CN115052333A - Method and device for time synchronization of a first vehicle and a second vehicle - Google Patents
Method and device for time synchronization of a first vehicle and a second vehicle Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04W56/00—Synchronisation arrangements
- H04W56/001—Synchronization between nodes
- H04W56/002—Mutual synchronization
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/001—Synchronization between nodes
- H04W56/0025—Synchronization between nodes synchronizing potentially movable access points
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- H—ELECTRICITY
- 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]
- H04W4/46—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P] for vehicle-to-vehicle communication [V2V]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/0055—Synchronisation arrangements determining timing error of reception due to propagation delay
- H04W56/0065—Synchronisation arrangements determining timing error of reception due to propagation delay using measurement of signal travel time
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Abstract
A method for time synchronization, comprising: transmitting a first message with a first vehicle; determining a first time point at which transmission ends in a low-level layer of a first vehicle; storing the first point in time in a high-level floor of the first vehicle; receiving a first message by means of a second vehicle; determining a second time point of the reception end in a lower-level layer of the second vehicle; storing the second point in time in a high-level floor of the second vehicle; transmitting a second point in time to the first vehicle by means of a second message, determining in a higher-level layer of the first vehicle a time interval between the stored first point in time and the transmitted second point in time; and/or transmitting the first point in time to the second vehicle by means of a third message, determining in a higher-level layer of the second vehicle a time interval between the stored second point in time and the transmitted first point in time; if the time interval is below the tolerance value, time synchronization is confirmed, and if the tolerance value is exceeded, the internal clock of the first vehicle and/or the second vehicle is adjusted.
Description
Technical Field
The invention relates to a method and a device for time synchronization between a first vehicle and at least one second vehicle.
Background
For safety-technical reasons, in particular in the field of semi-automatic or automatic driving, precise synchronization between the internal times of the vehicles concerned is becoming increasingly important. Therefore, the corresponding functional safety integrity level (ASIL) required for time synchronization will increase. Typically, time synchronization is based on an external source, such as a Global Navigation Satellite System (GNSS) or a cellular network with a reference time server. However, both options can only be used to a limited extent. For GNSS, accessibility may be reduced, for example, in tunnels or complex urban scenarios. Furthermore, in the case of cellular network based systems, the time delay may affect the accuracy of the received time signal and thus the time synchronization.
US 2020064859 a1 illustrates synchronization between a vehicle and a GPS sensor, however where the time stamp is not determined in a low level layer. The same applies to US2019/271989a1, which relates to wireless communication in a vehicle communication network, in particular to clock synchronization of vehicles.
Disclosure of Invention
The object of the present invention is therefore to further develop a method for time synchronization between different vehicles in order to increase the accuracy and thus the performance of safety-relevant automatic driving functions, while achieving a high functional safety requirement level. In summary, the safety of the relevant vehicle should be improved.
The above object is achieved by a method for time synchronizing a first vehicle and a second vehicle.
The method includes transmitting a first message by way of a first vehicle. This is in particular a vehicle-to-everything communication message, which preferably consists of a plurality of bits. Further, the first message may include a message identifier (e.g., a message counter) for identifying the message. The message identifier is provided, in particular together with the message, to each subsequent layer following the lower level layer, so that any layer can identify the corresponding message.
Before the first message is transmitted, in particular a first point in time of the transmission is determined in a lower-level layer of the first vehicle. The first point in time defines a transmission point in time. In detail, the first time point indicates that the transmission of the first message is ended. This is preferably done in real time. Further, the first point in time is stored in a high-level tier of the first vehicle with a message identifier of the first message.
Furthermore, the method comprises receiving the first message by means of the second vehicle and determining a second point in time of reception in a low-level layer of the second vehicle. The second point in time is in turn stored in a high-level floor of the second vehicle. The first time point thus describes a transmission time point on the first vehicle side, while the second time point describes a reception time point on the second vehicle side. The second point in time is defined by the end of reception of the first message.
