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Rate-Compatible SFBC-OFDM under Rapidly Time-Varying Channels
Kwanghoon Kim,Hyuncheol Park,Kwon, H. M. IEEE 2011 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.59 No.8
<P>An inter-carrier interference (ICI) occurs in an orthogonal frequency division multiplexing (OFDM) system when a channel is rapidly time-varying. The proposed scheme employs a polynomial cancellation code (PCC) to suppress this ICI, and uses a linear complex field (LCF) code as a transmit-diversity technique to make the transmission rate compatible up to {n<SUB>T</SUB>} / {(n<SUB>T</SUB>+1)}, where n<SUB>T</SUB> is the number of transmit antennas used. The conventional orthogonal code (OC), such as the Alamouti code, with accompanying PCC cannot achieve this rate. Both analysis and simulation results verify that the proposed scheme can achieve higher channel capacity as well as lower bit error rate (BER) than the other schemes in rapidly time-varying channels, even with a linear receiver and inaccurate channel estimation.</P>
New Subcarrier Allocation for Uplink-OFDMA under Time-Varying Channels
Kwanghoon Kim,Hyuncheol Park,Kwon, H. M. IEEE 2013 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.61 No.1
<P>Inter-carrier interference (ICI) and multiuser interference (MUI) occur in an uplink orthogonal frequency division multiple access system if a channel between a mobile user and a base station is rapidly time-varying. To reduce the ICI and MUI, this letter proposes a subcarrier allocation method. The key idea is to allocate a high-speed user's subcarrier near a low-speed user's one. Then, a wide Doppler spread of a high-speed user can be spilled over a low-speed user's subcarrier band with insignificant influence, and the signal-to-interference-plus-noise ratio (SINR) at each high-speed user's subcarrier can be maximized. This can provide a significant performance improvement of multiuser detection in an uplink-OFDMA.</P>
e-Lollapalooza: A Process-Driven e- Business Service Integration System for e-Logistics Services
( Kwanghoon Kim ),( Ilkyeun Ra ) 한국인터넷정보학회 2007 KSII Transactions on Internet and Information Syst Vol.1 No.1
There are two newly emerging research issues in the enterprise information systems literature. One is the scalability issue for rapidly increasing choreographic volumes between interrelated organizations. The other is the business intelligence issue for traceable and monitorable business processes and services interchanging e-Business data and applications across organizations. Based upon these emerging issues, through a functional extension of the ebXML technology we have developed a process-driven e- Business service integration (BSI) system, which is named `e-Lollapalooza`. It consists of three major components - the Choreography Modeler coping with the process-driven collaboration issue, the Runtime & Monitoring Client for coping with the business intelligence issue and the EJB-based BSI Engine coping with the scalability issue. This paper particularly focuses on the e-Lollapalooza`s development aspects for supporting the ebXML-based choreography and orchestration among the engaged organizations in a process-driven multiparty collaboration for e-Logistics and e- Commerce services. Here, it is fully deployed in an EJB-based middleware computing environment for e-Logistics process automation and B2B choreography.
Kwanghoon Kim,Mun Seok Choe,Woosang Lee,Joonho So,Eunmi Choi IEEE 2014 IEEE transactions on plasma science Vol.42 No.4
<P>This paper reports the estimation of the electric field from a large aperture cavity that generates a higher order mode by backpropagation of fields measured in free space. A higher order mode of a TE<SUB>6,2</SUB> mode at 94 GHz is designed and fabricated using a quasi-optical manner for the analysis. The backpropagating field at the aperture is compared with the measured field. The field estimated at the aperture is used to analyze the mode information, such as the amount of mode mixture of two different rotating fields and the phase difference between two modes. This paper provides a quantitative way to analyze the rotating cylindrical modes generated from an oversized cavity.</P>
Optimum Clustered Pilot Sequence for OFDM Systems under Rapidly Time-Varying Channel
Kwanghoon Kim,Hyuncheol Park,Kwon, H. M. IEEE 2012 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.60 No.5
<P>As channel time-variation increases, orthogonality among subcarriers in an orthogonal frequency division multiplexing (OFDM) symbol can be destroyed because of the relatively long symbol period, whereupon intercarrier interference (ICI) appears, and hence an irreducible error floor occurs. It was shown recently that grouping pilot tones into a number of equally spaced clusters can yield better channel estimation against the doubly selective channel than placing each pilot tone in an equally spaced manner. However, a random pilot sequence was used in the literature, and an optimal sequence has not yet been studied. This paper presents how to optimize the clustered pilot sequence. First, this paper (a) proves the existence of an optimum pilot sequence and (b) suggests a guideline for finding an optimum sequence. Second, this paper shows that an optimum sequence is independent of the signal-to-noise ratio and Doppler rate, and the sequence is generally optimum for any channels. Third, this paper verifies through analysis and simulation that the coded-OFDM system with an optimized cluster pilot sequence can yield a smaller mean square channel estimation error and lower bit error rate than the system with an equidistance pilot or a random cluster pilot under a rapidly time-varying channel.</P>
A Practical Intent Fuzzing Tool for Robustness of Inter-Component Communication in Android Apps
( Kwanghoon Choi ),( Myungpil Ko ),( Byeong-mo Chang ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.9
This research aims at a new practical Intent fuzzing tool for detecting Intent vulnerabilities of Android apps causing the robustness problem. We proposed two new ideas. First, we designed an Intent specification language to describe the structure of Intent, which makes our Intent fuzz testing tool flexible. Second, we proposed an automatic tally method classifying unique failures. With the two ideas, we implemented an Intent fuzz testing tool called Hwacha, and evaluated it with 50 commercial Android apps. Our tool offers an arbitrary combination of automatic and manual Intent generators with executors such as ADB and JUnit due to the use of the Intent specification language. The automatic tally method excluded almost 80% of duplicate failures in our experiment, reducing efforts of testers very much in review of failures. The tool uncovered more than 400 unique failures including what is unknown so far. We also measured execution time for Intent fuzz testing, which has been rarely reported before. Our tool is practical because the whole procedure of fuzz testing is fully automatic and the tool is applicable to the large number of Android apps with no human intervention.