CN113259899A - Clock synchronization method and device, road side unit and storage medium - Google Patents
Clock synchronization method and device, road side unit and storage medium Download PDFInfo
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/30—Services specially adapted for particular environments, situations or purposes
- H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
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- H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04W56/0055—Synchronisation arrangements determining timing error of reception due to propagation delay
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Abstract
The invention discloses a clock synchronization method, a clock synchronization device, a road side unit and a storage medium, which are applied to a Road Side Unit (RSU) which can not receive Global Navigation Satellite System (GNSS) signals and comprise the following steps: identifying a standard RSU according to the received at least one periodic signal; adjusting the frequency of a local clock according to a target periodic signal corresponding to the standard RSU so as to enable the local clock and the GNSS to keep frequency synchronization; and calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the local clock and the standard RSU, and performing timing adjustment on the local clock according to the receiving time delay and the frequency adjustment result so as to keep the local clock and the GNSS in timing synchronization. According to the technical scheme of the embodiment of the invention, the RSU which cannot receive the GNSS signal can be synchronized to the GNSS, and the communication performance between the RSUs and between the RSU and the OBU is improved.
Description
Technical Field
The embodiment of the invention relates to the technical field of communication, in particular to a clock synchronization method, a clock synchronization device, a road side unit and a storage medium.
Background
In recent years, with the intensive research of unmanned technology, Vehicle networking technology (Vehicle to X, V2X) based on information interaction between vehicles, drivers and roads has been developed. V2X includes Vehicle-to-Vehicle (V2V) technology, Vehicle-to-Infrastructure (V2I) technology, and Vehicle-to-Vehicle (V2P) technology, among others. Among them, V2V and V2I mainly include an On Board Unit (OBU) and a Road Side Unit (RSU) installed On the Road Side. The RSU as part of future road infrastructure will be installed in all parking routes including tunnels, garages, elevated roads, etc.
In V2X, information is transmitted in a broadcast manner, each device is independent, and in order to ensure synchronization between transmission and reception of each device, a synchronization scheme mainly based on a Global Navigation Satellite System (GNSS) is defined in the specification, that is, all devices can perform clock synchronization, including frequency synchronization and timing synchronization, by using GNSS signals.
However, when the GNSS signal cannot be received (for example, when the RSU cannot normally receive the GNSS signal in a tunnel or an overhead), the RSU cannot perform frequency adjustment, a large frequency deviation is caused by clock aging in a long-term operation, the frequency deviation is increased, and a timing deviation is accumulated, and these frequency deviation and timing deviation have a large influence on the transmission/reception performance between the RSU and the OBU. Fig. 1a is a schematic view of a scenario that RSUs are distributed inside and outside a tunnel, and taking fig. 1a as an example, it is assumed that three RSUs, namely RSU1, RSU2, and RSUn1, are arranged inside the tunnel. Two RSUs, RSU0 and RSUn, are disposed outside the tunnel. When the vehicle is at the point A, the vehicle and the RSU0 can both use the GNSS signal for synchronization, so the vehicle and the RSU0 can normally pass. When the vehicle travels to the point B, the vehicle can communicate with the RSU0 and the RSU1 at the same time, but since the RSU1 cannot normally receive GNSS signals in the tunnel, the clock of the RSU1 has a large frequency deviation and timing deviation, in this case, the vehicle may not normally analyze the signal of the RSU1 while communicating with the RSU0, and mutual interference between the two may be caused by clock asynchronization.
Disclosure of Invention
The embodiment of the invention provides a clock synchronization method, a clock synchronization device, a road side unit and a storage medium, which can realize that RSUs which cannot receive GNSS signals are synchronized to GNSS, and improve the communication performance between the RSUs and OBUs.
