CN113660075B - Non-homologous local oscillation light continuous variable quantum key distribution bit frame synchronization method and system - Google Patents
Non-homologous local oscillation light continuous variable quantum key distribution bit frame synchronization method and system Download PDFInfo
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Abstract
The invention provides a non-homologous local oscillator light continuous variable quantum key distribution bit frame synchronization method and a system, wherein the method comprises the following steps: step S1: firstly, constructing a constant envelope zero autocorrelation sequence, then constructing a key data sequence obeying Gaussian distribution, and finally, inserting a pilot sequence into the sequence to form an anti-phase-change synchronous frame; step S2: firstly, carrying out phase recovery on a received frame based on pilot signal phase information, then carrying out data frame head searching through a constant envelope zero autocorrelation sequence, and determining a data start bit. The invention combines the constant envelope zero autocorrelation sequence with the pilot signal, which not only can overcome the phase change caused by non-homologous local oscillation frequency offset and channel phase drift, but also can realize the bit frame synchronization of data under low signal to noise ratio, and only needs to change the data frame structure when actually realizing, thereby being beneficial to the realization of the non-homologous local oscillation light continuous variable quantum key distribution system.
Description
Technical Field
The invention relates to the technical field of computer information, in particular to a non-homologous local oscillator light continuous variable quantum key distribution bit frame synchronization method and a system, and especially relates to a non-homologous local oscillator light continuous variable quantum key distribution bit frame synchronization method.
Background
After the human society enters the 21 st century, information technology has rapidly developed, and various fields in the society also enter a new digital stage depending on the information technology. However, since fields such as finance and military have extremely high requirements on information security, ensuring that communications have as high security as possible is a very important study.
In recent years, quantum communication gradually entering the field of view of the public has extremely high communication security, and quantum key distribution is a key link for guaranteeing the communication security. The continuous variable quantum key distribution belongs to the category of quantum key distribution, and has the characteristics of easy integration into a classical optical communication system, easy acquisition of a laser source and the like, so that the continuous variable quantum key distribution is widely focused.
The widely used solution of continuous variable quantum key distribution is gaussian modulation continuous variable quantum key distribution, namely GG02 protocol, proposed by f.grosshans and p.grangier in 2002. The original scheme for realizing Gaussian modulation continuous variable quantum key distribution is a homologous local oscillation optical scheme, namely, signal light and local oscillation light are generated from a legal transmitting end and are transmitted to a legal receiving end together. However, the homologous local oscillation optical scheme has a certain weakness: the local oscillation light of the device can be manipulated by an eavesdropper, so that the actual security is threatened; and the local oscillation light and the signal light have great power difference, so that the signal light can be interfered, the communication performance is reduced, and the complexity of the system is improved. In 2015, a non-homologous local oscillator optical scheme is proposed, and the scheme can better overcome the weakness of the homologous local oscillator optical scheme. The non-homologous local oscillation optical scheme is to use a light source to generate local oscillation light at the receiving end and transmit the local oscillation light and the signal light separately. Although the non-homologous local oscillator optical scheme can overcome the weakness of the homologous local oscillator optical scheme, it has the following drawbacks: because the local oscillation light and the signal light are not homologous, in the two light paths in the transmission process, the local oscillation light and the signal light have different degrees of phase drift and frequency offset. The phase shift and frequency shift generated in this case cause phase change, resulting in serious influence on the bit frame synchronization effect after coherent detection. Therefore, a bit frame synchronization scheme is designed aiming at non-homologous local oscillation light continuous variable quantum key distribution, so that a legal transceiver is guaranteed to realize bit frame synchronization.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a non-homologous local oscillation optical continuous variable quantum key distribution bit frame synchronization method.
The invention provides a non-homologous local oscillation optical continuous variable quantum key distribution bit frame synchronization method, which comprises the following steps:
step S1: firstly, constructing a constant envelope zero autocorrelation sequence, then constructing a key data sequence obeying Gaussian distribution, and finally, inserting a pilot sequence into the sequence to form an anti-phase-change synchronous frame;
step S2: firstly, carrying out phase recovery on a received frame based on pilot signal phase information, then carrying out data frame head searching through a constant envelope zero autocorrelation sequence, and determining a data start bit.
