Method for clock synchronization of electric vehicle v2x terminal in defense of satellite navigation pps signal loss of lock

Abstract

The application provides a kind of electric vehicle V2X terminal clock synchronization method for defending satellite navigation PPS signal lockout, for the short-term lockout of GNSS, by judging the receiving state of PPS pulse and reference timestamp, the adaptive sampling step of reference timestamp is determined, and then combined with the established virtual clock model, high-precision reference time is obtained without switching clock source, effectively overcoming the lack of time synchronization accuracy caused by clock source switching in the prior art. Based on the adaptive timestamp acquisition means provided by the application, various virtual clock models and correction parameter estimation methods can be applied, and the application can also provide wider applicability compared to the prior art.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicle V2X satellite navigation signal processing technology, specifically relating to a method for synchronizing the clock of an electric vehicle V2X terminal to prevent loss of satellite navigation PPS signal. Background Technology

[0002] When electric vehicles apply V2X technologies, higher demands are placed on the quality and real-time performance of communication signals among numerous related devices within the vehicle network. How V2X terminals can coordinate their operations based on a stable, synchronized clock signal is crucial for achieving autonomous driving and intelligent transportation. Currently, V2X terminal synchronization is mostly based on GNSS signals, communication base station signals, or other devices directly or indirectly synchronized to GNSS signals as reference clock sources. Mechanisms such as broadcasting, NTP (Network Time Protocol), and PTP (Precision Time Protocol) are used to transmit timestamps, and time synchronization is achieved by parsing the timestamps to correct the phase deviation between the local time and the reference time. However, in actual driving scenarios such as tunnels, underground parking lots, and building obstructions, GNSS signal strength may be weak, or signal loss and errors may occur, resulting in the inability to obtain a normal reference time. For these GNSS signal-constrained scenarios, the main solution in existing technologies is to temporarily employ alternative clock sources when GNSS signals are lost for a short period. Examples include RSU (Road Side Unit) timing used in Chinese patent applications CN112040448A and CN112929851A, or analog clock sources used in CN113259902A, CN116567578A, and CN116528194A. However, the calibration accuracy of these alternative clock sources in existing technologies is still significantly lower than that of GNSS signals, resulting in the time synchronization performance of V2X terminal equipment not meeting the usage requirements. Summary of the Invention

[0003] In view of this, and to address the technical problems existing in this field, the present invention provides a method for synchronizing the clock of an electric vehicle V2X terminal to prevent loss of satellite navigation PPS signal, specifically including the following steps:

[0004] The V2X terminal is equipped with a GNSS module, a V2X communication module, and an auxiliary unit module. The GNSS module outputs an NMEA-0183 message and a 1PPS pulse signal at every whole second. The auxiliary module receives the NMEA-0183 message from the GNSS module, parses the Coordinated Universal Time (UTC) and date information, and transmits it to the V2X communication module as a reference timestamp. The V2X communication module receives the 1PPS pulse signal and the reference timestamp from the auxiliary module, triggers an interrupt based on the PPS signal at every whole second, and immediately reads the local timestamp upon entering the interrupt handling phase, thereby correcting the local time and completing time synchronization. After time synchronization, the V2X communication module continues to wait for the reference timestamp from the auxiliary module for a set time period.

[0005] The following time synchronization is performed based on the reception status of the GNSS signal:

[0006] a. When the GNSS signal is well received, the V2X communication module performs time synchronization directly based on the reference timestamp parsed from the GNSS signal;

[0007] b. When the GNSS signal experiences a short-term loss of lock, the GNSS module stops outputting the NMEA-0183 message (i.e., the reference timestamp) and only outputs a 1PPS pulse signal. In this case, the following operations are performed in sequence:

[0008] (1) The V2X communication module determines the adaptive sampling step size based on the sampling time points of the PPS signal and the reference timestamp acquired simultaneously but not continuously, and extracts the reference timestamp based on the adaptive sampling step size.

