Abstract
To provide reliable connectivity in recent and future wireless communication systems, it is necessary to deploy several relay nodes. Further, a full-duplex (FD) technique has been in the spotlight since it can significantly improve spectral efficiency, and thus recent studies in relaying networks have considered FD relays. In relaying networks, confidentiality between the source and destination nodes from the relay node should be carefully kept since the relay node cannot be fully trusted, so called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">untrusted</i> relay node. To this end, in this paper, we consider physical-layer security taking into account an untrusted FD relay node. We investigate a secure relaying protocol against the untrusted relay node where the destination generates artificial noise to prevent the untrusted relay from decoding the source information. We derive the analytical expression of the lower bound of the ergodic secrecy rate ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {R}$ </tex-math></inline-formula> ). We find two main factors affecting the secrecy performance: residual self-interference (RSI) at the FD-available nodes (i.e., relay and destination), and outdated channel state information (CSI) at the destination. Thereafter, we evaluate their effects on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {R}$ </tex-math></inline-formula> and suggest the algorithm to find the sub-optimal artificial noise power level at the destination for maximizing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {R}$ </tex-math></inline-formula> . Through simulations, we have verified our mathematical derivation and shown that our secure relaying protocol can achieve near-optimal secrecy performance. Numerical results imply that the artificial noise power level should be carefully considered when the channel is severely outdated and RSI is irresistible.
Highlights
Security in wireless communications is conducted through cryptographic techniques on the network layers by using secret key distribution, which rely on the computational complexity
We studied the secrecy performances of untrusted FD relay and FD destination networks under outdated channel state information (CSI)
When the CSI of the relay-to-destination link is outdated and the FD mode is used in relay and destination, the destination cannot perfectly cancel out the residual jamming interference (RJI) and the significant residual self-interference (RSI) occurs, causing significant deterioration of the secrecy performance
Summary
Security in wireless communications is conducted through cryptographic techniques on the network layers by using secret key distribution, which rely on the computational complexity (e.g., prime factorization). Based on the study of [10], the optimal control of the artificial noise power level under outdated CSI were derived to maximize the secrecy performance of wireless powered untrusted relay networks in [14], [15]. The performance of FD systems is limited by the residual self interference (RSI) in receive antenna This RSI from the signal transmission can deteriorate the performance of the PLS system, resulting in a need to control the artificial noise power level. For FD operations in relay/destination nodes, the resulting RSI is modeled as a complex Gaussian distribution model [21] Under these settings, we find out the sub-optimal jamming signal power level, ζ, according to the amount of RSI and RJI. Artificial(Jamming) noise (xj) channel Relaying signal (Gyr) channel Residual self interference
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