Physical-Layer Obfuscation in MIMO–SSK Systems With Imperfect CSI and Spatial Correlation

Abstract

A computationally secure physical-layer obfuscation framework for multiple-input multiple-output (MIMO) systems based on space shift keying (SSK) is proposed in this letter, while accounting for imperfect channel estimation and spatial channel correlation. The obfuscation principle relies on exploiting channel reciprocity in time-division duplexing (TDD), whereby the transmitter and the legitimate receiver independently estimate per-antenna fading powers and construct an identical permutation vector to reorder the transmit constellation in each coherence interval. For an SSK system with $N_{t}$ transmit antennas, the permutation is derived from the relative ordering of per-antenna channel powers. This design allows for refreshed key that avoids explicit key exchange with negligible signaling overhead. At the same time, an eavesdropper observing an independent or partially correlated channel is forced to decode using a mismatched constellation. Consequently, decoding ambiguity is significantly increased, enlarging the brute-force search space to the order of $N_{t}!$ , which render blind constellation recovery computationally infeasible. Results demonstrate that channel estimation errors and spatial correlation impairments introduce only modest performance degradation at the legitimate receiver while strongly suppressing the eavesdropper’s achievable information rate. Performance is investigated in terms of average bit error rate (ABER), mutual information (MI), generalized mutual information (GMI), equivocation, and information leakage.