In a first aspect, an embodiment of the present invention provides a clock synchronization method, where the method is applied to a current road side unit RSU that cannot receive GNSS signals of a global navigation satellite system, and the method includes:
identifying a standard RSU according to the received at least one periodic signal; the standard RSU is an RSU synchronized to the GNSS;
adjusting the frequency of a local clock according to a target periodic signal corresponding to the standard RSU so that the local clock and the GNSS keep frequency synchronization;
and calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the local clock and the standard RSU, and performing timing adjustment on a local clock according to the receiving time delay and a frequency adjustment result so as to keep the local clock and the GNSS in timing synchronization.
In a second aspect, an embodiment of the present invention further provides a clock synchronization apparatus, which is applied in a current RSU that cannot receive GNSS signals of a global navigation satellite system, and includes:
the standard RSU identification module is used for identifying a standard RSU according to the received at least one periodic signal; the standard RSU is an RSU synchronized to the GNSS;
a frequency adjusting module, configured to adjust a frequency of a local clock according to a target periodic signal corresponding to the standard RSU, so that the local clock and the GNSS maintain frequency synchronization;
and the timing adjustment module is used for calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the timing adjustment module and the standard RSU, and performing timing adjustment on a local clock according to the receiving time delay and a frequency adjustment result so as to enable the local clock and the GNSS to keep timing synchronization.
In a third aspect, an embodiment of the present invention further provides a road side unit, where the road side unit includes:
one or more processors;
storage means for storing one or more programs;
when executed by the one or more processors, cause the one or more processors to perform the clock synchronization method provided by any of the embodiments of the invention.
In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, where a computer program is stored on the storage medium, and when the computer program is executed by a processor, the computer program implements the clock synchronization method provided in any embodiment of the present invention.
In the technical scheme of the embodiment of the invention, the current RSU identifies the standard RSU according to at least one received periodic signal, adjusts the frequency of the local clock according to a target periodic signal corresponding to the standard RSU so as to enable the local clock and the GNSS to keep frequency synchronization, calculates the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the local clock and the standard RSU, and performs timing adjustment on the local clock according to the receiving time delay and the frequency adjustment result so as to enable the local clock and the GNSS to keep timing synchronization.
Drawings
Fig. 1a is a schematic view of a scenario that RSUs are distributed inside and outside a tunnel in an embodiment of the present invention;
FIG. 1b is a flowchart of a clock synchronization method according to a first embodiment of the present invention;
FIG. 2a is a flowchart of a clock synchronization method according to a second embodiment of the present invention;
FIG. 2b is a schematic diagram of a periodic signal in an embodiment of the present invention;
FIG. 2c is a schematic diagram of an adjusted periodic signal according to an embodiment of the present invention;
FIG. 3a is a flowchart of a clock synchronization method according to a third embodiment of the present invention;
FIG. 3b is a schematic diagram of a periodic signal in an embodiment of the present invention;
fig. 4 is a structural diagram of a clock synchronization apparatus according to a fourth embodiment of the present invention;
fig. 5 is a schematic structural diagram of a roadside unit in a fifth embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Example one
Fig. 1b is a flowchart of a clock synchronization method according to an embodiment of the present invention, where this embodiment is applicable to a situation where a roadside unit RSU cannot receive a GNSS signal, and the clock synchronization method is executed by a clock synchronization apparatus, where the apparatus may be implemented by software and/or hardware, and may be generally integrated in a current RSU that cannot receive a GNSS signal, and specifically includes the following steps:
In this embodiment, the RSU is installed at the roadside for communicating with the OBU, implementing functions such as vehicle identification and electronic deduction. If the current RSU is under an overhead, in a tunnel or under a bridge, the GNSS signal is shielded, and the positioning device in the current RSU cannot receive the GNSS signal, the periodic signal sent by the standard RSU is received. The standard RSU may be an RSU that is close to the current RSU and can normally receive the GNSS signal.