According to a first alternative, the method comprises transmitting the second point in time together with the message identifier of the first message from the second vehicle to the first vehicle by means of the second message. Furthermore, the method comprises determining a time interval between the stored first point in time and the transmitted second point in time in a high-level layer of the first vehicle.
According to a second alternative, the method may comprise transmitting the first point in time together with a message identifier of the first message from the first vehicle to the second vehicle by means of a third message, wherein a time interval between the stored second point in time and the transmitted first point in time is determined in a higher hierarchy level of the second vehicle.
Although a one-sided determination is sufficient for the availability of the method, it is preferred to exchange both the second and third messages, and the determination of the time interval takes place on both sides, since each vehicle plays the role of a sender and a receiver by exchanging messages between the two vehicles, preferably periodically.
The method may be understood in particular as a computer-implemented method. In particular by a processor of the first vehicle and a processor of the second vehicle.
The terms low-level layer and high-level layer are mainly based on the ISO layer model. The term lower-level layer is to be understood in particular as the basic, lowest layer, in other words it can be a lower hardware layer or a lower software layer which is close to the hardware or directly at a higher level of the hardware. For example, the lower level layer may be a transport layer through which, for example, bits are transmitted and/or received. Thus, the lower level layer receives the external message first. The lower level layer may preferably be a hardware access layer. The lower level layer may also be a geographic network or an OS (operating system) service.
The higher-level layer differs in particular from the lower-level layer but is a higher software layer, for example information from a message only arrives in the higher-level layer after a certain time, because the information is initially received in the lower-level layer and, if necessary, also passes through the other layers until it reaches the higher-level layer. In particular, the high-level layer is an application layer.
The first and second messages and preferably all messages exchanged between the two vehicles are preferably V2X messages, in other words vehicle-to-X messages, in particular vehicle-to-vehicle messages.
The message is transmitted, in particular, by the corresponding antenna of the vehicle via radio waves. Here, the low-level layers are in principle arranged closer to the antenna. Thus, the latency will be significantly reduced by determining the first and second points in time in the low level layers, since the determined points in time are as close as possible to the actual transmission and reception points in time.
Both vehicles have in particular a module for synchronizing with an external time source, such as a GNSS or a time server. An external time source may be understood as a time source that does not belong to the vehicle. The module is intended to receive messages of a time source for synchronization. Thus, the two vehicles are typically synchronized by an external time source. The method enables reliable verification of the synchronization, for example in case of insufficient reception of the GNSS and in case of synchronization with an external time source not meeting the required level of safety requirements.
Furthermore, the method preferably comprises receiving the second message by means of the first vehicle and determining, in a lower-level layer of the first vehicle, a fourth point in time at which the second message is received. The fourth point in time again relates to the end of reception. The fourth point in time of the second message and the message identifier can also be transmitted by means of the third message. The order of the second message and the third message is arbitrary here, i.e. a "follow-up message" from the second vehicle to the first vehicle can also be transmitted after a follow-up message from the first vehicle to the second vehicle. The first message may also already be a subsequent message, so that messages have been exchanged in advance.
The time intervals between the first and second points in time are thereby preferably determined in each vehicle independently of one another. Thus, the time synchronization between two vehicles can be determined or established by the exchange of the transmission time and the reception time, i.e. the time stamps for receiving and transmitting the messages.
The time interval between the first point in time and the second point in time is compared with the first tolerance value. The first tolerance value is in particular selected such that it comprises a possible time of flight of the message. For example, the first tolerance value may be 0.8ms, preferably 0.5ms, most preferably 0.4 ms. It is thus not necessary to take into account the time of flight, since the time of flight is contained in the first tolerance value. Furthermore, the method comprises adjusting an internal clock, in particular an internal central clock, of the first vehicle and/or of the second vehicle when the first tolerance value is exceeded.
For example, the internal clock may be adjusted based on an average value between the first and second points in time, respectively. In this case, the internal clock is adjusted according to the average value. Furthermore, one vehicle may be set as a "master" in order to adjust the internal clock of another vehicle when the first tolerance value is exceeded.
