In this paper, a multiple-input multiple-output (MIMO) communication system with frequency hopping (FH) aided orthogonal frequency division multiplexing differential chaotic shift keying (OFDM-DCSK) modulation is proposed. Our objective is to improve the security of MIMO communication system which is encoded by space time block coding (STBC). In order to combat the eavesdropping or malicious attacks due to the broadcast characteristics of wireless communication system, we propose to use DCSK and FH modules to encrypt the information, and hide the user data in the chaotic sequences, where the initial value of chaotic sequences and the method of generating FH module are only shared among legitimate users. Moreover, we derive the bit error rate (BER) and the secrecy capacity of the scheme in additive white Gaussian noise (AWGN) channel and Rayleigh fading channel. Simulation results show that the proposed scheme can effectively improve the security of MIMO communication system, which can be seen from the BER of eavesdroppers and legitimate users, and the secrecy capacity of the proposed scheme and the benchmark schemes.

In this paper, in order to improve the reliability of Multi-User Multiple-Input Multiple-Output Visible Light Communication (MU-MIMO-VLC) system, we propose a precoding scheme that based on Singular Value Decomposition (SVD) and Geometric Mean Decomposition (GMD) assisted Orthogonal Transformation (OT). In this design, we use SVD to conduct the decomposition of the user's complementary channel matrix. Then, the equivalent channel matrix is obtained by multiplying the user's channel matrix and the decomposed component. After that, the GMD is carried out to decompose the equivalent channel matrix. Finally, the precoding matrix of the proposed scheme is obtained. We then derive the theoretical Symbol Error Rate (SER) of the proposed scheme. The simulation results are provided to validate the effectiveness of the proposed scheme, and to demonstrate that the reliability of the proposed design is superior to benchmark schemes.