Preferably, the step S1 includes the steps of:
step S1.1: constructing a section of constant envelope zero autocorrelation sequence, and setting the sequence length according to different transmission distances;
step S1.2: constructing a Gaussian modulation data sequence, and generating by using a random number generator;
step S1.3: a pilot sequence is constructed that carries the determined initial phase information.
Preferably, the step S2 includes the steps of:
step S2.1: the receiver firstly distinguishes the pilot frequency position and the data position according to the power size, and then recovers the synchronous frame and the data frame by utilizing the phase information carried by the pilot frequency signal after the change;
step S2.2: and carrying out cross-correlation calculation on the synchronous frame and the data frame by using the same constant-envelope self-zero correlation sequence, and judging the current pulse signal as the starting position of the data if and only if correlation peaks appear in the correlation calculation.
Preferably, the constant envelope zero autocorrelation sequence is:
where r is the root index of the zero auto-correlation sequence, r e { 1., (N.) zc -1); n is the position index of the sequence, N e { 1.. zc }；N zc Is the length of a constant envelope zero autocorrelation sequence; z r [n]Position in zero auto-correlation sequenceA specific numerical value of n; exp represents an exponential function with the natural constant e as a base; i is an imaginary unit.
Preferably, the gaussian data sequence is:
g[n]＝x n +ip n
wherein x is n And p n The regular position and the regular momentum, respectively representing the continuous variable, are all subject to Gaussian distribution, i.e. x n ，p n ～N(0，V A )，V A Modulating variance for the signal; g [ n ]]As the complex amplitude of the continuous variable, N is the position index of the gaussian data sequence, N is ∈1, N data N, where N data Is the length of the Gaussian data sequence; i is an imaginary unit.
Preferably, the pilot sequence is:
wherein θ is 0 Is a fixed phase value, e is a natural constant, p [ n ]]A specific value representing a position index N in the pilot sequence, N e { 1.. zc +N data }。
Preferably, the anti-phase change frame structure is:
[p[1]，z r [1]，p[2]，z r [2]，…，p[N zc ]，z r [N zc ]，p[N zc +1]，g[1]，…，p[N zc +N data ]，g[N data ]]
wherein pi is]A specific numerical value with a position index of i in the pilot sequence; z r [i]A specific value with a position index i in the zero auto-correlation sequence; g [ i ]]Is a specific value of i at the position index in the gaussian data sequence.
Preferably, if the variance of the odd-numbered sequence data is greater than the variance of the even-numbered sequence data, the odd-numbered sequence is a pilot signal existence position, and the even-numbered sequence is a data signal existence position; otherwise, the odd sequence is the data signal existence position, and the even sequence is the pilot signal existence position.
Preferably, the pilot signal phase information recovery process is:
wherein g [ i ]]Is a specific value of position index i in Gaussian sequence, g [ i ]]' is a specific value after the corresponding Gaussian sequence is recovered, pi+N zc ]i+N for the corresponding pilot sequence position index zc Specific values of (2); z r [i]Z is a specific value of i in the position index in the Gaussian sequence r [i]' is a specific value after the corresponding Gaussian sequence is recovered, pi [ i ]]A specific numerical value with a position index of i in a corresponding pilot sequence;
will recover the resulting z r [n]' and g [ n ]]' combining results in a recovery sequence y [ n ]]＝[z r [n]′，g[n]′]；
The data frame header y [ n ] searching cross-correlation algorithm is as follows:
c[n]′＝cov(y[n]，z r [n])
wherein c [ n ]]' is a specific value with a position index of n in the cross-correlation calculation result, y [ n ]]To recover a particular value of position index n in the sequence, z r [n]A specific value of n for the position index in the zero auto-correlation sequence; cov is a cross-correlation calculation of two sequences: y [ n ]]And z r [n]After the cross-correlation operation, z is calculated r [n]One bit back from y [ n ]]Performing cross-correlation operation on the second repetition of the number of the pairs, and continuing to perform z after the operation is completed r [n]Shift backward and operate until y [ n ]]The last bit of (2) is c [ n ] obtained by each operation]' forming a sequence of correlation values; the index bit corresponding to the maximum correlation peak value in the obtained correlation value sequence is the initial bit of the constant envelope frame, and then N is added zc The sequence length is the start bit of the data frame.
