Collaborative data link mobile platform time synchronization method

Abstract

The invention provides a collaborative data link mobile platform time synchronization method, which comprises the following steps that: S1, a slave station mobile platform sends an inquiry message to a master station mobile platform, and the master station mobile platform sends a response message to the slave station mobile platform; s2, the master station mobile platform performs correlation calculation on the inquiry message and a locally generated PN code, and obtains the arrival time of the inquiry message based on a calculation result; s3, the slave station mobile platform performs correlation operation on the response message and a locally generated PN code, and obtains the arrival time of the response message based on a calculation result; s4, calculating to obtain a clock difference of the slave station mobile platform relative to the master station mobile platform based on a round-trip transmission distance between the master station mobile platform and the slave station mobile platform, the arrival time of the inquiry message and the arrival time of the response message; and S5, the slave station mobile platform calibrates the local clock based on the clock difference. The method has the advantages of being suitable for long-distance and dynamic scenes, high in time synchronization precision, good in stability and high in anti-interference performance.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a time synchronization method for a collaborative data link mobile platform. Background Art

[0002] With the continuous development of mobile communications, drones, radars and other application fields, mobile platforms are in a dynamically changing environment during operation, facing challenges such as dynamic environment, multipath effects, signal blocking, high latency jitter, etc., and need to provide stable and high-precision time synchronization to ensure the normal operation of their own systems. High-precision time synchronization between mobile platforms can ensure data integrity and reliability. Therefore, time synchronization of mobile platforms is crucial to ensure the normal operation of products.

[0003] Some time synchronization methods in the prior art have the following problems: ① They can only synchronize the time signal of the slave to the master, and cannot achieve two-way time synchronization. ② They can only achieve coarse synchronization, and the time synchronization accuracy cannot meet the requirements. ③ They are not suitable for long-distance communication, and the mobile platforms of both communicating parties must work at the same baud rate.

[0004] How to provide a high-precision time synchronization method for collaborative data link mobile platforms is an issue that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a method for time synchronization of a coordinated data link mobile platform, wherein the master station mobile platform and the slave station mobile platform perform correlation calculations on the messages received by each of them and the locally generated PN code (Pseudo-Noise Code) to obtain the corresponding message arrival time. Based on the message arrival time of the master station mobile platform, the message arrival time of the slave station mobile platform, and the round-trip transmission distance between the master station mobile platform and the slave station mobile platform, the clock difference between the master station mobile platform and the slave station mobile platform is calculated, and the local clocks of the master station receiving platform and the slave station receiving platform are calibrated according to the clock difference. The present invention can achieve high-precision time synchronization of a two-way wireless link between the master station mobile platform and the slave station mobile platform.

[0006] In order to achieve the above object, the present invention provides a collaborative data link mobile platform time synchronization method, comprising the steps of:

[0007] S1. The slave mobile platform sends an inquiry message to the master mobile platform, and the master mobile platform sends a response message to the slave mobile platform;

[0008] S2, the master station mobile platform performs correlation calculation on the inquiry message and the locally generated PN code, and obtains the arrival time of the inquiry message based on the calculation result;

[0009] S3, the slave mobile platform performs a correlation operation on the received response message and the locally generated PN code, and obtains the arrival time of the response message based on the calculation result; the PN codes generated by the master mobile platform and the slave mobile platform are the same;

[0010] S4, based on the round-trip transmission distance between the master station mobile platform and the slave station mobile platform, the arrival time of the inquiry message, and the arrival time of the response message, calculate the clock difference of the slave station mobile platform relative to the master station mobile platform;

[0011] S5. The slave mobile platform calibrates a local clock based on the clock difference.

[0012] Optionally, in step S2, the inquiry message is recorded as r(t), where t represents time; the inquiry message r(t) is sequentially subjected to RF modulation, high-speed analog-to-digital conversion, and digital down-conversion processing to generate a corresponding intermediate frequency signal r[n]; the intermediate frequency signal r[n] is correlated with the PN code generated by the master station mobile platform; and the sampling rate of the intermediate frequency signal r[n] is the same as the chip rate of the PN code.

