• Journal of electromagnetic engineering and science
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• 제1권2호
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• pp.113-119
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• 2001

Conventional channel estimation methods for orthogonal frequency division multiplexing (OFDM) system don't show the good characteristics in terms of fast fading channels. To solve this drawback in conventional methods, we propose the channel estimation method fur OFDM, assisted pilot for improvement and convergence in mobile system (APIM), which has a good performance and computational complexity in consideration of other methods. APIM uses the more developed concept of conventional methods and a block frame structure within a whole channel. This concept prevents overall performance from diverging or showing a poor one. The simulation results demonstrate the APIM outperforms pilot symbol assisted modulation (PSAM) and extended symbol aided estimation (ESAE) in terms of mean square error (MSE) and bit error rate (BER) performance under all Rayleigh fading environment. Considering the simulation performance and computational complexity, we can see APIM shows better characteristics than conventional methods for OFDM and has not any error floor even in a fast Rayleigh fading environment.

• Journal of electromagnetic engineering and science
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• 제7권4호
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• pp.201-206
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• 2007

When the M-ary signal experiences the Rayleigh fading, the diversity schemes can reduce the effects of fading since the probability that all the signals components will fade simultaneously are reduced considerably. The symbol error probabilities for various M-ary signals, such as MDPSK, MPSK and MQAM, are mathematically derived for the SC-2(Selection Combining 2) demodulation system, whereby the two signals with the two largest amplitudes are coherently combined among the L branches. On the other hand, maximum ratio combining(MRC) requires the individual signals from each path to be time-aligned, cophased, optimally weighted by their own fading amplitude, and then summed. The propagation model used in this paper is the frequency-nonselective slow Rayleigh fading channel corrupted by the Additive White Gaussian Noise(AWGN). The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• 한국통신학회논문지
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• 제15권7호
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• pp.565-573
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• 1990

본 논문에서는 육상 이동통신의 채널 환경인 fast Rayleigh 페이딩 상황하에서 discriminator형 GMSK변복조기의 수신 대역 필터에 의한 성능을 분석한 S.Elnoubi의 유도식을 이용하여 BbT=0.25인 경우의 최적 수신 대역폭을 시뮬레이션하였으며, 실제 실험장치를 구현하여 측정한 결과와 비교 검토하였다. 그 결과 static 페이딩(fbT=0)인 경우에는 BrT=0.7이 최적이나 fast 페이딩(fDT>0)인 경우에는 Eb/No의 비가 크고, 페이딩 rate fDT가 클수록 필터에 의한 영향이 작다는 결론을 얻었다.

• 전자공학회논문지A
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• 제33A권3호
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• pp.1-9
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• 1996

in this paper, we analyzed CDD-DLL code tracking loop for tracking of direct-sequence spread-spectrum signals in a multipath fading channel. The multipath fading channel is modeled as two-ray rayleigh fading channel which is well applicable in a land mobile communication environments. We use trackin jitter variance and mean-time-to-lose-lick as performance measures. From the numerical resutls, it is shown that the effect of multipath fading decreases as SNR/bit increases. Also it is shown that CDD-DLL provides superior jitter performance compared with noncoherent DLL and jitter performance improvement is more significant for a two-ray rayleigh fading channel than an AWGN channel.

• 한국통신학회논문지
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• 제11권4호
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• pp.287-295
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• 1986

