• Journal of Communications and Networks
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• v.6 no.3
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• pp.203-208
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• 2004

A combined precoding and turbo decoding strategy for multi-path frequency-selective fading channels is presented. The precoder and multi-path fading channel are jointly modeled as a finite-state probabilistic channel to provide the multi-stage turbo decoder with its statistics information. Both a priori and a posteriori probabilities are used in the metric computation to improve the system performance. Structures of the combined turbo-encoder, interleaver, and precoder in the transmitter and two-stage turbo decoder in the receiver are described. Performance of the proposed scheme in fixed, Rician and Rayleigh multi-path fading channels are evaluated by simulation. The results indicate that the combined precoding and two-stage turbo decoding strategy provides a considerable performance improvement while maintaining the same inner structure of a conventional turbo decoder.

• Journal of Communications and Networks
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• v.9 no.1
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• pp.1-10
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• 2007

This paper proposes a multimodal generalized Gaussian distribution (MGGD) to effectively model the varying statistical properties of the extrinsic information. A subsidiary maximum likelihood decoding (MLD) algorithm is subsequently developed to dynamically select the most suitable MGGD parameters to be used in the component maximum a posteriori (MAP) decoders at each decoding iteration to derive the more reliable metrics performance enhancement. Simulation results show that, for a wide range of block lengths, the proposed approach can enhance the overall turbo decoding performance for both parallel and serially concatenated codes in additive white Gaussian noise (AWGN), Rician, and Rayleigh fading channels.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.188-191
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• 2012

단일 주파수 방송 시스템에서 이레이저 현상이 생길 경우 기존의 공간 다중화 기법은 큰 성능 저하가 발생한다. 이에 본 논문에서는 라이시안 이레이저 페이딩 채널 환경에서 기존의 $2{\times}2$ 공간 다중화 기법에 직교 선부호기를 직렬 연접한 공간 다중화 기법의 성능을 분석하고, 수신 SER 성능을 최대화하는 선부호기 최적화를 수행한다. 전산 실험 결과, Rician 이레이저 페이딩 채널 환경에서 최적의 선부호화 공간 다중화 기법은 수신단에서 성상 모호성을 줄여 기존의 공간 다중화 기법에 비하여 우수한 성능 향상을 보였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.950-956
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• 1998

In this paper, we investigate the effects of impulsive noise on the DS/SSMA system using TCM. We obtain the bound on the probability of bit error of the system, considering bothing impulsive noise and Rician fading, which are unavoidable in mobile communication environments. it turns out that we can achieve some coding gain by using TCM under impulsive noise environment. It is observed that the bit error probability is dominated by the background noise variance when the SNR is low and by the tail noise variance when the SNR is high.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1699-1706
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• 1998

This paper presents a threshold decision technique for direct sequence code acquistion employing Pseudo-Noise(PN) matched filter. The probabilities of detection and false alarm are derived as a measure of the system performance in both nonfading and nonselective Rician fading channels. For received PN codes with different SNR, the proposed acquisition scheme is able to detect a desired threshold in the search mode so that this value is utilized as a threshold for the verification mode. Thus, there is no need to determine a threshold by applying the Neyman-Person ciriteron. It is shown that this scheme achieves lower probability of false alarm than the acquisition scheme based on the Neyman-Person criterion, giving comparable performance in terms of the probability of detection.

• ETRI Journal
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• v.23 no.3
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• pp.121-128
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• 2001

In this paper, the theoretical as well as experimental results of BER characteristics of three different modulation schemes, ASK, FSK and BPSK, in a multi-path Rician channel are addressed. These BER characteristics are analyzed as a function of $E_b/N_o$ and the power ratio of the line of sight (LOS) component to the Rayleigh scattered component. The theoretical as well as computer simulation results shows the ASK is the most suitable modulation scheme for the dedicated short range communication (DSRC) in terms of implemental cost and system complexity. The decision feedback equalizer is proved to be very effective in canceling the multi-path interference in the DSRC channel environment. The simulation result of the equalized ASK, reveals the performance enhancement achievable with decision feedback (DFE) equalizer for the first generation DSRC system. The multi-ray DSRC channel model is also provided to predict the received carrier power and fluctuation, which are quite dependent on the surroundings of a cell.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.8
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• pp.10-19
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• 1997

In this paper, perfodrmance of matched-filter (MF) acquisition scheme is analyzed for a direct-sequence/code-division-multiple-access (DS/CDMA) system in a microcellular environment. Mean acquistion time is used as a performance measure. It is demonstrated that acquisition performance is enhanced using interference suppression filter in a Rician fading channel. To apply for multiuser environments, multiple access interference is considered in the performance analysis. From the numerical results, it is shown that mean acquistion time decreases with the increasing SNR/chip, and acquisition performance is improved as the number of taps of interference suppression filter. It is also shown that mean acquisition time increases with the number of users in the system, and acquistion performance is degraded as the icrease of narrowband interference bandwidth. The analysis in this paper can be applied to a DS/CDMA overlay environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.6A
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• pp.913-922
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• 2001

Multi-Carrier CDMA 시스템에서 불완전한 채널 예측과 다중사용자 간섭은 시스템의 성능 저하를 유발한다. 본 논문에서는 역방향 링크에서 파일럿 심볼을 이용하여 채널을 예측하는 Multi-Carrier CDMA BPSK 시스템에서 불완전한 채널 예측과 다중사용자 간섭의 영향을 연구하였다. 더욱이, 라이시안 페이딩 채널의 역방향 링크에서 최대비 합성 공간 다이버시티와 선택 합성 공간 다이버시티 기법을 적용한 성능 개선에 대하여 연구하였다. 수치계산 결과, 파일럿 심볼을 이용하여 채널을 예측하는 Multi-Carrier CDMA BPSK 시스템의 BER 성능은 등가 잡음 대역폭의 분산($\sigma$$^2$$_{c}$)에 매우 민감하나 무선 채널에서의 신호 전력 대 잡음 전력비에는 그리 심하지 않았다. 불완전한 채널 예측에 의한 BER 열화와 파일럿 심볼 간격의 최적화는 라이시안 페이딩 채널에서 Multi-Carrier CDMA BPSK 시스템의 BER 계산을 통하여 얻을 수 있었다. 그리고 불완전한 채널 예측에 의한 BER 열화는 신호 전력 대 잡음 전력비와 채널 예측 필터의 등가 잡음 대역폭에 관계하고 있음을 알 수 있었다.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.327-330
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• 2002

In this paper, we have analyzed transmission time for WAP over CDMA using turbo code scheme. In order for SAR to improve the transfer capability, the transmission of messages have been simulated using a fragmentation that begins with the total package and incremental fragmentation for each layer using the WTP to define tile resultant packet size and the level of fragmentation for each proceeding layer. This turbo code scheme decreases transmission lime of RLP baseband packets. From the results, we arc able to obtain packet transmission time and optimal WTP packet size for WAP over CDMA in a Rician fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.4
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• pp.737-747
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• 1997

performance of the cellular CDMA overlay system is analyzed which shares the same band with existing microwave narrowband system to enhance the spectral efficiency. To suppress the interfreence from narrowband system, we used a linear predicition filter that adopts the adaptive least mean square algorithm. Alalyzing the performance in the Personal Communication Services channel, characterized as a multipath Rician fadng channels, we considered the power control to solve the near-far problem, and-off and multipath diversity. We also considered interleaving and channel coding to improve BER performance of the CDMA system.