A physical layer security transmission mechanism based on joint channel characteristics in relay system

To solve the problem of untrusted relays, we propose a physical layer security transmission mechanism in relay system. We get the joint channel characteristics by combining the two channels, source node to relay and relay to destination node, into one. Based on this, we construct artificial noise and add it to the transmission signal, in order to make the internal and external wire-tappers get none of the information. The optimal signal transmission power is calculated subsequently. Simulation results show that when the artificial noise lies in the null space of the legitimate receiver´s channel, secrecy capacity of the cooperative relay system can be improved and the bit-error rate of the legitimate receiver is much smaller than wire-tappers.