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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.