• The KIPS Transactions:PartB
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• v.19B no.3
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• pp.165-176
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• 2012

In recent years, due to rapidly increasing user-created internet contents coupled with the development of community-based websites, the internet resource recommendation systems are attracting attentions of the users. However, most of the systems have failed in properly reflecting users' characteristics and thus they have difficulty in recommending appropriate resources to users. In this paper, we propose an internet resource recommendation method using FOAF and SNA which fully reflects the characteristics of users. In our method, 1) we extract the data about user characteristics and tags using FOAF; 2) we generate graphs representing users, user characteristics and tags after inserting data into 3 matrixes and integrating them; 3) we recommend the appropriate internet resources after selecting common characteristics of the recommended items and Hot tags by analyzing social network. For verification of our proposed method, we implemented our method to establish and analyze an experimental social group. We verified through our experiments that the more users added in the social network, the higher quality of recommendation result we got than the item-based recommendation method. By using the suggested idea in this paper, we can make a more appropriate recommendation of resources to users while effectively retrieving explosively increasing internet resources.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.6
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• pp.1193-1199
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• 2015

Studies applying multiple carrier method such as OFDM(Orthogonal Frequency Division Multiplexing) or FMT(Filtered Multi-Tone) to Underwater acoustic communication(UAC) system are actively under way as UAC is utilized in the various fields and the demand of high speed data transmission increases. In the existing OFDM method, the use of virtual carrier, which is inserted not to affect the adjacent channel in the frequency domain, and the cyclic prefix, which is used to reduce the impact of Inter Symbol Interference and Inter Channel Interference, decrease the throughput. In particular, the length of cyclic prefix to be used becomes longer under water since underwater has a rapidly changing channel characteristic, and the data throughput diminishes because it has to allocate more subcarrier on virtual carrier. This study therefore suggests FMT-OFDM system, a combination of OFDM and FMT, for the purpose of enhanced throughput in the underwater channel environment. Besides, in this study, channel is modeled based on data measured in real sea and the performance is analyzed after setting system parameters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.10
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• pp.2181-2190
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• 1997

The synchronous stream cipher has the problem of synchronization loss by cycle slip. Synchronization loss make the state which sender and receiver can't communicate and it may make the receiving system disordered. To lessen the risk, we usually use a continuous resynchronization which achieve resynchronization at fixed timesteps by inserting synchronization pattern and session key. While we can get effectively resynchronizationby continuous resynchronization, there are some problems. In this paper, we proposed an adaptive resynchronization algorithm for cipher system using LAPB protocol. It is able to solve the problem of the continunous resynchronization.The proposed adaptive algorithm make resynchronization only in the case that the resynchronization is occurred by analyzing the address field of LAPB. It measure the receiving rate of the address field in the decesion duration. If the receiving rate is smaller than threshold value, it make resynchronization or not. By using adaptively resynchronization, it solves the problems of continunous resynchronization. When the proposed adaptive algorithm is applied to the synchronous stream cipher system which is used in X.25 packet network, it reduced the time for resynchronization by ten times. It means that 11.3% of total data for transmit is compressed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1239-1247
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• 2003

OFDM(orthogonal frequency division multiplexing) communications system is very attractive for the high data rate transmission in the frequency selective lading channel. Since OFDM has high PAPR(peak-to-average power ratio), OFDM signal may be distorted by the nonlinear HPA(high power amplifier). In this paper, we propose the DSI(dummy sequence insertion) method for OFDM communication system. Some sub-carriers are inserted for PAPR reduction. They carry the specified dummy data sequence which are used for only PAPR reduction and do not work as side information like the conventional PTS(partial transmit sequence) or SLM(selected mapping) method. We use the complementary sequence and the combination of the correlation sequence as the dummy sequence. Flipping technique is used for the DSI method to get the effective PAPR reduction. It is important that BER of the proposed method is independent of the damage of the dummy data sequence. And DSI method has better spectral efficiency than the conventional block coding. On the other hand, threshold PAPR method is applied to cut down the processing time. However, this DSI method is not better than the conventional PTS method in the respect of the PAPR reduction performance. The DSI method includes the threshold PAPR lower than the PAPR of the OFDM signal, reduces the processing time and improves the BER performance.

