Research On Physical Layer Network Coding Security Technology Based On Secrect Keys Generated From Channels

The application of network coding technology also brings more complex security problems.In network coding systems,the relay node will mix different data and mask the original source message data.Compared with traditional communication mode,its security problem becomes more complex.When network coding is combined with relay cooperation,network coding is applied to wireless bidirectional relay system,resulting in physical layer network coding technology.Physical layer network coding technology makes use of the characteristics of radio electromagnetic wave superposition in the air,shortens the communication time of two-way relay network to two slots,but improves network throughput at the same time brings more complex security problems.This dissertation not only studies the physical layer network coding technology itself,but also studies the security of the physical layer network coding system.The main innovations are as follows:(1)A physical layer network coding scheme based on channel pre-equalization is proposed,in order to solve the problem that superposed signals can be decoded correctly in the network coding system with channel noise and multipath effect.This thesis studies the security technology in the physical network coding systems.The first premise of system security is that legitimate users can decode correctly.The complexity of the physical layer network coding technology in the actual system lies in that the superposed signal received by the relay node passes through the different distortion of the channels on both sides and simultaneously superposed white different Gaussian noise,so it is necessary to extract the undistorted information from the superposed signal.In the multipath channel environment,the channel distortion is more serious,and how to extract the information from the superposed signal is difficult in the case of the intersymbol interference(ISI).In order to solve the problem that superposition signal can be decoded smoothly in network coding system with noise and multipath effect,two physical layer network coding schemes based on channel pre-equalization are proposed.It includes the physical layer network coding scheme based on channel time domain pre-equalization and the physical layer network coding scheme based on channel frequency domain pre-equalization.The former is suitable for the system of time domain equalization,and the latter is suitable for the system of frequency domain equalization.In the physical layer network coding scheme based on time domain pre-equalization,the adaptive time domain pre-equalization technique is used in the physical layer network coding,and the equalizer parameters are adaptively adjusted according to the channel characteristics.The equalizer parameters are simultaneously used for pre-equalization and equalization by two users(Alice or Bob),and the equalizer is not needed at the relay side,which saves the cost and improves the efficiency.In the physical layer network coding scheme based on frequency domain pre-equalization,Alice and Bob use frequency domain pre-equalization to pre-equalize to transmit signals,and post-equalize to receive signals using frequency-domain equalization.There is also no need for equalizers on the relay side.This scheme combines the advantages of single carrier frequency domain equalization,pre-equalization and physical layer network coding,and will provide a new perspective for the research of physical layer network coding.The simulation results show that the performance of the physical layer network coding system with channel frequency domain pre-equalization is better than that of the physical layer network coding system with channel time domain pre-equalization.(2)An adaptive quantization channel key generation algorithm in time domain is propsed and used to build a secure physical layer network coding scheme,in order to solve the security problem of physical layer network coding system based on time domain pre-equalization.Channel key generation belongs to the category of physical layer security,which combines traditional encryption and physical layer security.It has the advantages of easy implementation of traditional encryption and high security of physical layer.In this dissertation,the principle of key generation based on channel time domain in two-way relay network is studied,the key generation process and key exchange process are analyzed,two key combination mechanisms are given,and the key capacity of the two key combination mechanisms in multipath channel environment is deduced and verified by using mutual information theory.An adaptive quantization channel key generation algorithm in time domain is proposed.The algorithm can improve the reliability of the key while ensuring the key generation rate by selecting the quantization parameters adaptively.The key generation rate and the key mismatch rate under the two key combination mechanisms are also studied.Then,the key generated by the adaptive quantization channel time domain key generation algorithm is encrypted and decrypted in the physical layer network coding system based on time domain pre-equalization.A secure physical layer network coding scheme based on the combination of channel time domain key generation technology and time domain pre-equalization technology is proposed.The security scheme not only focuses on the key generation process,but also on the encryption and decryption of the generated key in the process of transmitting useful information in the network coding system.The combination of physical layer security and physical layer network coding provides a new solution for the security of network coding system.The simulation results show that the security scheme based on channel time domain key generation can ensure the security of physical layer network coding system,and effectively prevent illegal users from eavesdropping attacks.(3)An adaptive quantization channel frequency domain key generation algorithm is propsed and used to build a secure physical layer network coding scheme,in order to solve the security problem of physical layer network coding system based on frequency domain pre-equalization.The key generated in the physical layer security system is closely related to the channel characteristics.For multi-path Rayleigh fading channels,the frequency domain of the channel is frequency-selective,and its frequency domain value distribution is more dispersed.Compared with the time domain impulse response,it can bring more information.Therefore,the research of key extraction based on channel frequency domain characteristics is also worthy of attention.Firstly,this dissertation proves that the frequency domain response of Rayleigh channel can be used as a random source to generate the key,which provides a theoretical basis for the feasibility of generating the key based on the frequency domain of the channel.Secondly,in order to construct a mechanism that can generate the key simultaneously using the amplitude and phase characteristics of the channel frequency domain,a single carrier frequency domain equalization system is studied.Based on the key generation technique of channel frequency domain response,an adaptive quantization channel frequency domain key generation algorithm is proposed,and its key capacity is deduced.Compared with the channel time-domain key generation algorithm,the channel frequency-domain key generation algorithm can increase the key capacity several times and the key generation rate greatly.Then,the key generated by the adaptive quantization channel frequency domain key generation algorithm is encrypted and decrypted in the physical layer network coding system based on frequency domain pre-equalization.A secure physical layer network coding scheme based on the combination of channel frequency domain key generation technology and frequency domain pre-equalization technology is proposed.The simulation results show that the security scheme based on channel frequency domain key generation can ensure the security of the physical layer network coding system and effectively prevent illegal users from eavesdropping attacks.Compared with the channel based time domain key generation scheme,the key capacity and key generation rate based on channel frequency domain are higher,and the bit error performance is better.(4)In the above two security schemes,the process of key exchange is needed when the key is generated,which results in the disclosure of part of the key information.In order to solve this problem,a joint channel key generation algorithm is propsed and used to build a secure physical layer network coding scheme.In the two-way relay network,there is no direct communication link between the two source nodes of the communication,only through the relay node to communicate.When using the channel-based key generation technology,the two source nodes of the communication only generate and know their own key.In order to communicate with each other,they need to know the key generated by each other.Therefore,when using channel-based key generation technology in two-way relay network,the key exchange process is also needed.The problem is that in the process of key exchange,the XOR information of the key of both nodes will be obtained by illegal users,resulting in the leakage of some key information.In order to solve this problem,a key generation algorithm based on channel joint is proposed,which can be divided into two types: time domain joint key generation and frequency domain joint key generation.The joint key generation algorithm avoids key exchange and naturally performs key exchange in the process of key generation.It not only solves the problem of some cryptographic information leakage,but also keeps the key secret to the relay node,which further enhances the security of the system.Then,the time domain joint key generation and frequency domain joint key generation algorithms are used to encrypt and decrypt the key in the physical layer network coding system based on time domain and frequency domain pre-equalization,respectively,to solve the security problem.The simulation results show that the security scheme based on joint channel key generation can ensure the security of physical layer network coding system and effectively prevent illegal users from eavesdropping attacks.And the performance of system with the channel frequency domain joint key generation is better tha the system with the channel time domain joint key generation on the whole.