Eavesdropping-Resilient OFDM System Using CSI-Based Dynamic Subcarrier Allocation

In this paper, we propose a simple and effective eavesdropping-resilient OFDM system achieved by dynamic subcarrier allocation, exploiting the independent frequency selectivities of different wireless channels. The transmitter utilizes the channel state information (CSI) between the legitimate receiver and itself for the OFDM subcarrier allocation. The highly faded subcarriers are dropped for the data transmission and the constellation size of subcarriers with excellent channel conditions is increased in order to retain the overall throughput. Based on channel reciprocity, the channel behaves in the same manner at each pair of users. The subcarrier allocation scheme is thus shared by the transmitter and the legitimate receiver without additional signaling. In contrast, with an independent multipath channel, the eavesdropper at a separate location cannot derive an identical subcarrier allocation scheme. Consequently, mismatched demodulation is carried out at the eavesdropper so that disrupts the information recovery for eavesdropping. Moreover, due to the time-varying nature of wireless channels, the subcarrier allocation is frequently updated which further enhances the security. Theoretical analysis and simulation results are provided to evaluate the performance of the proposed secure OFDM system. It is validated that the proposed system is much more resilient to eavesdropping compared to the conventional OFDM system.