CN110545142A - Continuous variable quantum key distribution method based on super-Nyquist technology - Google Patents
Continuous variable quantum key distribution method based on super-Nyquist technology Download PDFInfo
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- CN110545142A CN110545142A CN201910871208.3A CN201910871208A CN110545142A CN 110545142 A CN110545142 A CN 110545142A CN 201910871208 A CN201910871208 A CN 201910871208A CN 110545142 A CN110545142 A CN 110545142A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/70—Photonic quantum communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0819—Key transport or distribution, i.e. key establishment techniques where one party creates or otherwise obtains a secret value, and securely transfers it to the other(s)
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
- H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
- H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
- H04L9/0852—Quantum cryptography
Abstract
the invention discloses a continuous variable quantum key distribution method based on a super-Nyquist technology, which comprises the steps that a sender performs Gaussian modulation on signal light through a coherent state; the signal light of a sender is up-sampled, converted into a super-Nyquist signal and transmitted; the receiving end processes the received signal to obtain the data sent by the sending end. According to the continuous variable quantum key distribution method based on the super-Nyquist technology, the super-Nyquist transmission technology is introduced, the traditional Nyquist rate limit is broken through, and aiming at the problem of intersymbol crosstalk artificially introduced by Nyquist transmission, data post-processing technologies such as cyclic prefix adding, equalization technology and iterative detection are adopted, so that the influence of intersymbol crosstalk on the system safety is effectively eliminated, and the frequency band utilization rate and the channel capacity of the system are improved; the method has high reliability and good safety.
Description
Technical Field
the invention particularly relates to a continuous variable quantum key distribution method based on a super-Nyquist technology.
background
quantum key distribution enables two remotely located users, Alice and Bob, to share a common secure key in a quantum channel. Quantum communication and its security are receiving wide attention from all the world of society. The key to quantum communication is Quantum Key Distribution (QKD), which includes two aspects, Continuously Variable Quantum Key Distribution (CVQKD) and Discretely Variable Quantum Key Distribution (DVQKD). Although quantum key distribution of continuous variables has emerged late, quantum key distribution of continuous variables has achieved significant success in recent years. Compared with DVQKD, the source preparation of CVQKD is simple. The DVQKD system requires the preparation of strict single photon quantum states, and CVQKD can use a small number of photon coherent states. The continuously variable quantum key distribution can be combined with existing classical optical communication spectrum utilization schemes. If the quadrature amplitude modulation continuous variable sub-key distribution technology is adopted, a single photon detector is not needed, the manufacturing cost of the detection equipment is low, the detection efficiency is high, and the detection process is simple. However, the theoretical security of the continuously variable subkey distribution protocol has been strictly proven, but the security distance that can be achieved by system experiments is still short (less than 80 km). In 2016, researchers at Shanghai university of transportation performed experiments to achieve CVQKD with a safety distance of over 100 km. However, in order to reduce the influence of intersymbol interference to control the system noise on the system performance, the highest working frequency of the existing international continuous variable quantum key distribution Gaussian modulation protocol experimental system is still lower than 100MHz, and the key rate is lower than 1 Mbps. Therefore, in the original nyquist theory framework, besides the improvement of physical hardware performance, the development bottleneck is faced for further improving the security code rate of the single-path system.
In 1975, Mazo proposed the concept of Faster Than Nyquist (FTN). The FTN signal can realize a symbol rate faster than the Nyquist rate under the same bandwidth, error rate and power consumption. The FTN optical transmission technology re-examines the code element rate, the spectrum efficiency and the detection mode, breaks through the original constraint rule and further excavates the spectrum resources. The minimum Euclidean distance derivation of the super-Nyquist system signal can theoretically obtain that under the condition of using a specific pulse shaping filter, the system error code performance can be ensured to be unchanged even if the system speed breaks through the Nyquist speed. Bell labs Mazo et al propose that when the signal pulse is a Sinc pulse, the euclidean distance between the signals does not change, although the system introduces intersymbol interference, as long as the signal rate does not exceed the nyquist rate by 25%, and the minimum acceleration factor that does not change the minimum euclidean distance is called the Mazo boundary. In recent years, researchers have conducted researches on a multi-carrier faster-than-nyquist technique for simultaneous transmission of time and frequency domains, a clock recovery technique and a laser carrier recovery technique with high inter-code interference tolerance, an enhanced detection receiving mechanism and the like, so as to solve the problem that inter-code interference artificially introduced affects system performance.
however, no application research of the super-nyquist technique in the field of Continuous Variable Quantum Key Distribution (CVQKD) exists, so that the band utilization rate and the channel capacity in the process of Continuous Variable Quantum Key Distribution (CVQKD) are influenced, and the technical application and development of the Continuous Variable Quantum Key Distribution (CVQKD) are also restricted.
