Security Strategy Design Of MIMO-OFDM Based On Modulation Artificial Noise Scrambling

Security is an important issue in communication system. Wireless communication system is facing with tremendous challenges due to the openness of wireless transmission environment, the mobility of wireless terminal and the variation of network topology. Traditional wireless encryption scheme uses the experience of cable system, which adopted classical cryptosystem to guarantee the security of wireless communication networks over the Link Layer of OSI protocol. This encryption scheme is a kind of weak security because it is based on the amount of calculation, and it is not as safe as usual with the rapid development of computer technology. In recent years, physical layer security technology based on Shannon’s information theory has become a hot topic in the field of wireless communication. What’s more, MIMO and OFDM are chosen as the key technology of new generation wireless communication system because its stability of signal transmitting and high utilization rate of frequency spectrum. A lot of research on the basis of MIMO-OFDM is emerging in the past few years and MIMO-OFDM technology greatly enhancing the research content on physical layer security.By analyzing the characteristics and physical layer security mechanisms of MIMO and OFDM technology respectively, we designed a security strategy combining OFDM modulation constellation rotation encryption with MIMO artificial noise scrambling. The encryption scheme consists of two parts. The first part is constellation rotation encryption scheme which can be seen as symmetric key cryptography. Thinking about the natural characteristics of the physical layer, we use the channel state information between legitimate correspondents as a common key. Then the generated rotated angle is used to encrypt and decrypt OFDM symbols. The second part is MIMO artificial noise scrambling, making use of the advantage of multiple antennas. Artificial noise can be transmitted to the null space of the main channel to interfere with the eavesdropper. Theoretical analysis shows that the encryption scheme only increases transmitting power and will not affect the inherent performance of the communication system. In order to evaluate the safety performance of the designed system, a large number of simulation experiments were carried out in this dissertation, with three kinds of decryption strategies were figured out. Simulation results show that only use constellation rotation encryption can’t achieve the complete secrecy of information. Due to the limitation of the rotated angle, eavesdropper is able to obtain some symbols. As we know, low intensity of artificial noise can’t impact eavesdropper quite much while strong artificial noise will increase the burden on the whole system. Eavesdropper will not get any information through those decryption strategies when the system is encrypted with two kinds of security strategies. Strong security can be achieved with the help of weak artificial noise. In summary, the designed MIMO-OFDM security strategy based on modulation encryption and artificial noise scrambling won’t have a negative impact on legitimate receiver and can guarantee the secure transmission of wireless communication system at the cost of transmitting power.