[0013] Optionally, step S2 includes:

[0014] S21, perform discrete Fourier transform on the intermediate frequency signal r[n] to obtain the corresponding frequency domain signal R[k],

[0015]

[0016] Where k represents the independent variable in the frequency domain, and N represents the number of sampling points;

[0017] S22, the master station mobile platform generates a local PN code c(t), and samples the PN code c(t) to obtain a corresponding discrete signal c(n);

[0018] S23, performing discrete Fourier transform on the discrete signal c(n) to obtain the corresponding frequency domain signal C[k],

[0019]

[0020] S24, calculating the cross-correlation value G[k] between the frequency domain signal R[k] and the frequency domain signal C[k],

[0021] G[k]=R[k]·C[k] * ;

[0022] Where C[k] * is the result of taking the conjugate of the complex part of C[k];

[0023] S25, performing inverse discrete Fourier transform on the cross-correlation value G[k] to obtain the corresponding discrete time domain signal g[n],

[0024]

[0025] n∈[1,N], |·| represents the modulus calculation;

[0026] like If it is greater than the preset threshold, The corresponding time is taken as the arrival time TOA of the query message I .

[0027] Optionally, in step S3, the response message is recorded as r′(t), where t represents time; the response message r′(t) is sequentially subjected to RF modulation, high-speed analog-to-digital conversion, and digital down-conversion processing to generate a corresponding intermediate frequency signal r′[n]; the intermediate frequency signal r′[n] is correlated with the PN code generated by the slave station mobile platform; the sampling rate of the intermediate frequency signal r′[n] is the same as the chip rate of the PN code.

[0028] Optionally, step S3 includes:

[0029] S31, performing discrete Fourier transform on the intermediate frequency signal r'[n] to obtain the corresponding frequency domain signal R'[k],

[0030]

[0031] Where k represents the independent variable in the frequency domain, and N represents the number of sampling points;

[0032] S32, the slave mobile platform generates a local PN code c′(t), and samples the PN code c′(t) to obtain a corresponding discrete signal c′(n);

[0033] S33, performing discrete Fourier transform on the discrete signal c′(n) to obtain the corresponding frequency domain signal C′[k],

[0034]

[0035] S34, calculating the cross-correlation value G′[k] between the frequency domain signal R′[k] and the frequency domain signal C′[k],

[0036] G′[k]=R′[k]·C′[k] * ;

[0037] Where C′[k] * is the result of taking the conjugate of the complex part of C′[k];

[0038] S35, performing inverse discrete Fourier transform on the cross-correlation value G′[k] to obtain the corresponding discrete time domain signal g′[n],

[0039]

[0040] n∈[1,N], |·| represents the modulus calculation;

[0041] like If it is greater than the preset threshold, The corresponding time is used as the arrival time TOA of the response message R .

[0042] Optionally, in step S4, let ε represent the clock difference,

[0043]

[0044] where t d is the duration of the inquiry message.

[0045] Optionally, step S4 further includes:

[0046] The uplink and downlink transmission delay t generated by the relative motion between the master station mobile platform and the slave station mobile platform ε Correct the clock difference ε, after correction

[0047]

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1) The collaborative data link mobile platform time synchronization method of the present invention is that the slave station mobile platform sends an inquiry message to the master station mobile platform, and the master station mobile platform sends a response message to the slave station mobile platform after receiving the inquiry message, and both the master station mobile platform and the slave station mobile platform can generate the same PN code. The master station mobile platform performs a correlation calculation on the received inquiry message and the locally generated PN code, and obtains the arrival time of the inquiry message based on the calculation result. The slave station mobile platform performs a correlation calculation on the received response message and the locally generated PN code, and obtains the arrival time of the response message based on the calculation result. Based on the round-trip transmission distance between the master station mobile platform and the slave station mobile platform, the arrival time of the inquiry message, and the arrival time of the response message, the clock difference between the master station mobile platform and the slave station mobile platform is calculated. Finally, the local clocks of the master station receiving platform and the slave station receiving platform are calibrated based on the calculated clock difference. The present invention can achieve high-precision time synchronization of the two-line wireless link between the master station mobile platform and the slave station mobile platform, and the time resolution measurement accuracy can reach one percent of the code chip width.

[0050] 2) The present invention has strong anti-interference ability. Since Beidou timing is not used (this method has poor stability and weak anti-interference ability), the present invention has better adaptability to the environment.

