Eavesdropping-Resilient OFDM System Using Sorted Subcarrier Interleaving

In this paper, we present a novel eavesdropping-resilient OFDM system through sorted subcarrier interleaving. The transmitter interleaves subcarriers in each OFDM signal according to its dynamic channel state information (CSI) to the legitimate receiver. More specifically, subcarriers are interleaved according to the sorted order of their instantaneous channel gains that are observed at the transmitter. Based on channel reciprocity, the legitimate receiver can derive the interleaving pattern initiated by the transmitter through its local channel estimate, and then de-interleave the received signals. In contrast, since spatially separated wireless channels in rich multipath environments are independent of each other, an eavesdropper at a third location cannot follow the dynamic subcarrier interleaving permutation, and thus fails to eavesdrop this transmission. Considering the imperfect reciprocity of noisy channel estimates at the legitimate terminals, only a subset of subcarriers in each OFDM signal is involved in the interleaving. A subcarrier selection algorithm is investigated to realize a trade-off between the eavesdropping resilience and transmission reliability. Theoretical analysis and Monte Carlo simulations have been provided to validate the proposed system. Compared with prior security enhancement schemes, the proposed approach requires only minor modifications to off-the-shelf systems and avoids additional resource consumption.