• 한국전자파학회논문지
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• 제12권2호
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• pp.251-256
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• 2001

부분대역 잡음 간섭이 존재하는 Rayleigh fading 전송 채널에서 , MSK 변조방식을 사용하는 hybrid DS/SFH 확산 스펙트럼 시스템의 성능을 분석한다. 비트오율 성능을 수신기에서의 평균 신호 대 잡은 $E_{b}/N_{0}(SNR)$와 신호 대 간섭 비 $E_{b}/N_{J}(SJR)$, 그리고 다양한 채널 파라메터의 함수로 유도한다. 그 결과 집접파 대 간접파의 전력비인 Rician factor K 가 클수록 최악의 BER 성능을 일으키는 것은 부분 대역 간섭이지만, 간접 파만이 존재하는 Rayleigh fading 채널(K=0) 에서는 전 대역 간섭($\rho$=1)이다. 시스템의 성능이 K에 따라서 많은 변화를 보이는데, K=10인 Rician fading 채널에서 $10^{-2}$의 동일한 BER을 얻기 위해 AWGN 채널보다 1.9dB 정도의 SNR을 더 필요로 하지만, K=0인 Rayleigh fading 채널보다 5dB 정도의 SNR이득을 갖는다.

• Journal of information and communication convergence engineering
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• 제14권4호
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• pp.227-232
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• 2016

In this study, the performance of a 32-quadrature amplitude position modulation (QAPM) system is analyzed under a Rician fading channel condition when the maximal ratio combining (MRC) diversity technique is used in the receiver. The fading channel is modeled as a frequency non-selective slow Rician fading channel corrupted by additive white Gaussian noise (AWGN). QAPM is available to improve BER performance without amplifying transmit power, and MRC diversity makes the performance improvement of QAPM system even bigger by intentionally maximizing SNR. Error performances are shown for the 32-QAPM system and a 32-phase silence shift keying (PSSK) system in order to examine the effects of fading severity, for various values of the Rician parameter, K. The dependence of error rates on MRC diversity is also analyzed. The simulation results show that the BER performance of the 32-QAPM system is better than that of the 32-PSSK system under the above mentioned conditions.

• ETRI Journal
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• 제26권6호
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• pp.622-634
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• 2004

In this paper, we discuss the design problem and the robustness of space-frequency trellis codes (SFTCs) for multiple input multiple output, orthogonal frequency division multiplexing (MIMO-OFDM) systems. We find that the channel constructed by the consecutive subcarriers of an OFDM block is a correlated fading channel with the regular correlation function of the number and time delay of the multipaths. By introducing the first-order auto-regressive model, we decompose the correlated fading channel into two independent components: a slow fading channel and a fast fading channel. Therefore, the design problem of SFTCs is converted into the joint design in both slow fading and fast fading channels. We present an improved design criterion for SFTCs. We also show that the SFTCs designed according to our criterion are robust against the multipath time delays. Simulation results are provided to confirm our theoretic analysis.

• ETRI Journal
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• 제33권3호
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• pp.320-325
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• 2011

This paper considers the effects of simultaneous correlated multipath fading and shadowing on the performances of a signal-to-interference ratio (SIR)-based dual-branch selection combining (SC) diversity receiver. This analysis includes the presence of cochannel interference. A generalized fading/shadowing channel model in an interference-limited correlated fading environment is modeled by generalized-K distribution. Closed-form expressions are obtained for probability density function and cumulative distribution function of the SC output SIR, as well as for the outage probability. Based on this, the influence of various fading and shadowing parameter values and the correlation level on the outage probability is examined.

• 디지털콘텐츠학회 논문지
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• 제5권1호
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• pp.28-34
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• 2004

본 논문은 주파수 선택성 라이시안 페이딩 환경에서 직교 다중반송파 16 QAM 신호의 블록 오류율 성능을 알아보았다. 블록 오류율을 느린 페이딩과 빠른 페이딩의 경우로 나누어서 구하였는데 파라미터로서는 정규화 된 시간 지연 $(\gamma/T_S),$ 비트 에너지 대 잡음 전력비 $(E_b/N_0),$ 희망 신호 전력대 지연된 비희망 신호 전력비 (DUR)를 고려하였다. 오류정정개수가 t = 1, 2인 블록 부호를 사용하면 느린 페이딩보다 빠른 페이딩에서 성능 개선이 있음을 알 수 있었다.