• The KIPS Transactions:PartD
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• v.18D no.4
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• pp.225-236
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• 2011

Various applications of LBS (Location Based Services) are being developed to provide the customized service depending on user's location with progress of wireless communication technology and miniaturization of personalized device. To effectively process an amount of vehicles' location data, LBS requires the techniques such as vehicle observation, data communication, data insertion and search, and user query processing. In this paper, we propose the historical location index, GIP-FB (Group Insertion tree with Flexible Buffer Node) and the flexible buffer node technique to adjust the cost of data insertion and search. the designed GIP+ based index employs the buffer node and the projection storage to cut the cost of insertion and search. Besides, it adjusts the cost of insertion and search by changing the number of line segments of the buffer node with user defined time interval. In the experiment, the buffer node size influences the performance of GIP-FB by changing the number of non-leaf node of the index. the proposed flexible buffer node is used to adjust the performance of the historical location index depending on the applications of LBS.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.847-854
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• 2001

The Web continues to grow fast rate in both a large aclae volume of traffic and the size and complexity of Web sites. Along with growth, the complexity of tasks such as Web site design Web server design and of navigating simply through a Web site have increased. An important input to these design tasks is the analysis of how a web site is being used. The is paper proposes a Page logging System(PLS) identifying reliably user sessions required in Web mining system PLS consists of Page Logger acquiring all the page accesses of the user Log processor producing user session from these data, and statements to incorporate a call to page logger applet. Proposed PLS abbreviates several preprocessing tasks which spends a log of time and efforts that must be performed in Web mining systems. In particular, it simplifies the complexity of transaction identification phase through acquiring directly the amount of time a user stays on a page. Also PLS solves local cache hits and proxy IPs that create problems with identifying user sessions from Web sever log.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.101-110
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• 2010

In this paper, it has been studied about the CRCO to maintain or rehabilitate the aged JCP. The CRCO and JCO was constructed at useless section of Seo-Hae-Ahn express highway in South Korea. The performance evaluation was conducted. Especially, it was focused on the roll of longitudinal reinforced steels inserted into the CRCO. On crack survey results from field construction section, the reflection cracks at joint of the existing pavement occurred in CRCO. However, due to the constraints of longitudinal reinforced steels, crack width was small. Total crack length and quantity in the CRCO more than that in the JCO. And crack spacing in the CRCO was narrower than it in the CRCP. Through the bonding strength test results, if the cold milling and cleaning as well as surface treatment is applied, there will be no debonding problem at interlayer in the early age. From analysis of the horizontal behavior at the joint, the longitudinal reinforced steels constrained crack width which became wider than initial state over time. Also, that steel in the CRCO reduced the horizontal movement due to temperature variation(4 times than that in the JCO). But, if interface is debonded, the roll decreased. Vertical VWG data showed that CRCO did not occur debonding problem at steel location, but there was some problem in JCO. It was confirmed by field coring. The tensile strain appeared in the CRCO, But the compressive strain occurred in the JCO in early age. Through the FWD test result, deflection in the CRCO was less than that in the JCO. And K value in the CRCO was greater than it in the JCO.

• Journal of the Korea Society of Computer and Information
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• v.14 no.2
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• pp.9-16
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• 2009

While the broadband network and multimedia technology are being developed, the commercial market of digital contents as well as using IPTV has been widely spreading. In this background, Time-Shift system is developed for requirement of multimedia. This system is independent of Time but is not independent of Place and Occasion. For solving these problems, in this paper, we propose the TPO(Time, Place, Occasion)-Shift system for mobile multimedia devices. The profile that can be applied to the mobile multimedia devices is much different from that of the setter-box. And general mobile multimedia devices could not have such large memories that is for multimedia data. So it is important to continuously store and manage those multimedia data in limited capacity with mobile device's profile. Therefore we compose the basket in a way using defined time unit and manage these baskets for effective buffer management. In addition. since the file name of basket is made up to include a basket's time information, we can make use of this time information as DTS(Decoding Time Stamp). When some multimedia content is converted to be available for portable multimedia devices, we are able to compose new formatted contents using such DTS information. Using basket based buffer systems, we can compose the contents by real time in mobile multimedia devices and save some memory. In order to see the system's real-time operation and performance, we implemented the proposed TPO-Shift system on the basis of mobile device, MS340. And setter-box are desisted by using directshow player under Windows Vista environment. As a result, we can find the usefulness and real-time operation of the proposed systems.

