Beamforming and Artificial Noise for Cross-Layer Location Privacy of E-Health Cellular Devices

With the widespread use of e-health devices (e-HDs) connected to cellular networks that monitor vital signals and support e-health applications, our privacy is at risk. Among exposed personal details, our location reveals our habits, acquaintances, work, and health conditions. Since location can be obtained at several layers of cellular networks, cross-layer solutions (from the physical to the network layers) should be pursued. Recently, a location-private mobile network has been proposed to protect location privacy. In this context, e-HDs communicate among them, and only gateway user equipments (GUEs) are connected to the new-generation node base (gNB), thus only the GUEs' position is revealed to the network. Still, by overhearing e-HD-GUE communications, the network can locate the e-HDs. In this paper we aim at preventing such an attack, designing a location-private beamformer to be used by the e-HD to maximize the data rate, while limiting the signal-to-noise ratio (SNR) at the gNB. Moreover, when multiple GUEs are available, we propose that other GUEs transmit suitably beamformed artificial noise to the gNB, further reducing the SNR and relaxing the design of the location-private beamformer. Numerical results confirm the validity of the proposed solutions, also in comparison with existing approaches, such as zero-forcing and maximal ratio combining transmit beamforming.