Disclosure of Invention
The invention aims to provide a continuous variable quantum key distribution method based on the super-Nyquist technology, which has high frequency band utilization rate and high channel capacity, and is safe and reliable.
The continuous variable quantum key distribution method based on the super-Nyquist technology provided by the invention comprises the following steps:
S1, a sender performs Gaussian modulation on signal light in a coherent state;
s2, the sender up-samples the signal light obtained in the step S1, converts the signal light into a super-Nyquist signal and transmits the signal light;
and S3, the receiving end processes the received signal so as to obtain the data sent by the sending end.
The sender stated in step S1 performs gaussian modulation on the signal light in a coherent state, specifically, the sender divides the light source into the signal light and the local oscillation light by the beam splitter, and then performs amplitude modulation and phase modulation on the signal light.
The sender in step S2 up-samples the signal light obtained in step S1, converts the signal light into a super-nyquist signal, and transmits the super-nyquist signal, specifically, the sender up-samples the modulated signal light by an up-sampler, then obtains a super-nyquist transmission signal by a super-nyquist pulse former, and finally transmits the processed signal light and the local oscillator light obtained in step S1 to a receiver through an optical fiber channel by time division polarization multiplexing after adding a cyclic prefix to the super-nyquist transmission signal.
the sender up-samples the modulated signal light through an up-sampler, specifically, the sender up-samples the signal and introduces intersymbol interference by changing a sampling factor N of the up-sampler.
The super-Nyquist transmission signal is obtained through the super-Nyquist pulse former, and specifically, the super-Nyquist transmission signal is obtained through the up-sampled signal through the super-Nyquist pulse former; the oversampling factor of the super-Nyquist pulse former is M, and N is less than M; the acceleration factor of the super-nyquist signal is N/M.
the receiving end in step S3 processes the received signal, specifically, the following steps are adopted for processing:
A. Removing a cyclic prefix from a received signal by a receiving end, and then performing super-Nyquist matching filtering;
B. B, carrying out down-sampling of a corresponding sampling interval on the signal obtained in the step A;
C. b, processing the down-sampled signal obtained in the step B to obtain a processed signal;
D. And C, the receiver calculates the mutual information quantity of the legal communication party through channel parameters according to the processing signals obtained in the step C to obtain the key rate, and finally outputs the final key through security enhancement.
And C, processing the down-sampled signal obtained in the step B, specifically, equalizing and iteratively detecting the down-sampled signal obtained in the step B.
According to the continuous variable quantum key distribution method based on the super-Nyquist technology, the super-Nyquist transmission technology is introduced, the traditional Nyquist rate limit is broken through, and aiming at the problem of intersymbol crosstalk artificially introduced by Nyquist transmission, data post-processing technologies such as cyclic prefix adding, equalization technology and iterative detection are adopted, so that the influence of intersymbol crosstalk on the system safety is effectively eliminated, and the frequency band utilization rate and the channel capacity of the system are improved; the method has high reliability and good safety.
Drawings
FIG. 1 is a schematic process flow diagram of the process of the present invention.
fig. 2 is a schematic diagram of a quantum key transmitting end and a quantum key receiving end according to an embodiment of the method of the present invention.
Detailed Description
Fig. 1 is a schematic diagram of a method flow of the method of the present invention, and a schematic diagram of a quantum key transmitting end and a quantum key receiving end corresponding thereto is shown in fig. 2. In fig. 2, CW laser is a continuous laser, AM is an amplitude modulator, PM is a phase modulator, PD is a photodetector, CP is a cyclic prefix, DAC is a digital/analog converter, LPF is a low pass filter, and ADC is an analog/digital converter.
