DE102017217818A1 - A method for issuing a time and method for sending and receiving vehicle-to-X messages - Google Patents

Abstract

The invention relates to a method for outputting a time by means of a continuous counter, wherein in addition to the time a confidence interval is also output. The invention further relates to a method of transmitting or receiving vehicle-to-X messages using such a method of outputting a time.

Description

The invention relates to a method for outputting a time by means of a continuous counter and associated methods for sending and receiving vehicle-to-X messages.

Vehicle-to-X communication, for example based on IEEE 802.11p, ITS-G5 or IEEE 1609, is prior art and at least partially already standardized and tested in field tests. This technology allows messages to be exchanged between vehicles, allowing drivers to be notified of potential hazardous situations. Typically, all messages receive a timestamp and a position specification in order to filter out, plausibility or further processing outdated messages in applications.

For the function of a vehicle-to-X system, a precise time source is particularly advantageous.

Satellite navigation receivers (also known as GNSS receivers GNSS = Global Navigation Satellite System) using GNSS satellite signals in addition to the position also determine a highly accurate world time, with a precision in the nanosecond range is achieved. If satellite reception is available, such a receiver can typically create a fix and set the time, which it outputs every second via a 1PPS signal (1PPS = one pulse per second) for synchronization.

However, if the satellite signal breaks off, which may be the case, for example, when driving into a tunnel or into a building such as, for example, a parking garage, the synchronization signal typically also falls away. Subsequent applications that synchronize to the 1PPS signal then lose accuracy. This loss of accuracy is not quantifiable in prior art designs.

While there are already methods that can be used to calculate an accurate system time using a GNSS signal, such methods do not include the ability to recalculate system time while losing a GNSS signal while maintaining a measure of accuracy.

In addition, it was necessary to optimize the GNSS failure bridging time, which was not sufficiently possible with known implementations.

It is therefore an object of the invention to provide a method of outputting a time which provides improved results particularly in the event of failure of a satellite signal or other synchronization signal. It is a further object of the invention to provide methods for transmitting and receiving vehicle-to-X messages using such a method of outputting a time.

This is achieved according to the invention by methods according to the respective main claims. Advantageous embodiments can be taken, for example, the respective subclaims. The content of the claims is made by express reference to the content of the description.

• - Festsetzen einer Ausgangszeit, wobei der Zähler zur Ausgangszeit einen Ausgangszählerstand hat,
• - Ausgeben der Zeit basierend auf einem aktuellen Zählerstand des Zählers, dem Ausgangszählerstand und der Ausgangszeit, und
• - Berechnen eines Konfidenzintervalls der ausgegebenen Zeit basierend auf einer Differenz zwischen der ausgegeben Zeit und der Ausgangszeit.

The invention relates to a method for outputting a time by means of a continuous counter, the method comprising the following steps:

• Setting an output time, the counter having an output counter reading at the output time,
• Outputting the time based on a current count of the counter, the output count and the output time, and
• Calculating a confidence interval of the output time based on a difference between the output time and the output time.

Such a method also works without synchronization by external signals, for example, without satellite signals. It can thus spend a time even when a vehicle is traveling through a tunnel or in a building, for example, so that the reception of satellite signals typically used for synchronization is difficult or impossible.

Output time and / or output count can be stored, for example, in respective registers or other memory units. The current counter reading can be read in particular when a time is to be output, which can be done, for example, in response to a corresponding request from an application or another unit.

The confidence interval also calculated according to the described method allows a receiver of the time spent to judge how reliable the time spent is. This can be used, for example, to prevent the time being considered reliable, even though it has not been able to be synchronized for a long time and is therefore already too unreliable or too inaccurate for some applications.

According to one embodiment, the time is output without drift correction of the counter. So it will be in other words, no correction of the counter made, which corrects any drift due to various influences. The counter is typically rather used directly and / or unchanged for calculating the time to be output. This allows a simple execution.

