Compensation of imperfect channel reciprocity through MMSE prediction for physical-layer confidentiality enhancement

In this paper, we utilize the minimum mean squared error (MMSE) prediction to compensate imperfect channel reciprocity in achieving physical-layer confidentiality enhancement, particularly for our recently developed secure OFDM system with dynamic subcarrier coordinate interleaving [1]. In the proposed method, the transmitter first estimates the correlation coefficient between the forward and backward channel estimates based on historical observations and then uses this correlation coefficient to predict the channel estimate that would be observed by the legitimate receiver. Relying on this predicted channel, the transmitter interleaves the real and imaginary components of a subcarrier symbol when its associated channel phase is larger than a predefined threshold. Improved channel reciprocity is thus established and the frequently updated interleaving pattern can be shared between legitimate users. In contrast, adversaries at a third location are not able to de-interleave the OFDM signals so that communication confidentiality is achieved. Compared with existing imperfect channel reciprocity compensation solutions in physical-layer confidentiality enhancement, the proposed technique requires no additional resource and is not sensitive to the origin of the imperfect channel reciprocity. Simulations are carried out to validate the proposed design.