The internal clock is in particular a central clock, with which all other clocks of the respective vehicle can also be synchronized internally when the time of the central clock is adjusted. In particular, if the time in the lower level layer does not itself represent the central clock, the time used in the lower level layer and the central clock are synchronized with each other.
The adjustment is only made when the time interval exceeds the first tolerance value. Whereby time synchronization will be established in this case.
If it is lower than the first tolerance value, time synchronization can be confirmed. In other words, it will be confirmed that the internal clocks of the vehicles are sufficiently synchronized and do not need to be adjusted. Thus, a method for time synchronization is generally preferred.
It can also be provided that the adjustment is only carried out after the checking by means of at least one security mechanism. In other words, the adjustment is only made when the safety mechanism controlling the time measurement does not detect any anomaly. The security mechanism may comprise, for example, a plausibility check for a certain time, preferably by means of a previous measurement. Adjustments based on erroneous measurements are thereby excluded.
A first tolerance value is set. The first tolerance value can in particular be defined as a fixed variable or set dynamically.
Preferably, the first tolerance value is set as a function of the accuracy required for the desired automatic driving function and/or the requirement for the availability of the desired driving function and/or the current traffic situation and/or the quality of the message transmission and/or the time delay determined for the first and second point in time, preferably determined by testing or calculation.
With regard to the adjustment of the vehicle internal clock, an external time source may also be considered. For example, as long as the GNSS reception can be performed again, its time can be taken into account for the adjustment. A kalman filter may be used here. In particular, the first tolerance value, which has been compared to the time interval, and the confidence value of the further external time source can then be taken into account. Furthermore, the security mechanism may also include a plausibility check for a specific time based on the time of an external time source (e.g., GNSS signals).
In particular each message in the respective higher level layer is accompanied by security related content, wherein the method further comprises encrypting each message before it is transmitted and before the point in time of transmission is determined, e.g. encrypting the first message before the first point in time is determined. Encryption occurs in particular in a layer between the high level layer and the low level layer. This layer may be the application layer, the communication layer or the V2X or Car2X layer. Since the determination of the first point in time of transmission is made only in low-level layers in respect of the first message, it is as close as possible to the actual transmission time, thereby significantly minimizing the time delay (i.e. the delay in determining the first point in time) since it comprises the time required to transmit or receive the message in addition to the optical propagation time, i.e. the time of flight. If the message transmission is also done internally to other higher layers, the transmission time as well as the delay time will increase.
After reception, the decryption of the first message and of each further message can also take place on the receiving side, the decryption taking place after the second point in time has been determined. Decryption is also performed in layers between the respective upper and lower layers, so that the reception time point is again as close as possible to the actual reception time point, and the delay is also reduced at the receiving side. In particular, the delay of two measurements on the transmitting side and the receiving side is reduced to less than 1ms in total, so that the time synchronization can be checked with very high accuracy and established if necessary. Thus, time synchronization based on information exchange is sufficient for safety-relevant time-critical autonomous driving operations.
Each message comprises in particular a message identifier for identification, wherein the message identifier is added to the message in particular by the sending vehicle and can be read and stored by the receiving vehicle. The message identifier is a message identification, i.e. a flag of the message, for unique identification of the message.
Furthermore, the method may comprise comparing the time interval between the second point in time and the first point in time with a second safety-relevant tolerance value. The safety-relevant second tolerance value can in particular be different from or identical to the first tolerance value for the clock adjustment. The second safety-relevant tolerance value is preferably greater than the first tolerance value for the clock adjustment. The method may in particular comprise the activation of at least one safety measure when a second safety-relevant tolerance value is exceeded. The safety measures may include, for example, increasing a safe distance from other vehicles or denying autonomous driving operation. This can preferably be done on both vehicle sides. A particularly high level of safety of the associated vehicle can thereby be achieved.
