LAUSR

In this paper, we consider a centralized cooperative cognitive radio network (CCRN), where a primary base station sends a message to a primary user. Meanwhile, a secondary user transmitter (SU-Tx) acts as a friendly jammer that sends jamming signals (artificial noise) to protect the transmitted message from a potential eavesdropper (Eve). However, the SU-Tx may not be completely honest in sending jamming signals for selfish reasons, i.e., it may be untrusted. To select a trustworthy SU-Tx as a friendly jammer, we adopt the concept of trust degree as a selection criterion. We investigate the trust degree's influence on the secrecy performance of a CCRN in cases of perfect channel state information (CSI) and statistical CSI, respectively. In the case of perfect CSI, the accurate expected secrecy rate is derived to evaluate the secrecy performance. In the case of statistical CSI, we calculate the probabilities of the transmission and secrecy outage events, and the secrecy performance is evaluated in terms of effective secrecy throughput. In both cases, we obtain the target trust degree thresholds based on the target secrecy performance thresholds, respectively. Next, we investigate how to calculate the trust degree of each SU-Tx and establish a trust degree list of all SU-Txs. Finally, according to the trust degree list and the target trust degree thresholds, we can select a trustworthy SU-Tx as a friendly jammer in both two cases. A comprehensive simulation study is carried out to validate our secrecy performance analyses and the trust degree management.