The continuous variable quantum key distribution method based on the super-Nyquist technology provided by the invention comprises the following steps:
s1, a sender performs Gaussian modulation on signal light in a coherent state; the method comprises the steps that a light source is divided into signal light and local oscillation light by a beam splitter at a sending end, and then amplitude modulation and phase modulation are carried out on the signal light;
s2, the sender up-samples the signal light obtained in the step S1, converts the signal light into a super-Nyquist signal and transmits the signal light; the method comprises the steps that a sender performs up-sampling on modulated signal light through an up-sampler, then obtains super-Nyquist transmission signals through a super-Nyquist pulse former, finally adds cyclic prefixes to the super-Nyquist transmission signals, and transmits the processed signal light and local oscillation light obtained in the step S1 to a receiver through an optical fiber channel through time division polarization multiplexing;
During up-sampling, a sender up-samples signals, introduces intersymbol interference by changing a sampling factor N of an up-sampler, and simultaneously reduces a guard interval between adjacent pulses to increase the number of signal pulses, so that a working system can send more pulse signals in a fixed time-frequency interval; meanwhile, the signals subjected to up-sampling pass through a super-Nyquist pulse former to obtain super-Nyquist transmission signals; the oversampling factor of the super-Nyquist pulse former is M, and N is less than M; the acceleration factor of the super-Nyquist signal is N/M;
Second, the faster-than-nyquist signal introduces intersymbol interference while "speeding up" the signal pulse. But when the pulse is an orthogonal pulse (root raised cosine signal is used in the invention) which is not a sinc pulse, the transmission rate is increased to be higher than the nyquist rate, or the pulse h (t) is a band-limited signal with the bandwidth of W, then when the acceleration factor is increased, compared with the nyquist transmission, the higher limit channel capacity can be obtained;
Finally, the cyclic prefix is formed by moving the signal at the tail part of the symbol to the front part, so that the difference between all sub-carriers in the time length of the fast Fourier integration of each path of sub-carriers is always an integer period, the interference between the signals is avoided, and the demodulation complexity is greatly reduced;
s3, the receiving end processes the received signal so as to obtain data sent by the sending end; the method specifically comprises the following steps:
A. removing a cyclic prefix from a received signal by a receiving end, and then performing super-Nyquist matching filtering;
B. b, carrying out down-sampling of a corresponding sampling interval on the signal obtained in the step A;
C. Processing the down-sampled signal obtained in the step B (including equalizing and iterative detection of the down-sampled signal obtained in the step B) to obtain a processed signal;
D. C, the receiver calculates the mutual information quantity of the legal communication party through channel parameters according to the processing signals obtained in the step C to obtain a key rate, immediately measures the received signal light by adopting a low-noise homodyne detector, obviously reduces the excessive noise caused by overlapping, and finally outputs a final key through confidentiality enhancement;
in specific implementation, equalization and iterative detection are carried out on the down-sampled signals, and intersymbol interference of the super-Nyquist signals is reduced by increasing the number of iterations. The iterative detection algorithm is as follows:
Firstly, calculating a correlation matrix between subcarriers, then carrying out iteration operation according to a previous signal and the correlation matrix, and carrying out constellation mapping on the iterated signal to reduce the size of intersymbol interference. The above steps are repeated by increasing the number of iterations.
The process of the invention is further illustrated below with reference to one example:
consider a CV-QKD based on FTN signals with binary phase shift keying modulation that consists of quantum transmission and classical data processing. In the quantum part, the CV-QKD system employs Gaussian Modulated Coherent States (GMCS). On the Alice side, 1550nm Continuous Wave (CW) light is converted into a 2MHz clock square wave train by an Amplitude Modulator (AM) during pulse modulation, with an extinction ratio close to 65 dB. The pulses are decomposed into Local Oscillator (LO) paths and signal paths using an asymmetric mach-zehnder interferometer (AMZI). The transmission signal is generated by binary sequence of the signal path, through BPSK baseband modulation. The transmitted symbols are first encoded through a channel, and then the encoded symbols are modulated and then inserted with a cyclic prefix for active monitoring. By modeling the FTN filter, the signal transmitted by the FTN at the boundary of the transmission interval Ts is obtained. Finally, the signal is converted into a signal suitable for transmission over an optical fiber by digital/analog (D/a) conversion and a low pass filter. At Bob, the received signal first goes through a low-pass filter and analog/digital (a/D) conversion. Then the received signal passes through FTN matched filter, after removing the cyclic prefix, the filtered signal is sampled by symbol interval tTs, and finally the sampled symbol is restored to the original information by equalization and decoder.
