CN113839734B - Time synchronization method and device, electronic equipment, storage medium and vehicle - Google Patents
Time synchronization method and device, electronic equipment, storage medium and vehicle Download PDFInfo
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- CN113839734B CN113839734B CN202111410365.8A CN202111410365A CN113839734B CN 113839734 B CN113839734 B CN 113839734B CN 202111410365 A CN202111410365 A CN 202111410365A CN 113839734 B CN113839734 B CN 113839734B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
- H04J3/0658—Clock or time synchronisation among packet nodes
- H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
- H04J3/0658—Clock or time synchronisation among packet nodes
- H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
- H04J3/067—Details of the timestamp structure
Abstract
The embodiment of the invention discloses a time synchronization method and device, electronic equipment, a storage medium and a vehicle, and relates to the field of automatic driving. The embodiment comprises the following steps: acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source is a satellite signal, and the second clock source is a time synchronization signal of a road side unit; when only the first clock source signal is acquired, taking the first clock source signal as a global clock source; when only the second clock source signal is obtained, the second clock source signal is used as a global clock source; when a first clock source signal and a second clock source signal are obtained simultaneously, a clock source with higher precision in the first clock source and the second clock source is used as a global clock source; and synchronizing the local time of the vehicle-mounted unit based on the global clock source. The embodiment provides the double clock sources, and ensures that the vehicle end can obtain stable and accurate time service in a severe environment through clock source redundancy, thereby ensuring the realizability and low cost of vehicle-road cooperation.
Description
Technical Field
The present application relates to the field of automatic driving technologies, and in particular, to a time synchronization method and apparatus, an electronic device, a storage medium, and a vehicle.
Background
With the high-speed development of automatic driving and intelligent traffic technologies, vehicle-road cooperation is a high-level development form of an intelligent traffic system, and is an important application of the technology of the internet of things in the field of traffic transportation. The time synchronization between the control units cannot be left at the beginning of the vehicle-road cooperation technology, namely, the time synchronization of the vehicle-mounted control unit, the road side unit or the cloud end is needed. At present, a vehicle-mounted control unit and a road side unit are subjected to time service through a PPS (pulse per second) signal of a GNSS (global navigation satellite system) module, or a high-precision crystal clock source is adopted for time service. However, the GNSS module has a high requirement on the environment, for example, when there is a large interference in a downtown area, there is no GPS signal in a tunnel or an overpass, or the GPS signal is affected by weather differences, the GNSS module cannot output a stable and accurate PPS signal, and cannot continuously perform time service. The high-precision crystal clock source has high cost, is not suitable for batch products, and is easy to be influenced by temperature to generate accumulated errors.
Disclosure of Invention
In order to solve the technical problem or at least partially solve the technical problem, embodiments of the present invention provide a time synchronization method, an apparatus, an electronic device, a computer-readable storage medium, and a vehicle.
In a first aspect, an embodiment of the present invention provides a time synchronization method, including: acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit; under the conditions that the first clock source signal is obtained and the second clock source signal is not obtained, taking the first clock source signal as a global clock source; under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source; under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and using the clock source signal with higher precision as a global clock source; and synchronizing the local time of the vehicle-mounted unit based on the global clock source.
In an alternative embodiment, comparing the precision between the first world time and the second world time to determine a clock source signal of higher precision from the first clock source signal and the second clock source signal comprises: acquiring adjacent two satellite signals, and acquiring a first candidate universal time and a second candidate universal time respectively based on the two satellite signals; calculating the difference value between the second candidate universal time and the first candidate universal time to obtain a first time difference; acquiring two adjacent time synchronization signals, and acquiring a third candidate universal time and a fourth candidate universal time respectively based on the two time synchronization signals; calculating a difference value between the fourth candidate universal time and the third candidate universal time to obtain a second time difference; comparing the first time difference to the second time difference to compare the accuracy between the first world time and the second world time; if the first time difference is smaller than the second time difference, the clock source signal with higher precision is the first clock source signal, otherwise, the clock source signal with higher precision is the second clock source signal.
In an optional embodiment, before comparing the first time difference with the second time difference, the method further comprises: and determining that the first time difference and the second time difference are not greater than a first preset threshold value.
In an alternative embodiment, obtaining the third candidate universal time or the fourth candidate universal time based on the time synchronization signal comprises: determining link propagation delay time and a clock frequency ratio of the vehicle-mounted control unit and the road side unit based on a time synchronization signal; and determining a third candidate universal time or a fourth candidate universal time according to the link propagation delay time and the clock frequency ratio.
