Secrecy multiuser diversity for distributed antenna systems from the perspective of user-scaling law

In this paper, we introduce the notions of a user-scaling function and a user-scaling exponent and multiuser diversity (UEMD) pair. Our notions for the UEMD pair could be utilized as a basic tool for analyzing user-scaling laws. We derive a secure user-scaling law in terms of SNR, the number of eavesdroppers, the number of distributed antennas in distributed antenna systems, and design parameter λ. Through analytical and numerical results, we characterize the effect of the number of distributed antennas on the user-scaling behavior in terms of achievable secrecy rate. Compared with the conventional results based on a single antenna system, our results indicate that installing a small number of distributed antennas could provide a significant performance gain in terms of the achievable secrecy rate.