A Flexible Phase Compensation Method for CVQKD Systems

Abstract

This invention provides a flexible phase compensation method suitable for CVQKD systems, comprising: S1, constructing N random number sequences and M phase drift check sequences at the transmitting end; S2, modulating the M phase drift check sequences; S3, transmitting the modulated M phase drift check sequences through the channel and detecting and acquiring them at the receiving end; S4, applying Wiener filtering to the detection and acquisition results of the M phase drift check sequences; S5, calculating the phase drift value of the Wiener-filtered phase drift check sequences; and S6, compensating the calculated phase drift value onto the corresponding random number sequence. This invention designs multiple sets of shorter check sequences based on the Wiener filtering principle, performs time-domain denoising, and calculates the phase drift value, which can significantly shorten the check sequence length, flexibly adjust the data frame length, and split and combine long and short frames, thereby effectively improving data utilization and obtaining a higher security code rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of CVQKD system, in particular to a flexible phase compensation method suitable for CVQKD system. BACKGROUND

[0002] In modern communication, information security is very important. Quantum secure communication technology based on quantum key distribution (QKD) can establish a secure communication key between the legal communication parties (Alice and Bob), and has theoretical unconditional security, which is an important development direction of secure communication technology. Quantum key distribution can be divided into discrete variable protocol and continuous variable protocol according to the encoding mode. Among them, continuous variable quantum key distribution (CVQKD) has the advantages of high compatibility with classical optical communication industry, good performance of co-fiber transmission with classical signal, high rate in metropolitan area, and the advantage of realizing point-to-multipoint QKD protocol, and is one of the most practical quantum information technologies at present, which has great strategic demand and practical application value.

[0003] However, in the CVQKD system, after the signal light is transmitted through the channel, it is affected by environmental changes, fiber stress, and the asymmetry of the MZ interference optical path, and its phase changes randomly, which is called phase drift. The phase drift will cause a phase difference between the detection result of the signal light at the receiving end and the modulation phase at the sending end, which will lead to the failure of key agreement in the system processing process and the inability to obtain secure and consistent key information. Therefore, it is necessary to compensate for the phase drift of the signal light before data agreement, which is called phase compensation, which can be realized by hardware structure or software design.

[0004] Unlike classical optical communication systems, the signal-to-noise ratio of the CVQKD system is very low, and it is not possible to use a phase-locked loop or other scheme for phase compensation. The commonly used scheme is to use a verification sequence to estimate the phase drift value of the signal light. Specifically, a sinusoidal verification sequence with a fixed frequency is inserted into the signal light sequence, and the phase drift value of the signal light is estimated by the interference result of the verification sequence and the reference light. The typical signal light sequence data frame structure is shown in Figure 1 , and the detection result is shown in Figure 2 , and Figure 2 The sinusoidal wave in the above formula is a verification sequence waveform. From Figure 2It can be seen that the proportional distribution of the check sequence and the random number sequence is close to 1:1, and the effective data utilization rate is only about 50%. The phase compensation is mainly divided into two parts, one part is to estimate the phase drift value, and the other part is phase compensation. After the receiving end detects the check sequence, the estimated phase drift value is calculated by calculating the phase change of the interference waveform. When the interference waveform is a sine wave, the phase drift can be estimated by a time domain autocorrelation calculation method max The scheme needs to traverse the entire measured waveform l, and the obtained p max is compared with the length of the entire measured waveform, and the corresponding phase drift value is obtained.

[0005]

[0006] Therefore, the estimation accuracy of the phase drift value is related to the length l of the check sequence. The longer the length of the check sequence, the more information data point positions it will contain, and the more accurate the phase drift value will be, but at the same time, the effective data utilization rate is reduced. And the design of this scheme cannot flexibly adjust the length of the data frame in time sequence, the check sequence is a single complete sine waveform, which cannot be split and combined, limiting the applicability to different CVQKD systems. In addition, longer check sequences will increase the time for traversal, which will seriously increase the system overhead. Finally, when the noise becomes severe, it will be very difficult to find the peak position, the estimation accuracy will decrease, and the compensation effect will be poor. Therefore, in the CVQKD system, a more flexible phase compensation scheme that can adjust the data frame structure and adapt to severe noise is needed to improve the system performance. SUMMARY

[0007] The present application aims to provide a flexible phase compensation method suitable for CVQKD system, to solve the problem that in the CVQKD system, a more flexible phase compensation scheme that can adjust the data frame structure and adapt to severe noise is needed.