In an optional embodiment, the method further comprises determining the link propagation delay time according to the following steps: sending an event message to the road side unit, and determining a first timestamp for sending the event message; receiving a response message and a following message sent by the road side unit, determining a second timestamp of the road side unit receiving the event message according to the response message, and determining a third timestamp of the road side unit sending the response message according to the following message; determining a fourth timestamp of receiving the response message; determining the link propagation delay time based on the first, second, third, and fourth timestamps;
determining the clock frequency ratio according to: periodically determining a plurality of the third timestamps and a plurality of the fourth timestamps, and determining the clock frequency ratio based on the plurality of the third timestamps and the plurality of the fourth timestamps.
In an optional embodiment, the method further comprises: according to the clock frequency ratio, modifying the counting period of the local clock of the vehicle-mounted control unit so that the counting frequency of the vehicle-mounted control unit is consistent with the counting frequency of the road side unit.
In an alternative embodiment, prior to acquiring the first world time, the method further comprises determining that the satellite signal satisfies a predetermined condition.
In an alternative embodiment, determining that the satellite signal satisfies a preset condition includes: determining the number of available satellites according to the satellite signals; judging whether the number of the available satellites is larger than or equal to a second preset threshold value or not; and if so, determining that the satellite signal meets a preset condition.
In an alternative embodiment, determining whether the number of available satellites is greater than or equal to a second threshold comprises: judging whether the signal-to-noise ratio of the available satellite is greater than a third preset threshold value or not, and taking the available satellite with the signal-to-noise ratio greater than the third preset threshold value as an effective satellite; and judging whether the number of the effective satellites is larger than or equal to a second preset threshold value.
In a second aspect, an embodiment of the present invention further provides a time synchronization apparatus, including: the clock source acquisition module is used for acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit; a global clock determining module, configured to use the first clock source signal as a global clock source when the first clock source signal is acquired and the second clock source signal is not acquired; under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source; under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and using the clock source signal with higher precision as a global clock source; and the time synchronization module is used for synchronizing the local time of the vehicle-mounted unit based on the global clock source.
In an optional embodiment, the global clock determination module is further configured to: acquiring adjacent two satellite signals, and acquiring a first candidate universal time and a second candidate universal time respectively based on the two satellite signals; calculating the difference value between the second candidate universal time and the first candidate universal time to obtain a first time difference; acquiring two adjacent time synchronization signals, and acquiring a third candidate universal time and a fourth candidate universal time respectively based on the two time synchronization signals; calculating a difference value between the fourth candidate universal time and the third candidate universal time to obtain a second time difference; comparing the first time difference to the second time difference to compare the accuracy between the first world time and the second world time; if the first time difference is smaller than the second time difference, the clock source signal with higher precision is the first clock source signal, otherwise, the clock source signal with higher precision is the second clock source signal.
In an optional embodiment, the global clock determination module is further configured to: before comparing the first time difference with the second time difference, determining that the first time difference and the second time difference are not greater than a first preset threshold.
In an optional embodiment, the global clock determination module is further configured to: determining link propagation delay time and a clock frequency ratio of the vehicle-mounted control unit and the road side unit based on a time synchronization signal; and determining a third candidate universal time or a fourth candidate universal time according to the link propagation delay time and the clock frequency ratio.
In an optional embodiment, the global clock determination module is further configured to: sending an event message to the road side unit, and determining a first timestamp for sending the event message; receiving a response message and a following message sent by the road side unit, determining a second timestamp of the road side unit receiving the event message according to the response message, and determining a third timestamp of the road side unit sending the response message according to the following message; determining a fourth timestamp of receiving the response message; determining the link propagation delay time based on the first, second, third, and fourth timestamps; periodically determining a plurality of the third timestamps and a plurality of fourth timestamps, and determining the clock frequency ratio based on the plurality of the third timestamps and the plurality of fourth timestamps.
In an optional embodiment, the apparatus further comprises an update module configured to: according to the clock frequency ratio, modifying the counting period of the local clock of the vehicle-mounted control unit so that the counting frequency of the vehicle-mounted control unit is consistent with the counting frequency of the road side unit.
In an optional embodiment, the apparatus further comprises a determining module configured to determine that the satellite signal satisfies a predetermined condition before the first world time is acquired.
In an optional embodiment, the determining module is further configured to: determining the number of available satellites according to the satellite signals; judging whether the number of the available satellites is larger than or equal to a second preset threshold value or not; and if so, determining that the satellite signal meets a preset condition.
In an optional embodiment, the determining module is further configured to: judging whether the signal-to-noise ratio of the available satellite is greater than a third preset threshold value or not, and taking the available satellite with the signal-to-noise ratio greater than the third preset threshold value as an effective satellite; and judging whether the number of the effective satellites is larger than or equal to a second preset threshold value.