In a specific embodiment, there is a direct path between the standard RSU and the current RSU, and the information of the other party can be reliably received. Optionally, the standard RSU may always send a periodic signal to the outside, and after the current RSU receives the periodic signal, the standard RSU corresponding to the periodic signal may be identified according to the source information and the sending address corresponding to the periodic signal, or the identification information of the standard RSU carried in the periodic signal.
Taking the RSUs distributed in fig. 1a as an example, RSU0 and RSUn are located outside the tunnel respectively, and can synchronize to GNSS. The RSU1, RSU2, and RSUn1 are located in the tunnel and cannot receive GNSS signals. Optionally, if the communication mode adopted among the RSUs is line-of-sight communication, the shortest distance of signal transmission among the RSUs is a corresponding line-of-sight distance, when the RSUs outside the tunnel and the RSUs located at the boundary position in the tunnel are installed, the line-of-sight communication needs to be ensured, and when the RSUs in the tunnel are installed, the line-of-sight communication also needs to be ensured; the shortest distance of signal transmission between RSUs may be the transmission distance of one or more reflections, if not line-of-sight communication.
Assuming that the current RSU is RSU1, the standard RSU corresponding to RSU1 may be RSU 0. The RSU0 may always send a periodic signal to the outside, and after receiving the periodic signal, the RSU1 may identify a standard RSU (i.e., RSU0) according to the identification information carried in the periodic signal.
In this embodiment, optionally, the target periodic signal may carry a transmission frequency of the target periodic signal by a standard RSU. After the current RSU receives the target periodic signal, it may count the frequency (i.e., the receiving frequency) of the received target periodic signal, then calculate the difference between the transmitting frequency and the receiving frequency, and adjust the frequency of the local clock according to the difference, so that the local clock and the standard RSU keep frequency synchronization. Since the standard RSU is an RSU synchronized to the GNSS, the above steps can achieve that the local clock of the current RSU keeps frequency synchronization with the GNSS.
In this embodiment, optionally, the current RSU stores in advance identification information of each standard RSU and a shortest distance for signal transmission between the current RSU and each standard RSU. After receiving the target periodic signal, the current RSU may find the shortest distance of signal transmission between the current RSU and the corresponding standard RSU according to the identification information of the standard RSU carried in the target periodic signal, and then calculate the receiving delay corresponding to the target periodic signal according to the shortest distance.
After calculating the receiving time delay corresponding to the target periodic signal, the receiving time of the target periodic signal may be adjusted according to the receiving time delay, and then the local clock may be adjusted in timing according to the adjusted receiving time of the target periodic signal and the frequency adjustment result, so that the local clock and the standard RSU maintain timing synchronization. Since the standard RSU is an RSU synchronized to the GNSS, the above steps can achieve that the local clock of the current RSU keeps timing synchronization with the GNSS. And the frequency adjustment result is the frequency adjusted by the local clock.
In a specific embodiment, before the current RSU adjusts the receiving time of the target periodic signal according to the receiving delay, the number n of rotations of the local clock second hand between the receiving time of the target periodic signal and the current time may be counted. After the current RSU adjusts the receiving time of the target periodic signal according to the receiving delay, assume that the adjusted receiving time of the target periodic signal is t1The frequency adjustment result is f, and the current time after the local clock adjustment is t2Then, there are: t is t2＝t1+n/f。
In the technical scheme of the embodiment of the invention, the current RSU identifies the standard RSU according to at least one received periodic signal, adjusts the frequency of the local clock according to a target periodic signal corresponding to the standard RSU so as to enable the local clock and the GNSS to keep frequency synchronization, calculates the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the local clock and the standard RSU, and performs timing adjustment on the local clock according to the receiving time delay and the frequency adjustment result so as to enable the local clock and the GNSS to keep timing synchronization.
