Along with the ongoing evolution of multiple antennascommunication systems, new physical layer security techniquesare continuing to achieve higher levels of secrecy. Mostphysical layer approaches, however, concern time division duplex(TDD) channels which rely on using the channel reciprocityfeature as a shared randomness, and tend to be associated witha large computational burden. In this paper, we propose a newphysical layer method which utilizes private random precodingfor exchanging the secret key bits in multiple-input multipleoutput(MIMO) systems. The principle of this method is to exploitthe precoding matrix index (PMI) in a manner that produces lowcorrelation at the adversary. A robust key exchange between thetransmitter and the receiver is established by uniquely relatingthe secret key bits to the channel precoding matrix using aprivate version of the universal codebooks. What’s more is thatthe proposed method is applicable in, both, frequency divisionduplex (FDD) and TDD channels. The results demonstrate thatthe proposed method can offer superior performance in termsof the key agreement, secrecy level and computational load.
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