An Overview of Information-Theoretic Secrecy Analysis over Classical Wiretap Fading Channels

An alternative or supplementary approach named as physical layer security has been recently
proposed to afford an extra security layer on top of the conventional cryptography technique. In this
paper, an overview of secrecy performance investigations over the classic Alice-Bob-Eve wiretap fading
channels is conducted. On the basis of the classic wiretap channel model, we have comprehensively listed
and thereafter compared the existing works on physical layer secrecy analysis considering the small-scale,
large-scale, composite, and cascaded fading channel models. Exact secrecy metrics expressions, including
secrecy outage probability (SOP), the probability of non-zero secrecy capacity (PNZ), and average secrecy
capacity (ASC), and secrecy bounds, including the lower bound of SOP and ergodic secrecy capacity, are
presented. In order to encompass the aforementioned four kinds of fading channel models with a more
generic and flexible distribution, the mixture gamma (MG), mixture of Gaussian (MoG), and Fox’s H-
function distributions are three useful candidates to largely include the above-mentioned four kinds of fading
channel models. It is shown that all they are flexible and general when assisting the secrecy analysis to
obtain closed-form expressions. Their advantages and limitations are also highlighted. Conclusively, these
three approaches are proven to provide a unified secrecy analysis framework and can cover all types of
independent wiretap fading channel models. Apart from those, revisiting the existing secrecy enhancement
techniques based on our system configuration, the on-off transmission scheme, artificial noise (AN) &
artificial fast fading (AFF), jamming approach, antenna selection, and security region are presented.