The invention also provides a non-homologous local oscillator light continuous variable quantum key distribution bit frame synchronization system, which comprises the following modules:
module M1: firstly, constructing a constant envelope zero autocorrelation sequence, then constructing a key data sequence obeying Gaussian distribution, and finally, inserting a pilot sequence into the sequence to form an anti-phase-change synchronous frame;
module M2: firstly, carrying out phase recovery on a received frame based on pilot signal phase information, then carrying out data frame head searching through a constant envelope zero autocorrelation sequence, and determining a data start bit;
the module M1 comprises the following modules:
module M1.1: constructing a section of constant envelope zero autocorrelation sequence, and setting the sequence length according to different transmission distances;
module M1.2: constructing a Gaussian modulation data sequence, and generating by using a random number generator;
module M1.3: constructing a pilot sequence, wherein the pilot sequence carries determined initial phase information;
the step S2 includes the following modules:
module M2.1: the receiver firstly distinguishes the pilot frequency position and the data position according to the power size, and then recovers the synchronous frame and the data frame by utilizing the phase information carried by the pilot frequency signal after the change;
module M2.2: and carrying out cross-correlation calculation on the synchronous frame and the data frame by using the same constant-envelope self-zero correlation sequence, and judging the current pulse signal as the starting position of the data if and only if correlation peaks appear in the correlation calculation.
Compared with the prior art, the invention has the following beneficial effects:
1. the bit frame synchronization method provided by the invention applies the pilot signal, is beneficial to overcoming the phase change problem caused by phase drift and frequency offset generated by non-homology of local oscillation light and signal light in a non-homologous local oscillation light continuous variable subkey distribution system, and can immediately complete phase compensation;
2. the invention also has the advantage of flexible use, and the synchronous training sequence formed by the constant envelope zero autocorrelation sequence can carry out bit number adjustment according to the actual communication requirement;
3. the invention has better synchronization effect under the condition of low signal-to-noise ratio.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
fig. 1 is a schematic diagram of frame synchronization based on a constant envelope zero autocorrelation sequence used in a non-homologous local oscillation optical continuous variable quantum key distribution scheme of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
Referring to fig. 1, the invention provides a non-homologous local oscillation optical continuous variable quantum key distribution bit frame synchronization method, which comprises the following steps:
step S1: constructing a phase-change-resistant synchronous frame: firstly, constructing a constant envelope zero autocorrelation sequence, then constructing a key data sequence obeying Gaussian distribution, and finally, inserting a pilot sequence into the sequence to form an anti-phase-change synchronous frame; step S1.1: constructing a section of constant envelope zero autocorrelation sequence, and setting the sequence length according to different transmission distances; step S1.2: constructing a Gaussian modulation data sequence, and generating by using a random number generator; step S1.3: a pilot sequence is constructed that carries the determined initial phase information.
Step S2: searching a data start bit: firstly, carrying out phase recovery on a received frame based on pilot signal phase information, then carrying out data frame head searching through a constant envelope zero autocorrelation sequence, and determining a data start bit; step S2.1: the receiver firstly distinguishes the pilot frequency position and the data position according to the power size, and then recovers the synchronous frame and the data frame by utilizing the phase information carried by the pilot frequency signal after the change; step S2.2: the same constant-envelope self-zero correlation sequence is used for carrying out cross-correlation calculation on the synchronous frame and the data frame, and if and only if correlation peak appears in the correlation calculation, the current pulse signal can be judged to be the starting position of the data.
The continuous variable is a signal which is continuously valued and is adopted by the key distribution system; the constant envelope zero autocorrelation sequence is a frame synchronization and autocorrelation effect ideal sequence with special structure; the correlation operation is a mathematical cross-correlation operation of the local data and the received data.
The constant envelope zero autocorrelation sequence is:
where r is the root index of the zero auto-correlation sequence, r e { 1., (N.) zc -1); n is the position index of the sequence, N e { 1.. zc }；N zc Is the length of a constant envelope zero autocorrelation sequence; z r [n]A specific value of n for the position index in the zero auto-correlation sequence; exp represents an exponential function with the natural constant e as a base; i is an imaginary unit.
The gaussian data sequence is:
g[n]＝x n +ip n
wherein x is n And p n The regular position and the regular momentum, respectively representing the continuous variable, are all subject to Gaussian distribution, i.e. x n ，p n ～N(0，V A )，V A Modulating variance for the signal; g [ n ]]As the complex amplitude of the continuous variable, N is the position index of the gaussian data sequence, N is ∈1, N data N, where N data Is the length of the Gaussian data sequence; i is an imaginary unit.
