• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.539-542
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• 2011

In this paper, we have implemented a performance analysis of $2{\times}1$ Alamouti scheme suggested by Alamouti, composed of the transmit space-time code and the simple linear decoding processing, in perfectly time-varying and spatially correlated channels. In addition, we derived the closed-form probability density function (PDF) of the output signal-to-noise ratio (SNR) and the outage probability of the Alamouti scheme as a function of the spatial correlation coefficient in the consideration of no correlation in time. As a result, it was found that the performance of the Alamouti scheme could be significantly degraded particularly in the case that the channels are time-varying and spatially correlated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.1
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• pp.237-243
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• 2017

In this paper, the detection performance of the electro-optical telescopes which observes and surveils space objects including artificial satellites, is analyzed. To perform the Modeling & Simulation(M&S) based analysis, satellite orbit model, telescope model, and the atmospheric model are constructed and a detection scenario observing the satellite is organized. Based on the organized scenario, pointing accuracy is analyzed according to the Field of View(FOV), which is one of the key factors of the telescope, considering pointing angle command error. In accordance with the preceding result, detection possibility according to the pixel-count of the detector and the FOV of the telescope is analyzed by discerning detection by Signal-to-Noise Ratio(SNR). The result shows that pointing accuracy increases with larger FOV, whereas the detection probability increases with smaller FOV and higher pixel-count. Therefore, major specification of the telescope such as FOV and pixel-count should be determined considering the result of M&S based analysis performed in this paper and the operational circumstances.

• Information and Communications Magazine
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• v.15 no.7
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• pp.75-94
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• 1998

In this paper, HFC CATV networks are introduced. HFC CATV networks are currently considered as a most effective and plausible solution for subscriber access networks in the information superhighway, among others such as ADSL and B-WLL. The advantages of HFC CATV networks include its broad upstream and downstream channel bandwidths, much wider than PSTN's and its readiness. The HFC CATV networks are already well spread among the general subscribers in Korea. This fact will shorten the installation period and significantly reduce its cost. In addition, The structure and channel environment of the HFC CATV networks are introduced. At the same time, in this paper included are major problems in the HFC CATV networks and the solutions for these problems. Also discussed are data transmission, medium access control, IEEE802.14, and MCNS for standardizations. Moreover, additional telecommunications service activities in both Korea and other countries, using HFC CATV networks are also included. The topics which are covered in detail are the ones such as interoperation between HFC CATV networks and trunk line and the digital transmission performance test for the CATV networks. In the performance test, it is concluded that HFC CATV networks can satisfy the QoS for various additional services if the number of the subscribers in a cell is limited to less than 500 and other minor requirements are satisfied. Based on all these discussions and conclusions, HFC CATV networks are suggested in this paper for the subscriber access networks of the so called information superhighway.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8A
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• pp.610-617
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• 2009

This paper proposes a cross-layer design combining adaptive modulation and coding (AMC) with truncated hybrid automatic repeat request (HARQ) for wireless multicast transmission, in order to increase the spectral efficiency while meeting the target quality-of-service (QoS). In the design, we provide the selection criterion of AMC so as to satisfy the target packet error rate (PER) of all users when the multicast data is received through the common channel and the number of retransmission is limited by the delay constraint of the service. The analytically derived results show that the cross-layer design using HARQ provides a better spectral efficiency than the AMC without HARQ by allowing retransmission and code combining. It is also observed that the design for multicast outperforms that for unicast in the mid to high signal-to-noise ratio region.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.4A
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• pp.371-376
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• 2008

In this paper, we explain the unified inter-cell interference avoidance and cancellation in OFDM mobile cellular systems. Interference avoidance is used for cell-interior or two-cell-edge users, and interference cancellation is applied to three-cell-edge users. The performance of the unified scheme is evaluated by simplified system simulation. Link simulation results are used in the interpretation of system simulation output. We compare three schemes which are "no interference management," "only interference avoidance," "both avoidance and cancellation." Primary performance measures are the data rate of the 5th percentile user and the mean data rate. Simulation results show that interference management schemes greatly improve the cell edge performance, but slightly reduce the mean data rate. Use of both avoidance and cancelaltion is better than that of only avoidance in terms of the cell edge throughput and the mean data rate.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.1
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• pp.78-84
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• 2012