In a third aspect, an embodiment of the present invention further provides an electronic device, including a processor, a communication interface, a memory, and a communication bus, where the processor, the communication interface, and the memory complete mutual communication through the communication bus;
the memory is used for storing at least one executable instruction, and the executable instruction causes the processor to execute the following steps: acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source is a satellite signal, and the second clock source is a time synchronization signal of a road side unit; under the conditions that the first clock source signal is acquired and the second clock source signal is not acquired, taking the first clock source signal as the global clock source; under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source; under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and using the clock source signal with higher precision as a global clock source; and synchronizing the local time of the vehicle-mounted unit based on the global clock source.
In a fourth aspect, the embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the time synchronization method of the embodiment of the present invention.
In a fifth aspect, an embodiment of the present invention further provides a vehicle, where the vehicle includes the time synchronization apparatus according to any of the above embodiments.
One or more of the above embodiments may have at least some or all of the following advantages:
by using the satellite signal as a first clock source and using the time synchronization signal from the road side unit as a second clock source (which is equivalent to using the road side unit as a second clock source), clock redundancy is realized, a clock source with better time precision is determined under the condition that the time synchronization signal and the stable satellite signal can be received at the same time, the time source with better time precision is used as a global clock source, namely a synchronous clock source, and time synchronization is performed based on the global clock source; under the condition that only a first clock source signal can be acquired and a second clock source signal cannot be acquired, taking the first clock source signal as a global clock source; under the conditions that only a second clock source signal can be obtained and the first clock source signal cannot be obtained, taking the second clock source as a global clock source; based on the global clock source, the technical means for synchronizing the local time of the vehicle-mounted unit realizes the time synchronization of the whole environment, and the second clock source is used as the global clock source to perform the time synchronization under the condition that stable satellite signals cannot be obtained under severe weather or severe environments such as tunnels, overpasses and the like, so that stable and accurate universal time is obtained, the vehicle-mounted control unit can obtain stable and accurate time service under any environment, and the low cost is ensured.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the related art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 schematically shows a flow chart of the main steps of a time synchronization method of an embodiment of the invention;
FIG. 2 schematically illustrates a scene diagram of a time synchronization method according to an embodiment of the present invention;
fig. 3 schematically shows a flowchart for measuring a link propagation delay time in the time synchronization method of the embodiment of the present invention;
FIG. 4 is a timing diagram schematically illustrating measuring link propagation delay time in a time synchronization method according to an embodiment of the present invention;
FIG. 5 schematically shows a timing diagram of a clock frequency ratio in the time synchronization method of the embodiment of the present invention;
FIG. 6 schematically illustrates a sub-flow diagram of a method of time synchronization according to an embodiment of the present invention;
FIG. 7 is a flow chart that schematically illustrates the main steps of a method for time synchronization in accordance with another embodiment of the present invention;
fig. 8 is a schematic structural diagram showing a time synchronization apparatus according to an embodiment of the present invention;
fig. 9 schematically shows a block diagram of an electronic device provided in an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Fig. 1 schematically shows a schematic diagram of the main steps of a time synchronization method according to an embodiment of the present invention. The method is applied to an on-board unit. As shown in fig. 1, the method includes:
step S101: acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit;
step S102: under the conditions that the first clock source signal is acquired and the second clock source signal is not acquired, taking the first clock source signal as the global clock source;
step S103: under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source;
step S104: under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal;
step S105: comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and using the clock source signal with higher precision as a global clock source;
step S106: and synchronizing the local time of the vehicle-mounted unit based on the global clock source.
The time synchronization method provided by the embodiment of the invention can be applied to an automatic driving scene, as shown in fig. 2, in the automatic driving scene, a vehicle performs data interaction with a road side unit (such as a road end base station) based on a V2X protocol, the road side unit can receive a satellite signal and a cloud end signal, and the road side unit can obtain accurate time service through the satellite signal or the cloud end. The road side units can be arranged at intervals of a preset distance, and can communicate with each other in a wired or wireless communication link or an optical fiber cable mode. The time synchronization method of the embodiment of the invention can be applied to the vehicle-mounted unit.
In this embodiment, a GNSS module (Global Navigation Satellite System) is disposed on the vehicle, and receives a Satellite signal through the GNSS module, where the Satellite signal is a signal of a Navigation Satellite System, such as a GPS signal or a beidou signal. The first world time is derived based on the satellite signal, and the satellite signal may be used as the first clock source signal. For example, after receiving a GPS signal, a PPS signal (pulse per second) is analyzed from the GPS signal, and the first world time is acquired based on the PPS signal.
The embodiment may receive the Time synchronization signal of the roadside unit based on the V2X technical specification (technical specification for implementing information interaction between the vehicle and any entity that may affect the vehicle) and the 802.1AS Protocol (Generalized Precision Time Protocol). The second universal time may be obtained based on the time synchronization signal, and therefore the time synchronization signal of the road side unit is used as the second clock source signal.
