A joint random weighting method for physical layer security in wireless relay system

In the wireless cooperative relay system, the private information can be intercepted by the untrusted relays. The traditional method of artificial noise based on physical layer security consumed much more power to protect the security of private information. To solve this problem, this paper combines amplify-and-forward coefficient of the relays with the joint channel state information (JCSI), and constructs the joint channel between the sender and the receiver. According to the joint channel characteristics the sender designs randomized weighting vector for its antenna, which is constant by multiplied with the joint channel characteristics. This method can make the equivalent channel be constant between the sender and the legitimate receiver while the equivalent channels change fast between the sender and the relays. Simulation results show that the bit error rate (BER) of Relays is almost 0.5 constantly and the BER of receiver is 10^-3 simultaneously when the received SNR is 10dB. Compared with the method based on artificial noise, 1.6dB power can be saved in the proposed method.