IEEE Transactions on Vehicular Technology
Tournament-Based Index Obfuscation for Secure Space Shift Keying MIMO Systems
Raed Mesleh, Mohammad Ali Abudayah, Saud Althunibat
Abstract
A tournament-based index obfuscation framework is proposed and analyzed for space shift keying (SSK) multiple-input multiple-output (MIMO) systems. Algebraic properties of Paley tournaments are exploited to construct deterministic yet nontrivial permutations of the transmit antenna indices. These permutations are refreshed on a per-channel basis through a channel-dependent cyclic shift derived from reciprocity. As a result, a matched index-domain channel is observed at the legitimate receiver, whereas an eavesdropper is forced to operate under a mismatched decoding metric. In contrast to conventional physical-layer security techniques, the proposed framework operates exclusively in the index domain and preserves the inherent energy-efficiency and low-complexity advantages of SSK. In practical SSK implementations where the number of transmit antennas is not a power of two, only a subset of valid antenna indices is used for information mapping, while the remaining antennas participate only in the obfuscation mechanism. Reliability and secrecy are characterized through average bit error rate, mutual information, generalized mutual information, secrecy rate, equivocation, and information leakage. Both passive and active adversarial scenarios are considered. Passive attacks include uninformed mismatched eavesdropping as well as partially correlated eavesdropping channels that emulate spatial proximity and common scattering. Active training-phase attacks, including pilot contamination and forced permutation manipulation, are also examined and mitigated through tournament-structure consistency checks leading to block acceptance/rejection. The proposed cyclic-shift realization is shown to operate effectively when the legitimate nodes observe consistent channel information, while its sensitivity to channel estimation mismatch is also discussed. Numerical results demonstrate that reliable communication is preserved at the legitimate receiver, while a substantial loss in the eavesdropper' achievable rate is induced even under correlated and active attack conditions. For benchmarking purposes, a comparison with artificial-noise based SSK is also included, highlighting the fundamental difference between power-domain and index-domain physical layer security mechanisms.