[0008] The present application provides a flexible phase compensation method suitable for CVQKD system, comprising the following steps:

[0009] S1, constructing N random number sequences and M phase drift check sequences at the sending end;

[0010] S2, modulating the M phase drift check sequences;

[0011] S3, after the modulated M phase drift check sequences are transmitted through the channel, they are detected and collected at the receiving end;

[0012] S4, Winer filtering is performed on the detection and collection results of the M phase shift calibration sequences;

[0013] S5, phase shift value calculation is performed on the Winer filtered phase shift calibration sequences;

[0014] S6, the calculated phase shift value is compensated to the corresponding random number sequence.

[0015] Further, in step S1, the method for constructing N random number sequences and M phase shift calibration sequences at the sending end comprises:

[0016] At the sending end, R groups of sequences are constructed as signal light within a communication time T; in each group of sequences, n pulse signals are modulated as a group of random number sequences and m pulse signals are modulated as a group of phase shift calibration sequences according to the protocol requirements, and finally N random number sequences and M phase shift calibration sequences are obtained, i.e. N=n*R and M=m*R.

[0017] Further, for the constructed N random number sequences and M phase shift calibration sequences, Winer filtering principle needs to be performed.

[0018] Further, the method for interleaving comprises:

[0019] After combining multiple groups of repeated phase shift calibration sequences, the multiple groups of random number sequences are interleaved, i.e. N random number sequences and M calibration sequences are interleaved;

[0020] Or,

[0021] The phase shift calibration sequence is interleaved with the random number sequence, i.e. n random number sequences and m phase shift calibration sequences are interleaved.

[0022] Further, in step S2, the method for modulating the M phase shift calibration sequences comprises:

[0023] A phase modulator is used to modulate each group of m phase shift calibration sequences, wherein:

[0024] The amplitude modulation is the same amplitude;

[0025] The phase modulation is 0~2V π The corresponding uniform increasing sequence of voltage values, V π is the half-wave voltage of the phase modulator.

[0026] Further, in step S4, the method for Winer filtering the detection and collection results of the M phase shift calibration sequences comprises:

[0027] The order L of the Winer filter is set, i.e. the number of iterations, and in the iteration, the iteration filtering is performed according to steps S41-S44:

[0028] S41, input the detection and acquisition result x(n) of M phase shift verification sequences, wherein s(n) is a sine verification sequence with phase shift, and v(n) is electrical noise and shot noise in the detection process;

[0029] S42, respectively calculate the autocorrelation coefficients R xx and R vv of x(n) and v(n), wherein R ss is the autocorrelation coefficient of s(n) obtained by subtracting R sx from R ss ; xx vv ;

[0030] S43, calculate the Wiener filter coefficient h

[0031] S44, perform convolution operation on the detection and acquisition result x(n) of M phase shift verification sequences and the Wiener filter coefficient h, to obtain the sine verification sequence y(n) processed by the Wiener filter.

[0032] Further, in step S5, the method for calculating the phase shift value of the Wiener filtered phase shift verification sequence includes an extreme value searching method or an autocorrelation calculation method.

[0033] Further, in step S5, the phase shift value is calculated after interpolation of the Wiener filtered phase shift verification sequence.

[0034] Further, the communication time T, the pulse number m and n, and the group number R are all related to the system repetition frequency, the data amount for system parameter estimation, and the data combination mode, and are adjusted in proportion according to the performance of the actual operation of the system.

[0035] Further, the pulse signal is a coherent state pulse signal, including optical pulse signals generated by an external modulation continuous laser and an internal modulation pulse laser.

[0036] As described above, by adopting the technical solutions, the present application has the following advantages:

[0037] 1. The present application can realize flexible data frame adjustment and long and short frame mixing by processing the verification sequence through the Wiener filter.

