Key agreement over Gaussian wiretap models with known interference at the transmitter

We investigate the (forward) key capacity of a Gaussian state-dependent wiretap channel (G-SWC) paralleled with a public channel having capacity C_p ϵ [0, ∞). This model consists of a sender, a main receiver, and a wiretapper. The channel state information (CSI) is an additive white Gaussian interference (AWGI) which is non-causally known at the sender. A lower bound (LB) on the key capacity is achieved by using a generalized version of the dirty paper coding (DPC) in which the transmitted signal is correlated with the interference. The correlation coefficient is to be determined by C_p. The achievable scheme is asymptotically optimum as C_p → ∞. This optimum key capacity is also asymptotically achievable for any C_p ≥ 0 in high signal to interference ratio (SIR) regime. In this regime, the public channel has negligible contribution in key generation. Generally, the CSI enhances the key capacity such that it exceeds the main channel capacity of the G-SWC in low SIR regime.