A second tolerance value is also set. The second tolerance value may preferably be defined as a fixed variable or set dynamically. Preferably, the second tolerance value is set as a function of the accuracy required for the desired automatic driving function and/or the requirement for the availability of the desired driving function and/or the current traffic situation and/or the quality of the message transmission and/or the time delay determined for the first and second points in time, preferably determined by testing or calculation.
All the steps described above can also be performed in respect of other regularly transmitted messages. For example, a second message will be generated and safety-related content will be added to a higher level layer of the second vehicle. The second message is encrypted in a layer between the upper level layer and the lower level layer, and a third transmission time point is determined in the lower level layer of the second vehicle. The third point in time is again related to the end of the transmission. The time point may be stored in a high-level layer. As described above, the second message is sent and received by the first vehicle, wherein the fourth reception time point is determined in the lower-level layer and can in turn be stored in the corresponding upper-level layer of the first vehicle. The second message may have been previously decrypted in a layer between the lower level layer and the higher level layer. The same applies to the transmission of the third message, wherein the fifth and sixth points in time can be determined and stored separately. These points in time are in turn related to the end of transmission or reception.
The method may in particular comprise the periodic transmission of a corresponding message, so that the time synchronization can be checked at regular time intervals and established if necessary. The method is triggered in particular by each message received from another vehicle.
To achieve a higher level of security requirements, the following actions are preferably performed in a high level layer:
a) storing a first point in time in a first vehicle
b) Storing the second point in time in the second vehicle
c) End-to-end checking of transmissions of a first and a second point in time in a second and a third message
d) Determining a time interval between a first point in time and a second point in time
e) Other security mechanisms
f) Triggering security measures
In general, the method may in particular relate to the time synchronization of a plurality of vehicles, wherein the steps described above for time synchronization are carried out in pairs. All vehicles communicate with each other in pairs, in particular by means of messages. In other words, corresponding messages can be exchanged between all vehicles within the effective range, preferably between all vehicles at a distance of less than 1 km. In addition to the message identifier, the message may also include a station ID so that the message may be assigned to a particular vehicle. Thus, by identifying an ID that is unknown so far, a "new" vehicle can also be added to a large number of vehicles. Thus, in general, synchronization with all vehicles within the effective range is possible. In particular, if the reception of the external time source can only be carried out poorly or not, a time average of all relevant vehicles can be calculated. This may be used to adjust the internal clock of the vehicle that received poor or no external time source.
Furthermore, the method may comprise exchanging messages with the roadside units, i.e. with fixed devices that participate in the communication by means of messages. Thus, the roadside unit can also be used as an external time source with high accuracy and a high level of safety requirements.
The quality of the individual time sources can be taken into account by assigning a confidence value to each time source when synchronizing with a plurality of vehicles and possibly available external time sources. In the calculation of the mean value for adapting the internal clock, the confidence value can be taken into account by calculating the mean value as a weighted mean value of all available time sources, wherein the confidence value is used as a weighting factor.
t 0 +∑(C i ×Δ i )/∑C i
Here, C represents the confidence value of the time of the different time sources i. 0 represents the first vehicle on which the method is performed. The corresponding confidence value may be determined from an available time source (e.g., GNSS, cellular network, or other vehicle). The confidence value may be transmitted from a time source or may be calculated from the received signal (e.g., the quality of the GNSS satellite signals compared to other satellites or the quality of an internet Network Time Protocol (NTP) server).
For example, a confidence value may be assigned to the internal clock of a first vehicle, wherein confidence values are assigned to the respective internal clocks of a large number of other vehicles, respectively. In other words, a confidence value is assigned to each internal clock of a large number of vehicles. As described above, the first vehicle receives the second time point from each of the plurality of vehicles, respectively, and averages the times. The method comprises determining, in a high-level layer of the first vehicle, a time interval between the stored first point in time and the transmitted average of the second point in time. The average is preferably weighted according to the confidence value. The time interval is compared to the first tolerance value.
