Relay-Assisted Secure Short-Packet Communications in Cognitive Internet of Things.

This paper investigates the secrecy performance of relay-assisted dual-hop short-packet communications in cognitive Internet of Things (IoT). Specifically, there is a relay that uses the decode-and-forward (DF) mode to forward short-packet signals to ensure the ultra-reliable low-latency communication in cognitive IoT. To meet the security demand, the relay uses the maximum ratio combining/zero forcing beamforming (MRCIZFB) scheme. Considering the impact of blocklength on transmission delay and secrecy performance, we derive the approximations for secrecy throughput in a closed-form under the secrecy and decoding error probability constraints. The numerical results illustrate the impact of the system parameters on the tradeoff between transmission delay and reliability, i.e., the optimal value of the blocklength. In addition, the simulation results confirm that the proposed scheme achieves better secrecy performance than the amplify-and-forward (AF) scheme and the single-hop transmission scheme in short-packet communications.