Downlink physical layer security transmission confronted with synergistic eavesdroping

The most of existing physical layer security research focus on the situation where decentralized nodes transmit signals to the Base Station(BS). But considering a scenario where nonorthogonal transmission is allowed, when the BS transmits signals to decentralized nodes, the multi-downlinks will interfere each other, decreasing the signal-to-interference-plus-noise ratios (SINRs) at receivers. Focusing on the above problem, this paper optimizes the downlink beamforming and power allocation jointly to meet the SINRs requirement. On this basis, when confronted with synergistic eavesdroping where a malicious jammer helps the eavesdropper to eavesdrop, the BS transmits the artificial noise(AN) to improve the secrecy rate. Then zero-sum game model is proposed to obtain the strategies and corresponding expectation value of the secrecy rate when system reaches the mixed strategy equilibrium. By simulation, this method will obtain a good secrecy rate.