• 한국통신학회논문지
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• 제35권8A호
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• pp.785-790
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• 2010

This paper proposes new suboptimum, yet very efficient demapping methods for Turbo coded noncoherent MFSK systems under AWGN and Rayleigh fading channels with channel state information. Simulation results show that the proposed methods achieve performance within 0.2 dB of the maximum-likelihood decoder and the previously proposed suboptimum demapping schemes with a fraction of the complexity.

• Journal of Communications and Networks
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• 제14권3호
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• pp.267-272
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• 2012

In this paper, we study multi-hop cooperative transmission protocols using fountain codes. The proposed protocols can reduce the end-to-end delay and number of stages compared to those in conventional multi-hop transmission. VariousMonte-Carlo simulations are presented to evaluate and compare performance of the protocols over Rayeigh fading channels.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권11호
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• pp.3026-3045
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• 2012

In this paper, diversity-multiplexing tradeoff (DMT) of three-user wireless multiple-antenna cooperative systems is investigated in general fading channels when half-duplex and decode-and-forward relay is employed. Three protocols, i.e., adaptive protocol, receive diversity protocol, and dual-hop relaying protocol, are considered. The general fading channels may include transmit and/or receive correlation and nonzero channel means, and are extensions of independent and identically distributed Rayleigh or Rician fading channels. Firstly, simple DMT expressions are derived for general fading channels with zero channel means and no correlation when users employ arbitrary number of antennas. Explicit DMT expressions are also obtained when all users employ the same number of antennas and the channels between any two users are of the same fading statistics. Finally, the impact of nonzero channel means and/or correlation on DMT is evaluated. It is revealed theoretically that the DMTs depend on the number of antennas at each user, channel means (except for Rayleigh and Rician fading statistics), transmit and/or receive correlation, and the polynomial behavior near zero of the channel gain probability density function. Examples are also provided to illustrate the analysis and results.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3540-3550
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• 2022

The supercritical carbon dioxide (S-CO₂) Brayton cycle is an important energy conversion technology for the fourth generation of nuclear energy. Since the printed circuit heat exchanger (PCHE) used in the S-CO₂ Brayton cycle has narrow channels, Rayleigh-Bénard (RB) convection is likely to exist in the tiny channels. However, there are very few studies on RB convection in supercritical fluids. Current research on RB convection mainly focuses on conventional fluids such as water and air that meet the Boussinesq assumption. It is necessary to study non-Boussinesq fluids. PRB convection refers to RB convection that is affected by horizontal incoming flow. In this paper, the computational fluid dynamics simulation method is used to study the PRB convection phenomenon of non-Boussinesq fluid-supercritical carbon dioxide. The result shows that the inlet Reynolds number (Re) of the horizontal incoming flow significantly affects the PRB convection. When the inlet Re remains unchanged, with the increase of Rayleigh number (Ra), the steady-state convective pattern of the fluid layer is shown in order: horizontal flow, local traveling wave, traveling wave convection. If Ra remains unchanged, as the inlet Re increases, three convection patterns of traveling wave convection, local traveling wave, and horizontal flow will appear in sequence. To characterize the relationship between traveling wave convection and horizontal incoming flow, this paper proposes the relationship between critical Reynolds number and relative Rayleigh number (r).

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.799-818
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• 2014

Spectrum sensing is a key technical challenge for cognitive radio (CR). It is well known that multi-cycle cyclostationarity (MC) detector is a powerful method for spectrum sensing. However, conventional MC detector is difficult to implement due to its high computational complexity. This paper pays attention to the fact that the computation complexity can be reduced by simplifying the test statistic of conventional MC detector. Based on this simplification process, an improved MC detector is proposed. Compared with the conventional one, the proposed detector has the low-computational complexity and sufficient-accuracy on sensing performance. Subsequently, the sensing performances are further investigated for the cases of Rayleigh, Nakagami-m, Rician, composite Rayleigh fading-lognormal shadowing and composite Nakagami fading-lognormal shadowing channels, respectively. Furthermore, the square-law combining (SLC) is introduced to improve the detection capability over fading-shadowing channels. The corresponding closed-form expressions of average detection probability are derived for each case by the moment generation function (MGF) approach. Finally, illustrative and analytical results show that the efficiency and reliability of proposed detector and the improvement on sensing performance by SLC over composite fading-shadowing channels.

• 대한기계학회논문집
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• 제13권4호
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• pp.771-779
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• 1989

본 연구에서는 기판의 양면에 부품이 SMT방법으로 탑재되어 있는 경우에 기판사이에 형성되는 유동채널에서의 열전달 및 유동특성을 연구하였다.

• Journal of Communications and Networks
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• 제6권1호
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• pp.1-8
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• 2004

In this paper, we investigate the properties and performance of space-time bit-interleaved coded modulation (STBICM) systems in fast Rayleigh fading channels. We first show that ST-BICM with QPSK signaling in fast fading channels possesses the uniform distance property, which makes performance analysis tractable. We also derive the probability distribution of the squared Euclidean distance between space-time symbols assuming uniform bit-interleaving. Based on the distribution, we show that the diversity order for each codeword pair becomes maximized as the frame length becomes sufficiently long. This maximum diversity order property implies that the bit-interleaver transforms an ST-BICM system over transmit diversity channels into an equivalent coded BPSK system over independent fading channels. We analyze the performance of ST-BICM in fast fading channels by deriving an FER upper bound. The derived bound turns out very accurate, requiring only the distance spectrum of the binary channel codes of ST-BICM. Numerical results demonstrate that the bound is tight enough to render an accurate estimate of performance of ST-BICM systems.

• Journal of electromagnetic engineering and science
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• 제12권1호
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• pp.8-12
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• 2012

In this paper, we evaluate performances of dual-hop decode-and-forward relaying systems with the $N^{th}$ best-relay selection scheme. In some schemes, such as scheduling or load balancing schemes, the best relay is unavailable and hence the system must resort the second best, third best, or generally the $N^{th}$ best relay. We derive the expressions of the outage probability and symbol error rate (SER) for this scenario over Rayleigh fading channels. Monte-Carlo simulations are presented to verify the analytical results.

• Journal of electromagnetic engineering and science
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• 제10권3호
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• pp.190-198
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• 2010

This paper evaluates the performance of two methods of spectrum sensing: the linear combining method and the selection combining method which is based on maximum SNR of sensing channel. We proposed a rule for global detection for the purpose of combating hidden terminal problems in spectrum sensing. Our analysis considers a situation when sensing channels experience the non-identically, independently distributed(n.i.d) Rayleigh fading. The average probabilities of global detection in these methods are derived and compared. In the scope of this paper, the reporting channels are assumed to be the AWGN channel with invariant and identical gain during the system's operation.