• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.7
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• pp.1-11
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• 1993

The bit error rates of DS/SSMA DPSK system with diversity and FEC channel coding in Rayleigh fading and log-normal shadowing channel are evaluated. Microscopic postdetection diversity and macroscopic selection diversiity are used to mitigate the effects of Rayleigh fading and log-normal shadowing, respectively. The numerical results show that the composite use of diversity and channel coding is very efficient for improving system performance compared to their respective uses.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1995.06a
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• pp.155-159
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• 1995

• Journal of Astronomy and Space Sciences
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• v.37 no.4
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• pp.219-228
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• 2020

A CubeSat platform has become a popular choice due to inexpensive commercial off-the-shelf (COTS) components and low launch cost. However, it requires more power-efficient and higher-data rate downlink capability for space applications related to remote sensing. In addition, the platform is limited by the size, weight and power (SWaP) constraints as well as the regulatory issue of licensing the radio frequency (RF) spectrum. The requirements and limitations have put optical communications on promising alternatives to RF communications for a CubeSat platform, owing to the power efficiency and high data rate as well as the license free spectrum. In this study, we analyzed the performance of optical downlink communications compatible with CubeSat platforms in terms of data rate, bit error rate (BER) and outage probability. Mathematical models of BER and outage probability were derived based on not only the log-normal model of atmospheric turbulence but also a transmitter with a finite extinction ratio. Given the fixed slot width, the optimal guard time and modulation orders were chosen to achieve the target data rate. And the two performance metrics, BER and outage data rate, were analyzed and discussed with respect to beam divergence angle, scintillation index and zenith angle.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1451-1454
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• 2002

In recent years, there are growing concerns about land mobile satellite (LMS) communication systems and mobile stratospheric communication systems (SCS) for the purpose of service upgrade of personal and mobile communications in near future. It is important to possess accurate channel model for prediction of the above system performance. Thus, in this paper, we evaluate the bit error rates of a coded BPSK system based on realistic channel model which can be applied to stratospheric communication systems. The channel data was made by fitting the parameters of probability distribution model to measured data. This approach was proposed by Corraza〔1〕and modified by You〔2〕. And also the effects of channel codings on the system performance are analyzed. As results, we can get the performance curve characteristics on realistic Rician log-normal fading channels with various communication environments.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.4
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• pp.67-73
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• 2002

There have been increased concerns on mobile stratospheric communication system(SCS) for the purpose of advanced service of personal and high speed communication systems. In fact, this SCS is considered and studied for IMT-2000 service by ITU. Although, it is important to make accurate channel model for prediction of the SCS performance, there is no measured channel data in this system. Thus, in this paper, we estimate the performance of SCS bye use of channel model provided by Corazza(2) and modified by You(3). And also, the effects of channel codings on system performance are analyzed by deriving bit error performance based on realistic Rician log-normal fading channel models. The performance results are divided into three kinds of areas with three kinds of elevation angles 20$^\cire$, 45$^\cire$, and 80$^\cire$. And also the effects of forward error correction channel codings on system performance with Hamming(7,4), HCH( IS,7) and convolutional code of constraint length 3 and code rate R=1/2.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.1843-1853
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• 1997

The channel throughput and packet delay of wireless media control (MAC) protocols with Rayleigh fading, log-normal shoadowing and near-far effects are analyzed. We consider CSMA/CA protocols as the wireless MAC protocols, since CSMA/CA protocols are based on the standard for wireless Local Area Networks (LANs) IEEE 802. 11. We have found that the performance of CSMA/CA in radion channel model is reduced above 50% than those of error free channel model in low traffic load. We also found that 4-Way Handshake CSMA/CA protocol is supterior to the other CSMA/CA protocols in high traffic load.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8A
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• pp.1107-1114
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• 1999

In this paper, we analyze the effect of co-channel interferers coming from other systems with composite log-normal shadowing and Nakagami fading on the capacity of the imperfect power-controlled DS/CDMA cellular system. The analytical results are compared with the results of Prasad and Jansen in which they derive the result under the condition of imperfect power-control of DS/CDMA system and without considering interference. And the outage probability is calculated fro the effect of the log-normal/Nakagami faded inferers on DS/CDMA system using Schwartz and Yeh's method. With the deviation of outage probability, we analyzed the decreases in the capacity of DS/CDMA system with the variation of the paramenters of the imperfect power-control, the fadig index, the processing gain, the power ratio, the voice activity factor, and the number of interferers. Analysis reuslts have shown that the capacity of DS/CDMA system is very sensitive to the imperfect power-control and the number of interferers. It is shown that the DS/CDMA system capacity decreased according to increase of the deviation of the impertect power-control, the increase of the fading, and the increase of interferer number.

• Journal of the Korean Chemical Society
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• v.11 no.1
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• pp.12-16
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• 1967

Fading of Chlorantine Fast Red 5B (C.I. Direct Red 81) on cotton fabric exposed to carbon are light was examined. It was observed that the dye had anomaly in CF curve slope, while normal in CFG one. Auther considered that the reason for discrepancy of the one with the other curve slope might be appeared from Weber-Fechner law, and derived following equation $F_v=[logC_0-log(C_0-C_0F_t/100)]{\times}100/(logC_0+b)$ where $F_t$; the proportion of dye faded after t hour exposure. $F_v$; the proportion of dye faded after t hour exposure, when a pattern is judged by visual method $C_0$; initial dye concentration. b; constant. also, the reason for increasing lightfastness with dye concentration was discussed on view of the above equation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.9
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• pp.1668-1679
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• 1994

The cochannel interference probability has been estimated both in the environment of Nakagami fading and Gasussian noise and in the environments of Gaussian noise and Nakagami fading plus log-normal shadowing. In noise and Nakagami fading environments, a theoretical analysis has been performed in order to calculate the cochannel interference probability in addition to computer simulation. In the environments of noise and Nakagami fading plus shadowing, only a simulation technique is used due to complexity in analysis. The spectrum efficiency is discussed on each case.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.1
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• pp.100-109
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• 1993

In this paper, the performance of DS /SSMA BPSK communication system with maximal ratio combining microscopic diversity and selection macroscopic diversity is analyzed. The effects of Rayleigh fading and log normal shadowing on system performance are analyzed, and the validity of microscopic and macroscopic diversity to mitigate the two fading effects are estimated. The increase of the number of chips is effective for mitigating log norma; shadowing, while the increase of the order of microscopic diversity is not. And the higher the standard deviation of shadowing, the more effective the macroscopic diversity.