Secrecy Performance in Ultra-Dense Networks with Multiple Associations

Network densification is a promising approach to support the ever-increasing required capacity in cellular networks. Besides, securing the gigantic amount of sensitive data transferred within the network has become a critical issue. Ultra-Dense Networks (UDNs) with a massive number of deployed Small Cells (SCs) constitute the new trait of network densification. Exploiting this massive number of small cells and their proximity to served users, we can enhance the achievable secrecy rate in the network. In this paper, we study Physical Layer Security (PLS) in a multiple-association scenario where each user is served simultaneously by a group of the M closest SCs. This approach helps to mitigate the limitations in the backhaul link capacities of the SCs. Besides, it provides spatial diversity for the users when their data traffic is split into different paths which enhances secrecy performance. Using tools from stochastic geometry, we provide a lower bound analytical expression for the average secrecy rate per user. The obtained results via both analysis and system-level simulations show the significant gain in secrecy performance that can be attained from the proposed multiple associations scheme.