Artificial fast fading (AFF) is one of the physical layer security schemes that achieve secure communications. In the AFF scheme, the signal to be transmitted is multiplied by a random weight which is called the AFF weight. As a result, the effect like fast fading is added to the transmitting signal, and the demodulation performance of an eavesdropper is degraded. In contrast, since the AFF weight is generated to be canceled out by the effect of channel between a transmitter and a legitimate receiver, it does not degrade the demodulation performance of the legitimate receiver. In the existing AFF scheme, only single-stream transmission is considered. However, recent wireless communications systems mostly adopt multiple-stream transmission. In this paper, we propose an AFF generation scheme for multiple-input multiple-output (MIMO) systems employing orthogonal frequency division multiplexing (OFDM). Simulation results show that the AFF produced by our AFF generation scheme is successfully canceled out at the legitimate receiver, and the mutual information of the legitimate receiver is increased along with the number of transmitted streams.
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