Example two
This embodiment is a further refinement of the first embodiment, and the same or corresponding terms as those in the first embodiment are explained, and this embodiment is not repeated. Fig. 2a is a flowchart of a clock synchronization method applied to a current RSU that cannot receive GNSS signals according to a second embodiment of the present invention. In this embodiment, the technical solution of this embodiment may be combined with one or more methods in the solutions of the foregoing embodiments, and in this embodiment, as shown in fig. 2a, the method provided in this embodiment of the present invention may further include:
In this embodiment, the target periodic signal further includes identification information corresponding to the standard RSU. Wherein, if the signal transmitted by the standard RSU has periodicity, the identification information of the standard RSU can be added in the transmitted periodic signal; if the signal transmitted by the standard RSU itself has no periodicity, it is necessary to add identification information in the signal transmitted by it at a preset period. Specifically, the identification information may be an Identity (ID) of the standard RSU, such as a device name or a device number of the standard RSU.
After receiving the target periodic signal, the current RSU may identify the standard RSU according to the identification information of the standard RSU carried in the target periodic signal.
In this embodiment, the receiving period is a period corresponding to a target periodic signal received by the current RSU. The sending period is a period corresponding to the target periodic signal when the standard RSU sends the target periodic signal. Taking the RSUs distributed in fig. 1a as an example, fig. 2b is a schematic diagram of a periodic signal, and assuming that the sending period of the target periodic signal by the standard RSU (i.e., RSU0 in fig. 2 b) is T0, after the target periodic signal is received by the current RSU (i.e., RSU1 in fig. 2 b), the period of the target periodic signal is calculated to be T1 according to the received frame header signal. Assuming that the calculated frequency deviation is Δ f, then:
Δf＝1/T1-1/T0
and step 230, adjusting the frequency of the local clock according to the frequency deviation so as to keep the local clock and the GNSS frequency synchronized.
In this embodiment, after the frequency deviation is calculated, the clock adjustment control unit may be used to adjust the frequency of the local clock according to the frequency deviation.
And step 240, acquiring the shortest distance of signal transmission between the current RSU and the standard RSU according to the identification information corresponding to the standard RSU.
In an implementation manner of this embodiment, the shortest distance between the current RSU and the standard RSU for signal transmission may be a straight-line distance between the current RSU and the standard RSU; in another embodiment, if the communication mode adopted between the current RSU and the standard RSU is line-of-sight communication, the shortest distance of signal transmission between the current RSU and the standard RSU is the corresponding line-of-sight; if not line-of-sight communication, the shortest distance for signal transmission between the current RSU and the standard RSU may be the transmission distance of one or more reflections.
The shortest distance between the current RSU and the standard RSU for signal transmission is preset according to the actual communication condition, which is not limited in this embodiment. The current RSU is pre-stored with identification information corresponding to each standard RSU and the shortest distance of signal transmission between each standard RSU and the current RSU. After the current RSU acquires the identification information corresponding to the standard RSU, the shortest distance of signal transmission between the standard RSU and the current RSU can be found according to the identification information.
And step 250, calculating the receiving time delay corresponding to the frame header signal in the target periodic signal according to the shortest distance.
In this step, assuming that the shortest distance between the current RSU and the standard RSU for signal transmission is L, and the calculated reception delay is Δ t, then: and delta t is L/c. Where c is the speed of light.
And step 260, adjusting the receiving time of the frame header signal according to the receiving time delay corresponding to the frame header signal in the target periodic signal, so that the received frame header signal is completely aligned with the frame header signal in the target periodic signal sent by the standard RSU.
In this embodiment, after the receiving delay corresponding to the frame header signal in the target periodic signal is obtained through calculation, the receiving time of the frame header signal may be moved forward according to the receiving delay. Taking the RSUs distributed in fig. 1a as an example, fig. 2c is a schematic diagram of an adjusted periodic signal, wherein a schematic diagram of a target periodic signal sent by a standard RSU (i.e., RSU0) is shown above fig. 2c, a schematic diagram of a target periodic signal received by a current RSU (i.e., RSU1) is shown in the middle, and a schematic diagram of a target periodic signal adjusted by a current RSU (i.e., RSU1) is shown below fig. 2 c. Assuming that the receiving delay calculated in step 250 is Δ t, the receiving time of the frame header signal (the signal shown in the middle of fig. 2 c) received by the current RSU may be moved forward by Δ t, so that the frame header signal (the signal shown below fig. 2 c) received by the current RSU is completely aligned with the frame header signal (the signal shown above fig. 2 c) in the target periodic signal sent by the standard RSU, that is, the current RSU and the standard RSU maintain frame header timing synchronization.
