Secret Key Exchange using Private Random Precoding in MIMO FDD and TDD Systems

Along with the ongoing evolution of multiple antennas
communication systems, new physical layer security techniques
are continuing to achieve higher levels of secrecy. Most
physical layer approaches, however, concern time division duplex
(TDD) channels which rely on using the channel reciprocity
feature as a shared randomness, and tend to be associated with
a large computational burden. In this paper, we propose a new
physical layer method which utilizes private random precoding
for exchanging the secret key bits in multiple-input multipleoutput
(MIMO) systems. The principle of this method is to exploit
the precoding matrix index (PMI) in a manner that produces low
correlation at the adversary. A robust key exchange between the
transmitter and the receiver is established by uniquely relating
the secret key bits to the channel precoding matrix using a
private version of the universal codebooks. What’s more is that
the proposed method is applicable in, both, frequency division
duplex (FDD) and TDD channels. The results demonstrate that
the proposed method can offer superior performance in terms
of the key agreement, secrecy level and computational load.