The Physical Layer Security Implementation Of The Wireless Communication System Based On LDPC Code

The physical layer security was first investigated by Wyner in his landmark paper on the wiretap channel. Wyner first pointed out that using a special channel coding technique, the eavesdropper of the wiretap channel model can not obtain any information about the transmitted messages, and there is no need to use secret keys to encrypt the rnessages. After the wiretap channel model proposed, the construction of the practical channel code that can achieve Shannon's theoretical security has become a new research direction in the coding field. Wyner's research on the wiretap channel is mainly aimed at discrete memoryless and Gaussian noise channel, but there is quite a difference from the actual wireless channel. The actual wireless channel is a time-varying fading channel, usually using Rayleigh fading channel to simulate it. At present, how to design coding and decoding scheme for the actual wireless channel in physical layer security is an extremely important and challenging issue.Based on Wyner's work, in this paper, the main contribution can be outlined as follows: First, according to the security coding conditions and the engineering implementation method of the physical layer security, using LDPC code,we have designed practical coding scheme for the Gaussian wiretap channel,and have successfully applied it to the Rayleigh fading channel. Then considersing the situation that the legitimate receiver feeds back his output to the transmitter, based on the LDPC code, we have designed practical coding scheme for the Gaussian system with feedback, and have successfully applied it to the Rayleigh fading system with feedback. In addition, this paper has designed the corresponding coding scheme which can achieve the security of information theory for different channel noise. Finally the simulation of each scheme has been carried out and the results have been analyzed, including the comparison of the same coding scheme under different channel conditions: comparison between fading channel and non-fading channel and comparison between feedback and non-feedback. And comparison of different coding schemes have been made under the same channel.The simulation results show that the eavesdropper's bit error rate can reach 0.5 when the wiretap channel noise gets bigger, which means the schemes proposed in this paper can realize the physical layer security. And the larger the wiretap channel noise is, the more secure the proposed coding scheme is.Moreover, we find the feedback enhance the security of the system, and the eavesdropper's bit error rate of the Rayleigh fading environment is higher than that of the Gaussian environment.