[0038] 2. The present application can shorten the length of the verification sequence and effectively improve the data utilization rate by processing the verification sequence through the Wiener filter.

[0039] ​3、The Wiener filtering of the present application has shorter noise tolerance, and can effectively restore the peak and valley positions of the interference waveform under severe noise;

[0040] 4、The Wiener filtering of the present application can realize accelerated operation of Wiener filtering, and effectively reduce system overhead;

[0041] 5、The present application can be directly applied in the existing CVQKD system without changing the hardware design of the system, and has low implementation difficulty. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0043] Figure 1 Schematic diagram for setting the check sequence and the random number sequence for the sending end.

[0044] Figure 2 Schematic diagram for detecting the check sequence and the random number sequence for the receiving end.

[0045] Figure 3 Flowchart of the flexible phase compensation method suitable for the CVQKD system in the embodiments of the present application.

[0046] Figure 4a Schematic diagram of combining the multiple sets of repeated phase drift check sequences and interleaving the multiple sets of random number sequences in the embodiments of the present application.

[0047] Figure 4b Schematic diagram of separately interleaving the phase drift check sequence and the random number sequence in the embodiments of the present application.

[0048] Figure 5 Flowchart of the Wiener filtering in the embodiments of the present application.

[0049] Figure 6 Comparison diagram of the Wiener filtering result and the expected signal in the embodiments of the present application. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0051] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0052] Example

[0053] like Figure 3 As shown, this embodiment proposes a flexible phase compensation method for CVQKD systems with random phase changes that require compensation, including the following steps:

[0054] S1. At the transmitting end, N random number sequences and M phase drift check sequences are constructed. Specifically, at the transmitting end, R sets of sequences are constructed as signal light within a communication time T. In each set of sequences, n pulse signals are modulated as a set of random number sequences according to the protocol requirements, and m pulse signals are modulated as a set of phase drift check sequences, ultimately obtaining N random number sequences and M phase drift check sequences, i.e., N = n*R, M = m*R. In this embodiment, the pulse signals are coherent pulse signals, including optical pulse signals generated by an externally modulated continuous laser and an internally modulated pulse laser. Furthermore, the communication time T, the number of pulses m and n, and the number of groups R are all related to the system repetition frequency, the amount of data used for system parameter estimation, and the data combination method, and are adjusted proportionally according to the actual performance of the system during operation.

[0055] Considering the principle of Wiener filtering, multiple sets of sinusoidal interference waveforms are needed after detection; therefore, the verification sequence needs to be designed as multiple repeating sequences. In the data frame design at the transmitting end, the constructed N random number sequences and M phase drift verification sequences need to be interleaved according to the principle of Wiener filtering. Interleaving methods include:

[0056] like Figure 4a As shown, multiple sets of repeated phase drift check sequences are combined and interspersed with multiple sets of random number sequences, i.e., N random number sequences and M check sequences are interspersed; specifically, r sets are selected from the R sets of sequences and then alternately arranged, as shown in the figure. Among them, S n*r Let S represent a random number sequence of length n*r. m*r This represents a phase drift check sequence of length m*r, where r is an integer less than R, and its value can be chosen considering the applicable scope of the system and the computational complexity.

[0057] or,

[0058] like Figure 4bAs shown, the phase drift verification sequence is interleaved with the random number sequence alone, i.e. n random number sequences and m phase drift verification sequences are interleaved; specifically: n random number sequences and m verification sequences can be alternately arranged in the arrangement order within the communication time T, denoted as wherein S n represents a random number sequence with a length of n, S m represents a phase drift verification sequence with a length of m;

[0059] The verification sequence can be flexibly adjusted according to the use system when designing the verification sequence, and different long and short data frames can be constructed; the verification sequence can also be combined or grouped when collecting the detection results for data processing.

