Secrecy Outage Analysis for Massive MIMO-Enabled Multi-Tier 5G Hybrid HetNets

The existing cellular systems operating in ultra high frequency bands suffer from severe bandwidth congestion and therefore the paradigm of cellular spectrum is shifting towards millimeter wave (mmWave) bands under the umbrella of fifth generation (5G) networks to provide higher capacity. On the other hand, providing secure and reliable transmission of data to the desired users is gaining more importance in recent years. This paper analyzes the impact of co-existence of mmWave small cells and massive multiple-input multiple- output (MIMO) on connection outage and secrecy outage of the network. Specifically, we consider a three-tier network consisting of small cells operating at both the sub-6 GHz and mmWave frequency bands overlaid with massive MIMO-enabled macro base stations where eavesdroppers under variable eavesdroppers density and antenna gains are present. The user location of both the desired entities and eavesdroppers are modeled by independent Poisson point processes. Based on this stochastic model, we investigate the downlink secrecy outage probability and connection outage probability of the entire network. Numerical results show that massive MIMO-enabled hybrid heterogeneous networks (HetNet) alongside mmWave small cells significantly reduces both the connection outage and secrecy outage probability of the network for higher small cells base station density.