Aiming at the detection failure of strong noise interference in the dual channel of the dual-sequence frequency hopping(DSFH),the scale transformation stochastic resonance(STSR)is applied for the first time,and the ou...Aiming at the detection failure of strong noise interference in the dual channel of the dual-sequence frequency hopping(DSFH),the scale transformation stochastic resonance(STSR)is applied for the first time,and the output signal to noise ratio(SNR)is raised effectively,at the same time,the symbol reception is completed for DSFH at low input SNR.Firstly,the radio frequency(RF)and intermediate frequency(IF)signals are analyzed based on the super-heterodyne reception of DSFH;secondly,the equations of probability density function(PDF),output power spectrum and SNR of the STSR output are derived for the IF signal;finally,the algorithm of the optimal matching STSR is proposed with the optimal matching parameters.The simulation results show that the algorithm can effectively solve the detection failure,as the global output SNR of DSFH is strongly improved that the output SNR can reach-17.72 d B when the input SNR is-20 d B after the processing of the optimal matching STSR.展开更多
Quantum secure direct communication(QSDC) promotes high security and instantaneousness in communication by conveying secret messages directly via the quantum channel.In particular,the continuous variable(CV) scheme of...Quantum secure direct communication(QSDC) promotes high security and instantaneousness in communication by conveying secret messages directly via the quantum channel.In particular,the continuous variable(CV) scheme of QSDC is already compatible with current room-temperature telecommunication networks and is very robust to the free-space background noise,making it a unique choice in certain applications.However,to date,the security proofs of CV-QSDC are poorly advanced,as the eavesdropper Eve in these proofs is limited,either can not apply the optimal collective measurements,or does not have full access to the quantum channel.In this paper,we refine and advance the previous theory in this area,providing a tight secrecy capacity bound for the CV-QSDC protocol.We study the secrecy capacity achievable by the two-step scheme,for both(one-mode) collective Gaussian attack and two-mode Gaussian attack,from the standard Markovian assumption on the environment to a more challenging scenario with a time-like and spatial non-Markovian model.Numerical results show that the best attack strategy for Eve is the entangled attack using maximally entangled states(with a positive correlation parameter).More interestingly,we find that the protocol with the standard Markovian model can,in theory,achieve a longer transmission distance in the communication channel affected by high thermal noise.展开更多
The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-seq...The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of syn-chronous generators.Based on the model,the synchronization characteristics of the VSC system under asymmetric grid faults are described,and the interaction mechanisms,as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained.Using the equal area criterion,the influences of sequence control switching action,detection delay,and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed,respectively.In addition,a transient stabil-ity assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed.Finally,the analytical results are validated through simulation and experiments.展开更多
基金the Natural Science of Foundation of Hebei Province(No.F2017506006)
文摘Aiming at the detection failure of strong noise interference in the dual channel of the dual-sequence frequency hopping(DSFH),the scale transformation stochastic resonance(STSR)is applied for the first time,and the output signal to noise ratio(SNR)is raised effectively,at the same time,the symbol reception is completed for DSFH at low input SNR.Firstly,the radio frequency(RF)and intermediate frequency(IF)signals are analyzed based on the super-heterodyne reception of DSFH;secondly,the equations of probability density function(PDF),output power spectrum and SNR of the STSR output are derived for the IF signal;finally,the algorithm of the optimal matching STSR is proposed with the optimal matching parameters.The simulation results show that the algorithm can effectively solve the detection failure,as the global output SNR of DSFH is strongly improved that the output SNR can reach-17.72 d B when the input SNR is-20 d B after the processing of the optimal matching STSR.
基金supported by Quantum Science and Technology-National Science and Technology Major Project (Grant No.2021ZD0300703)。
文摘Quantum secure direct communication(QSDC) promotes high security and instantaneousness in communication by conveying secret messages directly via the quantum channel.In particular,the continuous variable(CV) scheme of QSDC is already compatible with current room-temperature telecommunication networks and is very robust to the free-space background noise,making it a unique choice in certain applications.However,to date,the security proofs of CV-QSDC are poorly advanced,as the eavesdropper Eve in these proofs is limited,either can not apply the optimal collective measurements,or does not have full access to the quantum channel.In this paper,we refine and advance the previous theory in this area,providing a tight secrecy capacity bound for the CV-QSDC protocol.We study the secrecy capacity achievable by the two-step scheme,for both(one-mode) collective Gaussian attack and two-mode Gaussian attack,from the standard Markovian assumption on the environment to a more challenging scenario with a time-like and spatial non-Markovian model.Numerical results show that the best attack strategy for Eve is the entangled attack using maximally entangled states(with a positive correlation parameter).More interestingly,we find that the protocol with the standard Markovian model can,in theory,achieve a longer transmission distance in the communication channel affected by high thermal noise.
基金supported in part by the National Natural Science Foundation of China under Grant 51977019in part by the Joint Research Fund in Smart Grid(U1966208)under cooperative agreement between the National Natural Science Foundation of China and State Grid Corporation of China.
文摘The stability of a voltage source converters(VSC)system based on phase-locked loop(PLL)is very important issue during asymmetric grid faults.This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of syn-chronous generators.Based on the model,the synchronization characteristics of the VSC system under asymmetric grid faults are described,and the interaction mechanisms,as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained.Using the equal area criterion,the influences of sequence control switching action,detection delay,and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed,respectively.In addition,a transient stabil-ity assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed.Finally,the analytical results are validated through simulation and experiments.
