Research On The TCM-COFDM System Physical Layer Security Algorithm

With the rapid development of wireless communication technology and extensive application, the security of the information transmission has caused widespread concern. Especially with the superior computing power equipments appearing, the traditional encryption techniques that depend on the decoding complexity theoretical foundation are no longer reliable. Therefore, to achieve secure communication in an absolute sense, the study of the physical layer security schemes have attracted extensive attentions.This paper presents the concepts of physical layer security, methods and evaluation criteria, analysis of the BER and security performance of TCM-COFDM system under different channel environments and different coding parameters. Based on this, two security transmission schemes are proposed, PTCM-COFDM (Punctured Trellis Coded-Modulation Coded Orthogonal Frequency Division Multiplexing) and based on artificial noise of PTCM-COFDM. The main idea is using the differentiated channel theory. By puncturing during the information encoding process and adding artificial noise, the legitimate user can normally receive information. But with the eavesdropper’s channel faint degradation results in bit error rate increases rapidly, and thus eavesdropper can’t get any useful information, and achieve absolute security in a generic sense. On the basis of designing security verification algorithms, the physical layer security of the system is verified by simulation. Simulation results show that PTCM-COFDM system not only has higher bandwidth efficiency and stronger anti-interference ability, but also the security gap was reduced by 10.5dB and 8.5dB with respect to TCM-COFDM system in the Gaussian wiretap channel and the fading wiretap channel; The introduction of artificial noise, PTCM-COFDM system shows better security performance in fading channel, and the security gap can reduce by 17dB. Reducing the security gap, indicating that smaller wiretap channel degradation, the eavesdropper’s error rate is higher than 0.4, achieving absolute security.