In the technical solution of the embodiment of the present invention, the current RSU identifies the standard RSU according to at least one received periodic signal, calculates a receiving period corresponding to a target periodic signal, calculates a frequency deviation according to the receiving period and the transmitting period corresponding to the target periodic signal, adjusts the frequency of the local clock according to the frequency deviation, then obtains the shortest distance of signal transmission between the current RSU and the standard RSU according to the identification information corresponding to the standard RSU, calculates a receiving delay corresponding to a frame header signal in the target periodic signal according to the shortest distance, finally adjusts the receiving time of the frame header signal according to the receiving delay corresponding to the frame header signal in the target periodic signal, and performs a timing adjustment on the local clock according to the receiving time corresponding to the adjusted frame header signal and a frequency adjustment result, thereby realizing the technical means that the RSU which cannot receive GNSS signals is synchronized to the GNSS signal, the frequency deviation and the timing deviation caused by clock aging are avoided, and the communication performance between the RSUs and the OBUs is greatly improved.
EXAMPLE III
This embodiment is a further refinement of the above embodiment, and the same or corresponding terms as those of the above embodiment are explained, and this embodiment is not described again. Fig. 3a is a flowchart of a clock synchronization method applied to a current RSU that cannot receive GNSS signals according to a third embodiment of the present invention. In this embodiment, the technical solution of this embodiment may be combined with one or more methods in the solutions of the foregoing embodiments, and in this embodiment, as shown in fig. 3a, the method provided in this embodiment of the present invention may further include:
And step 320, calculating a receiving period corresponding to the target periodic signal, and calculating the frequency deviation according to the receiving period and the sending period corresponding to the target periodic signal.
In one implementation manner of the embodiment of the present invention, calculating a receiving period corresponding to a target periodic signal includes: calculating the receiving time interval corresponding to each two adjacent signals according to the receiving time corresponding to each signal in the target periodic signal; and calculating an average time interval according to a plurality of receiving time intervals, and taking the average time interval as a receiving period corresponding to the target periodic signal.
In this embodiment, fig. 3b is a schematic diagram of a periodic signal, and taking fig. 3b as an example, assuming that a receiving time interval between a first signal and a second signal, a receiving time interval between the second signal and a third signal, and a receiving time interval between the third signal and a fourth signal in a target periodic signal received by a current RSU is T2, T3, and T4 … …, an average time interval may be calculated according to the receiving time intervals, and the average time interval is taken as a receiving period corresponding to the target periodic signal.
The advantages of such an arrangement are: the influence of the quality of different signals on the receiving period can be reduced, and the calculation error of the receiving period can be reduced through multiple measurements.
And step 350, sending a periodic signal according to the identification information corresponding to the current RSU, so that a target RSU which cannot receive the GNSS signal in a preset area around the current RSU can not receive the GNSS signal, and completing frequency synchronization and timing synchronization according to the periodic signal.
In this embodiment, taking each RSU distributed in fig. 1a as an example, assuming that the current RSU is RSU1, after the RSU1 completes clock synchronization, a periodic signal may be always sent to the outside according to the identification information corresponding to RSU 1. After receiving the periodic signal transmitted by the RSU1, the RSU2 may complete frequency synchronization and timing synchronization according to the periodic signal. After the RSU2 completes the frequency synchronization and the timing synchronization, the RSUn1 may complete the frequency synchronization and the timing synchronization in the same manner as described above.
