Secure Physical Layer using Dynamic Permutations in Cognitive OFDMA Systems

This paper proposes a novel lightweight mechanism for a secure physical (PHY) layer in cognitive radio network (CRN) using orthogonal frequency division multiplexing (OFDM). User´s data symbols are mapped over the physical subcarriers with a permutation formula. The PHY layer is secured with a random and dynamic subcarrier permutation which is based on a single pre-shared information and depends on dynamic spectrum access (DSA). The dynamic subcarrier permutation is varying over time, geographical location and environment status, resulting in a very robust protection that ensures confidentiality. The method is shown to be effective also for existing non-cognitive systems. The proposed mechanism is effective against eavesdropping even if the eavesdropper adopts a long-time patterns analysis, thus protecting cryptography techniques of higher layers. The correlation properties of the permutations are analyzed for several DSA patterns. Simulations are performed according to the parameters of the IEEE 802.16e system model. The securing mechanism proposed provides intrinsic PHY layer security and it can be easily implemented in the current IEEE 802.16 standard applying almost negligible modifications.