Short-Packet Covert Communication in Interweave Cognitive Radio Networks

In this work, we investigate short-packet covert communication in interweave cognitive radio networks (CRNs), where a secondary transmitter (ST) opportunistically accesses the occasionally idle spectrum under the supervision of a primary transmitter (PT). Considering that PT occupies the spectrum in a random manner, inevitable packet collisions occur when ST is transmitting while PT also starts to occupy its spectrum. To address this issue, we jointly optimize the block-length and the transmit power of ST's transmission to strike a balance between the packet collision and the decoding error subject to a covertness constraint. In particular, we first derive the packet collision probability, the covertness constraint, and the average packet error probability, characterizing the analytical expression for the average effective spectral efficiency (AESE). To further improve the system performance, an optimization problem is formulated to maximize AESE and the corresponding optimal block-length and transmit power are obtained for different kinds of channel information available at ST. Simulation results show that there is an optimal block-length to reduce the packet collision and decoding error in the interweave covert CRN.