Electronics and Communications in Japan (Part III: Fundamental Electronic Science)最新文献

Changes are occurring in the environment surrounding business organizations, such as the development of open networks and flexible migration of employees. In the context of such changes, it has recently been considered more important to prepare measures against information leaks from inside the organization. Among these, an urgent issue in ordinary organizations is to reinforce the existing business system so as to realize highly cost-effective security functions. This paper considers an actual case of information leakage as a model and systematically summarizes the conditions regarding security functions, based on the views of legal specialists. An actually introduced security system based on fingerprint identification is investigated, and it is shown that practical security measures can be established. A development configuration is then proposed in which part of the security system is placed in a data center and shared by multiple organizations. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(10): 54– 62, 2007; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ecjc.20346

A structure is proposed for an adaptive system with an adaptive filter located before the unknown system (pre-inverse adaptive system) for estimation of the inverse of the transfer function (inverse transfer function) of the unknown system. In general, when an adaptive transversal filter is used as an adaptive filter, the delay signal of the output of the unknown system is needed in the adaptive algorithm for the weights. Since an adaptive filter is inserted in the front stage, this signal cannot be observed, so that a replica of the unknown system is needed. In this paper, an adaptive system that does not require this replica is discussed. Estimation of the inverse transfer function of the minimum phase of the unknown system is performed by an adaptive exponential filter and an inverse copy of the weights of the exponential filter placed in front of the unknown system. The signal within the adaptive algorithm consists of the observable input signal to the adaptive exponential filter and the estimation error. Estimation of the inverse transfer function for the allpass transfer function of the unknown system is performed by the adaptive transversal filter and the reversing copy of the weight to the transversal filter located before the unknown system. The signal in the adaptive system consists of the observable input signal to the exponential filter and the estimation error. Convergence of the weight is studied from the point of view of monotonic increase of the gradient. The unique feature of the approach is that the algorithm of the two adaptive filters consists of a gradient algorithm with guaranteed convergence for the weights and of copies of the weights after updating. Finally, a performance evaluation of the adaptive system and a comparison with conventional systems are performed by numerical simulation. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(9): 10– 17, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20305

This paper discusses a method for increasing the eigenmode SNR by using a space-time linear precoder designed on a maximum likelihood (ML) basis (henceforth called the space-time linear ML precoder). First, the effect of the length of the precoded signal generated in the ML precoder on the eigenmode SNR is studied. It is shown that the eigenmode SNR can be increased by varying the precoded signal length depending on the condition of the channel. Next, a transceiver configuration for increasing the eigenmode SNR by the space-time linear ML precoder is presented. In the proposed method, error propagation may be generated due to the transceiver configuration and the BER characteristics may be degraded, even if the eigenmode SNR is increased. In this paper, in order to reduce the effect of the error propagation on the BER characteristics, the relationship between the average length of the error propagation and the precoded signal length in the proposed configuration is presented. It is demonstrated that the effect of error propagation can be minimized by limiting the region of search for the precoded signal length. Finally, the effectiveness of the proposed method is verified by numerical simulation. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 90(10): 1– 8, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20304