Prevention of Eavesdropping in OFDMA Systems

In this paper, a novel anti-eavesdropping OFDM system through dynamic subcarrier coordinate interleaving is proposed by exploiting the reciprocal, location-dependent and time-varying nature of wireless channels. The transmitter performs coordinate interleaving at some of the OFDM subcarriers in an opportunistic manner, where the secret interleaving pattern is determined by the instantaneous channel state information (CSI) between the transmitter and intended receiver. More specifically, a subcarrier symbol associated with a channel phase larger than a predefined threshold is coordinate interleaved. Since wireless channels associated with each pair of users at separate locations exhibit independent multipath fading, the frequently updated coordinate interleaving pattern can only be shared between legitimate users based on channel reciprocity. Consequently, eavesdropping is prevented due to mismatched de-interleaving at the eavesdropper. Theoretical analysis and simulation results are provided to validate the proposed system.