[0060] S2, modulating M phase drift verification sequences; specifically, a phase modulator is used to modulate each group of m phase drift verification sequences, wherein: the amplitude modulation is the same amplitude; the phase modulation is 0~2V π a uniformly increasing sequence of corresponding voltage values, so that a sinusoidal waveform can be obtained based on coherent detection at the receiving end. The modulation process mainly utilizes a phase modulator, and the basic principle is linear electro-optic effect, and the corresponding transfer function is as follows:

[0061]

[0062] wherein Δn eff , l el is the parameter of the crystal inside the phase modulator, V π is the half-wave voltage of the phase modulator. The phase modulator can realize phase modulation of the pulse signal, and can be a modulator modulated according to the system protocol requirement, or a separate modulator independent of the system modulation.

[0063] S3, after the M modulated phase drift verification sequences are transmitted through the channel, detection and collection are performed at the receiving end; the detection and collection can adopt a pulse sampling method, and the pulse sampling method can adopt a peak finding method or a pulse position finding method.

[0064] S4, performing Wiener filtering on the detection and collection results of the M phase drift verification sequences;

[0065] In the Wiener filtering, the input signal x(n) is represented as:

[0066] x(n) = s(n) + v(n)

[0067] wherein s(n) is a useful signal, and v(n) is noise interference;

[0068] The output signal y(n) is an estimation of the useful signal s(n) In the Wiener filtering, let the useful signal s(n) be the expected signal, the observation signal actually output by the Wiener filter, the error is defined as:

[0069]

[0070] The mean square error J is expressed as:

[0071]

[0072] wherein h is the coefficient of the Wiener filter;

[0073] When the mean square error J takes the minimum value J min , at this time the Wiener filtering effect is the best.

[0074] Therefore, in the CVQKD system, the detection and collection results of the M phase shift calibration sequences are subjected to the Wiener filtering, specifically, the order L of the Wiener filter is set, that is, the number of iterations, and the iteration filtering is performed according to steps S41-S44, as shown in the following figure: Figure 5

[0075] S41, input the detection and collection results x(n) = s(n) + v(n) of the M phase shift calibration sequences, wherein s(n) is a sinusoidal calibration sequence with phase shift; v(n) is the electrical noise and shot noise in the detection process, and the statistical characteristics can be measured in advance;

[0076] S42, respectively calculate the autocorrelation coefficients R xx and R vv of x(n) and v(n), since x(n) and v(n) are independent of each other, the autocorrelation coefficient R ss of s(n) is obtained by subtracting the two, the cross-correlation coefficient R sx of the expected signal s(n) and x(n) is calculated as R ss = R xx -R vv ;

[0077] S43, calculate the Wiener filter coefficient At this time, the coefficient h of the Wiener filter can make the mean square error J of the signal be the minimum value, and the main principle is based on the solution of the Wiener-Hoff equation.

[0078] S44, perform convolution operation on the detection and collection results x(n) of the M phase shift calibration sequences and the Wiener filter coefficient h, to obtain the sinusoidal calibration sequence y(n) subjected to the Wiener filtering.

[0079] ​The above-mentioned Wiener filtering function can be completed by programming, and can be realized by MATLAB or C language. Through the above steps, the denoised check sequence can be obtained, and the filtering effect is as shown in Figure 6 It can be seen that the waveform after Wiener filtering obviously maintains the positions of the peaks and valleys of the expected signal, which is beneficial to the estimation of the high-precision phase drift value.

[0080] S5, phase drift value calculation is performed on the phase drift check sequence after Wiener filtering; specifically, the check sequence after the order L of the Wiener filter is taken to perform phase drift value calculation, that is, the L+1 to M pulse signals in the check sequence are considered, and the check sequence before the order L is discarded because it has been iterated for many times and the recovery effect is poor; further, interpolation is performed on the phase drift check sequence after Wiener filtering, and then phase drift value calculation is performed, so as to further improve the calculation precision. In the embodiment, the method for calculating the phase drift value includes an extreme value finding method or an autocorrelation calculation method.

[0081] S6, the calculated phase drift value is compensated to the corresponding random number sequence.

