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IEEE photonics journal

High-Speed Reconciliation for CVQKD Based on Spatially Coupled LDPC Codes

Xueqin Jiang, Siyuan Yang, Peng Huang, Guihua Zeng

Published Jul 11, 2018• 19 citations
Publisher

Abstract

The speed of continuous variable quantum key distribution is limited by the reconciliation efficiency and the reconciliation frame error rate (FER) in the reconciliation phase. In this paper, we propose an approach that may increase the reconciliation efficiency and decrease the FER. In detail, to increase the reconciliation efficiency, rather than using the block low-density parity-check (LDPC) codes, such as quasi-cyclic LDPC codes, multiedge-type LDPC codes, and punctured LDPC codes, this paper introduces spatially coupled (SC) LDPC codes to the reconciliation phase. To decrease the FER, we propose a new reconciliation scheme based on the special structure of SC-LDPC codes. To demonstrate the performance of the proposed approach, we construct the SC-LDPC codes based on quasi-cyclic repeat-accumulate codes. It is shown that the proposed scheme leads to higher reconciliation speed than that of the previous reconciliation schemes.

DOI
10.1109/jphot.2018.2853736

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The speed of continuous variable quantum key distribution is limited by the reconciliation efficiency and the reconciliation frame error rate (FER) in the reconciliation phase. In this paper, we propose an approach that may increase the reconciliation efficiency and decrease the FER. In detail, to increase the reconciliation efficiency, rather than using the block low-density parity-check (LDPC) codes, such as quasi-cyclic LDPC codes, multiedge-type LDPC codes, and punctured LDPC codes, this paper introduces spatially coupled (SC) LDPC codes to the reconciliation phase. To decrease the FER, we propose a new reconciliation scheme based on the special structure of SC-LDPC codes. To demonstrate the performance of the proposed approach, we construct the SC-LDPC codes based on quasi-cyclic repeat-accumulate codes. It is shown that the proposed scheme leads to higher reconciliation speed than that of the previous reconciliation schemes.
Due to the rapid development of quantum computing technology, encryption systems based on computational complexity are facing serious threats. Based on the fundamental theorem of quantum mechanics, continuous-variable quantum key distribution (CVQKD) has the property of physical absolute security and can effectively overcome the dependence of the current encryption system on the computational complexity. In this paper, we construct the spatially coupled (SC)-low-density parity-check (LDPC) codes and quasi-cyclic (QC)-LDPC codes by adopting the parity-check matrices of LDPC codes in the Advanced Television Systems Committee (ATSC) 3.0 standard as base matrices and introduce these codes for information reconciliation in the CVQKD system in order to improve the performance of reconciliation efficiency, and then make further improvements to final secret key rate and transmission distance. Simulation results show that the proposed LDPC codes can achieve reconciliation efficiency of higher than 0.96. Moreover, we can obtain a high final secret key rate and a long transmission distance through using our proposed LDPC codes for information reconciliation.
The information reconciliation (IR) stage is a critical component of post-processing in continuous-variable quantum key distribution (CV-QKD), which is essential to ensure high secret key rates and long transmission distances. Currently, improving reconciliation efficiency is a key research focus in the CV-QKD field. Additionally, the low-density parity-check (LDPC) decoding speed in IR is a post-processing bottleneck in high-speed CV-QKD. In this paper, we propose a construction scheme for spatially coupled (SC) LDPC codes in CV-QKD systems and maintain a constant code rate when extending the code length as required. Furthermore, we investigate the relationship between the syndrome variation pattern (SVP) and the frame error rate. Adaptively adjusting the number of decoding iterations according to the distinct convergence behaviors of the SVP, the convergence-based early termination (C-ET) scheme is proposed, which can reduce invalid iterations. The simulation results show that the proposed construction scheme for SC-LDPC codes can improve the reconciliation efficiency to 97% and achieve a flexible code length. The C-ET scheme achieves a 292% improvement in information throughput compared to the original ET scheme when the reconciliation efficiency reaches 97%. Moreover, the C-ET scheme also achieves a reduction in decoding latency compared to the existing syndrome-based early termination scheme. These advances provide a substantial step toward improving reconciliation efficiency and breaking the post-processing bottleneck in CV-QKD systems.
Seeking good error correcting codes to improve the efficiency of continuous-variable quantum key distribution (CVQKD) reconciliation is a concerning issue. Due to the introduction of multidimensional reconciliation, the error correcting techniques in the classical binary-input additive white Gaussian noise channel are applicable to CVQKD. In this Letter, we apply the quasi-cyclic low-density parity-check (QC-LDPC) codes, which are specified in 5G protocol, to the reconciliation process. Simulation results show that the reconciliation efficiency can reach 92.6% when the code rate is 22/68 and the signal-to-noise ratio is 0.623. Such a new error correcting code points out a new direction for the development of CVQKD.
Reconciliation is a necessary step in postprocessing of continuous-variable quantum key distribution (CV-QKD) system. We use globally coupled low-density parity-check (GC-LDPC) codes in reconciliation to extract a precise secret key from the raw keys over the authenticated classical public channel between two users. GC-LDPC codes have excellent performance over both the additive Gaussian white noise and binary-erasure channels. The reconciliation based on GC-LDPC codes can improve the reconciliation efficiency to 95.42% and reduce the frame error rate to 3.25 × 10–3. Using distillation, the decoding speed can achieve 23.8 Mbits/s and decrease the cost of memory. Given decoding speed and low memory usage, this makes the proposed reconciliation method viable approach for high-speed CV-QKD system.
In continuous-variable (CV) quantum key distribution (QKD), the reconciliation efficiency and frame error rate of the information reconciliation have a significant impact on the secret key rate. For a fixed-rate multiedge-type low-density parity-check (LDPC) code, the reconciliation efficiency and frame error rate will inevitably vary due to the fluctuations of the signal-to-noise ratio (SNR) of the CV QKD system, which degrades the performance of the system. We propose a high-efficiency rate-adaptive information reconciliation scheme by combining raptorlike (RL) LDPC codes with the addition of trusted noises. We establish the model of adding trusted noises and combine it with the RL LDPC codes to optimize the secret key rate under the time-varying channel. The simulation results show that our scheme can maintain a high reconciliation efficiency of more than 94.4% and a low frame error rate within 15% fluctuation range of the SNR. Furthermore, we implement the hardware acceleration of the proposed rate-adaptive scheme on a graphics processing unit and achieve a decoding throughput of 65.5 Mbits/s by optimizing the storage of the parity-check matrix. Our results are useful for the practical CV QKD under the realistic time-varying channel.
Information reconciliation in the continuousvariable quantum key distribution (CVQKD) plays a vital role on affecting secret key rate as well as maximum transmission distance. It is necessary to search good error-correcting codes in order to improve the performance of reconciliation efficiency. In this work, we construct Quasi-Cyclic (QC) low-density paritycheck (LDPC) codes based on LDPC codes in the digital video broadcasting second generation terrestrial (DVB-T2) standard, and then combine these codes with information reconciliation in the CVQKD system, which can extremely ameliorate the performance of secret key rate and maximum transmission distance. The simulation results show that our proposed QC-LDPC codes can achieve higher reconciliation efficiency of 93.05% compare to DVB-T2 LDPC codes, which means our proposed QC-LDPC codes can obtain better performance of secret key rate and longer maximum transmission distance.