The method has the advantages that the super-Nyquist transmission technology is introduced, the traditional Nyquist rate limit is broken through, the intersymbol interference problem caused by artificial introduction of Nyquist transmission is solved, the influence of intersymbol interference on the system safety is effectively eliminated by adopting data post-processing technologies such as cyclic prefix addition, equalization technology and iterative detection, the frequency band utilization rate and the channel capacity of the system are improved, and a new technical support is provided for the distribution of the high-code-rate continuous variable quantum key.
the variation of channel capacity brought by the super-nyquist transmission is specifically analyzed as follows:
According to the channel capacity formula:
For a gaussian channel with bilateral power spectral density of N0/2, the super-nyquist transmission technique limits the channel capacity to: where P is the signal power, the limiting channel capacity of nyquist transmission is such that the acceleration factor obviously exists CFTN > CN.
Claims (7)
1. a continuous variable quantum key distribution method based on the super-Nyquist technology comprises the following steps:
s1, a sender performs Gaussian modulation on signal light in a coherent state;
S2, the sender up-samples the signal light obtained in the step S1, converts the signal light into a super-Nyquist signal and transmits the signal light;
and S3, the receiving end processes the received signal so as to obtain the data sent by the sending end.
2. The continuous variable quantum key distribution method based on the faster-than-nyquist technique as claimed in claim 1, wherein the sender in step S1 performs gaussian modulation on the signal light through coherent states, specifically, the sender divides the light source into the signal light and the local oscillator light through a beam splitter, and then performs amplitude modulation and phase modulation on the signal light.
3. The continuous variable quantum key distribution method based on the super-nyquist technique as claimed in claim 2, wherein the sender in step S2 up-samples the signal light obtained in step S1, converts the signal light into a super-nyquist signal and transmits the signal light, specifically, the sender up-samples the modulated signal light via an up-sampler, then obtains a super-nyquist transmission signal via a super-nyquist pulse former, and finally adds a cyclic prefix to the super-nyquist transmission signal, and transmits the processed signal light and the local oscillator light obtained in step S1 to the receiver via an optical fiber channel by time-division polarization multiplexing.
4. the continuous variable quantum key distribution method based on the faster-than-nyquist technique as claimed in claim 3, wherein the sender up-samples the modulated signal light by an up-sampler, specifically, the sender up-samples the signal and introduces inter-symbol crosstalk by changing a sampling factor N of the up-sampler.
5. the continuous variable quantum key distribution method based on the super-nyquist technique as claimed in claim 6, wherein the super-nyquist transmission signal is obtained by the super-nyquist pulse shaper, specifically, the super-nyquist transmission signal is obtained by passing the up-sampled signal through the super-nyquist pulse shaper; the oversampling factor of the super-Nyquist pulse former is M, and N is less than M; the acceleration factor of the super-nyquist signal is N/M.
6. the continuous variable quantum key distribution method based on the faster-than-nyquist technique as claimed in claim 5, wherein the receiving end in step S3 processes the received signal, specifically, the following steps are adopted for processing:
A. removing a cyclic prefix from a received signal by a receiving end, and then performing super-Nyquist matching filtering;
B. B, carrying out down-sampling of a corresponding sampling interval on the signal obtained in the step A;
C. B, processing the down-sampled signal obtained in the step B to obtain a processed signal;
D. and C, the receiver calculates the mutual information quantity of the legal communication party through channel parameters according to the processing signals obtained in the step C to obtain the key rate, and finally outputs the final key through security enhancement.
7. The continuous variable quantum key distribution method based on the super-nyquist technique as claimed in claim 6, wherein the step C processes the down-sampled signal obtained in step B, specifically, equalizes and iteratively detects the down-sampled signal obtained in step B.
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