In the technical scheme of the embodiment of the invention, the current RSU identifies the standard RSU according to at least one received periodic signal, calculates the receiving period corresponding to the target periodic signal, calculates the frequency deviation according to the receiving period and the sending period, calculates the frequency deviation according to the frequency deviation, adjusting the frequency of the local clock, calculating the receiving time delay corresponding to the target periodic signal, and according to the receiving time delay and the frequency adjusting result, timing adjustment is carried out on the local clock, finally, a periodic signal is sent according to the identification information corresponding to the current RSU, so that the target RSU within a predetermined area around the current RSU cannot receive GNSS signals, according to the technical means of completing frequency synchronization and timing synchronization according to the periodic signal, the RSU which cannot receive the GNSS signal can be synchronized to the GNSS, frequency deviation and timing deviation caused by clock aging are avoided, and communication performance between the RSUs and between the RSU and the OBU is greatly improved.
Example four
Fig. 4 is a structural diagram of a clock synchronization apparatus according to a fourth embodiment of the present invention, where the apparatus is applied to a current RSU that cannot receive GNSS signals, and the apparatus includes: a standard RSU identification module 410, a frequency adjustment module 420, and a timing adjustment module 430.
The standard RSU identifying module 410 is configured to identify a standard RSU according to the received at least one periodic signal; the standard RSU is an RSU synchronized to the GNSS;
a frequency adjusting module 420, configured to adjust a frequency of a local clock according to a target periodic signal corresponding to the standard RSU, so that the local clock and the GNSS maintain frequency synchronization;
a timing adjustment module 430, configured to calculate, according to the shortest distance between the local clock and the standard RSU, a receiving delay corresponding to the target periodic signal, and perform timing adjustment on a local clock according to the receiving delay and a frequency adjustment result, so that the local clock and the GNSS maintain timing synchronization.
In the technical solution of the embodiment of the present invention, a standard RSU is identified by a current RSU according to at least one received periodic signal, a frequency of a local clock is adjusted according to a target periodic signal corresponding to the standard RSU to keep the local clock and the GNSS frequency synchronized, a receiving delay corresponding to the target periodic signal is calculated according to a shortest distance between the local clock and the standard RSU for signal transmission, and a local clock is adjusted in a timing manner according to the receiving delay and a frequency adjustment result to keep the local clock and the GNSS timing synchronized, so that the RSU that cannot receive GNSS signals can be synchronized to the GNSS, thereby avoiding frequency deviation and timing deviation caused by clock aging, and greatly improving communication performance between the RSUs and the OBUs.
On the basis of the above embodiments, the target periodic signal includes identification information corresponding to the standard RSU.
The frequency adjustment module 420 may include:
the frequency deviation calculation unit is used for calculating a receiving period corresponding to the target periodic signal and calculating frequency deviation according to the receiving period and the sending period corresponding to the target periodic signal;
the adjusting unit is used for adjusting the frequency of the local clock according to the frequency deviation;
the time interval calculation unit is used for calculating the receiving time interval corresponding to each two adjacent signals according to the receiving time corresponding to the signals in the target periodic signal;
and the average interval calculation unit is used for calculating an average time interval according to a plurality of receiving time intervals and taking the average time interval as a receiving period corresponding to the target periodic signal.
The timing adjustment module 430 may include:
a distance obtaining unit, configured to obtain, according to identification information corresponding to the standard RSU, a shortest distance between the current RSU and the standard RSU for signal transmission;
a receiving delay calculating unit, configured to calculate, according to the shortest distance, a receiving delay corresponding to a frame header signal in the target periodic signal;
a receiving time adjusting unit, configured to adjust receiving time of the frame header signal according to a receiving time delay corresponding to the frame header signal in the target periodic signal, so that the received frame header signal is completely aligned with a frame header signal in the target periodic signal sent by a standard RSU;
the timing adjusting unit is used for performing timing adjustment on the local clock according to the receiving time corresponding to the adjusted frame header signal and the frequency adjusting result;
and the signal sending unit is used for sending a periodic signal according to the identification information corresponding to the current RSU so as to enable a target RSU which cannot receive the GNSS signal in a preset area around the current RSU to complete frequency synchronization and timing synchronization according to the periodic signal.
