Physical layer security by robust masked beamforming and protected zone optimisation

The authors address the physical layer security in multiple-input-single-output communication systems. This study introduces a robust strategy to cope with the channel state information errors in the main link to convey confidential information towards a legitimate receiver while artificial noise is broadcast to confuse an unknown eavesdropper. The authors study how an eavesdropper physically located in the vicinity of the transmitter can put at risk the network´s security, and hence, as a countermeasure, a `protected zone´ was deployed to prevent the close-quarters eavesdropping attacks. The authors determine the size of the protected zone and transmission covariance matrices of the steering information and the artificial noise to maximise the worst-case secrecy rate in a resource-constrained system and to minimise the use of resources to ensure an average secrecy rate. The proposed robust masked beamforming scheme offers a secure performance even with erroneous estimates of the main channel showing that a protected zone not only enhances the transmission security but it allows us to make an efficient use of energy by prioritising the available resources.