"The Medium is The Message": Secure Communication via Waveform Coding in MIMO Systems

In this paper, we look at multiple antenna systems and code information on the communication medium itself to improve the link security. In the case of single data stream transmission, the medium refers to the response across the receive sensor array. In multiple data stream transmission, the medium is the set of virtual orthogonal channels that result from the singular value decomposition of the channel transfer matrix. We code phase information on the orthogonal channels by rotating the received signal constellation. This does not impair the signal detection of differential-phase coded signals on the intended receiver. However the rotation at an eavesdropper location is different from the one on the intended receiver even at a distance of lambda/10 (6 mm), and therefore security is enhanced.