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A robust and secure time-domain cancellation is proposed for inter-carrier interference (ICI) reduction in OFDM systems for ubiquitous environments. To cope with the problem of the conventional time-domain canceller, which does not work in deep fades, simple repetition (de)coding and modulation order increasing techniques are exploited in our proposal. The approximated repetition decoding provides reliable symbols in the regeneration operation, and the increased modulation order maintains the spectral efficiency. Simulation results indicate that the proposed method using 16QAM significantly improves the BER performance compared with the conventional method using QPSK, while the spectral efficiency is maintained. Moreover, the proposed method using 64QAM concurrently improves both the BER performance and the spectral efficiency.

The existing block encryption algorithms have been designed for the encryption key value to be unchanged and applied to the round functions of each block, and enciphered. Therefore, it has such a weak point that the plain text or encryption key could be easily exposed by differential cryptanalysis or linear cryptanalysis, both are the most powerful methods for decoding block encryption of a round--repeating structure. In order to cope with this weak point, an encryption algorithm using a more efficient key should be designed.In this paper, a block encryption algorithm which is designed for each encryption key value to be applied to each round block with a different value is proposed. This algorithm needs a short processing time in encryption and decryption, has a high intensity, can apply to electronic commerce and various applications of data protection.

As the Internet sites and users have rapidly been increased, the development for search engines has also been accelerated to satisfy users' expectations. As the result, not only the action of collecting documents through many search engines gave hosts workload, but also regular updating all the information is needed since information is newly added. With any circumstances, the necessity of the technology to collect massive information in hosts has been increased for the speed which is a basic requisite of search systems, and for more accurate collection of documents. Also, the role of search engines grows the bigger for Internet users' various demands and flexible process through World Wide Web. In this paper, we design and implement an intelligent robot agent and a remote control system which doesn't give an excessive workload on a target server and makes the collection of documents done in a short period by considering an average workload rate on the target server and the rate of the workload that a robot experience in collection time, after we compare and analyze the existing Robot Agent Systems and supplement their weak points.

The ontology is an essential component to demonstrate the semantic Web, which is being described as the next Web generation. A semantic information search based on the ontology can provide the inferred and associated information between data. To develop an ontology application in the real world, we design the architecture of search systems based on the ontology using Web services. Our system consists of ontology modules, search procedure modules for searching, RDQL generator modules, and client modules for user interfaces. Also, we construct a hotel ontology integrated with the related terms and implement a search example with the defined ontology.