For steps S102 to S105, the embodiment of the present invention provides two clock sources, and selects different clock sources as a global clock source for time synchronization under different conditions, for example, under the conditions that a first clock source signal is obtained and a second clock source signal is not obtained, the first clock source signal is used as the global clock source; under the conditions that a second clock source signal is obtained and a first clock source signal is not obtained, the second clock source signal is used as a global clock source; under the condition of simultaneously acquiring a first clock source signal and a second clock source signal, the precision of the first clock source signal and the second clock source signal is compared, and a clock source with higher precision is selected from the first clock source signal and the second clock source signal as a global clock source. Wherein the process of comparing the accuracy of the first clock source signal and the second clock source signal comprises: calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal; comparing the accuracies between the first world time and the second world time to compare accuracies of the first clock source signal and the second clock source signal.
In an alternative embodiment, the step of obtaining the second universal time from the second clock source signal may comprise:
determining link propagation delay time and a clock frequency ratio of an on-board unit and the road side unit based on the second clock source; and determining a second universal time according to the link propagation delay time and the clock frequency ratio.
The link propagation delay time is a time required for a communication link between nodes (such as an on-board unit and a roadside unit in the present embodiment) to communicate to propagate in a single direction, and is also referred to as a link average propagation time. The clock frequency ratio is a ratio of the counting frequencies of the communicating nodes, and since the frequencies of the clocks between the communicating nodes may have a difference and are not always completely consistent, the time measurement references are different, and errors are introduced, so that the adjustment is required through the clock frequency ratio. The present embodiment determines the link propagation delay time and clock frequency ratio according to the 802.1AS protocol. The messages in the 802.1AS protocol comprise event messages and general messages, the event messages generate timestamps in the sending and receiving processes, and the general messages do not need to generate the timestamps. The event message includes: sync messages, PDelay _ Req messages, PDelay _ Resp messages. The common messages include a Follow _ up message and a PDelay _ Resp _ Follow message. The Sync message and the Follow _ up message are a group of messages, the Sync message is sent periodically to trigger and record the local time, and the Follow _ up message is responsible for sending the recorded local time to the node. The PDelay _ Req message, PDelay _ Resp message, and PDelay _ Resp _ congestion message are used to measure the link propagation delay time between nodes in the case of peer-to-peer delay mechanism. Specifically, as shown in fig. 3, 4, and 5, the ratio between the propagation delay time of the link and the clock frequency is determined according to the following steps:
step S301: sending an event message to the road side unit, and determining a first timestamp T1 for sending the event message;
step S302: receiving a response message and a following message sent by the road side unit, determining a second timestamp T2 when the road side unit receives the event message according to the response message, and determining a third timestamp T3 when the road side unit sends the response message according to the following message;
step S303: determining a fourth timestamp T4 of receiving the response packet;
step S304: determining the link propagation delay time based on the first, second, third, and fourth timestamps;
step S305: periodically determining a plurality of the third timestamps and a plurality of the fourth timestamps, and determining the clock frequency ratio based on the plurality of the third timestamps and the plurality of the fourth timestamps.
Fig. 4 schematically shows a timing diagram for determining the link propagation delay time in the present embodiment. In fig. 4, the requesting party may be the on-board unit control unit in the present embodiment, and the responding party may be the roadside unit.
As shown in fig. 4, the requester sends an event message (i.e., PDelay _ Req message) to the responder, requesting that the link delay time be measured. When the PDelay _ Req message leaves the physical layer of the requestor, the requestor uses the local clock to obtain T1. When the PDelay _ Req message reaches the physical layer of the responder, the responder obtains T2 using the local clock. The responder generates a response message (i.e., PDelay _ Resp message) and sends the response message to the requester at time T3, where the PDelay _ Resp message carries T2. The requestor receives the PDelay _ Resp message and captures the T4 of the received PDelay _ Resp message using the local clock. After sending the PDelay _ Resp message, the responder sends a follow-up message (i.e., PDelay _ Resp _ following message) to the requester, where the PDelay _ Resp _ following message carries T3. Thus, the requestor obtains T1, T2, T3, and T4, and then calculates the link propagation delay time Pdelay using the following equation:
fig. 5 schematically shows a timing chart of the measurement clock frequency ratio in the present embodiment. As shown in fig. 5, the requesting party periodically sends an event message to the responding party, the responding party periodically feeds back a response message (PDelay _ Resp message) and a following message (PDelay _ Resp _ following message), and periodically determines a third timestamp and a fourth timestamp, such as t31、t41、t32、t42Then, the clock frequency Ratio is calculated using the following equation to calibrate the clocking frequency of the in-vehicle unit control unit.
After determining the link propagation delay time and the clock frequency ratio, determining a second universal time T corresponding to the vehicle-mounted unit control unit at any time T by using the link propagation delay time and the clock frequency ratio, as shown in the following formula (3):
wherein, Ta represents the time stamp of sending the Sync message by the responder, and Tb represents the time stamp of receiving the Follow _ up message by the requester.
