Practical Physical Layer Security Schemes for MIMO-OFDM Systems Using Precoding Matrix Indices

• Published in: IEEE journal on selected areas in communications 2013-09, Vol.31 (9), p.1687-1700
• Main Authors: Wu, Chih-Yao, Lan, Pang-Chang, Yeh, Ping-Cheng, Lee, Chia-Han, Cheng, Chen-Mou
• Format: Article
• Language: English
• Subjects: Channel estimation; Communication system security; cryptography; MIMO; MIMO-OFDM; Physical-layer security; precoding matrix index; secret key generation; Security; Transmitters; Vectors; Wireless communication
• ISSN: 0733-8716; 1558-0008
• DOI: 10.1109/JSAC.2013.130904

In physical-layer security, secret bits are extracted from wireless channels. With the assumption of channel reciprocity, the legitimate users share the same channel which is independent of the channels between the legitimate users and the eavesdropper, leading to secure transmissions. However, practical implementation of the physical layer security faces many challenges. First, for the correlated channel such as the multiple-input and multiple-output (MIMO) channel, the security is decreased due to the correlation between the generated secret bits. Second, the nearby eavesdropper posts a security threat due to observing the same channel as the legitimate user's. Third, the eavesdroppers might try to reconstruct the wireless environments. In this paper, we propose two practical physical layer security schemes for the MIMO orthogonal frequency-division multiplexing (MIMO-OFDM) systems: the precoding matrix index (PMI)-based secret key generation with rotation matrix (MOPRO) and the channel quantization-based (MOCHA) scheme. The former utilizes PMI and rotated reference signals to prevent the eavesdroppers from learning the secret key information and the latter applies channel quantization in order to extract more secret key bits. It is shown that not only the secure communication but also the MIMO gain can be guaranteed by using the proposed schemes.