Preferably, if the time interval is greater than the first tolerance value and the confidence values of the times of the other vehicles are each greater than the confidence value of the first vehicle, the internal clock of the first vehicle is adjusted. In the adjustment, the internal clock of the first vehicle is synchronized with the average value.
Alternatively, the first time point and its confidence value may also be taken into account in the determination of the preferred weighted average. When the time interval from the preferred weighted average is greater than the first tolerance value, then the internal clock of the first vehicle is adjusted.
In another aspect, the invention relates to an apparatus designed to perform the above method. The device may comprise in particular an antenna for transmitting and/or receiving messages. Furthermore, the apparatus preferably comprises a processor with a memory, which is designed to perform the method. The processor may include a low level unit and a security unit to perform steps with respect to the low level layer and the high level layer. Further, the processor may include an application unit and a V2X or Car2X unit, in which the steps of the respective middle layer are performed.
The invention can realize the synchronization with higher functional safety requirement level. The method may be used in conjunction with an external time source such as a GNSS. In particular, it will be achieved: the higher level of safety requirements can always be maintained even if the external time source (e.g., GNSS) fails or is unavailable or difficult to reach. Thereby, a higher level of security requirements is achieved compared to solutions that may rely only on external time sources.
Drawings
In the drawings:
fig. 1 schematically shows a flow chart of a method according to the invention;
FIG. 2 schematically illustrates the method of FIG. 1 in conjunction with the embedding of an external time source; and is provided with
Fig. 3 shows schematically in chronological order the method according to the invention in the different layers.
Detailed Description
Fig. 1 shows a flow chart of a method 100 according to the invention. The method 100 according to the invention comprises generating 101 a first message 27a and adding safety-relevant content in a high-level layer of the first vehicle, encrypting 102 the first message before sending 105 the first message, and determining 103 a first point in time t1 for the sending in the low-level layer. Furthermore, the first point in time t1 may be stored 104 together with a message identifier of the message.
The first message is received 106 on the second vehicle side and a second point in time t2 is determined 107. The second point in time t2 is stored 108 in the higher level layer together with the message identifier of the first message and the first message is decrypted 109.
The second point in time t2 can be transmitted 110 from the second vehicle to the first vehicle together with the message identifier of the first message by means of the second message. All previous steps may be performed again, such as determining 110a third point in time t3 of the transmission and storing the third point in time t3 in the low level layer, transmitting 110b the second message, receiving 110c the second message on the first vehicle side, and determining 110d a fourth point in time t4 of the second message in the low level layer of the first vehicle.
Preferably, the time interval between the stored first point in time t1 and the transmitted second point in time t2 is determined 111 in a high level floor of the first vehicle.
Furthermore, as an alternative or in addition to the second message 26b, the first time t1 can be transmitted 112 from the first vehicle to the second vehicle together with the message identifier 26a of the first message 27a by means of the third message 26 c. This may in turn comprise determining 112a fifth point of time t5 for transmission, actually transmitting 112b the third message 27c, receiving 112c the third message on the second vehicle side and determining 112d a sixth point of time t6 for receiving the third message in the lower level layer. The time interval between the stored second point in time t2 and the transmitted first point in time t1 may then be determined 113 in a higher level floor of the second vehicle.
The time interval between the second point in time t2 and the first point in time t1 is compared 114 with a first tolerance value and if the first tolerance value is exceeded, the internal clock of the second vehicle is adjusted 115. A first tolerance value is set.
Further, the time interval may be compared 116 with the second tolerance value. Furthermore, the current outcome of the security mechanism may be evaluated. If the second tolerance value is exceeded, at least one safety measure may be initiated 117, such as increasing 118 a safe distance from the other vehicle and/or denying 119 an autonomous driving operation.