After the first world time and the second world time are obtained, the precision of the first world time and the second world time is compared, a clock source corresponding to the world time with higher precision is selected as a global clock source, and time synchronization is carried out on the vehicle-mounted unit based on the global clock source. In an alternative embodiment, as shown in FIG. 6, the accuracy of the first world time and the second world time are compared by:
step S601: acquiring adjacent two satellite signals, and acquiring a first candidate universal time and a second candidate universal time respectively based on the two satellite signals; calculating the difference value between the second candidate universal time and the first candidate universal time to obtain a first time difference;
step S602: acquiring two adjacent time synchronization signals, and acquiring a third candidate universal time and a fourth candidate universal time respectively based on the two time synchronization signals; calculating a difference value between the fourth candidate universal time and the third candidate universal time to obtain a second time difference;
step S603: comparing the first time difference to the second time difference to compare the accuracy between the first world time and the second world time;
step S604: if the first time difference is smaller than the second time difference, the clock source signal with higher precision is the first clock source signal, otherwise, the clock source signal with higher precision is the second clock source signal.
For step S601, two adjacent satellite signals are acquired, and a first candidate universal time is acquired based on the first acquired satellite signal
Acquiring a second candidate universal time based on the second acquired satellite signal
. Calculating a second candidate universal time
And a second candidate universal time
Difference between them, obtaining a first time difference
。
For step S602, two adjacent clock synchronization signals are obtained, and for each clock synchronization signal, the universal time is obtained as a third candidate universal time with reference to the step of obtaining the second universal time
And fourth candidate world time
Calculating a third candidate world time
And fourth candidate world time
To obtain a second time difference
。
For steps S603-604, the comparison is made
And
if, if
Is less than
If the precision of the universal time obtained based on the satellite signal is high, that is, the precision of the first clock source is high, the first clock source is used as a global clock source, and the universal time obtained based on the global clock source is the universal time of the vehicle-mounted control unit. If it is
Is less than or equal to
If the precision of the universal time obtained based on the time synchronization signal of the road side unit is high, that is, the precision of the second clock source is high, the second clock source is used as a global clock source, the universal time obtained based on the global clock source is the universal time of the vehicle-mounted control unit, that is, the time T of the vehicle-mounted control unit at any time is calculated according to the above formula (3) to determine the corresponding universal time T.
According to the time synchronization method, the satellite signal is used as the first clock source, the time synchronization signal from the road side unit is used as the second clock source (equivalently, the road side unit is used as the second clock source), clock redundancy is achieved, the clock source with better time precision is determined under the condition that the time synchronization signal and the stable satellite signal can be received at the same time, the time source with better time precision is used as the global clock source, namely, the synchronization clock source, and time synchronization is carried out based on the global clock source; under the condition that only a first clock source signal can be acquired and a second clock source signal cannot be acquired, taking the first clock source signal as a global clock source; under the conditions that only a second clock source signal can be obtained and the first clock source signal cannot be obtained, taking the second clock source as a global clock source; based on the global clock source, the technical means for synchronizing the local time of the vehicle-mounted unit realizes the time synchronization of the whole environment, and the second clock source is used as the global clock source to perform the time synchronization under the condition that stable satellite signals cannot be obtained under severe weather or severe environments such as tunnels, overpasses and the like, so that stable and accurate universal time is obtained, the vehicle-mounted control unit can obtain stable and accurate time service under any environment, and the low cost is ensured.
The time synchronization method of the embodiment of the invention can be periodically executed according to the preset time interval so as to periodically perform time synchronization on the time of the vehicle-mounted unit and reduce the error.
In an optional embodiment, the time synchronization method further includes, before comparing the first time difference with the second time difference, determining that the first time difference and the second time difference are not greater than a first preset threshold. If the first time difference and the second time difference are both larger than the first preset threshold, the time synchronization is determined to be invalid, and the time synchronization of the next period is waited. The first preset threshold may be flexibly set according to an application scenario, and the present invention is not limited herein. Wherein, the first time difference and the second time difference are not greater than the first preset threshold value, and the condition comprises:
the first time difference is smaller than or equal to a first preset threshold, and the second time difference is larger than the first preset threshold;
the second time difference is smaller than or equal to a first preset threshold, and the first time difference is larger than the first preset threshold;
the first time difference and the second time difference are both smaller than or equal to a first preset threshold.
In this embodiment, a first preset threshold is set to limit a basic requirement or a minimum requirement for time accuracy, and if both the first time difference and the second time difference are greater than the first preset threshold, it is indicated that the time accuracy does not satisfy the basic requirement or the minimum requirement, and neither the satellite signal nor the clock synchronization signal is used for performing time synchronization nor the requirement is satisfied.