[0009] (2) Based on the extracted reference timestamp, adaptive sampling time and local time correction reference time, time synchronization is achieved.

[0010] Furthermore, the process for determining the adaptive sampling step size in step (1) is as follows:

[0011] (1-1) First, based on whether the PPS signal and the reference timestamp are obtained simultaneously, two PPS signal states are defined: 1 and 0; where 1 indicates that the PPS signal and the reference timestamp are obtained simultaneously, and 0 indicates that only the PPS signal is received, but the reference timestamp is not received.

[0012] (1-2) Set a theoretical sampling step size S;

[0013] (1-3) The PPS signal state corresponding to the nth time (n=1,2,3,...) is sampled at intervals of the theoretical sampling step size S, and each sampling time is defined as a theoretical sampling point;

[0014] (1-4) Based on the PPS signal state at each theoretical sampling point, the actual sampling points are re-determined, including:

[0015] ① If the PPS state at the theoretical sampling point is 1, then that point is determined to be the actual sampling point;

[0016] ② If the PPS state at the theoretical sampling point is 0, then with a detection interval of 1 second, the moment when the PPS state changes to 1 after detecting the theoretical sampling point is determined as the actual sampling point;

[0017] This yields the adaptive step size for actually extracting the reference timestamp.

[0018] Furthermore, step (2) specifically involves establishing the following virtual clock model for time synchronization:

[0019] R p (t)=a(C(t)-R f )+b+R f

[0020] Where a is the frequency correction coefficient; b is the phase correction coefficient; t is the absolute time; C(t) represents the local time; R p (t) is the corrected reference time; R f Represents the overall offset of the data;

[0021] Based on the collected reference timestamp information, the following matrix equation can be constructed to obtain the parameters to be estimated:

[0022]

[0023]

[0024] Where L is the capacity of the timestamp sequence; {R(i)} is the reference timestamp sequence, where i = 1, 2, ..., L; {C(i)} is the local timestamp sequence, where i = 1, 2, ..., L; It is guaranteed that... Non-singular, the correction factors in the virtual clock model are estimated as follows:

[0025]

[0026] After calculating the frequency correction coefficient a and the phase correction coefficient b, and then substituting them into the established virtual clock model, the corrected reference time can be obtained based on the local time C(t) reading of the V2X communication module.

[0027] The electric vehicle V2X terminal clock synchronization method for preventing PPS signal loss in satellite navigation provided by the present invention, in the case of short-term GNSS loss, determines the adaptive sampling step size of the reference timestamp by judging the reception status of the PPS pulse and the reference timestamp, and then combines it with the established virtual clock model to obtain high-precision reference time without switching the clock source. This effectively overcomes the shortcomings of insufficient time synchronization accuracy caused by clock source switching in the prior art. Based on the adaptive timestamp acquisition method provided by the present invention, various forms of virtual clock models and correction parameter estimation methods can be applied, providing wider applicability compared to the prior art. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the principle of determining the adaptive sampling step size in the method provided by the present invention. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a method for synchronizing the clock of an electric vehicle V2X terminal to prevent loss of satellite navigation PPS signal, specifically including the following steps:

[0031] The V2X terminal is equipped with a GNSS module, a V2X communication module, and an auxiliary unit module. The GNSS module outputs an NMEA-0183 message and a 1PPS pulse signal at every whole second. The auxiliary module receives the NMEA-0183 message from the GNSS module, parses the Coordinated Universal Time (UTC) and date information, and transmits it to the V2X communication module as a reference timestamp. The V2X communication module receives the 1PPS pulse signal and the reference timestamp from the auxiliary module, triggers an interrupt based on the PPS signal at every whole second, and immediately reads the local timestamp upon entering the interrupt handling phase, thereby correcting the local time and completing time synchronization. After time synchronization, the V2X communication module continues to wait for the reference timestamp from the auxiliary module for a set time period.