본 논문에서는 디지털 이동 무선통신을 위한 음성신호와 부호화 기법으로 SBC(sub-bnad coding)를 제안하고, SBC의 레일리(Rayleigh) 페이딩 채널에서의 음질의 강인성을 컴퓨터 시뮬레이션을 통해 조사하였다. 먼저 레일리 페이딩 채널, 시뮬레이터 및 16-ary DPSK(differential phase shift key) 수신기 모델을 제시한 후, 모델의 타당성을 이론치와 비교하여 입증하였다. 채널에러에 대한 영향은 SNR, LPC(linear predictive codin) 거리척도 및 주관적인 청각조사를 통해 검토하였다. BER(bit error rate) =$10_{-3}$, $10_{-2}$, 5$ imes$$10_{-2}$에 대한 시뮬레이션결과 BER=$10_{-2}$에서도 음성의 이해도는 확인되었으며, BER=5$ imes$$10_{-2}$에서도 음성통신에 사용하기는 충분하였다. 따라서 SBC는 ECC(error correction code) 사용없이 BER=$10_{-4}$~$10_{-2}$정도의 레일리 페이딩 채널에서 디지탈 이동무선통신에 응용이 가능함을 알 수 있었다.

• 한국통신학회논문지
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• 제21권4호
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• pp.1019-1026
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• 1996

이제까지 변조 분류에 대한 연구는 가산성 백색 가우시안 잡음에서만 해석되어 연구되어 왔다. 이 논문에서는 Rayleigh 페이딩 채널에서 통계적 모멘트에 근거한 BPSK와 QPSK 신호의 디지틀 변조 분류기를 제시하고 성능을 분석한다. 백색 가우시안 잡음과 Rayleigh 페이딩이 존재하는 환경에서 복조된 신호의 샘플 모멘트를 계산한다. 계산된 모멘트 값을 바탕으로 중심 극한 정리를 이용하여 샘플 모멘트의 평균과 분산을 계산한다. 이로부터 샘플 모멘트의 확률 밀도 함수를 구하고 베이즈 검정을 적용하여 통계적 모멘트에 기초한 BPSK와 QPSK 신호의 디지틀 변조 분류기를 제시하고 오분류 확률을 유도하여 성능을 분석한다.

• 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.

• Journal of electromagnetic engineering and science
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• 제4권4호
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• pp.175-182
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• 2004

When the M-ary signal experiences the Rayleigh fading, the diversity schemes can reduce the effect of fading since the probability that all the signals components will fade simultaneously is reduced considerably. The symbol error probabilities for various M-ary signals, such as MDPSK(M-ary DPSK) and MPSK(M-ary PSK), are mathematically derived for the Selection Combining 2(SC-2) and Selection Combining 3(SC-3) demodulation system which requires a less complex receiver than Maximum Ratio Combining(MRC). The propagation model used in this paper is the frequency-nonselective slow Rayleigh fading channel corrupted by the Additive White Gaussian Noise(AWGN). The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• Journal of electromagnetic engineering and science
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• 제7권4호
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• pp.183-189
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• 2007

When the M-ary signal experiences the Rayleigh fading, the diversity schemes can reduce the effect of fading since the probability that all the signals components will fade simultaneously is reduced considerably. The symbol error probabilities for various M-ary signals, such as MDPSK(M-ary DPSK) and MPSK(M-ary PSK), are mathematically derived for the Selection Combining 2(SC-2) and Selection Combining 3(SC-3) demodulation system which requires a less complex receiver than maximum ratio combining(MRC). The propagation model used in this paper is the frequency-nonselective slow Rayleigh fading channel corrupted by the additive white gaussian noise(AWGN). The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• 한국통신학회논문지
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• 제38C권3호
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• pp.288-295
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• 2013

본 논문에서는 4S (Ship to Ship, Ship to Shore) 해상통신을 위해 다른 채널 조건 하에서 기존의 채널 추정 기법을 비교하였다. 일반적으로 수신 신호는 다중경로나 부호 간 간섭에 의해 손상을 받게 된다. 시간 변화 다중 페이딩 채널의 추정은 수신기에서 어려운 작업이며, 적절한 채널 추정 필터를 사용함으로써 수신기의 성능을 향상시킬 수 있다. 모의실험은 MATLAB을 사용하여 AWGN (Additive White Gaussian Noise), Rician, Rayleigh 채널에서 채널 추정 알고리즘으로 주로 사용되어지는 LMS (Least Mean Square)와 RLS (Recursive Least-Squares) 알고리즘을 비교 하였다.