• - einer Genauigkeit bei der Bestimmung der Ausgangszeit und
• - einem Produkt aus einem maximalen Drift des Zählers multipliziert mit der Differenz zwischen der ausgegebenen Zeit und der Ausgangszeit

berechnet werden.The confidence interval may in particular in this case as the sum of

• - An accuracy in the determination of the output time and
• a product of a maximum drift of the counter multiplied by the difference between the output time and the output time

be calculated.

Such a procedure in the calculation of the confidence interval has proved to be a practicable estimation of the accuracy, in particular in the case of dispensing with a drift correction of the counter.

According to one embodiment, the time is output with drift correction of the counter. As a result, drift effects, which, for example due to frequency errors of a counter or clock, which may be a quartz and example instead of 8, 0 Mhz only 7, 99 MHz as a frequency and thus drifts away over the term, or due to temperature or aging of the counter can be taken into account, in whole or in part, and thus the accuracy of outputting the time can be significantly improved. In other words, the time is spent considering a drift correction.

• - Empfangen eines ersten Referenzzeitpulses eines Satellitensignals, wobei der erste Referenzzeitpuls eine erste Referenzzeit anzeigt, darauf ansprechend Abspeichern eines momentanen ersten Zählerstands des Zählers in einem Register,
• - Empfangen eines zweiten Referenzzeitpulses eines Satellitensignals, wobei der zweite Referenzzeitpuls eine zweite Referenzzeit anzeigt, wobei der Zähler beim Empfang des zweiten Referenzzeitpulses einen momentanen zweiten Zählerstand aufweist,
• - Berechnen einer Zählerdifferenz zwischen dem zweiten Zählerstand und dem ersten Zählerstand,
• - Berechnen eines Driftwerts basierend auf der Zählerdifferenz und einer Zeitdifferenz zwischen der zweiten Referenzzeit und der ersten Referenzzeit.

According to a preferred embodiment, a drift value used for drift correction is determined by means of satellite signals before outputting the time as follows:

• Receiving a first reference time pulse of a satellite signal, the first reference time pulse indicating a first reference time, responsively storing a current first count of the counter in a register,
• Receiving a second reference time pulse of a satellite signal, wherein the second reference time pulse indicates a second reference time, the counter having a current second counter reading upon receipt of the second reference time pulse,
• Calculating a counter difference between the second count and the first count,
• Calculating a drift value based on the counter difference and a time difference between the second reference time and the first reference time.

The drift value can be calculated, for example, by dividing the time difference by a time calculated based on the counter difference and subtracting the value 1 from it. If, for example, the counter runs a little too fast, this results in a drift value which has a small negative amount, ie, for example, is greater than -1 or greater than -0.1 but less than 0. This is consistent with a possible drift correction approach given below, for example. Mathematical transformations of the approach described herein are possible and are deemed to be disclosed. They are considered equivalent, in particular if they give the same result.

By the procedure just described, a drift value can be determined, which is advantageously indicative of a drift of the counter.

The procedure just described in the calculation of the drift value can be used in particular as long as satellite signals or other signals for synchronization are present.

It should be understood that instead of satellite signals, for example, terrestrial signals can also be used for synchronization. This is considered equivalent here.

The drift value determined as described above indicates a measure of the drift or of the instantaneous counter speed, so that the instantaneous speed of the counter can be used for calculating or correcting the time to be output. As a result, a considerably higher accuracy can be achieved. The time difference may be, for example, between 0.5 s and 1.5 s, preferably 1 s. This corresponds, for example, to a typical time interval between 1PPS signals of the GPS satellite navigation system.

The drift value may preferably indicate a deviation between a time calculated by means of the counter difference and the time difference between the second reference time and the first reference time. As a result, the counter can be evaluated according to its current state and a corresponding correction of the time to be output can be made.

The drift correction can preferably take place by adding a correction value, which is a product of the Driftwert and a difference between the current counter reading and the output counter reading is calculated. This allows easy drift correction to correct for corresponding errors.

