• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.3
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• pp.51-58
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• 2010

According to dramatic increase of wireless communication demand, more spectrum resources are needed to support considerable and various wireless services, so cognitive radio(CR) was proposed to reuse unused frequency efficiently. Also, FCC revises its policies regarding the usage of the TV white spaces by unlicensed users. CR is an intelligent wireless communication system that is aware of the radio environment and is capable of adapting its operation to the statistical variations. Spectrum sensing is the key task of the CR systems. However, since spectrum sensing performance changes according to the received signal that is received various geography environment, regional characteristics are considered to estimate the path-loss. Therefore, for more accurate analysis and simulation, we demonstrate the spectrum sensing performance of CR system by various method applying Okumura-hata propagation model.

• Journal of electromagnetic engineering and science
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• v.10 no.4
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• pp.290-295
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• 2010

In this paper, an interference analysis method with a site-specific path loss model for a wireless personal area network (WPAN) is proposed. The site-specific path loss model is based on geometrical optics and geometric probability to consider both site-specific radio propagation characteristics and a closed-form expression to obtain the mean interference from which the uniformly distributed multiple interferers are derived. Therefore, the proposed interference analysis method can achieve more computational simplicity than the Monte-Carlo (MC) simulation, which uses the ray-tracing (RT) technique. In addition, better accuracy than the conventional interference analysis model that uses stochastic method can also be achieved. To evaluate the proposed method, a signal to the interference-noise ratio with a mean interference concept for uniformly distributed interferers is calculated and compared in two simulation scenarios. As a result, the proposed method produces not only better matched results with the MC simulation using the RT technique than the conventional interference analysis model, but also simpler and faster calculation, which is due to the site-specific path loss model and closed-form expression for interference calculation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.12
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• pp.1140-1147
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• 2013

In this paper, The path loss model of Air Traffic Control(ATC) telecommunication radio channel has been studied at the Incheon International Airport(IIA) Cargo Terminal. We measured one frequency among VHF channel bands. The transmitting site was located at different locations with different heights. The transmitting site radiated the Continuous Wave(CW). The propagation measurement was taken using the moving vehicle equipped with receiver and antenna. The transmitting power, frequency and antenna height are the same as the current operating condition. The path loss exponent and intercept parameters were extracted by the basic path loss model and hata model. The path loss exponent at IIA Cargo terminal area were 3.67 and 3.39 respectively in first and second transmitting sites. The deviation of prediction error is 14.42 and 10.38. The new path loss equation at the IIA Cargo terminal area was also developed using the derived path loss parameters. The new path loss was compared with other models. This result will be helpful for the ATC site selection and service quality evaluation.

• Journal of the Optical Society of Korea
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• v.19 no.5
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• pp.437-443
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• 2015

In this paper, we analyze the performance of the all-optical multihop radio over a free space optical (RoFSO) communication system with amplify-and-forward (AF) relays under varying weather conditions. The proposed channel model considers the propagation loss, attenuation and atmospheric fading modeled by the Gamma-Gamma (GG) distribution. Both the amplified spontaneous emission (ASE) noise in the all-optical relays and the background noise projected onto receiver apertures have been considered in the analysis. The lower bound analytical expressions for the end-to-end bit error rate (BER) and outage probability are derived for the multihop system employing the all-optical relays with the full channel state information (CSI). Meanwhile, the exact results for BER and outage probability are obtained via Monte Carlo simulation. Results indicate the performance of the proposed system will be improved by the multihop transmission technology. For a fixed number of relays, the BER and outage probability will be increased with the deterioration of the weather conditions.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.7
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• pp.684-690
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• 2015

This paper presents a modified residual-based EKF (Extended Kalman Filter) for performance improvement of indoor positioning using WiFi RSSI (Received Signal Strength Indicator) measurement. Radio signal strength in indoor environments may have irregular attenuation characteristics due to obstacles such as walls, furniture, etc. Therefore, the performance of the RSSI-based positioning with the conventional trilateration method or Kalman filter is insufficient to provide location-based accurate information services. In order to enhance the performance of indoor positioning, in this paper, error analysis of the distance calculated by using the WiFi RSSI measurement is performed based on the radio propagation model. Then, an IARM (Irregularly Attenuated RSSI Measurement) error is defined. Also, it shows that the IARM error is included in the residual of the positioning filter. The IARM error is always positive. So, it is presented that the IARM error can be estimated by taking the absolute value of the residual. Consequently, accurate positioning can be achieved based on the IEM (IARM Error Mitigated) EKF with the residual modified by using the estimated IARM error. The performance of the presented IEM EKF is verified experimentally.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.745-745
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• 2002