[0051] 3) The present invention can correct the clock difference based on the uplink and downlink transmission delay generated by the relative movement between the master station mobile platform and the slave station mobile platform. It is suitable for calibrating the clocks of the mobile platforms of both communicating parties in long-distance dynamic scenarios, and effectively improves the time synchronization accuracy in different dynamic scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for the description. Obviously, the drawings described below are an embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

[0053] Figure 1 This is a flow chart of a method for coordinating a data link mobile platform time synchronization in an embodiment of the present invention;

[0054] Figure 2 4 is a flow chart of a parallel code phase acquisition algorithm in an embodiment of the present invention. DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0057] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0058] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0059] As used in this specification and the appended claims, the term "if" may be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if [described condition or event] is detected" may be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0060] In addition, in the description of the present application, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0061] This embodiment provides a method for coordinating the time synchronization of a data link mobile platform. Figure 1 As shown, the steps include:

[0062] S1, the slave station mobile platform sends an inquiry message to the master station mobile platform, and the master station mobile platform sends a response message to the slave station mobile platform;

[0063] S2, the master station mobile platform performs correlation calculation on the inquiry message and the locally generated PN code, and obtains the arrival time of the inquiry message based on the calculation result;

[0064] In this embodiment, the inquiry message is recorded as r(t), where t represents time; the inquiry message r(t) is subjected to radio frequency modulation, high-speed analog-to-digital conversion, and digital down-conversion in sequence to generate a corresponding intermediate frequency signal r[n]. The intermediate frequency signal r[n] is correlated with the PN code generated by the master station mobile platform; the sampling rate of the intermediate frequency signal r[n] is the same as the chip rate of the PN code (recorded as c(t)).

[0065] In order to meet the requirements of high-precision time synchronization, the time of two-way time calibration needs to be reduced. This embodiment uses a parallel code frequency domain phase capture algorithm to obtain the arrival time of the inquiry message. The parallel code phase capture algorithm performs correlation calculations on the intermediate frequency signal r[n] and the PN code c(t) generated locally by the master station mobile platform. The intermediate frequency signal r[n] and the PN code c(t) in the time domain are converted to the frequency domain through Fourier transform. After the two frequency domain signals are complex multiplied, the result of the complex multiplication operation is converted to the time domain through inverse Fourier transform to obtain the correlation value with each phase of the PN code in the time domain. In this way, at a certain local oscillation frequency, the correlation values ​​with all phases in the PN code are calculated simultaneously through the parallel code frequency domain phase capture algorithm. Since the PN code has pseudo-randomness and good autocorrelation, the autocorrelation is the largest when the phase is zero shifted, and the correlation is close to zero when other phases are shifted. The time of the PN code phase corresponding to the maximum correlation value is the arrival time of the inquiry message.

[0066] like Figure 2 As shown, the steps of the parallel code phase acquisition algorithm are as follows:

[0067] S21, perform Discrete Fourier Transform (DFT) on the intermediate frequency signal r[n] to obtain the corresponding frequency domain signal R[k], ( Figure 2 The FFT in the formula stands for Fast Fourier Transform, and the IFFT stands for Fast Inverse Fourier Transform)

[0068]

[0069] Where k represents the independent variable in the frequency domain, and N represents the number of sampling points;

[0070] S22, the master station mobile platform generates a local PN code c(t), and samples the PN code c(t) to obtain a corresponding discrete signal c(n);

[0071] S23, performing discrete Fourier transform on the discrete signal c(n) to obtain the corresponding frequency domain signal C[k],

[0072]

[0073] S24, calculating the cross-correlation value G[k] between the frequency domain signal R[k] and the frequency domain signal C[k],

[0074] G[k]=R[k]·C[k] * ;

[0075] Where C[k] * is the result of taking the conjugate of the complex part of C[k];

[0076] S25, performing an inverse discrete Fourier transform (IDFT Inverse Discrete Fourier Transform) on the cross-correlation value G[k] to obtain a corresponding discrete time domain signal g[n],

[0077]

[0078] n∈[1,N], |·| represents the modulus calculation;

[0079] like If the value is greater than the preset threshold (indicating that the inquiry message is captured), The corresponding time is taken as the arrival time TOA of the query message I .

[0080] S3, the slave mobile platform performs a correlation operation on the received response message and the locally generated PN code, and obtains the arrival time of the response message based on the calculation result; the PN codes generated by the master mobile platform and the slave mobile platform are the same;

[0081] In this embodiment, the response message is recorded as r′(t), where t represents time; the response message r′(t) is sequentially subjected to radio frequency modulation, high-speed analog-to-digital conversion, and digital down-conversion processing to generate a corresponding intermediate frequency signal r′[n]; the intermediate frequency signal r′[n] is correlated with the PN code generated by the slave station mobile platform; the sampling rate of the intermediate frequency signal r′[n] is the same as the chip rate of the PN code.

