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Detection of active attacks based on random orthogonal pilots

Active attacks threat the security of communication dramatically. In this paper, we propose a secure transmission scheme based on random orthogonal pilots to detect the presence of active eavesdropping attacks on channel estimation in time-division-duplex (TDD) systems. The scheme only needs to replace some regular pilot sequences with random orthogonal pilot sequences occasionally without any prior channel knowledge. Our analysis shows that the proposed detection algorithm is robust even if the eavesdropper knows the pilot structures all the time. Numerical results are presented to further demonstrate the performance of the proposed scheme.