Mean physical-layer secrecy capacity in mobile communication systems

The security of mobile communication systems depends on the mean physical-layer secrecy capacity as the user moves. In realistic propagation environments, the physical-layer secrecy capacity varies over a vast range because of the user motion. A mean physical-layer secrecy capacity of a legitimate user is defined to characterize the secure communication performance of the system. The distribution characteristics of the mean physical-layer secrecy capacity are derived based on the impact of the eavesdropper's position on the mean physical-layer secrecy capacity. A scheme is then given to improve the mean physical-layer secrecy capacity according to the distribution characteristics. The mean physical-layer secrecy capacity can be made to be not lower than a specified value by limiting the eavesdropper's positions. Theoretical and numerical results demonstrate that this scheme can effectively guarantee the mean physical-layer secrecy capacity in mobile communication systems.