Secrecy satellite-terrestrial downlink transmissions against randomly located eavesdroppers

The satellite-terrestrial downlink transmissions with larger coverage areas face more severe security challenges than terrestrial cellular communications due to the limitation of the satellite's power and the complexity of the channel. In this paper, the system model consists of one satellite, one legitimate user and multiple randomly distributed eavesdroppers while taking into account practical hardware impairments (HIs) at all transceivers involved. The Shadowed-Rician fading model is adopted since it is a perfect fit for the satellite-terrestrial channel. Besides, the full-duplex (FD) operation is introduced in the destination where the receiver acquires the information signal and simultaneously emits the artificial noise (AN) to interfere with the nearby eavesdroppers. The maximal ratio combination scheme is applied to the destination to improve security. To facilitate evaluation of the effect of various parameters on the security performance, the closed-form expressions of secrecy outage probability and ergodic secrecy capacity for the system are derived under the stochastic geometry framework. Finally, the simulation results show that the AN plays a pivotal role in improving the security performance, while the HIs can greatly deteriorate the performance, especially in the high transmit power regime. In addition, compared with the traditional half-duplex receiver, the FD receiver have better security performance and can significantly alleviate the performance deterioration caused by HIs.