• The Korean Journal of Nuclear Medicine
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• v.32 no.4
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• pp.382-390
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• 1998

Purpose: The purpose of this study was to evaluate the accuracy of radioactivity quantitation in Tc-99m SPECT by using combined scatter and attenuation correction. Materials and Methods: A cylindrical phantom which simulates tumors (T) and normal tissue (B) was filled with varying activity ratios of Tc-99m. We acquired emission scans of the phantom using a three-headed SPECT system (Trionix, Inc.) with two energy windows (photopeak window: $126{\sim}154keV$ and scatter window: $101{\sim}123keV$). We performed the scatter correction with dual-energy window subtraction method (k=0.4) and Chang attenuation correction. Three sets of SPECT images were reconstructed using combined scatter and attenuation correction (SC+AC), attenuation correction (AC) and without any correction (NONE). We compared T/B ratio, image contrast [(T-B)/(T+B)] and absolute radioactivity with true values. Results: SC+AC images had the highest mean values of T/B ratios. Image contrast was 0.92 in SC+AC, which was close to the true value of 1, and higher than AC (0.77) or NONE (0.80). Errors of true activity by SPECT images ranged from 1 to 11% for SC+AC, $22{\sim}47%$ for AC, and $2{\sim}16%$ for NONE in a phantom which was located 2.4cm from the phantom surface. In a phantom located 10.0cm from the surface, SC+AC underestimated by 24%, NONE 40%. However, AC overestimated by 10%. Conclusion: We conclude that accurate SPECT activity quantitation of Tc-99m distribution can be achieved by dual window scatter correction combind with attenuation correction.

• The Korean Journal of Nuclear Medicine
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• v.39 no.3
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• pp.191-199
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• 2005

Purpose: In order to obtain better quantitation of kidney uptake, this study is to evaluate a conjugate view method (CVM) using a geometric mean attenuation correction for kidney uptake and to compare it to Gate's method. Materials & Methods: We used a Monte Carlo code, SIMIND and a Zubal phantom, to simulate kidney uptake. SIMIND was both simulated with or without scatter for the Zubal phantom. Also, a real phantom test was carried out using a dual-head gamma camera. The activity of 0.5 mCi was infused into two small cylinder phantoms of 5 cm diameter, and then, they were inserted into a cylinder phantom of 20 cm diameter. The results by the CVM method were compared with ideal data without both of attenuation and scatter and with Gate's method. The CVM was performed with or without scatter correction. The Gate's method was performed without scatter correction and it was evaluated with regards to $0.12cm^{-1}\;and\;0.15cm^{-1}$ attenuation coefficients. Data were analyzed with comparisons of mean counts in the legions of interest (ROI), profiles drawn over kidney images and linear regression. Correlation coefficients were calculated with ideal data, as well. Results: In the case of the computer simulation, mean counts measured from ideal data, the CVM and the Gate's method were (right $998{\pm}209$, left: $896{\pm}249$), (right: $911{\pm}207$, left: $815{\pm}265$), and (right: $1065{\pm}267$, left: $1546{\pm}267$), respectively. The ideal data showed good correlation with the CVM and the correlation coefficients of the CVM, Gate's method were (right: 0.91, left: 0.93) and (right: 0.85, left: 0.90), respectively. Conclusion: The conjugate view method using geometric mean attenuation correction resulted in better accuracy than the Gate's method. In conclusion, the conjugate view method independent of renal depths may provide more accurate kidney uptake.