[0032] The following time synchronization is performed based on the reception status of the GNSS signal:

[0033] a. When the GNSS signal is well received, the V2X communication module performs time synchronization directly based on the reference timestamp parsed from the GNSS signal;

[0034] b. When the GNSS signal experiences a short-term loss of lock, the GNSS module stops outputting the NMEA-0183 message (i.e., the reference timestamp) and only outputs a 1PPS pulse signal. In this case, the following operations are performed in sequence:

[0035] (1) The V2X communication module determines the adaptive sampling step size based on the sampling time points of the PPS signal and the reference timestamp acquired simultaneously but not continuously, and extracts the reference timestamp based on the adaptive sampling step size.

[0036] (2) Based on the extracted reference timestamp, adaptive sampling time and local time correction reference time, time synchronization is achieved.

[0037] In a preferred embodiment of the present invention, the process of determining the adaptive sampling step size in step (1) is as follows:

[0038] (1-1) First, based on whether the PPS signal and the reference timestamp are obtained simultaneously, two PPS signal states are defined: 1 and 0; where 1 indicates that the PPS signal and the reference timestamp are obtained simultaneously, and 0 indicates that only the PPS signal is received, but the reference timestamp is not received.

[0039] (1-2) Set a theoretical sampling step size S;

[0040] (1-3) The PPS signal state corresponding to the nth time (n=1,2,3,...) is sampled at intervals of the theoretical sampling step size S, and each sampling time is defined as a theoretical sampling point;

[0041] (1-4) Based on the PPS signal state at each theoretical sampling point, the actual sampling points are re-determined, including:

[0042] ① If the PPS state at the theoretical sampling point is 1, then that point is determined to be the actual sampling point;

[0043] ② If the PPS state at the theoretical sampling point is 0, then with a detection interval of 1 second, the moment when the PPS state changes to 1 after detecting the theoretical sampling point is determined as the actual sampling point;

[0044] This yields the adaptive step size for actually extracting the reference timestamp.

[0045] Figure 1 An example of PPS state determination and adaptive sampling step size determination is shown:

[0046] In the first sampling, the PPS status of the theoretical sampling point is 1, which means that the timestamp information of the point is valid and that point is the actual sampling point.

[0047] During the second sampling, since the PPS state at the theoretical sampling point is 0, we wait for the next PPS state until the PPS state is 1. At this time, the actual sampling point is S+2, and the actual sampling interval is S+1.

[0048] During the third sampling, the PPS state at the theoretical sampling point is 1, and this point is the actual sampling point. At this time, the actual sampling interval is S-1.

[0049] During the fourth sampling, the PPS state at the theoretical sampling point is 0. Until 3S+3, the PPS state becomes 1, which is the actual sampling point. At this time, the actual sampling interval is S+2.

[0050] Therefore, during the entire sampling process, the actual sampling step size is S+1, S-1, and S+2, fluctuating around the preset step size S.

[0051] In a preferred embodiment of the present invention, step (2) specifically involves establishing the following virtual clock model for time synchronization:

[0052] R p (t)=a(C(t)-R f )+b+R f

[0053] Where a is the frequency correction coefficient; b is the phase correction coefficient; t is the absolute time; C(t) represents the local time; R p (t) is the corrected reference time; R f Represents the overall offset of the data;

[0054] Based on the collected reference timestamp information, the following matrix equation can be constructed to obtain the parameters to be estimated:

[0055]

[0056]

[0057] Where L is the capacity of the timestamp sequence; {R(i)} is the reference timestamp sequence, where i = 1, 2, ..., L; {C(i)} is the local timestamp sequence, where i = 1, 2, ..., L; It is guaranteed that... Non-singular, the correction factors in the virtual clock model are estimated as follows:

[0058]

[0059] After calculating the frequency correction coefficient a and the phase correction coefficient b, and then substituting them into the established virtual clock model, the corrected reference time can be obtained based on the local time C(t) reading of the V2X communication module.

