In this study, the physical layer (PHY) security performance of orthogonal space-time block coding (OSTBC) employing a coordinate interleaved orthogonal design (CIOD) is analysed and investigated using two metrics: average secrecy capacity and secrecy outage probability. It is shown that the CIOD system is superior than OSTBC in terms of secrecy outage probability. Closed-form expressions for PHY security metrics in OSTBC as well as CIOD are presented and compared. Then, an extended model of

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... D with arbitrary number of antennas is considered. Furthermore, the effects of artificial noise and imperfect channel estimation on PHY security of OSTBC and CIOD systems are investigated. The validity of theoretical expressions is verified by simulation, and it is shown that in practical cases the CIOD system has a better secrecy outage performance than that of the OSTBC system. System model and main assumptions We consider a wireless transceiver composed of a transmitter (Alice), employing N transmit (Tx) antennas, an intended receiver