부호 기법이 DS-CDMA 시스템에서 기존의 컨볼루션 코드보다 유사한 복잡도에서 더 나은 성능과 유연성을 제공함을 알 수 있다. 또한 제안한 기법이 SUD를 하는 DS-CDMA 시스템에 적용될 때, 처리 이득(Processing Gain)이나 간섭 억제 여파기의 탭 개수를 증가시킴으로써 성능 향상이 일어나며, 원근 간섭 전력 문제가 심한 경우에 성능 저하가 일어남을 알 수 있다.

• Journal of Communications and Networks
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• v.7 no.1
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• pp.13-20
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• 2005

In this paper, a new multi carrier, direct sequence code division multiple access (MC-DS-CDMA) system is proposed. Our new signal construction is based on convolutional encoding of the transmitted data, serial-to-parallel (S/P) conversion of the encoded data, Walsh-Hadamard-transformation (WHT), a second S/P conversion of the WHT outputs, spread spectrum (SS) modulation with a common pseudo-noise (PN) sequence, and then multicarrier transmission. The system bit error rate (BER) performance in frequency selective fading channel in the presence of additive white Gaussian noise (AWGN) and a jamming tone is analyzed and simulated. The numerical results are compared with those from an orthogonal MC-DS-CDMA system of Sourour and Nakagawa [7]. It is shown that the two systems have almost the same BER performance, but the proposed scheme has better anti-jamming ability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9B
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• pp.1579-1587
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• 2000

This paper presents the properties of the RF part in the receiving system based in IMT-2000 terminal technology. It mainly discuss the RF parameter performance of the receiving system for mobile telecommunication comparable to IS-98A and J-STD-018 specifications of commercially available CDMA and PCS, and is to anticipate the processing gain of the IMT-2000 receiving system, processing gain according to data processing rate, and terminal noise figure according to processing gain, relationship between noise figures according to Eb/Nt, Ioc. It is performed by such analysis method as CDMA and PCS receiving systems. Transmission bandwidth is n$\times$1.25 MHz(n=1, 3, 6, 9, 12) which is recommended by Qualcomm and NTT, the leading company in cdma 2000. Data transmission rate of IMT-2000 is classified into three cases as in moving vehicle environment of 144Kbps, outdoor pedestrian environment of 384Kbps, and indoor office environment of 2Mbps

• Journal of the Korea Society of Computer and Information
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• v.11 no.3
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• pp.213-219
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• 2006

Interference occurs by signals received from directions that were different from the signals of the users in a mobile communication system. Various studies have been undertaken, including diversity, equalizer, etc., in order to reduce interference. In this study, the weighted value of the array antenna was obtained to improve signal-to-noise ratio. The weighted value was obtained as an eigen value and an eigen vector by using the correlation coefficient of the signal. The weighted value obtained was then applied to the CDMA system to increase system performance and capacity. Both QPSK and OQPSK modulation systems were applied to analyze performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.2
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• pp.131-140
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• 1998

MAI(Multi-Access Interference) and fast channel variation due to the fading environment are the major problems in the mobile CDMA communication systems. Recently, interest has been increasing in applying the Adaptive Linear MMSE Detector to MAI cancellation in the CDMA reverse link. In this paper, we propose a modified Adaptive Linear MMSE Detector structure which can be used in Long-duration code CDMA system in the presence of independent Rayleigh fading. We use independent multiple tap-weight vector structure to cope with the variation of spreading sequence pattern between neighbor symbols because of the Long-duration code. In this case, more exact channel parameter estimation is required. To solve this problem, we use coherent CDMA structure which can track the channel parameters like amplitude and phase by employing the low power pilot channel in the CDMA reverse link.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.433-436
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• 2000

In this paper, capacity of a multicarrier DS/CDMA system is analyzed and simulated in a Nakagami fading channel. It is confirmed that the adaptive antenna array is a very efficient solution to enhance system capacity of a multicarrier DS/CDMA system. The results in this paper can be applicable to receiver design for the third and fourth mobile communication systems.