The pilot sequence is:
wherein θ is 0 Is a fixed phase value, e is a natural constant, p [ n ]]A specific value representing a position index N in the pilot sequence, N e { 1.. zc +N data }。
The phase-change resistant frame structure is as follows:
[p[1]，z r [1]，p[2]，z r [2]，…，p[N zc ]，z r [N zc ]，p[N zc +1]，g[1]，…，p[N zc +N data ]，g[N data ]]
wherein pi is]A specific numerical value with a position index of i in the pilot sequence; z r [i]A specific value with a position index i in the zero auto-correlation sequence; g [ i ]]Is a specific value of i at the position index in the gaussian data sequence.
If the variance of the odd-numbered sequence data is larger than the variance of the even-numbered sequence data, the odd-numbered sequence is the pilot signal existence position, and the even-numbered sequence is the data signal existence position; otherwise, the odd sequence is the data signal existence position, and the even sequence is the pilot signal existence position.
The pilot signal phase information recovery process is:
wherein g [ i ]]Is a specific value of position index i in Gaussian sequence, g [ i ]]' is a specific value after the corresponding Gaussian sequence is recovered, pi+N zc ]i+N for the corresponding pilot sequence position index zc Specific values of (2); z r [i]Z is a specific value of i in the position index in the Gaussian sequence r [i]' is a specific value after the corresponding Gaussian sequence is recovered, pi [ i ]]Is a specific value for i, which is the position index in the corresponding pilot sequence.
Will recover the resulting z r [n]' and g [ n ]]' combining results in a recovery sequence y [ n ]]＝[z r [n]′，g[n]′]。
The data frame header y [ n ] looks up the cross-correlation algorithm as follows:
c[n]′＝cov(y[n]，z r [n])
wherein c [ n ]]' is a specific value with a position index of n in the cross-correlation calculation result, y [ n ]]To recover a particular value of position index n in the sequence, z r [n]A specific value of n for the position index in the zero auto-correlation sequence; cov is a cross-correlation calculation of two sequences: y [ n ]]And z r [n]After the cross-correlation operation, z is calculated r [n]One bit back from y [ n ]]Performing cross-correlation operation on the second repetition of the number of the pairs, and continuing to perform z after the operation is completed r [n]Shift backward and operate until y [ n ]]The last bit of (2) is c [ n ] obtained by each operation]' form a sequence of correlation values. The index bit corresponding to the maximum correlation peak value in the obtained correlation value sequence is the initial bit of the constant envelope frame, and then N is added zc The sequence length is the start bit of the data frame.
The invention designs an anti-phase bit frame synchronization scheme for synchronizing a constant envelope zero autocorrelation sequence and a pilot sequence, so as to complete the bit frame synchronization step of a quantum key distribution system, solve the problem of phase drift and frequency offset caused by different local oscillator light and signal light sources in a non-homologous local oscillator light scheme, and have a better bit frame synchronization effect under a low signal to noise ratio.
The whole frame mainly comprises three parts, namely: pilot sequence, constant envelope zero autocorrelation sequence, gaussian modulation data sequence. Because the constant-envelope zero-autocorrelation sequence has the advantages of unlimited length, good correlation performance, stability and the like, the constant-envelope zero-autocorrelation sequence is adopted as a synchronous training sequence in the invention (D.Chu, polyphase codes with good periodic correlation properties, IEEE Transactions on Information Theory, vol.18, no.4, pp.531-532, july 1972). The synchronous frame formed by constant envelope zero autocorrelation sequence is near the first half of the frame head; the data frame formed by Gaussian modulation data sequences is placed in the latter half; the pilot sequence interval is interspersed throughout the frame to recover phase changes of the sync frame and the data frame. The length of the sequence can be adjusted according to the actual communication condition.
The operation steps of the invention are as follows:
and constructing a communication frame. The synchronous frame is generated according to the expression of the constant envelope zero autocorrelation sequence, and the length of the frame is set according to the transmission distance; the Gaussian modulation data sequence in the data frame is generated by a random number generator; the pilot sequence carries information of an initial phase angle to recover phase change generated after the pilot sequence passes through a channel.