• - einer Genauigkeit bei der Bestimmung der Ausgangszeit und
• - einem Produkt aus einer Messgenauigkeit des Driftwerts multipliziert mit der Differenz zwischen der ausgegebenen Zeit und der Ausgangszeit

berechnet werden. Dies ermöglicht eine einfache und praktikable Berechnung des Konfidenzintervalls.The confidence interval may, according to one embodiment, be the sum of

• - An accuracy in the determination of the output time and
• a product of a measurement accuracy of the drift value multiplied by the difference between the output time and the output time

be calculated. This allows a simple and practical calculation of the confidence interval.

• - einer Genauigkeit bei der Bestimmung der Ausgangszeit und
• - einem Produkt aus einer Messgenauigkeit des Driftwerts multipliziert mit der Differenz zwischen der ausgegebenen Zeit und der Ausgangszeit und
• - einem Produkt aus einer Driftänderung multipliziert mit der quadrierten Differenz zwischen der ausgegebenen Zeit und der Ausgangszeit

berechnet werden.According to another embodiment, the confidence interval can be calculated as the sum of

• - An accuracy in the determination of the output time and
• a product of a measurement accuracy of the drift value multiplied by the difference between the output time and the output time and
• a product of a drift change multiplied by the squared difference between the output time and the output time

be calculated.

By the procedure just described, the confidence interval can be better adapted to the actual circumstances. The described procedures for calculating the confidence interval have proven to be practicable and advantageous for typical applications.

The accuracy in the determination of the output time can advantageously be calculated as the sum of an accuracy of a satellite-based reference time pulse and an accuracy of a measurement of the satellite-based reference time pulse. This corresponds to a typical accuracy in determining such an output time.

The outputting of the time is preferably performed during an interruption of reception of satellite signals or other synchronization signals. Such an interruption can be assumed, for example, if one or more synchronization signals or satellite signals were no longer received. For example, the method described herein may be applied after a predetermined number of sync signals no longer received, for example, one, two, three, four, five, or any number of sync signals no longer received.

The counter is preferably driven by a quartz oscillator. This has proved to be advantageous for typical applications.

The meter preferably has at least 1,000 counts per second and / or between two reference times. This allows, for example, a resolution of 1 ms or better.

The exit time is preferably determined by means of satellite signals. This allows a particularly accurate determination of the exit time. In particular, the output time can be determined by received reference time values of satellite signals. These are sent, for example, five times per second, so that the next synchronization signal can be terminated precisely.

Preferably, the satellite signals are satellite navigation signals. These typically provide corresponding reference times or synchronization signals. In addition, use of a corresponding system for at least two functions, in particular navigation and time acquisition, is made possible.

The confidence interval may, according to a preferred embodiment, be compared to a threshold, where the time spent is discarded when the confidence interval exceeds the threshold. This can prevent an unreliable time from being used. This can prevent, for example, the erroneous evaluation of vehicle-to-X messages. The discarding can already be carried out in a central unit which provides a time by means of the method according to the invention, as well as in other units which, for example, further process vehicle-to-X messages.

The invention further relates to a method for transmitting vehicle-to-X messages, wherein each vehicle-to-X message is provided with a time which has been output by means of a method according to the invention. The invention further relates to a method for receiving vehicle-to-X messages, wherein each vehicle-to-X message is provided with a time which is compared to a system time, the system time being output by a method according to the invention has been. With regard to the method according to the invention for outputting a time, it is possible in each case to make use of all the embodiments and variants described herein. The above-mentioned advantages of a precise Time determination and a confidence interval can be achieved.

The invention further relates to a control unit which is configured to carry out a method according to the invention. Moreover, the invention relates to a non-transitory computer-readable storage medium on which program code is stored, in the execution of which a processor carries out a method according to the invention. With regard to the method according to the invention, it is possible in each case to make use of all the embodiments and variants described herein.