Fig. 7 schematically shows a schematic diagram of the main steps of a time synchronization method of another embodiment of the present invention. As shown in fig. 7, the method includes:
step S701: acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit;
step S702: under the conditions that the first clock source signal is acquired and the second clock source signal is not acquired, taking the first clock source signal as the global clock source;
step S703: under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source;
step S704: determining whether the satellite signal meets a preset condition or not under the condition of simultaneously acquiring the first clock source signal and the second clock source signal; if the satellite signal meets the preset condition, executing steps S705-S706; if the satellite signal does not satisfy the preset condition, executing step S708;
step S705: calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal;
step S706: comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and using the clock source signal with higher precision as a global clock source;
step S707: synchronizing local time of the vehicle-mounted control unit based on the global clock source;
step S708: and if the satellite signal does not meet the preset condition, taking a second time source as a global clock source, and synchronizing the local time of the vehicle-mounted unit based on the global clock source.
For step S704, it may be determined whether the satellite signal satisfies a preset condition according to the following steps: determining the number of available satellites according to the satellite signals; judging whether the number of the available satellites is larger than or equal to a second preset threshold value or not; and if so, determining that the satellite signal meets a preset condition. The second preset threshold may be flexibly set according to an application scenario, and the present invention is not limited herein.
According to the time synchronization method, under the condition that the first clock source signal and the second clock source signal can be obtained, the precision of the universal time obtained based on the satellite signals is roughly judged according to the number of the satellites, if the number of the satellites is larger than or equal to a second preset threshold value, the universal time obtained based on the satellite signals preliminarily meets the precision requirement, if the number of the satellites is smaller than the second preset threshold value, the universal time obtained based on the satellite signals cannot meet the precision requirement, at the moment, the second time source is directly used as the universal time source for time synchronization, and the fact that vehicles can obtain high-precision and stable time service in tunnels, bridge openings or bad weather is guaranteed.
Fig. 8 schematically shows a structural diagram of a time synchronization apparatus 800 according to an embodiment of the present invention, and as shown in fig. 8, the apparatus 800 includes:
a clock source obtaining module 801, configured to obtain a first clock source signal and a second clock source signal in real time, where the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit;
a global clock determining module 802, configured to use the first clock source signal as the global clock source when the first clock source signal is obtained and the second clock source signal is not obtained; under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source; under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and using the clock source signal with higher precision as a global clock source;
and a time synchronization module 803, configured to synchronize the local time of the vehicle-mounted unit based on the global clock source.
Optionally, the global clock determining module 802 is further configured to: acquiring adjacent two satellite signals, and acquiring a first candidate universal time and a second candidate universal time respectively based on the two satellite signals; calculating the difference value between the second candidate universal time and the first candidate universal time to obtain a first time difference; acquiring two adjacent time synchronization signals, and acquiring a third candidate universal time and a fourth candidate universal time respectively based on the two time synchronization signals; calculating a difference value between the fourth candidate universal time and the third candidate universal time to obtain a second time difference; comparing the first time difference to the second time difference to compare the accuracy between the first world time and the second world time; if the first time difference is smaller than the second time difference, the clock source signal with higher precision is the first clock source signal, otherwise, the clock source signal with higher precision is the second clock source signal.
Optionally, the global clock determining module 802 is further configured to: before comparing the first time difference with the second time difference, determining that the first time difference and the second time difference are not greater than a first preset threshold.
Optionally, the global clock determining module 802 is further configured to: determining link propagation delay time and a clock frequency ratio of the vehicle-mounted control unit and the road side unit based on a time synchronization signal; and determining a third candidate universal time or a fourth candidate universal time according to the link propagation delay time and the clock frequency ratio.
Optionally, the global clock determining module 802 is further configured to: sending an event message to the road side unit, and determining a first timestamp for sending the event message; receiving a response message and a following message sent by the road side unit, determining a second timestamp of the road side unit receiving the event message according to the response message, and determining a third timestamp of the road side unit sending the response message according to the following message; determining a fourth timestamp of receiving the response message; determining the link propagation delay time based on the first, second, third, and fourth timestamps; periodically determining a plurality of the third timestamps and a plurality of the fourth timestamps, and determining the clock frequency ratio based on the plurality of the third timestamps and the plurality of the fourth timestamps.
Optionally, the apparatus further comprises an update module configured to: according to the clock frequency ratio, modifying the counting period of the local clock of the vehicle-mounted control unit so that the counting frequency of the vehicle-mounted control unit is consistent with the counting frequency of the road side unit.
Optionally, the apparatus further includes a determining module, configured to determine that the satellite signal satisfies a preset condition before the first world time is acquired.
Optionally, the determining module is further configured to: determining the number of available satellites according to the satellite signals; judging whether the number of the available satellites is larger than or equal to a second preset threshold value or not; and if so, determining that the satellite signal meets a preset condition.