[0060] After obtaining the timestamp in the V2X communication model, other forms of virtual clock models or other parameter estimation methods can be constructed based on the specific local clock characteristics.

[0061] It should be understood that the sequence number of each step in the embodiments of the present invention does not imply 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 invention.

[0062] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for synchronizing the clock of an electric vehicle V2X terminal to prevent loss of satellite navigation PPS signal, characterized in that: Specifically, the following steps are included: The V2X terminal is equipped with a GNSS module, a V2X communication module, and an auxiliary unit module. The GNSS module outputs an NMEA-0183 message and a 1PPS pulse signal at every whole second. The auxiliary module receives the NMEA-0183 message from the GNSS module, parses the Coordinated Universal Time (UTC) and date information, and transmits it to the V2X communication module as a reference timestamp. The V2X communication module receives the 1PPS pulse signal and the reference timestamp from the auxiliary module, triggers an interrupt based on the PPS signal at every whole second, and immediately reads the local timestamp upon entering the interrupt handling phase, thereby correcting the local time and completing time synchronization. After time synchronization, the V2X communication module continues to wait for the reference timestamp from the auxiliary module for a set time period. The following time synchronization is performed based on the reception status of the GNSS signal: a. When the GNSS signal is well received, the V2X communication module performs time synchronization directly based on the reference timestamp parsed from the GNSS signal; b. When the GNSS signal experiences a short-term loss of lock, the GNSS module stops outputting the NMEA-0183 message (i.e., the reference timestamp) and only outputs a 1PPS pulse signal. In this case, the following operations are performed in sequence: (1) The V2X communication module determines the adaptive sampling step size based on the sampling time points of the discontinuously acquired PPS signal and reference timestamp, and extracts the reference timestamp based on the adaptive sampling step size; the process of determining the adaptive sampling step size is as follows: (1-1) First, based on whether the PPS signal and the reference timestamp are obtained simultaneously, two PPS signal states are defined: 1 and 0; where 1 indicates that the PPS signal and the reference timestamp are obtained simultaneously, and 0 indicates that only the PPS signal is received, but the reference timestamp is not received. (1-2) Set a theoretical sampling step size S; (1-3) The PPS signal state corresponding to the nth time (n=1,2,3,…) is sampled at intervals of the theoretical sampling step size S, and each sampling time is defined as a theoretical sampling point; (1-4) Based on the PPS signal state at each theoretical sampling point, the actual sampling points are re-determined, including: ① If the PPS state at the theoretical sampling point is 1, then that point is determined to be the actual sampling point; ② If the PPS state at the theoretical sampling point is 0, then with a detection interval of 1 second, the moment when the PPS state changes to 1 after detecting the theoretical sampling point is determined as the actual sampling point; This yields the adaptive step size for actually extracting the reference timestamp; (2) Based on the extracted reference timestamp, adaptive sampling time and local time, the reference time is corrected and time synchronization is achieved.

2. The method as described in claim 1, characterized in that: In step (2), the following virtual clock model for time synchronization is specifically established: in, a This is the frequency correction factor; b This is the phase correction coefficient; t Absolute time; C ( t () represents local time; R p ( t This is the corrected reference time; R f Represents the overall offset of the data; Based on the collected reference timestamp information, the following matrix equation can be constructed to obtain the parameters to be estimated: in, L Let {R(i)} be the capacity of the timestamp sequence; {R(i)} be the reference timestamp sequence, where i = 1, 2, ..., L; and {C(i)} be the local timestamp sequence, where i = 1, 2, ..., L. It is guaranteed that... Non-singular, the correction factors in the virtual clock model are estimated as follows: The frequency correction coefficient is calculated. a and phase correction coefficient b Then, by substituting the established virtual clock model, the local time of the V2X communication module can be used. C ( t The reading yields the corrected reference time.

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