Physical Layer Security in Untrusted Lossy Decode-and-Forward Relay Networks with Finite Blocklength

Abstract

This paper investigates the physical layer security performance of an untrusted relay network in the finite blocklength regime. Lossy decode-and-forward (DF) relaying is considered at the untrusted relay. Different from conventional DF relaying, the relay always forwards information sequences to the destination even if error is detected at the relay, which can be utilized to enhance the security of the untrusted relay network. Based on the characteristics of short-packet communications, the reliable-and-secure probability is proposed and numerically derived for evaluating the security performance in the physical layer of the untrusted relay network. Reliable-and-secure probability represents the probability that the destination can recover the original message sent from the source, whereas the relays cannot. It is found that as long as the contribution of the transmit power of source and relays is balanced, a certain degree of reliable-and-secure probability can be held for short-packet communications in the untrusted relay network.