The phase change recovery is performed on the communication frame using the pilot sequence. Setting a power judgment scheme, designing the variance of pilot frequency sequence data into a numerical value with larger phase difference with a synchronous frame and a data frame, so that a legal receiving end Bob can judge according to the variance numerical value, and distinguishing pilot frequency from other sequences; and simultaneously, the phase information of the pilot frequency is used for recovering the phases of the synchronous frame and the data frame.
The start bit of the data is determined. After the phase compensated synchronous frame and the data frame are obtained, the cross-correlation calculation is carried out on the constant-envelope zero self-correlation sequence generated previously, the synchronous frame and the data frame, the cross-correlation calculation is carried out repeatedly by shifting the constant-envelope zero self-correlation sequence to the right one bit, and then the repeated operation is shifted backwards until the last bit of the synchronous frame and the data frame is reached, and the correlation value sequence is obtained. The position where the correlation peak appears in the correlation value sequence is calculated to be the starting position of the synchronous frame, the starting position of the data frame is obtained by adding the synchronous frame length, and the bit frame synchronization is realized.
Adopting ZadoffChu sequence in constant envelope zero autocorrelation sequence; in a non-homologous local oscillation light continuous variable quantum key distribution system, a legal sender Alice prepares signal light: the laser produces a beam that passes through an optical attenuator and is gaussian modulated. According to the formulaAnd preparing pilot frequency, and modulating a pilot frequency sequence to the signal light with stronger power. Likewise, according to the expression +.>Preparing an autocorrelation sequence carrying constant envelope zero, and modulating sequence information onto an optical signal, wherein the power of the optical signal is the same as that of signal light; wherein z is r [n]To generate constant envelope zero auto-correlation sequence, N ZC Is the length of the constant envelope zero autocorrelation sequence, and the value of n is0，1......，N zc -1，r∈{1，...，(N zc -1) is the root index of the constant envelope zero autocorrelation sequence, assuming in this example that the length of the sequence is 1000. Each pilot is then inserted between each synchronization frame and data frame and transmitted in the channel in accordance with the structure of the communication frame in fig. 1.
After the channel, the legal receiver Bob receives the optical signal, and the position of the pilot frequency and the positions of the synchronous frame and the data frame are distinguished by judging the power of the optical signal. Because the non-homologous local oscillation optical scheme can introduce phase change, after the corresponding position of each data is obtained, the pilot frequency of the previous bit is needed to be used for carrying out phase recovery on the synchronous frame or the data frame of the next bit, and the phase recovery formula of the Gaussian modulation data is as followsThe phase recovery formula of the constant envelope zero autocorrelation sequence is +.> Will recover good z r [n]' and g [ n ]]' New sequence y [ n ] is formed]＝[z r [n]′，g[n]′]Using previously generated z r [n]The sequence and the sequence are subjected to cross-correlation calculation, and z is calculated after calculation r [n]The sequence is shifted one bit back and then with y [ n ]]Performing cross-correlation calculation, shifting one bit after the calculation is finished, and repeating the previous process until z r [n]The sequence moves to y [ n ]]And a correlation value sequence consisting of all the cross-correlation calculation results is obtained. The only correlation peak in the correlation value sequence is the start bit of the sync frame, in this example, the sync frame length is 1000, so that the start bit of the gaussian modulation data can be determined to be 1001, and synchronization can be realized.
The invention also provides a non-homologous local oscillation light continuous variable quantum key distribution bit frame synchronization system, which comprises the following modules:
module M1: firstly, constructing a constant envelope zero autocorrelation sequence, then constructing a key data sequence obeying Gaussian distribution, and finally, inserting a pilot sequence into the sequence to form an anti-phase-change synchronous frame; module M1.1: constructing a section of constant envelope zero autocorrelation sequence, and setting the sequence length according to different transmission distances; module M1.2: constructing a Gaussian modulation data sequence, and generating by using a random number generator; module M1.3: a pilot sequence is constructed that carries the determined initial phase information.
Module M2: firstly, carrying out phase recovery on a received frame based on pilot signal phase information, then carrying out data frame head searching through a constant envelope zero autocorrelation sequence, and determining a data start bit; module M2.1: the receiver firstly distinguishes the pilot frequency position and the data position according to the power size, and then recovers the synchronous frame and the data frame by utilizing the phase information carried by the pilot frequency signal after the change; module M2.2: and carrying out cross-correlation calculation on the synchronous frame and the data frame by using the same constant-envelope self-zero correlation sequence, and judging the current pulse signal as the starting position of the data if and only if correlation peaks appear in the correlation calculation.
