Enhancing physical-layer security in wireless communications using signal space diversity

In this paper, we enhance the security of OFDM systems in frequency selective fading channels using signal space diversity. In rich multipath environments, spatially separated channels are independent to each other. Hence, by adapting the interleaving pattern to the channel of the legitimate user, more diversity gain is provided to the legitimate user compared to an eavesdropper. This ensures secrecy in a time division duplex system, where the eavesdropper has no information regarding the channel of the legitimate user. The scheme can also be used in the conventional frequency division duplex system, which is more challenging in terms of security aspects because of the channel state information leakage. We verify the gain of our scheme by showing the improvement in the bit error rate performance.