MU-MIMO aided secure transmission in cognitive downlink heterogeneous cellular networks

Cognitive heterogeneous cellular networks (CHCNs) and multi-user multiple-input multiple-output (MU-MIMO) are both promising technologies in the future network where wireless transmissions are inherently vulnerable to security breaches. Under an interference constraint set by the primary user, this study examines the impact of MU-MIMO technology on secure communication between cognitive base stations (BSs) and cognitive users (CUs) in downlink underlay CHCNs. First, based on stochastic geometry, we describe a CHCN model under a threshold-based protocols, and derive the expressions of the connection outage probability and achievable ergodic rate of the CUs. Second, the secrecy outage probability (SOP) of the CUs in the presence of non-colluding eavesdroppers as well as the lower bound of SOP for the CU in the presence of colluding eavesdroppers are given, respectively. Finally, the impacts of antenna system, eavesdropper density, eavesdropper case, and the received signal-to-interference-plus-noise-ratio threshold for security as well as reliability performance are analyzed, respectively.