  In this paper, we propose a physical layer security scheme that exploits a
novel index modulation (IM) technique for coordinate interleaved orthogonal
designs (CIOD). Utilizing the diversity gain of CIOD transmission, the proposed
scheme, named CIOD-IM, provides an improved spectral efficiency by means of IM.
In order to provide a satisfactory secrecy rate, we design a particular
artificial noise matrix, which does not affect the performance of the
legitimate receiver, while deteriorating the performance of the eavesdropper.
We derive expressions of the ergodic secrecy rate and the theoretical bit error
rate upper bound. In addition, we analyze the case of imperfect channel
estimation by taking practical concerns into consideration. It is shown via
computer simulations that the proposed scheme outperforms the existing IM-based
schemes and might be a candidate for future secure communication systems.
