Biblio

We consider the physical layer security (PLS) of non-orthogonal multiple access (NOMA) enabled multiple-input multiple-output (MIMO) visible light communication systems in the presence of a passive eavesdropper (Eve). In order to disrupt the decoding process at Eve, we propose a novel precoding scheme reinforced with random constellation coding. Multiple legitimate users (Bobs) will be served simultaneously using NOMA. For the proposed precoder design, we exploit the slow-fading characteristics of the visible light channel so that the transmitted symbols are successfully decoded at Bob, while Eve suffers from very high bit error ratios (BERs) due to precoding-induced jamming. Via computer simulations, we show that Bob can successfully decode their own information in various user configurations and receiver diversities. It is also shown that the BER at Eve's side is increased to the 0.5-level for similar and the asymmetrical positioning of Bob with respect to the transmitter, thus PLS is ensured by the proposed preceding technique.

Optical wireless communications (OWC) and its potential to solve physical layer security (PLS) issues are becoming important research areas in 6G communications systems. In this paper, an overview of PLS in visible light communications (VLC), is presented. Then, two new PLS techniques based on generalized space shift keying (GSSK) modulation with spatial constellation design (SCD) and non-orthogonal multiple access (NOMA) cooperative relaying are introduced. In the first technique, the PLS of the system is enhanced by the appropriate selection of a precoding matrix for randomly activated light emitting diodes (LEDs). With the aid of a legitimate user's (Bob's) channel state information (CSI) at the transmitter (CSIT), the bit error ratio (BER) of Bob is minimized while the BER performance of the potential eavesdroppers (Eves) is significantly degraded. In the second technique, superposition coding with uniform signaling is used at the transmitter and relays. The design of secure beamforming vectors at the relay nodes along with NOMA techniques is used to enhance PLS in a VLC system. Insights gained from the improved security levels of the proposed techniques are used to discuss how PLS can be further improved in future generation communication systems by using VLC.