Artificial Noise Hopping: A Practical Secure Transmission Technique with Experimental Analysis for Millimeter Wave Systems

Millimeter wave (mmWave) frequency band is a promising candidate for 5G wireless networks. In theory the communication is more secure, thanks to the narrow and directional beams of mmWave systems, but eavesdropping may still happen. Physical layer defenses for mmWave systems have raised lots of attentions recently, yet the practicality of these designs remains in question. In this article, we perform extensive experiments using commercial testbed and investigate practical secure transmission schemes for mmWave communication systems. We provide the first empirical results that demonstrate the severity of sidelobe eavesdropping in mmWave systems. We show that eavesdropping attacks on mmWave links are highly effective in both indoor and outdoor settings. We then analyze the practicality and vulnerability of existing defenses. We find that existing defenses either impose impractical hardware requirements, or remain vulnerable against multiple colluding eavesdroppers. Finally, we propose the artificial noise hopping (ANH), a practical secure transmission scheme that introduces minimal hardware complexity in hybrid beamforming. Our approach does not need symbol-level beam steering, and we only require two radio frequency chains. From both experimental and simulation results, we show that ANH can effectively reduce the hardware cost while maintaining comparable level of security with traditional hybrid beamforming schemes.