Resource Allocation for Secure Communication in $K$ -Tier Heterogeneous Cellular Networks: A Spatial-Temporal Perspective

Resource allocation in secure communication is of primary importance due to the fact that the next-generation wireless network (5G) aims to achieve high spectral efficiency and a high level of security. Different from previous studies, we study the resource allocation for secure transmission in K-tier dynamic heterogeneous cellular networks jointly considering the randomness of base stations (BSs) in spatial dimension and user equipment (UE) arrival and departure processes in temporal dimension. First, we develop a 3-D stochastic model by jointly taking into account the randomness of BSs in two spatial dimensions and UE arrival and departure processes in one temporal dimension. Second, we analyze the connection outage probability and secrecy outage probability of the typical UE. Their expressions admit quite simple closed-forms in some plausible special cases. Based on the outage analysis, the reliability and security performances of the network are evaluated, respectively. Third, we investigate the network-wide secrecy throughput in virtue of the outage analysis. Furthermore, we derive the optimal resource allocation factors of different tiers to maximize the secrecy throughput. Since the objective function of the maximization problem is not in closed form and non-convex, the concave upper and lower bounds are deduced and utilized, which leads to near-optimal solutions of the resource allocation factors of different tiers. It is demonstrated that apart from the spatial intensity and transmission power of each BS, UE arrival and departure processes are also key elements influencing the resource allocation factors of different tiers. Finally, numerical results show the usefulness and correctness of our theoretical conclusions.