Design And Security Performance Research Of Multi-Relay Physical Layer Network Coding System

Physical-layer Network coding(PNC)makes use of the superposition property of electromagnetic wave to greatly improve the throughput of communication system,and attracts the attention of scholars with this advantage.To give full play to the practical utility of PNC in communication network and meet the increasingly diversified demands of users has become a research hotspot.Moreover,due to the broadcast nature of electromagnetic waves,the information broadcast by source nodes can not only be received by the legitimate relay nodes,but also can be eavesdropped by the illegal nodes in the actual communication environment.In this thesis,we propose a joint scheme of multi-relay PNC system,modulation technology with LDPC channel coding and encryption algorithm based on this background.The primary contributions of this thesis can be summarized as follows:First,we analyze the effect of the number of relay nodes on the transmission efficiency and bit error rate(BER)performance of multi-relay PNC system,and elaborate the mapping rule and transmission principle of each node in PNC system when the number of relay nodes is even and odd respectively.To improve BER performance,we introduce LDPC code and design the scheme of multi-relay PNC system combined LDPC(MR-PNC-LDPC),and present the LDPC coding algorithm and decoding scheme.Numerical results show that the introduction of LDPC code effectively improves the BER performance of the system and reduces the performance loss among among different number of multi-relay systems.Then,we propose a scheme of joint encryption algorithm to solve the transmission security problem of multi-relay PNC system.The working principle of Advanced Encryption Standard(AES)and Data Encryption Standard(DES)in the communication system is described.Based on this,a three-relay PNC-AES/DES encryption system is constructed.It also solves the fusion problem of encryption algorithm and PNC system,and explains the application rules of encryption algorithm in PNC system in detail.Simulation results verify that both schemes have better encryption effect.However,the three-relay PNC-AES system is superior to the three-relay PNC-DES system in algorithm security and encryption efficiency.Finally,to further optimize the security performance of three-relay PNC-AES system,the Cipher Message Authentication Code(CMAC)mode that can identify illegal node tampering attacks is emploied.In addition,we also use RSA public key encryption algorithm to generate encryption keys to decrease the risk of illegal nodes obtaining key information by detecting ciphertext information.In conclusion,a three-relay PNC-RSA-AES hybrid encryption scheme is designed.Our analysis shows that,compared to the three-relay PNC-AES system,the proposed hybrid encryption scheme achieves more reliable security performance at the cost of certain encryption efficiency.