A major advantage of the drift correction approach is that accurate timing information can still be provided in the event of a long outage of synchronization signals, for example, over two hours, and the accuracy thereof can be determined with sufficient accuracy. Without drift correction, time can become inaccurate, especially with such long downtime. This concerns both the timing error and the confidence.

A drift change can also be measured during synchronization. However, effects such as aging or temperature influence, especially after prolonged GPS downtime, without synchronization, can eventually make the time too imprecise, as the drift over time is not constant.

• 1: ein Kraftfahrzeug sowie Satelliten.

Further features and advantages will be apparent to those skilled in the embodiments described below with reference to the accompanying drawings. Showing:

• 1 : a motor vehicle and satellite.

1 shows a motor vehicle 10 , It should be understood that this is a purely schematic representation. Also purely schematic are a total of four satellites 20 . 21 . 22 . 23 which belong to a global navigation satellite system such as GPS.

The car 10 has an electronic control module 30 which is likewise only shown schematically here and which is configured to carry out a method according to an exemplary embodiment of the invention. For this purpose, it contains processor means and memory means, wherein program code is stored in the memory means, in the execution of which the processor means execute such a method.

The car 10 has an antenna 32 on which with the control module 30 connected and which is adapted to receive satellite signals from the satellites 20 . 21 . 22 . 23 to recieve.

The control module 30 has a register 34 which stores values for later use.

The satellites 20 . 21 . 22 . 23 At each full second, according to the Global Positioning System (GPS) specification, they send out a respective reference time pulse, also referred to as 1PPS ("one pulse per second"). This will display the transition to each new second. Between these respective reference time pulses five reference time values are transmitted per second, which indicate the second-precise time to the next reference time pulse. Thus, by receiving the satellite signals from the satellites 20 . 21 . 22 . 23 be exactly determined, which second begins to the next reference time pulse.

The control module 30 has an internal counter 36 on which of a quartz 38 is operated under normal conditions and 1,000 counts per second continues. This corresponds to a resolution of 1 ms. The quartz 38 However, subject to unavoidable physical fluctuations, especially as a function of the respective temperature, which can assume very different values during operation of a motor vehicle.

Hereinafter, the outputting of a time for existing satellite signals will be described first.

The control module saves at each reference time pulse 30 the respective counter reading of the counter 36 in the register 34 from. If the respective next reference time pulse arrives, which in the present case happens after exactly 1 s, the respective counter reading is read out and subtracted from the stored value. Thus it is known how far the counter has counted for one second. The control module then calculates a respective correction factor as a quotient of the time difference of 1 s between two reference time pulses divided by the above-mentioned counter difference. Thereby, the above-mentioned physical fluctuations of the quartz driving the counter can be corrected.

If a time with a resolution <1 s is required, an intermediate time is calculated first. This results as the difference between a current counter reading at the time of dispensing and the counter reading at the last received reference time pulse, which is multiplied by the correction factor. This gives a very accurate time with a resolution of about 1 ms, which is independent of Variations in the quartz due to different temperatures or other physical influences. Such times are used in particular for vehicle-to-X communication, both to timestamp messages to be sent and to compare received messages with time, thereby assessing their relevance.

It should generally be mentioned that, for example, first GNSS signals can be read in at GPS time stream (current time) and pulses per second (for example hardware signal), which are available at a frequency of 1 s. Subsequently, correction factors based on GNSS signals can be determined. The correction factors compensate for an internal hardware counter, which physically and constructively drifts over time. A system time can then be calculated from the continuous counter or counter and the correction factor.

Overall, the procedure as described herein can provide a much more accurate time reference than would be possible using satellites' pure 1PPS signals. This would only allow a time resolution of 1 s (in the case of GPS). The mere use of a counter would not lead to the goal, as this is subject to strong fluctuations. Only through the approaches described herein does the accuracy required for applications such as vehicle-to-X communication be achieved.

The procedure for failure of satellite signals will now be described below, as it can occur, for example, when a vehicle passes through a tunnel.

