Modeling And Analysis Of The Physical Layer Security Over Wireless Fading Channels

Benefitted from the development of wireless technologies, instrumentation systems are propelled to the network and portable directions and can realize remote control and measurement. Information security is one of the core and key issues on whether wireless systems can provide users with reliable services or not. The security of wireless systems encounters severe challenges due to the openness of wireless channels and the mobility of terminals, as well as the diversity of networking structures. The security of traditional wireless communications mainly relies on the cryptography-based encryption technologies in upper-layer, such as AES(Advanced Encryption Standard), DES(Data Encryption Standard) and etc., the essence of which is to obtain information security through massive computing. With the development of semiconductor technologies and the emergence of quantum computing and cloud computing technology with a powerful parallel processing capability of data, the computing capability of the computer has been rapidly improved. Thus, the way of relying on the computational complexity degree to ensure information security is facing enormous challenges. On the other hand, it is clear that, the higher complexity of the security coding is, the higher complexity legitimate decoding users will meet. Therefore, it’s tough for the computing power and energy-constrained portable instrument systems to implement high-performance security code.Recently, with the development of multi-antenna, cooperative communications and coding technologies, secure information transmission in physical layer has become a hot issue of academic researches. Differing from the traditional encryption technologies, no encryption key is employed in physical layer security technologies but making use of the time-variable character of wireless channels to realize secure information delivery. Now, physical layer security has become the cross hotpot of information security and wireless communications, as well as one of the research and develop hotspots for the advanced instrument systems and military instruments both at home and abroad. In this paper, the physical secrecy performance over fading channels has been modeled and analyzed. In detail, the theoretical limit performance metrics are obtained for generalized small-scale fading and composite fading scenarios, which provides a theoretical basis for the future implementation of the physical layer security.First, most of the references about the physical layer security focus their concentration either on small-scale fading channels(i.e., Rayleigh, Nakagami-m fading) or on large-scale fading channels(i.e., log-normal fading). All these works just proposed analytical models for a particular type of fading channels and cannot cover various fading types in practical scenarios. In this paper, the generalized small-scale fading channel model is firstly studied, and the secrecy performance of Wyner’s model over Generalized Gamma channel is analyzed, and the closed-form expressions of average secrecy capacity(ASC), bound of secrecy outage probability(SOP) and probability of a non-zero secrecy capacity(PNSC) are derived, respectively.Second, the existing researches on the physical layer security either focus on small-scale fading(e.g. Rayleigh channel) or large-scale fading(e.g. Log-normal channels) scenarios. However, both small-scale fading and large scale fading may occur simultaneously in the actual environments. In this thesis, the composite fading channels are taken into account. The secrecy performance of Wyner’s model over Generalized-K(GK) fading channels are investigated, and the closed-form expressions of ASC, SOP and PNSC are derived, respectively.Third, multi-antenna technologies have become one of the key solutions to improve the performance of wireless communications since multi-antenna technologies can make full use of space resources and can effectively deal with the fading effects over wireless channels. This paper studies the secrecy performance of single-input multiple-output(SIMO) systems over composite fading channels and the closed-form expressions of ASC, SOP and PNSC over GK fading channels are derived by utilizing three different methods.Forth, cognitive radio networks are considered as one of the most effective solution to solve the issue on the lack of radio spectrum resources because of the flexibility and feasibility. This paper considers a SIMO cognitive wiretap system over Nakagami-m channels with generalized selection combining(GSC), where confidential messages transmitted from a single-antenna transmitter to a multiple-antennas legitimate receiver are overheard by a multiple-antennas eavesdropper. Passive eavesdropping scenario is considered, while the channel state information of the eavesdroppers channel is not available at the secondary transmitter. The closed-form expression for the exact SOP is derived and simulations are conducted to validate the accuracy of proposed analytical models.Fifth, this paper also analyzes the impact of different transmission antenna selection(TAS) strategies on the physical layer security of underlay MIMO cognitive radio system. Depending on whether the source node has the global CSI of both the main channels and wiretap channels, we investigate the secrecy outage performance of optimal antenna selection(OAS) and suboptimal antenna selection(SAS) schemes for MIMO underlay cognitive radio systems over Nakagami-m channels, and compare with space-time transmission(STT) scheme. The closed-form expressions for the exact secrecy outage probability for different schemes are derived. Simulations are conducted to validate the accuracy of our proposed analytical models.Based on these before-mentioned research topics, the physical secrecy performance of wireless system have been systematically modeled and analyzed in this paper. The closed-form analytical expressions of various performance metrics are derived. Numerical and Monte Carlo simulation results are presented to verify our derived analytical models. These results can provide a theoretical reference for the application of the physical layer security technologies in wireless systems and can offer an important guiding significance on the security-design of future wireless systems, as well as on the research and development of advanced instrument systems and military instruments.