Both geophysical and geospatial data provide important information in the establishment of the optimal telecommunication systems especially in the mobile telecommunication environment. The objective of this study is to utilize geophysical properties and geospatial information in the analysis of the telecommunication environment through point-to-point wave property modeling. Geophysical properties associated with wave propagation parameters of the earth surface were analyzed based on hierarchical land classification using Landsat ETM＋ and IKONOS images. Three-dimensional geospatial information was obtained by processing stereo aerial images. The results show that the accurate geospatial information and reliable geosphysical property of the surface improve the prediction of receiving power of the receivers located near corners of the buildings where diffractions occur. The wave property model developed from accurate telecommunication environment could be applied to optimal cell planning and delay time analysis.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.6
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• pp.90-97
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• 2012

In this paper, the new user mobility model which can be utilized to register user's location for interworking with heterogeneous overlay convergent networks under the time-varying radio propagation environment has been proposed. Thus the user mobility model is considered in order to evaluate the behaviors of users in the overlay convergent networks. This Mobile IP user mobility model will be very useful to model the user mobility behaviors and can be used to estimate the signaling traffic and frequency spectrum demands for massive data transfer for the heterogeneous overlay convergent networks.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1422-1430
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• 2016

Researches for oceans are limited to military purpose such as underwater sound detection and tracking system. Underwater acoustic communications with low-probability-of-interception (LPI) covert characteristics were received much attention recently. Covert communications are conducted at a low received signal-to-noise ratio to prevent interception or detection by an eavesdropper. This paper proposed optimal covert communication model based on direct sequence spread spectrum for underwater environments. Spread spectrum signals may be used for data transmission on underwater acoustic channels to achieve reliable transmission by suppressing the detrimental effect of interference and self-interference due to jamming and multipath propagation. The characteristics of the underwater acoustic channel present special problems in the design of covert communication systems. To improve performance and probability of interception, we applied BCJR(Bahl, Cocke, Jelinek, Raviv) decoding method and the direct sequence spread spectrum technology in low SNR. Also, we compared the performance between conventional model and proposed model based on turbo equalization by simulation and lake experiment.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.598-601
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• 2006

The radio signal in GNSS was intentionally designed with two frequencies in order to combat the dispersion error caused by trans-ionospheric propagation. By measuring the path delay independently at the two, widely spaced GPS frequencies, L1 & L2, the TEC along the path from satellite to receiver can be measured directly. The issue with dual frequency measurement of the ionosphere is the calibration of L1/L2 interfrequency biases. L1/L2 interfrequency biases are generated because physical electric signal paths of L1 and L2 circuits are different from each other for both satellites and receiver. Conventionally L1/L2 interfrequency bias is estimated and broadcasted by 2D ionospheric model. In this paper, we estimated IFB (interfrequency bias) by 2D & 3D ionospheric models including real time filter methods and compared the result of those and concluded the merit of 3D tomography model to recover the problem of 2D thin shell model. We confirmed our conclusion by experimental data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.5
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• pp.408-417
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• 1996

In this paper, we quantiatively analyze the broadband CDMA systems with high chip rate, which virually eliminates the multipath fading effects by distinguishing each reflected paths in the process of despreading. We model the broadband multipath propagation channel with random time-variant impulse response as a linear filter of tapped delay line to evaluate the performance of broadband CDMA systems in multipath fading environment. This statistical model, based on extensive experimental data, was established to characterize the urban radio propagation medium in various environments. We perform computer simulation of the transmission and reception of broadband CDMA systems by applying it to abve channel model. From the simulation results, we confirm that the broadband CDMA systems inherenly reduce the effects of multipath fading phenomena which causes to degrade the performance of mobile communication systems, based on the results of eye-diagram and BER curve.