Secure Joint Source-Channel Coding for Quasi-Static Fading Channels

Joint source-channel coding has been shown to yield optimal end-to-end performance in terms of overall expected distortion for quasi-static fading channels. Due to the inherent broadcast nature of the wireless medium, wireless communications are susceptible to eavesdropping. Thus, it is unclear how imposing additional secrecy constraint on the system will affect the end-to-end performance of the joint source-channel coding. In this paper, we consider the information theoretic secure source transmission in a classical three node wiretap channel, consisting of a source node, a destination node, and a wiretapper node. In the high signal-to-noise ratio regime, we quantify the cost of providing secure transmissions through secrecy outage probability and secrecy distortion exponent. Our results show that with the additional secrecy constraint, there exists a lower bound on the bandwidth expansion factor, below which perfect secrecy is impossible. Moreover, this lower bound on bandwidth expansion factor depends on the type of layered source transmission strategy used. In summary, this work indicates that source-channel coding strategies as well as the level of secrecy need to be carefully designed in order to maximize the secrecy distortion exponent.