• 한국통신학회논문지
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• 제25권4A호
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• pp.519-527
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• 2000

본 논문에서는 대역폭 효율적 고속전송이 가능한 직렬 인쇄 시·공간 부호(Serially Concatenated Space-Time Code; SCSTC)를 제안하고 성능을 분석한다. 제안된 직렬 연쇄 시·공간 부호와 외부의 컨볼루셔널 부호를 인터리버를 사용하여 직렬로 연결한 구조이다. 제안된 부호는 시·공간 부호의 장점인 고속전송 특성을 유지하면서 단점으로 낮은 BER 성능을 향상시킨다. 제안된 시스템의 성능은 기존의 대역폭 효율적 트렐리스 부호 방식인 직렬 연쇄 트렐리스 부호 변조(Serially Concatenated Trellis Coded Modulation; SCTCM) 및 병렬 연쇄 트렐리스 부호 변조(Turbo-Trellis Coded Modulation; Turbo-TCM)와 비교하였으며 이에 비해 향상된 BER 성능을 얻었다.

• 한국통신학회논문지
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• 제35권7C호
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• pp.587-593
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• 2010

본 논문에서는 extrinsic information transfer (EXIT) chart를 이용하여 다중 안테나 시스템에서 irregular low-density parity-check (LDPC) code를 설계하는 방법을 기술한다. 다중 안테나 기반의 Irregular LDPC code 설계를 위하여 maximum a posteriori probability (MAP) 방식의 다중 안테나 검출 방식이 사용되었으며 수신기는 다중 안테나 검출기와 LDPC 복호기 사이에서 복호된 soft 정보를 주고 받는 turbo iterative 구조를 가정하였다. 다중 안테나 기반의 irregular LDPC code의 edge degree 분포는 EXIT chart와 linear optimization programming 기법을 사용하여 얻을 수 있으며 컴퓨터 시뮬레이션을 통하여 제안된 방법으로 설계된 irregular LDPC code의 성능을 다양한 환경에서 검증하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.245-248
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• 2000

In this paper, we present the performance of a multi-code parallel combinatory CDMA system using bi-orthogonal modulation under multipath fading channel. In general, the dynamic range of the amplitude of the transmit signal is very large in conventional multi-code CDMA systems, resulting in severe nonlinear distortion due to high power amplifier and thus significant BER performance degradation. Since the number of simultaneously multiplexed code channels in the proposed system is reduced, the proposed system exhibits reduction of peak-to-average power ratio (PAPR) of the transmit signal amplitude with significant BER improvement. We verify the performance of the proposed system by computer simulations under the Vehicular B multipath fading channel model by ARIB.

• 한국통신학회논문지
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• 제22권1호
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• pp.104-115
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• 1997

This paper investigates PN code acquistion algorithm and demodulation performance of the RAKE receiver in the DS/CDMA(direct sequence code division multiple access) sysytems under a multipath fading channel with multiusers. To speed up the acquisition process, PN matched filter is applied and postdetection integration technique comable withthe dynamic threshold set method is proposed. the Maximum-Likelihood algorithmin serial fashion is able to find PN code delay estimates for the RAKE branches using sliding window in a multipath fading channel. The correct acquistion probability and mean acquistion time are used as a performance measure of the system using the Monte Carlo method. The performance of the RAKEreceiver, afte the code acquisition is achieved is the CDMA systems, is also investigated for three major combining techniques.

• 한국위성정보통신학회논문지
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• 제2권1호
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• pp.1-6
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• 2007

본 논문은 직접대역확산 방식에서 PN 코드탐색의 동기성능에 관한 내용으로 코드탐색회로의 상관기 출력 값의 평균편차로부터 수신 채널환경을 추정하고 추정된 채널환경에서 목표로 하는 코드 획득성능을 만족할 수 있도록 상관기의 탭 길이를 적응적으로 변경함으로써 고정된 상관기 탭 길이를 이용하는 방법에 비하여 획득성능을 향상시킬 수 있는 PN 코드탐색 알고리즘을 제안하였다.