Fig. 2 shows the embedding of the method 100 of fig. 1 in combination with an external time source 10 for outputting a time reference 12 with a high level of security requirements. Furthermore, a device 19 according to the invention for carrying out the method is shown. The method 100 according to the invention described above with reference to fig. 1 can be carried out in connection with the synchronization 13 with the external time source 10. The time synchronized with the external time source 10 is then checked by means of the method 100 described in fig. 1 by means of the message 27 and, if necessary, adjusted. Further, other security mechanisms 11 may also be provided. Overall, a time reference 12 with a high level of safety requirements is thus achieved.
The method 100 according to the invention in the different layers is shown chronologically in fig. 3. Time 40 increases in the direction of the arrow. The first vehicle 20 and the second vehicle 21 include a high-level layer 22, an application layer 23, a V2X layer 24, and a low-level layer 25, respectively. In the higher level layer 22 of the first vehicle 20 a message 27 is generated, i.e. a first message 27a, which is forwarded with a message identifier 26a via the application layer 23 and the V2X layer 24 to the lower level layer 25. The first message 27a is encrypted in the V2X layer 24. A first point in time t1 of the transmission is determined in the lower level layer 25. The first point in time t1 is returned to the higher level layer 22 along with the message identifier 26 a. This is used to determine the time interval from the second point in time t2 later. A first message 27a is sent.
The first message 27a is received by the lower level layer 25 of the second vehicle 21. The received second point in time t2 is determined in the lower level layer and the first message 27a together with the message identifier 26a and the second point in time t2 is then transmitted to the higher level layer 22, where the first message may be decrypted, for example, in an intermediate layer.
A second message is generated. The safety-relevant content is added to the new message 27, i.e. the second message 27b, in the high-level layer 22 of the second vehicle 21. The second message 27b is sent by means of the lower layer 25. The third point in time t3 of the transmission is determined in advance. T2 is transmitted by means of the second message 27 b. The second message 27b may also contain a message identifier 26 b. The time of reception t4 is determined in the lower hierarchy level 25 of the first vehicle 20. The second point in time t2 is transmitted to the higher layer so that the time interval between the second point in time t2 and the first point in time t1 can be determined 111.
A third message may be generated. Safety-relevant content can be added to the third message 27c in the high-level layer 22 of the first vehicle, t5 being determined as the transmission point in time in the low-level layer 25 before the third message is transmitted. The third message 27c comprises the message identifier 26c and a first point in time t 1. When the second vehicle 21 is received, a sixth point in time t6 of reception is determined. The first point in time t1 is provided to the high level layer 22, wherein the time interval between the first point in time t1 and the second point in time t2 is again determined 113.
Claims (10)
1. A method (100) for time synchronization of a first vehicle (20) and at least one second vehicle (21),
it is characterized in that the preparation method is characterized in that,
the method (100) comprises the steps of:
a) -sending (105) a first message (27a) by means of the first vehicle (20),
b) determining (103), in a lower level layer (25) of the first vehicle (20), a first point in time t1 of the transmission, wherein the first point in time t1 relates to an end of the transmission,
c) storing (104) the first point in time t1 in a higher level layer (22) of the first vehicle (20) together with a message identifier of the first message,
d) receiving (106) the first message (27a) by means of the second vehicle (21),
e) determining (107), in a lower level layer (25) of the second vehicle (21), a second point in time t2 of the reception of the first message (27a), wherein the second point in time t2 relates to the end of the reception,
f) storing (108) the second point in time t2 in a higher-level layer (22) of the second vehicle (21),
wherein the method comprises:
g) transmitting (110) the second point in time t2 together with the message identifier of the first message from the second vehicle (21) to the first vehicle (20) by means of a second message (27b), and
h) determining (111) a time interval between the stored first point in time t1 and the transmitted second point in time t2 in a high level floor (22) of the first vehicle (20),
and/or
i) Transmitting the first point in time t1 together with the message identifier of the first message from the first vehicle (20) to the second vehicle (21) by means of a third message (27c), and
j) determining (113) a time interval between the stored second point in time t2 and the transmitted first point in time t1 in a high-level layer (22) of the second vehicle (21),
wherein the method (100) comprises a comparison (114) of the time interval with a first tolerance value,
wherein the first tolerance value is set, and wherein the second tolerance value is set,
wherein if it is lower than the first tolerance value, time synchronization is confirmed, and
wherein an adjustment (115) of an internal clock of the first vehicle (20) and/or an internal clock (115) of the second vehicle (21) is made and the time synchronization is established if the first tolerance value is exceeded.
