Secrecy Transmission on Block Fading Channels: Theoretical Limits and Performance of Practical Codes

TL;DR

This paper investigates the theoretical limits and practical performance of physical layer security in parallel fading channels, deriving bounds on secrecy rates and evaluating practical coding schemes under realistic channel conditions.

Contribution

It extends secrecy rate bounds and security metrics to parallel Rayleigh fading channels and assesses practical coding performance in realistic scenarios.

Findings

Bounds on outage secrecy rates derived for parallel channels

Practical error-correcting codes can achieve secure communication under certain conditions

Security gap and equivocation rate extended to Rayleigh fading environments

Abstract

We consider a system where an agent (Alice) aims at transmitting a message to a second agent (Bob) over a set of parallel channels, while keeping it secret from a third agent (Eve) by using physical layer security techniques. We assume that Alice perfectly knows the set of channels with respect to Bob, but she has only a statistical knowledge of the channels with respect to Eve. We derive bounds on the achievable outage secrecy rates, by considering coding either within each channel or across all parallel channels. Transmit power is adapted to the channel conditions, with a constraint on the average power over the whole transmission. We also focus on the maximum cumulative outage secrecy rate that can be achieved. Moreover, in order to assess the performance in a real life scenario, we consider the use of practical error correcting codes. We extend the definitions of security gap and equivocation rate, previously applied to the single additive white Gaussian noise channel, to Rayleigh distributed parallel channels, on the basis of the error rate targets and the outage probability. Bounds on these metrics are also derived, taking into account the statistics of the parallel channels. Numerical results are provided, that confirm the feasibility of the considered physical layer security techniques.