Optionally, the determining module is further configured to: and taking the second time source as a global time source under the condition that the satellite signal does not meet the preset condition.
The time synchronization device of the embodiment of the invention realizes clock redundancy by taking the satellite signal as a first clock source and the time synchronization signal from the road side unit as a second clock source (equivalently, the road side unit is taken as the second clock source), determines the clock source with better time precision under the condition of simultaneously receiving the time synchronization signal and the stable satellite signal, takes the time source with better time precision as a global clock source, namely a synchronous clock source, and carries out time synchronization based on the global clock source; under the condition that only a first clock source signal can be acquired and a second clock source signal cannot be acquired, taking the first clock source signal as a global clock source; under the conditions that only a second clock source signal can be obtained and the first clock source signal cannot be obtained, taking the second clock source as a global clock source; based on the global clock source, the technical means for synchronizing the local time of the vehicle-mounted unit realizes the time synchronization of the whole environment, and the second clock source is used as the global clock source to perform the time synchronization under the condition that stable satellite signals cannot be obtained under severe weather or severe environments such as tunnels, overpasses and the like, so that stable and accurate universal time is obtained, the vehicle-mounted control unit can obtain stable and accurate time service under any environment, and the low cost is ensured.
Fig. 9 schematically shows a schematic view of an electronic device according to an embodiment of the invention. As shown in fig. 9, an electronic device 900 provided in an embodiment of the present invention includes a processor 901, a communication interface 902, a memory 903, and a communication bus 904, where the processor 901, the communication interface 902, and the memory 903 complete communication with each other through the communication bus 904; a memory 903 for storing at least one executable instruction; the processor 901 is configured to implement the time synchronization method as described above when executing the executable instructions stored in the memory.
Specifically, when the time synchronization method is implemented, the executable instructions cause the processor to perform the following steps: acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit; under the conditions that the first clock source signal is obtained and the second clock source signal is not obtained, taking the first clock source signal as a global clock source; under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source; under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, calculating a first world time corresponding to the first clock source signal and a second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and using the clock source signal with higher precision as a global clock source; and synchronizing the local time of the vehicle-mounted unit based on the global clock source.
The memory 903 may be an electronic memory such as a flash memory, an EEPROM (electrically erasable and programmable read only memory), an EPROM, a hard disk, or a ROM. The memory 903 has a storage space for program code for performing any of the method steps of the above-described method. For example, the memory space for the program code may comprise respective program codes for implementing respective steps in the above method, respectively. The program code can be read from or written to one or more computer program products. These computer program products comprise a program code carrier such as a hard disk, a Compact Disc (CD), a memory card or a floppy disk. Such computer program products are typically portable or fixed storage units. The storage unit may have a storage section or a storage space or the like arranged similarly to the memory 903 in the electronic device described above. The program code may be compressed, for example, in a suitable form. Typically, the memory unit comprises a program for performing the steps of the method according to an embodiment of the invention, i.e. a code readable by a processor, such as 901, for example, which code, when executed by an electronic device, causes the electronic device to perform the steps of the method described above.
The embodiment of the invention also provides a computer readable storage medium. The above-mentioned computer-readable storage medium has stored thereon a computer program which, when executed by a processor, implements the time synchronization method as described above.
The computer-readable storage medium may be contained in the apparatus/device described in the above embodiments; or may be present alone without being assembled into the device/apparatus. The computer-readable storage medium carries one or more programs which, when executed, implement the method according to an embodiment of the present invention.
According to embodiments of the present invention, the computer readable storage medium may be a non-volatile computer readable storage medium, which may include, for example but is not limited to: a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the present invention, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
The above-described solutions provided by the embodiments of the present invention may be implemented in hardware, in software modules running on one or more processors, or in a combination of them, in whole or in part. Those skilled in the art will appreciate that a microprocessor or Digital Signal Processor (DSP) may be used in practice to implement some or all of the functionality of some or all of the components in an electronic device according to embodiments of the present invention. Embodiments of the invention may also be implemented as apparatus or device programs (e.g., computer programs and computer program products) for performing a portion or all of the methods described herein. Programs that implement embodiments of the present invention may be stored on a computer-readable medium or may be in the form of one or more signals. Such a signal may be downloaded from an internet website or provided on a carrier signal or in any other form.
It is noted that, herein, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or step from another entity or step without necessarily requiring or implying any actual such relationship or order between such entities or steps. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. A method of time synchronization, the method comprising:
acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit;
under the conditions that the first clock source signal is obtained and the second clock source signal is not obtained, taking the first clock source signal as a global clock source;
under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source;
under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, determining the number of available satellites according to the satellite signals; judging whether the number of the available satellites is larger than or equal to a second preset threshold value or not; if the number of the available satellites is larger than or equal to a second preset threshold value, calculating first world time corresponding to the first clock source signal and second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and taking the clock source signal with higher precision as a global clock source; if the number of the available satellites is smaller than a second preset threshold value, taking the second clock source signal as a global clock source;
and synchronizing the local time of the vehicle-mounted unit based on the global clock source.
