• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.182-188
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• 2018

In order to increase the robustness of the uplink for UAS(Unmanned Aerial System), we propose a jamming signal rejection algorithm. In the UAS datalink system, DSSS (direct sequence spread spectrum) is used to reduce the radio noise or jamming signal. In general, jamming signals below the spreading gain are recoverable but the signals beyond the spreading gain can not be recovered. In this paper, these jamming signals beyond spreading gain are detected using the threshold detector in the spectrum area then, generate the estimated signals from the sine wave generator. Finally, we obtain the desired signal to remove jamming signals from the received signals. The proposed scheme can eliminate jamming signals while minimizing the hardware complexity and the original signal loss.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.8
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• pp.467-473
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• 2014

In the direct sequence spread spectrum system, the correct synchronization is very important; hence, several acquisition schemes based on the sequential estimation have been developed. Typically, the rapid acquisition sequential estimation (RASE) scheme, the seed accumulating sequential estimation (SASE) scheme, the recursive soft sequential estimation (RSSE) scheme have been developed for the correct acquisition. However, the objective performance comparison and analysis between former estimation schemes have not been performed so far. In this paper, we compare and analyze the performance of the above sequential estimation schemes by simulating the correct chip probability and the mean acquisition time (MAT).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11A
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• pp.1086-1095
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• 2007

This paper proposes a novel non-coherent TOA estimation scheme using multiple correlation process on the existence of multiple simultaneously operating piconets (SOPs). Impulse radio-ultra wideband (IR-UWB) based on direct sequence spread spectrum (DSSS) using Gold sequence is employed in order to discriminate each piconet. In order to enhance the characteristic of correlation, this paper presents the method of multiple mask operation (MMO). The time of arrival (TOA) of direct line of sight (DLOS) path is estimated via two step coarse/fine timing detection. To verify the performance of proposed scheme, two distinct channel models approved by IEEE 802.15.4a Task Group (TG) are considered. According to the simulation results, it could conclude that the proposed scheme have performed better performance than the conventional method well even in densed indoor multi-path environment as well as in the existence of multiple SOPs.

• Journal of Information Technology and Architecture
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• v.9 no.1
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• pp.43-55
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• 2012

In recent years, outsourcing of information systems, including decision support systems has become a key method for managing the system portfolio of a corporation. Since the outsourced DSSs provide their own models and solvers, which may be created on the basis of different modeling practices and system platforms, the decision maker wishing to solve business problems using the outsourced DSSs frequently faces a difficulty in selecting and/or applying appropriate models and solvers to the problems on hand. This paper proposes a DSS outsourcing architecture that enables a user to discover and execute appropriate models and solvers, even though the user is not knowledgeable enough about all the details of the models and solvers. Specifically, this paper adopts a Web services approach to integrate the heterogeneous models and solvers by encapsulating individual models and solvers as Web services and hiding all system specific implementation details from the users.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.304-313
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• 2021

This paper presents the results of a sea trial for long range underwater acoustic communication conducted in the East Sea in November 2020. Signals were collected through a moving transmitter and 16 vertically arranged receivers, and the range between the transmitter and receiver was about 20 km. The signal in the experiment is a conventional Direct Sequence Spread Spectrum (DSSS) method and a superimposed DSSS method that increases data rate by superimposing of multiple circulated Pseudo Noise (PN) sequences for each symbol. The results show that the uncoded bit error rate averaged over 16 channels to which the channel coding technique was not applied was 0.0005 for the conventional direct sequence spreading method, and was 0.00124 for the superimposed direct sequence spreading method.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.15 no.1
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• pp.20-26
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• 2015

It is very difficult to design an underwater communication system because of multipath, Doppler effects, noise, and attenuation. These factors lead to errors in the communication performance and maximum propagation distance. In this study, we calculate the distance that can be realized using the direct-sequence code division multiple access (DS-CDMA) technique with direct-sequence spread spectrum (DSSS) in an underwater communication system considering only the attenuation and noise. We also compare the estimated and calculated propagation distances obtained for several different scenarios.

• Korean Management Science Review
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• v.9 no.1
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• pp.53-65
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• 1992

Decision Support System(DSS) is an advanced information system concept prevailing since 1980s. It supports managers' decision making activities by providing not only information but decision alternatives. It essentially consists of the components of database, modelbase and dialogue systems. With the development of its databases, POSCO needs a number of modelbases in establishing DSSs in various areas such as production planning and investment. This research particularly focuses on establishment of a mid-and long-range investment DSS and investigates the necessity and the problems of an investment DSS and the decision criteria for investment priority. We (1) propose a modelbase which uses the concepts of Analytic Hierarchy Process(AHP) and Zero-Base Budgeting(ZBB), along with an appropriate scoring method, database and dialogue system to support the investment manager in evaluating investment proposals ; (2) implement the system using relational database management system ; and (3) discuss the results of implementing the investment DSS.

• Korean Management Science Review
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• v.11 no.2
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• pp.43-63
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• 1994

A new model management framework is proposed to accommodate wide-spreading algebraic modeling languages (AMLs), and to facilitate a full range of model manipulation functions. To incorporate different modeling conventions of the leading AMLs (AMPL, GAMS, and SML) homogeneously, generic model concepts are introduced as a conceptual basis and are embodied by the structural and operational constructs of an Object-Oriented Database Management System(ODBMS), enabling the framework to consolidate components of DSSs(database, modelbase, and associated solvers) in a single formalism effectively. Empowered by a database query language, the new model management framework can provide uniform model management commands to models represented in different AMLs, and effectively facilitate integration of the DSS components. A prototype system of the framework has been developed on a commercial ODBMS, ObjectStore, and a C++ programming language.

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.296-298
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• 2009

In this paper, we are performance analysis of IEEE 802.15.4b LR-WAPN(Low-Rate Wireless Personal Area Network; Zigbee) system noncoherent receivers at 915MHz under Jamming. IEEE 802.15.4b concerns itself with devices at 915MHz, which employ a higher data rate of up to 250 kbps, and which use O-QPSK(Offset Quradrature Phase Shift Keying modulation with DSSS(Direct Sequence Spread Spectrum). Communication between devices can still be hampered by the presence of interferers outside the network, whether the interference be intentional or not. Hence the receivers can not have stable receiving condition due to worse BER. To solve this problem, we present a mere stabilized receiver system of using noncoherent detection. In this paper, we look instead at the effect of jamming, i.e. intentional interference, on the BER performance of IEEE 802.15.4 devices.

• ETRI Journal
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• v.28 no.1
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• pp.95-98
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• 2006

In this letter, a novel M-ary code-selected direct sequence (DS) ultra-wideband (UWB) communication system is presented. Our purpose is to achieve a high data rate by an M-ary code-selected direct sequence bipolar pulse amplitude modulation (MCSDS-BPAM) scheme. In this system, a particular DS code sequence is selected by the $log_2M$/2 bits from the DS gold code set. This scheme can accomplish both a high data rate without increasing the system bandwidth or changing the pulse shape and improve the BER with an increase of modulation level M even at a lower signal-to-noise ratio (SNR). The receiver signal processing algorithm is given for an MCSDS-BPAM UWB system over an ideal AWGN channel and correlation receivers.