• 한국위성정보통신학회논문지
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• 제5권1호
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• pp.54-57
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• 2010

위성 기반 측위 시스템은 위치 기반 기술의 핵심 기술로서, CDMA 시스템을 사용한다. CDMA 시스템에서 원활한 위치 측위를 하기 위해서는 확산 부호의 정확한 동기가 이루어져야 한다. 본 논문은 확산 부호의 동기 기법 가운데 부호 추적 기법에 초점을 맞춘다. 특히 다중 경로 환경에서 기존의 부호 추적 기법인 DLL 방법은 적합하지 않다. 본 논문은 수신 신호에서 다중 경로 신호를 축출하여 이를 부호 추적 기법에 사용하는 방법을 제안한다. Spirent simulator를 이용하여 제안 기법을 검증하고 성능 평가를 보인다.

• 디지털산업정보학회논문지
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• 제4권1호
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• pp.17-24
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• 2008

This paper describes the measurements that provide a characterization of the code-domain channels of a CDMA base station transmitter. One of the measurements, called code-domain power(CDP), provides the distribution of power in the code domain channels. This measurement can be used to verify that the various channels are at expected power levels and to determine when one code channel is leaking energy into the other code channels. We develop module of CDP measurement in the CDMA system.

• Journal of information and communication convergence engineering
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• 제5권4호
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• pp.333-338
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• 2007

In this paper we propose a new structure of the long code MMSE receiver with pilot channel, which maintians excellent symbol detection capability even in the presence of Rayleigh fading. We explain analytically how the stability of the receiver weight vector, which is critical to the system performance, can be achieved by compensating the error signal as well as received signal vector distorted by fading channel. Computer simulation shows while maintaining better performance than the conventional matched filter receiver, the proposed long code MMSE receiver can extend its period up to $16{\times}T_b$ in a fading environment.

• Nuclear Engineering and Technology
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• 제41권5호
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• pp.677-690
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• 2009

A previous study demonstrated that the two-row fuel assembly has much more favorable neutron-physical and thermal-hydraulic behavior than the conventional one-row fuel assemblies. Based on the newly developed two-row fuel assembly, an SCWR core is proposed and analyzed. The performance of the proposed core is investigated with 3-D coupled neutron-physical and thermal-hydraulic calculations. During the coupling procedure, the thermal-hydraulic behavior is analyzed using a sub-channel analysis code and the neutron-physical performance is computed with a 3-D diffusion code. This paper presents the main results achieved thus far related to the distribution of some neutronic and thermal-hydraulic parameters. It shows that with adjustment of the coolant and moderator mass flow in different assemblies, promising neutron-physical and thermal-hydraulic behavior of the SCWR core is achieved. A sensitivity study of the heat transfer correlation is also performed. Since the pin power in fuel assemblies can be non-uniform, a sub-channel analysis is necessary in order to investigate the detailed distribution of thermal-hydraulic parameters in the hottest fuel assembly. The sub-channel analysis is performed based on the bundle averaged parameters obtained with the core analysis. With the sub-channel analysis approach, more precise evaluation of the hot channel factor and maximum cladding surface temperature can be achieved. The difference in the results obtained with both the sub-channel analysis and the fuel assembly homogenized method confirms the importance of the sub-channel analysis.

• 한국통신학회논문지
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• 제30권7A호
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• pp.628-638
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• 2005

The analysis of maximum diversity order and coding gain for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over time-and frequency-selective (or doubly-selective) channels is addressed in this paper. A novel channel time-space correlation function is developed given the spatially correlated doubly-selective Rayleigh fading channel model. Based on this channel-model assumption, the upper-bound of pairwise error probability (PEP) for MIMO-OFDM systems is derived under the maximum likelihood (ML) detection. For a certain space-frequency code, we quantify the maximum diversity order and deduce the expression of coding gain. In this wort the impact of channel time selectivity is especially studied and a new definition of time diversity is illustrated correspondingly