[0082] In step S3, the arrival time of the response message is calculated by the parallel code frequency domain phase acquisition algorithm, which specifically includes the following steps:

[0083] S31, performing discrete Fourier transform on the intermediate frequency signal r'[n] to obtain the corresponding frequency domain signal R'[k],

[0084]

[0085] Where k represents the independent variable in the frequency domain, and N represents the number of sampling points;

[0086] S32, the slave mobile platform generates a local PN code c′(t), and samples the PN code c′(t) to obtain a corresponding discrete signal c′(n);

[0087] S33, performing discrete Fourier transform on the discrete signal c′(n) to obtain the corresponding frequency domain signal C′[k],

[0088]

[0089] S34, calculating the cross-correlation value G′[k] between the frequency domain signal R′[k] and the frequency domain signal C′[k],

[0090] G′[k]=R′[k]·C′[k] * ;

[0091] Where C′[k] * is the result of taking the conjugate of the complex part of C′[k];

[0092] S35, performing inverse discrete Fourier transform on the cross-correlation value G′[k] to obtain the corresponding discrete time domain signal g′[n],

[0093]

[0094] n∈[1,N], |·| represents the modulus calculation;

[0095] like If it is greater than the preset threshold, The corresponding time is the arrival time TOA of the response message R .

[0096] S4, based on the round-trip transmission distance between the master station mobile platform and the slave station mobile platform, the arrival time of the inquiry message, and the arrival time of the response message, calculate the clock difference of the slave station mobile platform relative to the master station mobile platform;

[0097] Let ε denote the clock difference, where t d Indicates the duration of the inquiry message.

[0098] S5. The slave mobile platform calibrates a local clock based on the clock difference.

[0099] Theoretically, without considering the relative motion between the mobile platforms, the time resolution measurement accuracy of the present invention can reach 1% of the chip width.

[0100] A major factor affecting the measurement accuracy is the asymmetry of the uplink and downlink transmission delays caused by the relative motion between stations (mobile platforms). In the traditional principle of time synchronization based on RTT (Round-Trip Time), it is believed that the transmission delay of the uplink and downlink is t p are equal (in this embodiment, the uplink is the transmission link of the inquiry message, and the downlink is the transmission link of the response message). In fact, due to the time difference between the arrival of the inquiry message and the response message, when there is relative motion between the two stations, the delays of the uplink and downlink transmission links are different, and there is a time difference t between the two. ε , t ε The size of depends on the relative speed between the two stations and the time interval between sending inquiry and response messages. Where D, v r are the distance and relative speed between the master station mobile platform and the slave station mobile platform, C is the speed of light, t send The time taken to send a signal is the time from the moment the sender sends the signal to the moment the receiver receives the signal.

[0101] At this time, the calculation formula of the clock error is corrected to

[0102] In another embodiment, step S4 further includes:

[0103] The uplink and downlink transmission delay t generated by the relative motion between the master station mobile platform and the slave station mobile platform ε Corrected clock difference ε, after correction

[0104]

[0105] In another embodiment, another factor affecting the time synchronization accuracy is the change in the PN code period caused by the Doppler frequency shift. When there is a Doppler frequency shift, the arrival time of the response message extracted from the mobile platform of the slave station will be affected, resulting in an error. This error is also a fixed error. If the relative motion speed between the two stations can be obtained, the time difference between the two stations caused by the Doppler frequency shift can be compensated, and by further correcting ε, the time synchronization between the two stations can be made more accurate (this is a prior art and will not be repeated here).

[0106] The collaborative data link mobile platform time synchronization method of the present invention is that the slave station mobile platform sends an inquiry message to the master station mobile platform, and the master station mobile platform sends a response message to the slave station mobile platform after receiving the inquiry message, and both the master station mobile platform and the slave station mobile platform can generate the same PN code. The master station mobile platform performs correlation calculation on the received inquiry message and the locally generated PN code, and obtains the arrival time of the inquiry message based on the calculation result. The slave station mobile platform performs correlation calculation on the received response message and the locally generated PN code, and obtains the arrival time of the response message based on the calculation result. Based on the round-trip transmission distance between the master station mobile platform and the slave station mobile platform, the arrival time of the inquiry message, and the arrival time of the response message, the clock difference between the master station mobile platform and the slave station mobile platform is calculated. Finally, the local clocks of the master station receiving platform and the slave station receiving platform are calibrated based on the calculated clock difference. The present invention can realize high-precision time synchronization of a two-line wireless link between the master station mobile platform and the slave station mobile platform, and the time resolution measurement accuracy can reach one percent of the code chip width.

[0107] The present invention has strong anti-interference ability. Since Beidou timing is not used (this method has poor stability and weak anti-interference ability), the present invention has better adaptability to the environment. The present invention can correct the clock difference based on the uplink and downlink transmission delay generated by the relative motion between the master station mobile platform and the slave station mobile platform. It is suitable for calibrating the clocks of the mobile platforms of both communicating parties in long-distance dynamic scenes, and effectively improves the time synchronization accuracy in different dynamic scenes.

