Biblio

In this work, a digitally tunable Frequency Selec-tive Surface (FSS) for use in Physical Layer Security (PLS) systems is presented. The design of a unit cell is described, which is optimized by simulations for the frequency range of 5 GHz indoor Wi-Fi. Based on the developed unit cell, a prototype with 64 binary switchable elements is set up. The performance of the surface is demonstrated by measurements.

Given a selected complex orthogonal space-time block code (STBC), transformation algorithms are provided to build a set, S, of unique orthogonal STBCs with cardinality equal to \textbackslashtextbarS\textbackslashtextbar = 2r+c+k-1·r!·c!, where r, c, and k are the number of rows, columns, and data symbols in the STBC matrix, respectively. A communications link is discussed that encodes data symbols with a chosen STBC from the set known only to the transmitter and intended receiver as a means of providing physical layer security (PLS). Expected bit error rate (BER) and informationtheoretic results for an eavesdropper with a priori knowledge of the communications link parameters with the exception of the chosen STBC are presented. Monte Carlo simulations are provided to confirm the possible BER results expected when decoding the communications link with alternative STBCs from the set. Application of the transformation algorithms provided herein are shown to significantly increase the brute force decoding complexity of an eavesdropper compared to a related work in the literature.

Physical-layer security (PLS) has raised the attention of the research community in recent years, particularly for Internet of things (IoT) applications. Despite the use of classical cryptography, PLS provides security at physical layer, regardless of the computational power owned by the attacker. The investigations on PLS are numerous in the literature, but one main issue seems to be kept apart: how to measure the benefit that PLS can bring to cryptography? This paper tries to answer this question with an initial performance analysis of PLS in conjunction with typical cryptography of wireless communication protocols. Our results indicate that PLS can help cryptography to harden the attacker job in real operative scenario: PLS can increase the detection errors at the attacker's receiver, leading to inability to recover the cipher key, even if the plaintext is known.

Considering reflected light in physical layer security (PLS) is very important because a small portion of reflected light enables an eavesdropper (ED) to acquire legitimate information. Moreover, it would be a practical strategy for an ED to be located at an outer area of the room, where the reflection light is strong, in order to escape the vigilance of a legitimate user. Therefore, in this paper, we investigate the impact of multipath reflections on PLS in visible light communication in the presence of randomly located eavesdroppers. We apply spatial point processes to characterize randomly distributed EDs. The generalized error in signal-to-noise ratio that occurs when reflections are ignored is defined as a function of the distance between the receiver and the wall. We use this error for quantifying the domain of interest that needs to be considered from the secrecy viewpoint. Furthermore, we investigate how the reflection affects the secrecy outage probability (SOP). It is shown that the effect of the reflection on the SOP can be removed by adjusting the light emitting diode configuration. Monte Carlo simulations and numerical results are given to verify our analysis.