Physical layer security with hostile jammers and eavesdroppers: Secrecy transmission capacity

In the research of physical layer security, cooperative jamming has recently drawn considerable attention. Jammer plays a friendly role to transmit jamming signal to create interference at the eavesdroppers. However, few literatures consider the scenario in which jammer plays a hostile role to interfere legitimate users. In this paper, we study an ad hoc network where legitimate users transmit with the ALOHA protocol in the presence of hostile users. Each hostile user acts as a jammer or eavesdropper with probability q or 1 - q, respectively. We assess the network performance from both sides of the legitimate user and the hostile user. Particularly, from the perspective of the legitimate user, we evaluate how the connection outage and secrecy outage affect the secrecy transmission capacity, and then derive the optimal ALOHA transmission probability that maximizes the capacity. In view of the hostile user, we obtain the optimal jamming probability that can lead to the largest connection outage probability of legitimate users subject to a given successful eavesdropping probability constraint.