Abstract
In this paper, a secure communication model for cognitive multi-user massive multiple-input multiple-output (MIMO) systems with underlay spectrum sharing is investigated. A secondary (cognitive) multi-user massive MIMO system is operated by using underlay spectrum sharing within a primary (licensed) multi-user massive MIMO system. A passive multi-antenna eavesdropper is assumed to be eavesdropping upon either the primary or secondary confidential transmissions. To this end, a physical layer security strategy is provisioned for the primary and secondary transmissions via artificial noise (AN) generation at the primary base-station (PBS) and zero-forcing precoders. Specifically, the precoders are constructed by using the channel estimates with pilot contamination. In order to degrade the interception of confidential transmissions at the eavesdropper, the AN sequences are transmitted at the PBS by exploiting the excess degrees-of-freedom offered by its massive antenna array and by using random AN shaping matrices. The channel estimates at the PBS and secondary base-station (SBS) are obtained by using non-orthogonal pilot sequences transmitted by the primary user nodes (PUs) and secondary user nodes (SUs), respectively. Hence, these channel estimates are affected by intra-cell pilot contamination. In this context, the detrimental effects of intra-cell pilot contamination and channel estimation errors for physical layer secure communication are investigated. For this system set-up, the average and asymptotic achievable secrecy rate expressions are derived in closed-form. Specifically, these performance metrics are studied for imperfect channel state information (CSI) and for perfect CSI, and thereby, the secrecy rate degradation due to inaccurate channel knowledge and intra-cell pilot contamination is quantified. Our analysis reveals that a physical layer secure communication can be provisioned for both primary and secondary massive MIMO systems even with the channel estimation errors and pilot contamination.
Highlights
Massive multiple-input multiple-output (MIMO) is currently being investigated as one of the key enabling technologies for the 5th generation wireless standard [1]
The intra-cell pilot contamination effects in cognitive massive MIMO systems do not hinder the use of random pseudo-inverse based artificial noise (AN) shaping matrices
The extra degrees-of-freedom provided by the massive MIMO have been exploited to transmit AN sequences to incapacitate the eavesdropper’s ability to decode the confidential data
Summary
Massive multiple-input multiple-output (MIMO) is currently being investigated as one of the key enabling technologies for the 5th generation wireless standard [1]. There is a symbiotic relationship between massive MIMO and cognitive radio networks to achieve a groundbreaking spectral and energy efficiencies for future wireless systems, facilitating secrecy at the physical layer of cognitive massive MIMO systems has not yet received any attention in the existing studies in the literature To fill this gap, in this paper, a secure downlink transmission strategy is investigated for cognitive massive MIMO systems with underlay spectrum sharing in the presence of a passive multi-antenna eavesdropper. In this paper, a secure downlink transmission strategy is investigated for cognitive massive MIMO systems with underlay spectrum sharing in the presence of a passive multi-antenna eavesdropper To this end, a secondary massive MIMO system is allowed to access the licensed spectrum of a primary massive system subject to an interference temperature constraint, which is the maximum tolerable co-channel interference (CCI) power at the primary system. The system, channel, and signal models of a cognitive multi-user massive MIMO system are presented
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