Application Of Rate-adaptive Polar Codes To Continuous Variable Quantum Key Distribution

Quantum computing relies on quantum physics to achieve high rates of computation,and with the development of quantum computing,traditional cryptography is under serious threat.Quantum Key Distribution(QKD)provides unconditional secure keys for communication based on the theoretical support of the laws of quantum physics,and the QKD process does not involve highly complex mathematical operations,and quantum computing does not threaten its security.QKD can be divided into Discrete Variable Quantum Key Distribution(DVQKD)and Continuous Variable Quantum Key Distribution(CVQKD)according to the difference of information code carrier and measurement method.DVQKD has the high cost of quantum state preparation,cumbersome detection process,and short transmission distance.CVQKD can be installed in optical fiber networks,and the system can be connected to existing communication technologies.CVQKD is easy to implement,low in cost and stable in performance,and gradually replaces DVQKD.The performance of CVQKD system is influenced by various aspects,among which the information reconcileation phase has a great impact.In the information reconcileation phase,both communication parties need to rely on the channel coding to correct the errors caused by noise,the error correction capability of the channel coding restricts the efficiency of information reconcileation.Information reconcileation is the key to constrain the performance of QKD system,and as one of the key technologies for information reconcileation,channel coding has attracted much attention.Channel coding with excellent error correction performance,such as LowDensity Parity-Check Code(LDPC)and Polar code can be used for error correction in information reconcileation.Therefore,by improving the error correction capability of channel coding and reducing the complexity of decoding algorithm,the information reconcileation performance can be improved,which in turn improves the performance of the CVQKD system.In order to improve the CVQKD system performance,the main research in this thesis includes,optimizing the inverse multidimensional reconcileation CVQKD system,proposing the system Polar code rate-adaptive CVQKD protocol,and optimizing the code rate-adaptive decoding algorithm.The main works of this paper are as follow.1.The Finite-Dimensional Effect(FDE)of the reverse multidimensional reconcileation CVQKD system causes the performance of the CVQKD system to be overestimated.This paper proposes a correction scheme for the reverse multidimensional reconcileation CVQKD system based on Polar codes by analyzing the FDE.The FDE points out that the virtual channel noise obeys the T-distribution.The information reconcileation is performed after converting the T-distribution to normal distribution through the probability density function of the Tdistribution and the normal distribution;then the required decoding parameters |y| is replaced by using the estimated constants in the decoding stage to correct the overestimated performance while reducing the complexity of the system and the key generation time.2.In order to improve the performance of reverse multidimensional information reconcileation and thus enhance the performance of CVQKD system,this paper proposes the Successive-Cancellation Adaptive(SCA)decoding algorithm for Polar codes.This algorithm improves the information reconcileation efficiency by enhancing the error correction capability of Polar codes,which in turn improves the performance of CVQKD system in terms of security key rate and transmission distance.In addition,this paper optimizes the SCA algorithm by using the two-step encoding scheme of the systematic Polar code to further improve the information reconcileation and CVQKD system performance.3.It is shown that the computational complexity and decoding delay of SCA algorithm increase rapidly with the increase of code length and number of interactions.In this paper,we analyze Partitioned Successive-Cancellation Flip(PSCF)and Partitioned SuccessiveCancellation List(PSCL).Partition technology can effectively reduce the decoding complexity and time delay.In order to reduce the computational complexity,this paper applies partition technology to the SCA algorithm of Polar codes and proposes the Partitioned Successive-Cancellation Adaptive(PSCA)decoding algorithm.The algorithm divides the codeword into multiple partitions according to the estimated channel reliability,and each partition performs the SCA decoding algorithm independently.Simulation results show that the PSCA algorithm successfully reduces the computational complexity and latency of the SCA algorithm.