The bit frame synchronization method provided by the invention applies the pilot signal, is beneficial to overcoming the phase change problem caused by phase drift and frequency offset generated by non-homology of local oscillation light and signal light in a non-homologous local oscillation light continuous variable subkey distribution system, and can immediately complete phase compensation; the method has the advantage of flexible use, and the synchronous training sequence formed by the constant envelope zero autocorrelation sequence can be subjected to bit number adjustment according to the actual communication requirement; the method has better synchronization effect under the condition of low signal-to-noise ratio.
Those skilled in the art will appreciate that the invention provides a system and its individual devices, modules, units, etc. that can be implemented entirely by logic programming of method steps, in addition to being implemented as pure computer readable program code, in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc. Therefore, the system and various devices, modules and units thereof provided by the invention can be regarded as a hardware component, and the devices, modules and units for realizing various functions included in the system can also be regarded as structures in the hardware component; means, modules, and units for implementing the various functions may also be considered as either software modules for implementing the methods or structures within hardware components.
The foregoing describes specific embodiments of the present invention. It is to be understood that the invention is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily without conflict.
Claims (10)
1. The non-homologous local oscillation optical continuous variable quantum key distribution bit frame synchronization method is characterized by comprising the following steps of:
step S1: firstly, constructing a constant-envelope zero autocorrelation sequence, then constructing a key data sequence obeying Gaussian distribution, and finally, inserting a pilot sequence into the constant-envelope zero autocorrelation sequence and the key data sequence obeying Gaussian distribution to form an anti-phase-change synchronous frame;
step S2: firstly, carrying out phase recovery on a received frame based on pilot signal phase information, then carrying out data frame head searching through a constant envelope zero autocorrelation sequence, and determining a data start bit.
2. The method for synchronizing the bit frames for distributing the non-homologous local oscillation optical continuous variable quantum keys according to claim 1, wherein the step S1 comprises the following steps:
step S1.1: constructing a section of constant envelope zero autocorrelation sequence, and setting the sequence length according to different transmission distances;
step S1.2: constructing a Gaussian modulation data sequence, and generating by using a random number generator;
step S1.3: a pilot sequence is constructed that carries the determined initial phase information.
3. The method for synchronizing the non-homologous local oscillation optical continuous variable quantum key distribution bit frames according to claim 1, wherein the step S2 comprises the steps of:
step S2.1: the receiver firstly distinguishes the pilot frequency position and the data position according to the power size, and then recovers the synchronous frame and the data frame by utilizing the phase information carried by the pilot frequency signal after the change;
step S2.2: and carrying out cross-correlation calculation on the synchronous frame and the data frame by using the same constant-envelope self-zero correlation sequence, and judging the current pulse signal as the starting position of the data if and only if correlation peaks appear in the correlation calculation.
4. The non-homologous local oscillation optical continuous variable quantum key distribution bit frame synchronization method according to claim 2, wherein the constant envelope zero autocorrelation sequence is:
where r is the root index of the zero auto-correlation sequence, r ε {1, …, (N) zc -1); n is the position index of the sequence, N is {1, …, N zc }；N zc Is the length of a constant envelope zero autocorrelation sequence; z r [n]A specific value of n for the position index in the zero auto-correlation sequence; exp represents an exponential function with the natural constant e as a base; i is an imaginary unit.
5. The non-homologous local oscillation optical continuous variable quantum key distribution bit frame synchronization method according to claim 2, wherein the gaussian modulation data sequence is:
g[n]＝x n +ip n
wherein x is n And p n The regular position and the regular momentum, respectively representing the continuous variable, are all subject to Gaussian distribution, i.e. x n ,p n ～N(0,V A )，V A Modulating variance for the signal; g [ n ]]For complex amplitude of continuous variable, N is the position index of Gaussian modulation data sequence, N is {1, …, N data N, where N data For gaussian modulated data sequence length; i is an imaginary unit.
6. The method for synchronizing the non-homologous local oscillation optical continuous variable quantum key distribution bit frames according to claim 2, wherein the pilot sequence is:
wherein θ is 0 Is a fixed phase value, e is a natural constant, p [ n ]]A specific value representing a position index N in the pilot sequence, N e {1, …, N zc +N data I is an imaginary unit.