The clock synchronization device provided by the embodiment of the invention can execute the clock synchronization method provided by any embodiment of the invention, and has corresponding functional modules and beneficial effects of the execution method.
EXAMPLE five
Fig. 5 is a schematic structural diagram of a rsu according to a fifth embodiment of the present invention, where the rsu cannot receive GNSS signals, and as shown in fig. 5, the rsu includes a processor 510, a memory 520, an input device 530 and an output device 540; the number of processors 510 in the rsu may be one or more, and one processor 510 is taken as an example in fig. 5; the processor 510, the memory 520, the input device 530, and the output device 540 in the rsu may be connected by a bus or other means, and fig. 5 illustrates the connection by a bus as an example. The memory 520 may be used as a computer-readable storage medium for storing software programs, computer-executable programs, and modules, such as program instructions/modules corresponding to a clock synchronization method in any embodiment of the present invention (e.g., the standard RSU identification module 410, the frequency adjustment module 420, and the timing adjustment module 430 in a clock synchronization apparatus). The processor 510 executes various functional applications and data processing of the road side unit by running software programs, instructions and modules stored in the memory 520, i.e., implementing one of the clock synchronization methods described above. That is, the program when executed by the processor implements:
identifying a standard RSU according to the received at least one periodic signal; the standard RSU is an RSU synchronized to the GNSS;
adjusting the frequency of a local clock according to a target periodic signal corresponding to the standard RSU so that the local clock and the GNSS keep frequency synchronization;
and calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the local clock and the standard RSU, and performing timing adjustment on a local clock according to the receiving time delay and a frequency adjustment result so as to keep the local clock and the GNSS in timing synchronization.
The memory 520 may mainly include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application program required for at least one function; the storage data area may store data created according to the use of the terminal, and the like. Further, the memory 520 may include high speed random access memory, and may also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid state storage device. In some examples, memory 520 may further include memory located remotely from processor 510, which may be connected to the road side unit via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof. The input device 530 may be used to receive input numeric or character information and generate key signal inputs related to user settings and function control of the roadside unit, and may include a keyboard and a mouse, etc. The output device 540 may include a display device such as a display screen.
EXAMPLE six
The sixth embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program is executed by a processor to implement the method according to any embodiment of the present invention. Of course, the embodiment of the present invention provides a computer-readable storage medium, which can perform related operations in a clock synchronization method provided in any embodiment of the present invention. That is, the program when executed by the processor implements:
identifying a standard RSU according to the received at least one periodic signal; the standard RSU is an RSU synchronized to the GNSS;
adjusting the frequency of a local clock according to a target periodic signal corresponding to the standard RSU so that the local clock and the GNSS keep frequency synchronization;
and calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the local clock and the standard RSU, and performing timing adjustment on a local clock according to the receiving time delay and a frequency adjustment result so as to keep the local clock and the GNSS in timing synchronization.
From the above description of the embodiments, it is obvious for those skilled in the art that the present invention can be implemented by software and necessary general hardware, and certainly, can also be implemented by hardware, but the former is a better embodiment in many cases. Based on such understanding, the technical solutions of the present invention may be embodied in the form of a software product, which may be stored in a computer-readable storage medium, such as a floppy disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a FLASH Memory (FLASH), a hard disk or an optical disk of a computer, and includes instructions for enabling a roadside unit to execute the methods according to the embodiments of the present invention.