In this paper, we introduced the design technique about a Ka band receive module for millimeter wave seekers. The receiver module consists of a waveguide, circulator and transition for antenna connection, and a limiter and gain control amplifier for receiver protection. This module is comprised of a sum, azimuth and elevation channel for receiving monopules signal, and a SLB channel for the acquisition of jamming signal. In this paper, receiver gain and range of gain control dependent on ADC nonlinear characteristic was analyzed and designed for wide dynamic range receive. In the test result of the fabricated Ka-band receive, the frequency band is 1 GHz, the noise figure is as low as 8.2 dB, the gain is $56{\pm}2dB$, the dynamic range is 135 dB, the gain congtrol is more than 86 dB, the channel isolation is more than 35 dB.

• Journal of Environmental Science International
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• v.25 no.9
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• pp.1241-1251
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• 2016

A minimum threshold for the signal to noise ratio ($SNR_{min}$) has to be set in the data processing system of wind profiler radar (WPR). The data collection rate and the accuracy of the WPR wind vector depend on the $SNR_{min}$. The WPR at Uljin is operated with an $SNR_{min}$ of 1 dB which is a relatively large threshold. We found that the accuracy and the continuity of the WPR wind vector with height were directly related to the variability of the SNR and vertical gradient of the squared refractive index. We investigated a quantitative method for determining a new $SNR_{min}$ for the WPR at Uljin and it was evaluated with radiosonde data. The accuracy and continuity of the wind vector from an SNR of less than 1 dB, began to decrease at an altitude of 3.5 km. Most of the SNR values were less than -3.5 dB in altitudes higher than 3.5 km. We retrieved high-accuracy wind vectors at altitudes over 3 km where measurements were deficient with an $SNR_{min}$ of 1 dB.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.463-466
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• 2008

With the development of Information Technology in recent years, the image has been an important means to store or express information. Generally, during the process of acquiring and storing images, the images can be corrupted by noise of which typical types are Impulse(Impulse Noise) and AWGN(Addiction White Gaussian Noise). Impulse noise shows irregularly in black and white over the length and breadth of the image by sharp and sudden disturbance of the image signal. In the Impulse noise environment, SM(Standard Median) filter would be used because of its good noise removal performance and simple algorithm. However, when SM filter removes noise, it also produces error at the edge of image and causes whole image quality deterioration. In this paper, we propose a method based on modified nonlinear filter operation scheme which enhances the features of noise removal and detail image preservation when restoring image in Impulse noise environment. And, we compared it with existing methods and the performances through simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.10
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• pp.938-946
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• 2012

Interference alignment (IA) is a data transmission technique that achieves the maximum degrees-of-freedom (DoF) in the multiuser interference channel for high signal-to-noise ratios (SNRs). However, most prior works on IA are based on the unrealistic assumption that perfect and global channel-state information (CSI) is available at all transmitters and receivers. In this paper, we propose the efficient design of feedback framework for IA that substantially suppresses the feedback overhead. While the feedback overhead in the conventional IA quadratically increases with K, the proposed feedback scheme supports the sequential exchange of computed IA precoders between transmitters and receivers and reduces the feedback overhead that linearly scales with K. Moreover, we analyze the residual interference due to the quantization error in limited feedback and propose the ordered IA algorithm that selects IA pair to minimize the sum residual interference in given channel realizations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.733-738
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• 2013

In this paper, we consider a physical layer security of an amplify-and-forward (AF) transmission in a presence of an eavesdropper in a wiretap channel. The proposed wiretap channel consists of a source, a destination, a relay, and an eavesdropper. Specifically, we consider that the relay has multiple antennas to exploit a diversity gain and a receive/transmit antenna selection schemes are applied to maximize a signal-to-noise ratio. In a practical point of view, we focus on the practical scenario where the relay does not have any channel state information of the eavesdropper while performing an AF protocol at the relay. For a secrecy performance analysis, we analyze a secrecy outage probability of the proposed system in one-integral form and verify our analysis with the computer-based simulation.