Physical layer security of multi-hop aided downlink MIMO heterogeneous cellular networks

This study investigates physical layer security in downlink multiple-input multiple-output (MIMO) multi-hop heterogeneous cellular networks (MHCNs), in which communication between mobile users and base stations (BSs) is established by a single or multiple hops, to address the problem of insufficient security performance of MIMO heterogeneous cellular networks. First, two-dimensional homogeneous Poisson point processes (HPPPs) are utilized to model the locations of K-tier BSs in MIMO MHCNs and receivers, including those of legitimate users and eavesdroppers. Second, based on the channel gain distribution and the statistics property of HPPP, the achievable ergodic rates of the main and eavesdropper channels in direct and ad hoc links are derived, respectively. Third, the secrecy coverage probability and the achievable ergodic secrecy throughput of downlink MIMO MHCNs are explored, and their expressions are derived. Lastly, the correctness of the theoretical derivation is verified through Monte Carlo simulations.