It should be noted that, in the above embodiment of the clock synchronization apparatus, the included units and modules are only divided according to functional logic, but are not limited to the above division as long as the corresponding functions can be implemented; in addition, specific names of the functional units are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present invention.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. A clock synchronization method applied to a current Road Side Unit (RSU) incapable of receiving Global Navigation Satellite System (GNSS) signals comprises the following steps:
identifying a standard RSU according to the received at least one periodic signal; the standard RSU is an RSU synchronized to the GNSS;
adjusting the frequency of a local clock according to a target periodic signal corresponding to the standard RSU so that the local clock and the GNSS keep frequency synchronization;
and calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the local clock and the standard RSU, and performing timing adjustment on a local clock according to the receiving time delay and a frequency adjustment result so as to keep the local clock and the GNSS in timing synchronization.
2. The method of claim 1, wherein adjusting the frequency of the local clock based on the target periodic signal corresponding to the standard RSU comprises:
calculating a receiving period corresponding to the target periodic signal, and calculating frequency deviation according to the receiving period and the sending period corresponding to the target periodic signal;
and adjusting the frequency of the local clock according to the frequency deviation.
3. The method of claim 1, wherein the target periodic signal includes identification information corresponding to the standard RSU;
calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the standard RSU and the target periodic signal, wherein the calculating comprises the following steps:
acquiring the shortest distance of signal transmission between the current RSU and the standard RSU according to the identification information corresponding to the standard RSU;
and calculating the receiving time delay corresponding to the frame header signal in the target periodic signal according to the shortest distance.
4. The method of claim 3, wherein adjusting the local clock timing according to the receiving delay and the frequency adjustment result comprises:
adjusting the receiving time of the frame header signal according to the receiving time delay corresponding to the frame header signal in the target periodic signal, so that the received frame header signal is completely aligned with the frame header signal in the target periodic signal sent by a standard RSU;
and according to the receiving time corresponding to the adjusted frame header signal and the frequency adjustment result, performing timing adjustment on the local clock.
5. The method of claim 1, wherein after adjusting the local clock according to the receiving delay and the frequency adjustment result, further comprising:
and sending a periodic signal according to the identification information corresponding to the current RSU so as to enable a target RSU which cannot receive the GNSS signal in a preset area around the current RSU to complete frequency synchronization and timing synchronization according to the periodic signal.
6. The method of claim 2, wherein calculating the receiving period corresponding to the target periodic signal comprises:
calculating the receiving time interval corresponding to each two adjacent signals according to the receiving time corresponding to each signal in the target periodic signal;
and calculating an average time interval according to a plurality of receiving time intervals, and taking the average time interval as a receiving period corresponding to the target periodic signal.
7. A clock synchronization device applied to a current Road Side Unit (RSU) incapable of receiving Global Navigation Satellite System (GNSS) signals comprises:
the standard RSU identification module is used for identifying a standard RSU according to the received at least one periodic signal; the standard RSU is an RSU synchronized to the GNSS;
a frequency adjusting module, configured to adjust a frequency of a local clock according to a target periodic signal corresponding to the standard RSU, so that the local clock and the GNSS maintain frequency synchronization;
and the timing adjustment module is used for calculating the receiving time delay corresponding to the target periodic signal according to the shortest distance of signal transmission between the timing adjustment module and the standard RSU, and performing timing adjustment on a local clock according to the receiving time delay and a frequency adjustment result so as to enable the local clock and the GNSS to keep timing synchronization.
8. The apparatus of claim 7, wherein the frequency adjustment module comprises:
the frequency deviation calculation unit is used for calculating a receiving period corresponding to the target periodic signal and calculating frequency deviation according to the receiving period and the sending period corresponding to the target periodic signal;
and the adjusting unit is used for adjusting the frequency of the local clock according to the frequency deviation.
9. A roadside unit comprising:
one or more processors;
storage means for storing one or more programs;
the one or more programs when executed by the one or more processors such that the one or more processors implement the clock synchronization method of any of claims 1-6 when the programs are executed.
10. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the clock synchronization method according to any one of claims 1 to 6.
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