7. The non-homologous local oscillation optical continuous variable quantum key distribution bit frame synchronization method according to claim 2, wherein the anti-phase change synchronization frame structure is:
[p[1],z r [1],p[2],z r [2]，…，p[N zc ]，z r [N zc ]，p[N zc +1]，g[1]，…，p[N zc +N data ]，g[N data ]]
wherein pi is]A specific numerical value with a position index of i in the pilot sequence; z r [i]A specific value with a position index i in the zero auto-correlation sequence; g [ i ]]Is a specific numerical value with i as a position index in Gaussian modulation data sequence, N zc Is the length of constant envelope zero autocorrelation sequence, N data For gaussian modulated data sequence length.
8. The method for bit frame synchronization of non-homologous local oscillator optical continuous variable quantum key distribution according to claim 3, wherein if the variance of the odd-numbered sequence data is greater than the variance of the even-numbered sequence data, the odd-numbered sequence is a pilot signal existence position, and the even-numbered sequence is a data signal existence position; otherwise, the odd sequence is the data signal existence position, and the even sequence is the pilot signal existence position.
9. The method for synchronizing the non-homologous local oscillator optical continuous variable quantum key distribution bit frames according to claim 3, wherein the pilot signal phase information recovery process is as follows:
wherein g [ i ]]Is a specific value of i, g [ i ] of a position index in a Gaussian modulation data sequence]' is a specific value after recovery of the corresponding Gaussian modulated data sequence, pi+N zc ]i+N for the corresponding pilot sequence position index zc Specific values of (2); z r [i]Z is a specific value of i at a position index in a Gaussian modulated data sequence r [i]' is a specific value after recovery of the corresponding Gaussian modulated data sequence, pi [ i ]]A specific numerical value with a position index of i in a corresponding pilot sequence; nzc is the length of the constant envelope zero autocorrelation sequence; n (N) data For gaussian modulated data sequence length;
will recover the resulting z r [n]' and g [ n ]]' combining results in a recovery sequence y [ n ]]＝[z r [n]′,g[n]′]；
The data frame header y [ n ] searching cross-correlation algorithm is as follows:
c[n]'＝cov(y[n],z r [n])
wherein c [ n ]]' is a specific value with a position index of n in the cross-correlation calculation result, y [ n ]]To recover a particular value of position index n in the sequence, z r [n]A specific value of n for the position index in the zero auto-correlation sequence; cov is a cross-correlation calculation of two sequences: y [ n ]]And z r [n]After the cross-correlation operation, z is calculated r [n]One bit back from y [ n ]]Performing cross-correlation operation on the second repetition of the number of the pairs, and continuing to perform z after the operation is completed r [n]Shift backward and operate until y [ n ]]The last bit of (2) is c [ n ] obtained by each operation]' forming a sequence of correlation values; the index bit corresponding to the maximum correlation peak value in the obtained correlation value sequence is the constant envelope frameIs then added with N zc The sequence length is the start bit of the data frame.
10. The non-homologous local oscillator light continuous variable quantum key distribution bit frame synchronization system is characterized by comprising the following modules:
module M1: firstly, constructing a constant envelope zero autocorrelation sequence, then constructing a key data sequence obeying Gaussian distribution, and finally, inserting a pilot sequence into the sequence to form an anti-phase-change synchronous frame;
module M2: firstly, carrying out phase recovery on a received frame based on pilot signal phase information, then carrying out data frame head searching through a constant envelope zero autocorrelation sequence, and determining a data start bit;
the module M1 comprises the following modules:
module M1.1: constructing a section of constant envelope zero autocorrelation sequence, and setting the sequence length according to different transmission distances;
module M1.2: constructing a Gaussian modulation data sequence, and generating by using a random number generator;
module M1.3: constructing a pilot sequence, wherein the pilot sequence carries determined initial phase information;
the module M2 comprises the following modules:
module M2.1: the receiver firstly distinguishes the pilot frequency position and the data position according to the power size, and then recovers the synchronous frame and the data frame by utilizing the phase information carried by the pilot frequency signal after the change;
module M2.2: and carrying out cross-correlation calculation on the synchronous frame and the data frame by using the same constant-envelope self-zero correlation sequence, and judging the current pulse signal as the starting position of the data if and only if correlation peaks appear in the correlation calculation.
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