[0108] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0109] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for time synchronization of a collaborative data link mobile platform, characterized in that: Includes steps: S1. The slave mobile platform sends an inquiry message to the master mobile platform, and the master mobile platform sends a response message to the slave mobile platform; S2, the master station mobile platform performs correlation calculation on the inquiry message and the locally generated PN code, and obtains the arrival time of the inquiry message based on the calculation result; S3, the slave station mobile platform performs a correlation operation on the received response message and the locally generated PN code, and obtains the arrival time of the response message based on the calculation result; The PN code generated by the master mobile platform and the slave mobile platform is the same; S4, based on the round-trip transmission distance between the master station mobile platform and the slave station mobile platform, the arrival time of the inquiry message, and the arrival time of the response message, calculate the clock difference of the slave station mobile platform relative to the master station mobile platform; S5. The slave mobile platform calibrates a local clock based on the clock difference.

2. The collaborative data link mobile platform time synchronization method according to claim 1, characterized in that: In step S2, the inquiry message is recorded as r(t), where t represents time; the inquiry message r(t) is subjected to RF modulation, high-speed analog-to-digital conversion, and digital down-conversion in sequence to generate a corresponding intermediate frequency signal r[n]; the intermediate frequency signal r[n] is correlated with the PN code generated by the master station mobile platform; the sampling rate of the intermediate frequency signal r[n] is the same as the chip rate of the PN code.

3. The collaborative data link mobile platform time synchronization method as claimed in claim 2, characterized in that: Step S2 includes: S21, perform discrete Fourier transform on the intermediate frequency signal r[n] to obtain the corresponding frequency domain signal R[k], Where k represents the independent variable in the frequency domain, and N represents the number of sampling points; S22, the master station mobile platform generates a local PN code c(t), and samples the PN code c(t) to obtain a corresponding discrete signal c(n); S23, performing discrete Fourier transform on the discrete signal c(n) to obtain the corresponding frequency domain signal C[k], S24, calculating the cross-correlation value G[k] between the frequency domain signal R[k] and the frequency domain signal C[k], G[k]=R[k]·C[k] * ; Where C[k] * is the result of taking the conjugate of the complex part of C[k]; S25, performing inverse discrete Fourier transform on the cross-correlation value G[k] to obtain the corresponding discrete time domain signal g[n], n∈[1,N], |·| represents the modulus calculation; like If it is greater than the preset threshold, The corresponding time is taken as the arrival time TOA of the query message I .

4. The collaborative data link mobile platform time synchronization method as claimed in claim 3, characterized in that: In step S3, the response message is recorded as r′(t), where t represents time; the response message r′(t) is subjected to RF modulation, high-speed analog-to-digital conversion, and digital down-conversion in sequence to generate a corresponding intermediate frequency signal r′[n]; the intermediate frequency signal r′[n] is correlated with the PN code generated by the slave mobile platform; the sampling rate of the intermediate frequency signal r′[n] is the same as the chip rate of the PN code.

5. The collaborative data link mobile platform time synchronization method as claimed in claim 4, characterized in that: Step S3 includes: S31, performing discrete Fourier transform on the intermediate frequency signal r'[n] to obtain the corresponding frequency domain signal R'[k], Where k represents the independent variable in the frequency domain, and N represents the number of sampling points; S32, the slave mobile platform generates a local PN code c′(t), and samples the PN code c′(t) to obtain a corresponding discrete signal c′(n); S33, performing discrete Fourier transform on the discrete signal c′(n) to obtain the corresponding frequency domain signal C′[k], S34, calculating the cross-correlation value G′[k] between the frequency domain signal R′[k] and the frequency domain signal C′[k], G′[k]=R′[k]·C′[k] * ; Where C′[k] * is the result of taking the conjugate of the complex part of C′[k]; S35, performing inverse discrete Fourier transform on the cross-correlation value G′[k] to obtain the corresponding discrete time domain signal g′[n], n∈[1,N], |·| represents the modulus calculation; like If it is greater than the preset threshold, The corresponding time is used as the arrival time TOA of the response message R .

6. The collaborative data link mobile platform time synchronization method as claimed in claim 5, characterized in that: In step S4, let ε represent the clock difference, where t d is the duration of the inquiry message.

7. The collaborative data link mobile platform time synchronization method according to claim 1, characterized in that: Step S4 also includes: The uplink and downlink transmission delay t caused by the relative motion between the master station mobile platform and the slave station mobile platform ε Correct the clock difference ε, after correction

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