Secure Communication in Spectrum-Sharing Massive MIMO Systems With Active Eavesdropping

Secure communication in underlay spectrum sharing multi-user massive multiple-input multiple-output systems with active eavesdropping is investigated. The primary base-station (PBS) shares its licensed spectrum with the secondary base-station (SBS), which constrains its transmit power subject to a primary interference temperature. The active eavesdropper contaminates the uplink pilots in an attempt to intercept the confidential downlink transmissions toward the legitimate primary/secondary user nodes (PUs/SUs). The achievable PU/SU rates, the rates leaked into the active eavesdropper, and the achievable secrecy rates are derived for the finite and infinite PBS/SBS antenna regimes. A power-ratio-based active pilot attack detection scheme is investigated, and thereby, the probability of detection is derived. Our analysis and simulation results reveal that the active pilot attacks severely degrades the achievable secrecy rates even in the asymptotic PBS/SBS antenna regime. Hence, in order to provide guaranteed physical layer security, the active pilot attacks must be detected, and dynamic pilot decontamination techniques need to be employed.