2. A method according to claim 1, wherein comparing the precision between the first world time and the second world time to determine a more precise clock source signal from the first clock source signal and the second clock source signal comprises:
acquiring adjacent two satellite signals, and acquiring a first candidate universal time and a second candidate universal time respectively based on the two satellite signals; calculating the difference value between the second candidate universal time and the first candidate universal time to obtain a first time difference;
acquiring two adjacent time synchronization signals, and acquiring a third candidate universal time and a fourth candidate universal time respectively based on the two time synchronization signals; calculating a difference value between the fourth candidate universal time and the third candidate universal time to obtain a second time difference;
comparing the first time difference to the second time difference to compare the accuracy between the first world time and the second world time;
if the first time difference is smaller than the second time difference, the clock source signal with higher precision is the first clock source signal, otherwise, the clock source signal with higher precision is the second clock source signal.
3. The method of claim 2, wherein prior to comparing the first time difference to the second time difference, the method further comprises: and determining that the first time difference and the second time difference are not greater than a first preset threshold value.
4. The method of claim 2, wherein obtaining a third candidate universal time or a fourth candidate universal time based on the time synchronization signal comprises:
determining a link propagation delay time and a clock frequency ratio of the on-board unit and the roadside unit based on the time synchronization signal;
and determining a third candidate universal time or a fourth candidate universal time according to the link propagation delay time and the clock frequency ratio.
5. The method of claim 4, further comprising:
modifying the counting period of the local clock of the on-board unit according to the clock frequency ratio so that the counting frequency of the on-board unit is consistent with the counting frequency of the road side unit.
6. A time synchronization apparatus, characterized in that the apparatus comprises:
the clock source acquisition module is used for acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit;
a global clock determining module, configured to use the first clock source signal as a global clock source when the first clock source signal is acquired and the second clock source signal is not acquired; under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source; under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, determining the number of available satellites according to the satellite signals; judging whether the number of the available satellites is larger than or equal to a second preset threshold value or not; under the condition that the number of the available satellites is larger than or equal to a second preset threshold value, calculating first world time corresponding to the first clock source signal and second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and taking the clock source signal with higher precision as a global clock source; taking the second clock source signal as a global clock source under the condition that the number of the available satellites is smaller than a second preset threshold;
and the time synchronization module is used for synchronizing the local time of the vehicle-mounted unit based on the global clock source.
7. An electronic device is characterized by comprising a processor, a communication interface, a memory and a communication bus, wherein the processor, the communication interface and the memory are communicated with each other through the communication bus;
the memory is used for storing at least one executable instruction, and the executable instruction causes the processor to execute the following steps:
acquiring a first clock source signal and a second clock source signal in real time, wherein the first clock source signal is a satellite signal, and the second clock source signal is a time synchronization signal of a road side unit;
under the conditions that the first clock source signal is obtained and the second clock source signal is not obtained, taking the first clock source signal as a global clock source;
under the conditions that the second clock source signal is obtained and the first clock source signal is not obtained, taking the second clock source signal as the global clock source;
under the condition of simultaneously acquiring the first clock source signal and the second clock source signal, determining the number of available satellites according to the satellite signals; judging whether the number of the available satellites is larger than or equal to a second preset threshold value or not; if the number of the available satellites is larger than or equal to a second preset threshold value, calculating first world time corresponding to the first clock source signal and second world time corresponding to the second clock source signal; comparing the precision between the first world time and the second world time to determine a clock source signal with higher precision from the first clock source signal and the second clock source signal, and taking the clock source signal with higher precision as a global clock source; if the number of the available satellites is smaller than a second preset threshold value, taking the second clock source signal as a global clock source;
and synchronizing the local time of the vehicle-mounted unit based on the global clock source.
8. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the method of any one of claims 1-5.
9. A vehicle characterized in that it comprises the time synchronization device of claim 6.
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| CN112394634A (en) * | 2021-01-21 | 2021-02-23 | 国汽智控(北京)科技有限公司 | Time service method, device, equipment and storage medium for vehicle-mounted computing platform |
| CN113271169B (en) * | 2021-04-27 | 2023-03-24 | 东风汽车集团股份有限公司 | Vehicle time service method and system based on wireless communication terminal |
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| CN105281932A (en) * | 2014-06-23 | 2016-01-27 | 中兴通讯股份有限公司 | A clock time source selection method and device and network elements |
| CN110198529A (en) * | 2019-06-03 | 2019-09-03 | 深圳成谷科技有限公司 | A kind of clock synchronizing method, device, drive test unit and storage medium |
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