Research On Physical Layer Security In Untrusted Relay Systems

Physical layer security technology has become a hot topic in the past few years.Compared with conventional upper-layer encryption technologies,physical layer security has the advantage of naturally protecting information in the underlay.Besides,there are various channel information resources which can be utilized to enhance the communication system security.Existing physical layer security technologies have the problems of low spectral efficiency and high complexity.Therefore,based on the untrusted relay system,we propose novel physical layer security schemes,aiming to improve the spectral efficiency and reduce the algorithm complexity.Moreover,these proposed security schemes enable zero confidential information leakage at the eavesdropping node.We first study the physical layer security technology with high spectral efficiency,where the source signal and jamming signal are jointly designed.The source signal is based on Quadrature Amplitude Modulation(QAM),and one special non-gray code design and corresponding adjustable QAM constellation design are proposed.The jamming signal is based on Quadrature Phase Shift Keying(QPSK),and the transmit power and the signal phase are designed according to related channel state information.On this basis,the Bit Error Rates(BERs)of source and jamming signals at untrusted relay are derived,and the conditions of BERs approaching 0.5 are analyzed.Additionally,the channel phase feedback error is considered.Hence,our proposed security schemes are designed in two cases:ideal channel phase feedback and 1bit channel quantization feedback.Theoretical analysis and simulation results demonstrate that the BERs of source and jamming signals can approach 0.5 at the untrusted relay.Even though the untrusted relay attempts to demodulate jamming signal,information leakage of the source and jamming signals will still not occur at the relay.Compared with existing security schemes,all bits in the source signal in our proposed schemes are utilized to carry confidential information and the source signal can be designed as higher-order QAM signals.This indicates that the spectral efficiency of communication systems is highly improved.Besides,our proposed schemes are applicable for the situation where the eavesdropping node can demodulate and eliminate the jamming signal.Then,we study the physical layer security technology based on selective modulation,and general security schemes are proposed.The selective modulated source signal includes the source selection and transmission signals.The selection bits corresponding to source selection signal are used to carry the confidential information and select the transmitted slot/fiequency of the source transmission signal.While the source transmission signal does not bear useful information,acting to prevent selection bits leakage with the aid of j amming signal.According to whether cooperative jamming signal is transmitted randomly or not,the security technology is studied based on selective modulation.For the security scheme with continuous jamming signal,the design of source signal is based on 1-bit selective modulation,and the source transmission signal adopts M-ary Phase Shift Keying(MPSK)modulation.The jamming signal is based on MPSK,and the transmit power and the signal phase are designed to achieve zero leakage.For the security scheme with random jamming signal,the design of source signal is based on n-bit selective modulation.The source transmission and jamming signals adopt constant mode modulation.Only the transmit power of jamming signal is designed according to the relevant channel state information.Theoretical analysis and simulation results show that the BER of selection bits in the source signal tends to be 0.5 at the untrusted relay.That is,the Symbol Error Rate(SER)of the source selection signal tends to be 1-1/2n,so that no confidential information is leaked at the eavesdropping node.In conclusion,the proposed security schemes either considerably improve the frequency spectrum efficiency of communication systems or reduce the algorithm complexity.Meanwhile,these proposed schemes can prevent the untrusted relay eavesdropping confidential information absolutely.