2. The method as set forth in claim 1, wherein,
it is characterized in that the preparation method is characterized in that,
the first tolerance value is set as a function of the accuracy of the desired automatic driving function and/or the requirement for the availability of the desired driving function and/or the current traffic conditions and/or the quality of the message transmission and/or the time delays determined, preferably by testing or calculation, for determining the first time point t1 and the second time point t 2.
3. The method (100) of claim 1 or 2,
it is characterized in that the preparation method is characterized in that,
the method (100) comprises: -receiving the second message (27b) by means of the first vehicle (20), and-determining in a lower level layer (25) of the first vehicle (20) a fourth point of time t4 of the reception of the second message (27b), wherein the fourth point of time t4 relates to the end of the reception, wherein the fourth point of time t4 is also transmitted by means of the third message.
4. The method (100) according to any one of the preceding claims,
it is characterized in that the preparation method is characterized in that,
the method (100) comprises: -encrypting (102) said first message (27a) before said sending (105) and before determining (103) said first point in time t 1.
5. The method (100) of claim 4,
it is characterized in that the preparation method is characterized in that,
the method (100) comprises: -performing a decryption (109) of the first message (27a) after the receiving (106),
wherein the decrypting (109) is performed after determining (107) the second point in time t 2.
6. The method (100) according to any one of the preceding claims,
it is characterized in that the preparation method is characterized in that,
the method (100) comprises: the time interval between the second point in time t2 and the first point in time t1 is compared (116) with a second tolerance value.
7. The method (100) of claim 6,
it is characterized in that the preparation method is characterized in that,
the method (100) comprises: at least one safety measure is initiated (117) when the second tolerance value is exceeded.
8. The method (100) according to any one of the preceding claims,
it is characterized in that the preparation method is characterized in that,
the method (100) comprises: exchanging messages between the first vehicle (20) and a further plurality of vehicles,
wherein a confidence value is assigned to an internal clock of the first vehicle (20),
wherein respective internal clocks of the plurality of vehicles are respectively assigned confidence values,
wherein the first vehicle (20) receives a second point in time t2 from each of the plurality of vehicles respectively,
wherein the method comprises: determining in a high-level layer (22) of the first vehicle (20) a time interval between the stored first point in time t1 and the transmitted average of the second point in time t2,
wherein the method (100) comprises: -comparing the time interval with the first tolerance value, and-adjusting the internal clock of the first vehicle (20) if the time interval exceeds the first tolerance value and the confidence values of the internal clocks of the further vehicles are each greater than the confidence value of the first vehicle.
9. The method (100) according to any one of claims 1 to 7,
it is characterized in that the preparation method is characterized in that,
the method (100) comprises: exchanging messages between the first vehicle (20) and a further plurality of vehicles,
wherein a confidence value is assigned to an internal clock of the first vehicle (20),
wherein respective internal clocks of the plurality of vehicles are respectively assigned confidence values,
wherein the first vehicle (20) receives a second point in time t2 from each of the plurality of vehicles respectively,
wherein the method comprises: determining in a high-level layer (22) of the first vehicle (20) a time interval between the stored first point in time t1 and an average of the first point in time t1 and the transmitted second point in time t2,
wherein the method (100) comprises: -comparing the time interval with the first tolerance value, and-adjusting an internal clock of the first vehicle (20) if the time interval exceeds the first tolerance value.
10. A device (19) for time synchronizing a first vehicle (20) and a second vehicle (21),
it is characterized in that the preparation method is characterized in that,
the device (10) is designed for carrying out the method (100) according to any one of claims 1 to 9.
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