• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2A
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• pp.91-99
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• 2011

Several repeater systems are used to enhance the cell coverage to location such as shadow and rural areas in mobile systems. But the general RF repeater solutions are not suitable for high power outdoor environment because it has the weakness such as self oscillation problem With adoption of a adaptive digital filter technology, feedback interference cancellation repeater prevents oscillation by detecting and canceling the unwanted feedback signal between transmission and receiver antenna. In this paper, dual NLMS based interference cancellation method is proposed and the step size adaptation can be implemented by the estimation of the feedback channel Doppler frequency characteristics. The performance of the proposed algorithm is quantified via analysis and simulation for the static and multipath fading feedback channels.

• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.2
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• pp.93-99
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• 2013

Fractal theory has been adopted as an effective tool for modelling complex and irregular natural phenomena facing in the fields of Computer Science, Engineering, Medical, Climatology and so on. In this paper, we presents an algorithm which enhances the performance of the triangular prism method(TPM) which has been widely used for fractal dimension extraction of natural terrains and images. For this, existing sampling methods are analyzed and a new sampling method which takes their merits is proposed. The effectiveness of the proposed algorithm is tested on fractal terrain maps and its performance is compared with that of other methods.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.5
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• pp.29-36
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• 2009

Cost and Time for software test is gradually increasing as the software complexity increases. To cope with this problem, it is very important to reduce the number of test cases used in the software test. The interaction strength number is especially important in decision of the number of test cases for the unit test, where the interaction strength number means the number of arguments which affect the results of a function by the analysis of their combination used in source code of the function. This paper proposes the algorithm that computes the number of the interaction strength, where analyzes the patterns used in the source code of a function and increase its number when the pattern matches one of the specified patterns. The proposed algorithm is validated by some experiments finding coverage and the number of fault detection.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5A
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• pp.339-347
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• 2012

Femtocells as home base station for indoor coverage extension and wideband data service, have been studied with significant interests. When femtocell is deployed, the existing cell structural of changes causes various technical problems. In this paper, we investigate the femto-macro cell interference mitigation in OFDMA system. We propose dynamic downlink resource management scheme which adjust the transmitted power of femtocell according to the strength of received macrocell signal and allocates subcarrier to femtocells in a dynamic manner. In this way, the interference between the macrocell users and femtocells is reduced. The simulation results show that proposed scheme enhances both macrocell and femtocell throughputs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.8A
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• pp.691-701
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• 2011

In rotatable directional sensor networks, maximizing network lifetime while covering all the targets and forwarding the sensed data to the sink is a challenge problem. In this paper, we address the Maximum Directional Cover Tree (MDCT) problem of organizing the directional sensors into a group of non-disjoint subsets to extend the network lifetime. Each subset in which the directional sensors cover all the targets and forward the sensed data to the sink is activated at one time. For the MDCT problem, we first present an energy consumption model which mainly takes into account the energy consumption for rotation work. We also develop the Directional Coverage and Connectivity (DCC)-greedy algorithm to solve the MDCT problem. To evaluate the algorithm, we conduct simulations and show that it can extend the network lifetime.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.9
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• pp.1020-1025
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• 2016

In the recent, the communication market increased every year. Because of the user's demands and exhaustion of wireless resource, we needs a new technology of the communication system. The femtocell is one of the new technology of the communication system. 'Femto' means very small. By using the femtocell that made up the very small cell, the frequency efficiency increase. The femtocell has different cell environments. The Power Control is important for femtocell to avoid interference and unnecessary handover. In this paper, we propose a new femtocell power control that is improvement of handover probability and throughput. And we simulate and check the result.

• KIPS Transactions on Computer and Communication Systems
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• v.3 no.1
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• pp.7-14
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• 2014

The rapid increase of mobile devices such as smart phone and smart pad have raised the needs for seamless multimedia services during moving at anytime and anywhere. Current 4G mobile devices are equipped with both 4G (LTE) and WLAN (WiFi) interfaces, and mobile services operators provide wireless Internet services using 4G network with a wider coverage and WiFi zone. Generally users prefer to use the Internet services through WLAN rather than LTE in the coverage of WLAN. However, since WLAN has a long L2 handover latency, it is difficult to support seamless services during a handover. In this paper, we proposed an efficient handover scheme based on flow mobility for WLANs to support a seamless service during handovers by using the overlaid 4G network with a wider coverage. Also, we showed the outperformance of the proposed scheme on a testbed.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.2
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• pp.231-242
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• 2013

Recently, automated software testing methods such as fuzzing have been researched to find software vulnerabilities. The purpose of fuzzing is to disclose software vulnerabilities by providing a software with malformed data. In order to increase the probability of vulnerability discovery by fuzzing, we must solve the test suite reduction problem because the probability depends on the test case quality. In this paper, we propose a new method to solve the test suite reduction problem which is suitable for the long test case such as file. First, we suggested the length of test case as a measure in addition to old measures such as coverage and redundancy. Next we designed a test suite reduction algorithm using the new measure. In the experimental results, the proposed algorithm showed better performance in the size and length reduction ratio of the test suite than previous studies. Finally, results from an empirical study suggested the viability of our proposed measure and algorithm for file fuzzing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.1
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• pp.26-33
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• 2013

Femto-cells are low power/cost, micro-base stations and are main components in heterogeneous networks. However, some of technical issues arise when femto-cells are initially installed. One approach to resolve the problems is to control the transmission (TX) power autonomously via SON(Self-Organized Network) scheme. By controlling the femto-cell TX power, the system throughput performance can be improved or the system overhead is highly reduced. Generally, the TX power for maximizing the system throughput and that for reduced system overhead may not be identical. Therefore, we propose a TX power control scheme by which we can improve the system throughput and reduce the system overhead, simultaneously. When we apply the proposed method, the simulation results show that the system overhead can be reduced by up to 41% compared to the performance of the method which maximizes throughput performance only, and the throughput performance can be improved by up to 63% compared to that of the method which only optimizes the coverage area.

• Journal of the Korea Society for Simulation
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• v.15 no.3
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• pp.87-91
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• 2006

With the growth of the internet, the number of wireless internet users has increased continuously up to date. However, mobile communications could not support high speed transmission rate with cheap communication fee and wireless LAN has problems in providing terminal mobility and wide area connectivity, respectively. So the WMAN standard has been newly designed to make up for these limits. The initial 802.16 specification effectively offers a solution for providing fixed users with high speed wireless communication but it does not offer terminal mobility. So the 802.16d and 802.16e have been developed as the next generation solution that can support various PHY layer (SC, SCa, OFDM, OFDMA) and offer the terminal mobility. In this paper, we propose an effective uplink scheduling algorithm for VoIP with using UGS, and we show that our proposed algorithm is superior in view of average delay and management of uplink bandwidth to conventional rtPS algorithm and the scheme in reference, with using NS-2 network simulator.