Research On Physical Layer Secure Coding And Transmission Schemes With Variational Equivalent Channel Characteristic Model

The information security theory has revealed that the fundamental method of guaranteeing security for wireless transmission is to create legitimate channel quality advantage and transmit the classified information with the channel capacity differences. The natural channel characteristic differences are used as the distinction between different users’identities to ensure reliable communications while preventing eavesdropping by physical layer security technology. It is the direct and effective way to guarantee the information security. There are still the following questions:(1) Lack of the general physical layer security transmission model and design methods. (2) Lack of the channel matching design of secrecy coding and decoding algorithm. (3) Lack of the secrecy coding and transmission joint design. In this thesis, we use the differences of equivalent channel characteristics to achieve secure transmission and focus on secrecy coding and transmission schemes design with random scrambling model for different systems. The main results are as follows:1. We present a random scrambling model with variational equivalent channel characteristics for physical layer security. It can be proved that the proposed model increases the diversity of the equivalent channel characteristic equation from the information theory perspective. The random weighting matrix which is constructed by the equivalent channel characteristic equation is able to break the constant of both natural and equivalent characteristics. The system is no long confined to a finite field symbol set and larger security rate can be achieved when using the random weighting matrix to precode.This model can also be used to make a joint design of security transmission and secrecy coding which can further improve the robustness and security.2. In order to achieve secure transmission in the cooperative relay system, a random relay selection algorithm is proposed based on variational equivalent channel characteristics model. We analyze the effect of the MUSIC-like algorithm and adopt the reverse synchronization scheme to construct the fast changing equivalent channel characteristics. The power weighting coefficients and relay selection strategy are presented for improving the power utilization rate and guaranteeing secure transmission respectively. The proposed algorithm decreases the SINR of the wiretap channel and destroys the statistical properties of eavesdropper’s signal.3. The secure transmission schemes for both single-user and multi-user based on the random precoding at subcarriers are proposed in multi-carrier communication systems. We establish a physical layer secure transmission model for the OFDM system and design the random weighting coefficients based on variational equivalent channel characteristics model by acquiring the amplitude and phase of each subcarrier. The subcarrier transmit reference scheme is also proposed to guarantee the reliable receiving of the legitimate users under the fast variation of the equivalent channel characteristics. Finally, the multi-user secure transmission with spatial correlation is considerd. The random precoding algorithm is proposed to improve the system reliability and security capacity.4. A channel matching design of secrecy coding is proposed. We treat the variational equivalent channel characteristics as the fast fading channels, thus construct the bit error probability model with channel fading coefficients. The private information bit-interleaved hidden scheme is presented to realize super matching with the legitimate channel. We also analyze the reason of bit error diffusion in belief propagation decoding algorithm and propose two types of decoding algorithms for reducing security gap based on two-dimensional information correction.5. A joint design of the equivalent channel characteristic equation and secrecy coding is proposed. In order to minimize the total transmit power and secrecy outage possibility, an artificial additive noise and secrecy coding are jointly designed for increasing security performance. Furthermore, we calculate the security capacity of the artificial multiplicative noise scheme with differential entropy, and then present an artificial multiplicative noise and secrecy coding joint design. Finally, the performance of the two joint design schemes is analyzed.