Physical Layer Key Generation for Secure OAM Communication Systems

In this paper, we propose a physical layer secret key (PLSK) generation scheme for secure encrypted transmissions in orbital angular momentum (OAM) communication systems which improves the secret key capacity via taking advantage of OAM orthogonal modes. Based on the line-of-sight (LoS) quasi-static channel conditions in OAM systems, we propose a mode-based active defense phase in the PLSK scheme to invalidate keys generated by an eavesdropper when it is extremely close to the legitimate user. Our simulation results highlight that the key information generated by the eavesdropper is almost zero in the case of highly correlated legitimate and eavesdropping channels under LoS conditions. In addition, our proposed OAM PLSK scheme achieves a higher key generation rate (KGR) than existing works since mode-based active defense can disrupt the process of PLSK by the eavesdropper.