Research Oncross-layer Enhancing Security Approaches In MIMO-OFDM System

As to meet the demand of rapid growth in the communication business after 2020, 5G system develops gradually. 5G networks whose data transfer rate, resource utilization, wireless coverage performance, and user experience are improved significantly compared with 4G.However, the openness of thewireless channel, broadcasting, terminal mobility, network topology structureand the instability of wireless transmission lead to 5G smart mobile communication networks facing more and more security threats.With the rapid development of the parallel computing,high-speed computer andother technology, traditional security mechanisms constrained to computationneed to share increasingly longkeys. Thus, key distribution requires alongdelay during wireless accessing stage and computational complexity of the upper-layer grows. If the key is compromised or cracked, entire security of system will completely collapse.5G communication system requireslightweight, fast accessing, heterogeneous networks that only depending on upper-layercomputing security-based measures can’t meet the real secutity needs.New technologies of physical layer security for the 5G are concerned.The physical layer security is based on the statistics security. Althoughthe randomnaturemakes it impossible to crack, system has high complexityand lowtransmission efficiency.Physical layer security technologies rely on noise environment heavily, which can’t guarantee system security with probability 1.Throughthe above research background, this thesis focuses on MIMO-OFDM technology in LTE system and proposes schemes ofcross-layer securityby combining physical layer security technology with traditional cryptography technology. The proposed takes into consideration system reliability but also to ensure that the new security mechanism has higher safety performance.Deformation code sets are the key in cross-layer security MIMO transmission system. Firstly, this thesis researches the deformation code sets based on OSTBC. The simulation resultsshow that the OSTBC deformation code sets achieve the best security performance.Secondly, this thesisproposes STTC deformation code sets based on STTC. Under the control of the upper key streams, eavesdroppers’ frame error rate comes to 100% with STTC deformation code sets. Then, this thesis putts forward a cross-layer secure communication scheme byrotating precoding matrix 180 degreesin view of the precoding technique, which isn’t confined to channel characteristics and physical layer signalis easy to design, realizing secure communication with probability 1. Finally, the thesis discusses cross-layer encryptionsecurity of OFDM transmission technology detailedly. Studies show that the proposed can provide stronger security than traditional encryption, especially the high order modulation or partial key leak.Our schemes can be used for 4G, which is advantageous for the 5G compatible with 4G. Without significantly increasing system overhead, the new security mechanism has higher safety performance, giving attention to reliability and safety of the communication system.