• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.12C
• /
• pp.1135-1142
• /
• 2006

This article presents a new asynchronous MC-CDMA system to implement multiple data rate communications. In a W-CDMA downlink, the OVSF code is used for spreading code for various multimedia traffic. Proposed system utilizes the OVSF code that generated by generation property for spreading. The proposed MC-CDMA system use different lengths of OVSF code as a spreading code according to their data rate. The groupwise processing is accomplished by code grouping in OVSF code generation tree. Between each group, the code grouping interference canceller is performed to cancel other group interference. At that time the proposed receiver does not require any information about interference users. For the analysis of average BER performance, we propose system model and computer simulation were used. We also compare the system performance with that of a single rate MC-CDMA system used orthogonal code as a spreading code.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.3
• /
• pp.365-370
• /
• 2016

Recently, There are increasing number of studies that apply multi-carrier method, a land mobile communication method, to underwater channel environment in order to enhance the performance of underwater communication. Therefore, in this paper, in order to design a new system with improved communication performance compared to the multi-carrier method in underwater communication, we present that the RS(Resource Spreading) FMT-OFDM system has a diversity and repetition effect from resource spreading. Moreover, we verify the performance of RS FMT-OFDM system and existing FMT-OFDM system through simulations after modeling communication channels and setting the system parameter based on the data measured from the real sea. Our result indicate that, compared to the existing FMT-OFDM system, there has been an improvement in communication performance by 12dB based on BER $10^{-3}$ we also discovered that communication performance improves as the resource spreading rate increases.

• Journal of Satellite, Information and Communications
• /
• v.2 no.2
• /
• pp.22-28
• /
• 2007

Spectrum spreading, in its general form, can be conceived as an artificial expansion of the signal bandwidth with respect to the minimum Nyquist band required to transmit the desired information. Spreading can be functional to several objectives, including resilience to interference and jammers and reduction of power spectral density levels. In the paper, signal spreading is manly used for increasing the received energy, thus satisfying link budget constraints, for terminals with low aperture antennas, without increasing the transmitted EIRP. As a matter of fact, in many mobile scenarios, even when MODCOD configurations with very low spectral efficiency (i.e. QPSK-1/4) in DVB-S2 standard, are used, the link budget cannot be closed. Spectrum spreading has been recently proposed as a technique to improve system performance without introducing additional MODCOD configurations under the constraint of fixed power spectrum density level at the transmitter side. To this aim, the design of spectrum spreading techniques shall keep into consideration requirements such as spectrum mask, physical layer performance, link budget, hardware reuse, robustness, complexity, and backward compliance with existing commercial equipments. The proposed implementation allows to fully reuse the standard DVB-S2 circuitry and is inserted as an 'inner layer' in the standard DVB-S2 chain.

• Journal of Korea Multimedia Society
• /
• v.9 no.3
• /
• pp.333-341
• /
• 2006

Recently, Random Constant worm is increasing The worm retards the availability of the overall network by exhausting resources such as CPU resource and network bandwidth, and damages to an uninfected system as well as an infected system. This paper analyzes the Power-Law network which possesses the preferential characteristics to restrain the worm from spreading. Moreover, this paper suggests the model which dynamically controls the spread of the worm using information about depth distribution of the delivery node which can be seen commonly in such network. It has also verified that the load for each node was minimized at the optimal depth to effectively restrain the spread of the worm by a simulation.

• Journal of Communications and Networks
• /
• v.10 no.1
• /
• pp.89-97
• /
• 2008

Anomaly detection systems playa significant role in protection mechanism against attacks launched on a network. The greatest challenge in designing systems detecting anomalous exploits is defining what to measure. Effective yet simple, Shannon entropy metrics have been successfully used to detect specific types of malicious traffic in a number of commercially available IDS's. We believe that Renyi entropy measures can also adequately describe the characteristics of a network as a whole as well as detect abnormal traces in the observed traffic. In addition, Renyi entropy metrics might boost sensitivity of the methods when disambiguating certain anomalous patterns. In this paper we describe our efforts to understand how Renyi mutual information can be applied to anomaly detection as an offline computation. An initial analysis has been performed to determine how well fast spreading worms (Slammer, Code Red, and Welchia) can be detected using our technique. We use both synthetic and real data audits to illustrate the potentials of our method and provide a tentative explanation of the results.

• Journal of Distribution Science
• /
• v.12 no.9
• /
• pp.53-63
• /
• 2014

Purpose - The rapid spread of SNS and increase of SNS users have heralded great changes in the tourism industry. Therefore, this study focused on how SNS characteristics- usefulness, convenience, interactivity, and intimacy - influence diffusivity, reliability and, consequently, user's preference for tourist attractions. Research design, data, and methodology - This study is designed not only to collect data with a questionnaire survey but also to test hypotheses with SEM by SPSS 18.0 and AMOS 18.0. Results - Usefulness, interactivity, and intimacy positively affect diffusivity, whereas convenience does not positively affect diffusivity. In addition, intimacy has a negative influence on reliability. However, diffusivity and reliability have positive impacts on the preference for tourist places. Conclusions - Certain characteristics of SNS facilitates the spreading of SNS tourist information. Usability and interactivity have positive impacts on the reliance of tourist information. Better communication can enhance the reliance of travel information. The influence of spreading tourist information has a positive influence on its reliance. Extension and reliance can have positive effects on the preference for tourist attractions.

• Proceedings of the Korea Contents Association Conference
• /
• 2003.11a
• /
• pp.128-131
• /
• 2003

This paper enhanced similar components retrieval algorithm-spreading activation method. The solution is that retrieval speed is overcome and more efficiently components are retrieved. Also we implemented interface for component information and query, and constructed component retrieval system.

• Proceedings of the IEEK Conference
• /
• 1998.06a
• /
• pp.11-14
• /
• 1998

This paper introuces a new efficient method of synchronization acquisition which is the most important element in DS-CDMA system using the phase offset of binary code. This approach uses the binary code function which can easily estimate the phase offset from the received spreading waveforms which respect to the receiver-stored replica of the spreading code. This paper proposes the initial acquisition model with repeat error control device that is good for perfomance. The hardware is implemented by TMS320c30

• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.146.1-146
• /
• 2001

The researches of science and engineering need the latest information from internet resources. But searching and filtering processes of appropriate web documents from huge internet resources are very complex as well as having some repeated procedures. In this paper, I propose a Personalized Agent System(PAS), which can filter World Wide Web Documents that the user is interested, such as papers. To do this, PAS uses a modified spreading activation neural network which 1 propose here. PAS observes the user´s local paper database to analyze, adapt and learn the user interests, and the then constructs the user-specified neural network model by the analyzed interests ...

• Journal of Electrical Engineering and information Science
• /
• v.2 no.4
• /
• pp.19-22
• /
• 1997

In this paper, we propose a new communciation scheme combining both MT modulation and DS-CDMA with a concatenated orthogonal/PN spreading sequence. This scheme incorporates the advantages of both DS-CDMA wit a concatenated sequence, and an MT modulation technique to combat the effect of a multipath fading channel. It is shown that he proposed system outperforms the MT-CDMA system with a convetional PN sequence.