Secure Short-Packet Communications in Cognitive Internet of Things

To deal with the problem of spectrum scarcity in the Internet of Things (IoT), cognitive radio technology is introduced into IoT, namely, cognitive IoT. This paper investigates the secrecy performance of secondary wiretap networks in cognitive IoT. Specifically, the low-latency requirement and the security demand in cognitive IoT are guaranteed by using short-packet communications and maximal ratio transmission (MRT) scheme, respectively. 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 constraints and decoding error probability. In addition, we further analyze the secrecy throughput of the system from two scenarios of the high signal-to-noise ratio (SNR) regime and the infinite blocklength. The numerical results verify the accuracy of the proposed approximations and illustrate the impact of the system parameters on the tradeoff between transmission delay and reliability under a secrecy constraint.