• Tribology and Lubricants
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• 제14권1호
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• pp.70-78
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• 1998

Two different friction materials (organic and low-metallic pads) for automotive brakes were studied to investigate the anti-fading phenomena during stop. The anti-fading phenomena were pronounced more in the case of using low metallic friction materials than organic friction materials. The main cause of the anti-fading phenomena was the high dependence of friction coefficient on a sliding speed. The anti-fading was prominent when the initial brake temperature was high in the case of low-metallic friction materials due to the strong stick-slip event at high temperature. On the other hand, the anti-fading was not severe in organic friction materials and the effect was reduced at high braking temperature due to the thermal decomposition of organic friction materials. The strong stickslip phenomena of low metallic friction materials at high temperature induced high torque oscillations during drag test. During this experiment two different braking control modes (pressure controlled and torque controlled modes) were compared. The type of the control mode used for brake test significantly affected the friction characteristics.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권10호
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• pp.2493-2508
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• 2012

The performance of a MIMO system with adaptive modulation (AM) and space-time coding over Ricean fading channels for perfect and imperfect channel state information (CSI) is presented. The fading gain value is partitioned into a number of regions by which the modulation is adapted according to the region the fading gain falls in. Under a target bit error rate (BER) constraint, the switching thresholds for AM are given. Based on these results, we derive the calculation formulae of the theoretical spectrum efficiency (SE) and average BER. As a result, closed-form SE expression and accurate BER expression are respectively obtained. Besides, using the approximation of complementary error function, a tightly closed-form approximation of average BER is also derived to simplify the calculation of accurate theoretical BER. Computer simulation shows that the theoretical SE and BER are in good agreement with the corresponding simulation, and the approximate BER is also close to the accurate one. The results show that the AM scheme in Ricean fading channel provides better SE than that in Rayleigh fading channel due to the direct-path propagation, and has performance degradation in SE and BER for imperfect CSI.

• 대한전자공학회논문지TC
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• 제41권8호
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• pp.1-7
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• 2004

주파수 비선택적 Rayleigh 페이딩 채널에서 준 최적 빔 형성과 페이딩 상관이 폐루프 송신 안테나 다이버시티(CTD) 시스템에 주는 영향을 분석하였다. 이동국에서 채널을 완벽하게 예측하는 것은 빠르게 변하는 채널의 페이딩으로 매우 어렵기 때문에 각각의 송신 안테나에 불완전한 가중치를 곱하게 된다. 이 불완전한 가중치는 준 최적의 빔을 형성하게 되고, CTD 시스템의 성능을 저하시킨다. 무선 채널의 페이딩 상관 역시 다이버시티 이득을 감소시키는 하나의 요소이다. CTD 시스템의 비트오율을 채널 예측 에러, 채널 상관계수, 궤환지연, 그리고 페이딩 지수의 함수로 해석적으로 유도하였다. 해석 결과 채널 예측에러가 채널상관보다 시스템성능에 더 많은 영향을 주는 것을 알 수 있었다.

• 한국전자파학회논문지
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• 제10권6호
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• pp.855-865
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• 1999

본 논푼에서는 주파수 선택적 레일리 페이딩 채널에서 16 QAM-TCM의 BER 성능을 개선하는 방법을 제시한다. 주파수 선택적 페이딩 환경에서는 ISI 등, 페이딩에 의한 성능열화가 극히 심하므로 이에 대한 보상 방안으로 가우시안 보상기법을 이용한 다중 파일롯 심별에 의한 보상 방법을 제안하였다. 또한 대역폭 확장 없이 우수한 부호화 이득을 얻을 수 있는 트렐리스 부호화 방법을 적용하였으며 연집 에러를 방지하고자 비트 리버설 블럭 인터리벙 기법을 개선하여 적용하였다. 컴퓨터 시율레이션 결과 주파수 선택적 레일리 페이 딩 환경에서 기존의 PSAM 방법을 적용한 것보다 우수한 성능 개선 효과를 확인 할 수 있었다

• 전자공학회논문지A
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• 제33A권3호
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• pp.10-17
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• 1996

The performance of tau-dither loop (TDL) is evaluated for a direct-sequence spread-spectrum system in a multipath fading channel. The multipath fading channel is modeled as a two-ray rayleight fading channel. The code tracking perfomrance of TDL is analyzed in terms of tracking jitter and mean-tiem-to-lose-lick (MTLL). The tracking jitter performance is degraded while MTLL perfomrance is improved with increasing discriminator offset and decreasing power ratio of main to second paths. It is shown that for a large bit SNR, the effect of multipath fading becomes more significant. And it is also shown that tracking jitter and MTLL performance is less sensitive to delay spacing and discriminator offset for a small bit SNR than for a large bit SNR.