Three-Hop Untrusted Relay Networks With Hardware Imperfections and Channel Estimation Errors for Internet of Things

Cooperative relaying can be introduced as a promising approach for data communication in the Internet of Things (IoT), where the source and the destination may be placed far away. In this paper, by taking a variety of realistic hardware imperfections (HWIs) and channels estimation errors (CEEs) into account, the secrecy performance of a three-hop cooperative network with a source, a destination and two consecutive amplify-and-forward (AF) relays is investigated. The relays are considered to be untrusted, i.e., while they are mandatory helpers for data transmission, they may overhear the received signals. We adopt the artificial noise injection scheme, to keep the source message secret from being captured by the untrusted relays. Given this system model, a novel closed-form expression is obtained in the high signal-to-noise ratio (SNR) regime for the ergodic secrecy rate (ESR) performance over Nakagami- $m$ fading. Our simulation results highlight that the secrecy performance of the system is improved when the tolerable HWIs are distributed beneficially across the transmission and reception radio-frequency (RF) front-ends of each node. Our work reveals that unlike the ideal case, the realistic scenario of non-ideal hardware with CEEs faces with the secrecy rate ceiling. Finally, under a constraint on the total energy consumption which is applicable for battery-limited IoT equipment, we maximize the achievable secrecy rate. Our results highlight the importance of the destination's jamming cooperation and the first relay's role on the secrecy performance.