Physical Layer Security for Multiple-Input Multiple-Output Systems by Alternating Orthogonal Space-Time Block Codes
Michael R. Cribbs, Ric A. Romero, TRI T. HA · IEEE Open Journal of the Communications Society · 2020
Algorithms are provided to build a large set of unique complex-valued orthogonal space-time block codes (STBCs) from a known or standard STBC. A physical layer security (PLS) scheme is proposed to take advantage of this set by alternating the STBC in use over a multiple-input single-output (MISO) or multiple-input multiple-output (MIMO) communications link between base station (BS) and user equipment (UE). A practical procedure is proposed and demonstrated to build individual STBCs from the set without use of a lookup table. The sufficient statistic is given and proven to allow for maximal ratio combining (MRC) by the intended receiver for all STBCs in the set. An algorithm is offered for the UE to update the MRC matrix in use as the STBC alternates. Definitions are provided for cryptograms, key residues (KRs), key residue classes (KRCs), and message and cryptogram residue classes pertaining to STBC PLS schemes. These definitions are used to present analysis of the information-theoretic security of the proposed PLS scheme to include message and key equivocation. Theoretical expected bit error rate (BER) for a passive eavesdropper is proven and plotted along with Monte Carlo simulations for confirmation. Discussion of different attack models is provided. Cost and attack complexity are compared between the proposed scheme and two related techniques from the literature.