[0082] The above-mentioned only for the preferred embodiments of the present application, and does not limit the present application, for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A flexible phase compensation method suitable for a CVQKD system, characterized in that, The method comprises the following steps: S1, constructing N random number sequences and M phase shift check sequences at a sending end; S2, modulating the M phase shift check sequences; S3, transmitting the modulated M phase shift check sequences through a channel, and detecting and collecting the M phase shift check sequences at a receiving end; S4, performing Wiener filtering on the detection and collection results of the M phase shift check sequences; S5, calculating phase shift values of the Wiener filtered phase shift check sequences; S6, compensating the calculated phase shift values to corresponding random number sequences; The method of performing Wiener filtering on the detection and collection results of the M phase shift check sequences in step S4 comprises: Setting the order L of the Wiener filter, i.e. the number of iterations, and performing iterative filtering according to steps S41-S44 in the iteration: S41, inputting the detection and collection results x(n) of the M phase shift check sequences, wherein s(n) is a sinusoidal check sequence with phase shift, and v(n) is electrical noise and shot noise in the detection process; S42, the autocorrelation coefficients R of x(n) and v(b) are calculated respectively xx and R vv Since x(n) and v(n) are independent of each other, the autocorrelation coefficients R of s(n) are obtained by subtracting the two ss The cross-correlation coefficients R of the expected signal s(n) and x(n) are calculated sx = R ss = R xx -R vv ; S43, calculate the wiener filter coefficients S44, performing convolution operation on the detection and collection results x(n) of the M phase shift check sequences and the Wiener filter coefficient h to obtain the sinusoidal check sequence y(n) processed by the Wiener filtering.

2. The flexible phase compensation method suitable for CVQKD system according to claim 1, characterized in that, The method of constructing N random number sequences and M phase shift check sequences at the sending end in step S1 comprises: At the sending end, constructing R groups of sequences as signal light in a communication time T; in each group of sequences, modulating n pulse signals as a group of random number sequences and modulating m pulse signals as a group of phase shift check sequences according to a protocol requirement, and finally obtaining N random number sequences and M phase shift check sequences, i.e. N=n*R and M=m*R.

3. The flexible phase compensation method suitable for CVQKD system according to claim 2, characterized in that, The N random number sequences and the M phase shift check sequences need to be interleaved according to the principle of Wiener filtering.

4. The flexible phase compensation method suitable for CVQKD system according to claim 3, characterized in that, The interleaving method comprises: Combining multiple groups of repeated phase shift check sequences and interleaving the multiple groups of random number sequences, i.e. interleaving N random number sequences and M check sequences; Or, Interleaving the phase shift check sequences and the random number sequences separately, i.e. interleaving n random number sequences and m phase shift check sequences.

5. The flexible phase compensation method suitable for CVQKD system according to claim 2, characterized in that, The method of modulating the M phase shift check sequences in step S2 comprises: Modulating each group of m phase shift check sequences by using a phase modulator, wherein: The amplitude modulation is the same amplitude; Phase modulation is 0-2V π A uniform increasing sequence of corresponding voltage values, V π is the half-wave voltage of the phase modulator.

6. The flexible phase compensation method suitable for CVQKD system according to claim 1, characterized in that, The method of calculating phase shift values of the Wiener filtered phase shift check sequences in step S5 comprises an extreme value finding method or an autocorrelation calculation method.

7. The flexible phase compensation method suitable for CVQKD system according to claim 6, characterized in that, The method of calculating phase shift values of the Wiener filtered phase shift check sequences in step S5 comprises an extreme value finding method or an autocorrelation calculation method.

8. The flexible phase compensation method suitable for CVQKD system according to claim 2, characterized in that, The method of calculating phase shift values of the Wiener filtered phase shift check sequences in step S5 comprises an extreme value finding method or an autocorrelation calculation method.

9. The flexible phase compensation method suitable for CVQKD system according to claim 2, characterized in that, The communication time T, the pulse numbers m and n, and the grouping number R are all related to the system repetition frequency, the data amount for system parameter estimation, and the data combination mode, and are adjusted in proportion according to the performance of the actual system operation. The pulse signal is a coherent state pulse signal, and the pulse signal is generated by an external modulation continuous laser and an internal modulation pulse laser.

Images