Basically, the counter can 36 continue through the quartz 38 be driven and used to further determine the time. This can also be done without synchronization.

However, in this case, a confidence interval can be calculated, which indicates how reliable the corresponding time to be dispensed is still. In particular, the confidence interval can be greater the longer the last reception of a synchronization signal or satellite signal takes place.

If the accuracy is to be improved, then a drift value can be determined, which is still to be determined at a time when satellite reception still exists. This can for example be done continuously, so that the drift value is then available in the event of a failure of satellite signals. In particular, the drift value can be calculated based on the difference between counter readings and two reference time pulses. The corresponding drift value can then be used in case of synchronization failure to correct the output time. The confidence interval can be adjusted accordingly.

The calculation of the confidence interval represents an additional function compared to the prior art during operation or after loss of the synchronization signal or satellite signal. For example, if a 1PPS signal fails, in particular due to loss of the satellite signal, the crystal can 38 continue to run and the time will continue to be calculated according to previously described pattern.

Using a known quartz error, for example from a datasheet, a confidence interval can be calculated by integration. The time and time accuracy can now be further determined without satellite reception, and customers can use the time and confidence interval to determine if time still has the required precision. It is also possible to invalidate the time if the time accuracy or confidence exceeds a certain threshold of, for example, 10 ms.

It is also possible to calculate the confidence value or the confidence interval by assuming a static error, which may for example be a ppm value from the data sheet, and integrating it over time. The system accuracy, ie in particular an accuracy of the 1PPS signal and the measurement accuracy of a controller, should preferably be taken into account for the accuracy determination. These are typically <100 ns in one dimension. The quartz accuracy is typically the dominant factor influencing the time accuracy with errors of, for example, 100 ppm = 100 μs / s, which leads to an error of 1 ms, for example, after 10 s. The transmission time from receiver to controller typically corresponds to a pure, constant offset that can be measured and corrected. He has no influence on the time accuracy.

A quartz drift can also be determined by determining the quartz error by the time interval of two 1PPS signals or other synchronization signals. Since the drift is then known, it can be used for the time calculation and corrected in order to provide an accurate time even without GNSS signals or other synchronization signals in the long term. In the case of receiving synchronization signals, synchronization to the 1PPS signal is typically offset correction.

The determination of the confidence value or confidence interval can thus be optimized and the factor of the clock drift, which has the greatest influence on the accuracy, can be removed from the confidence estimation. As inaccuracy for the determination of confidence then remain only the accuracy of the Uhrendrifts and the change in the Uhrendrifts, both of which represent very low values.

The quartz accuracy from the data sheet largely corresponds to the clock drift (deviation ticks per second to quartz setpoint ticks per second). If these values differ, a time error of the measured time is integrated over time.

• Möglichkeit 1 (ohne Driftkorrektur):
  • Systemzeit = Zeit + Offset
  • Konfidenzintervall: Genauigkeit des 1PPS-Signals (Receiver) + Messgenauigkeit (Controller) + PPM-Wert × t
• Möglichkeit 2 (mit Driftkorrektur):
  • Systemzeit = Zeit + Offset + Drift × t
  • Konfidenzintervall: Genauigkeit 1PPS-Signal (Receiver) + Messgenauigkeit (Controller) + Messgenauigkeit des Uhrendrifts × t + Uhrendriftrate × t²

The overall equations for determining time and confidence may be given, for example, as follows:

• possibility 1 (without drift correction):
  • System time = time + offset
  • Confidence interval: Accuracy of the 1PPS signal (receiver) + measurement accuracy (controller) + PPM value × t
• possibility 2 (with drift correction):
  • System time = time + offset + drift × t
  • Confidence interval: Accuracy 1PPS signal (receiver) + measurement accuracy (controller) + measurement accuracy of clock pressure × t + clock rate × t ²

The time is typically a time of the quartz or a running time calculated on the basis of the quartz. The offset is typically a calculated value, using the correction factor to convert the quartz time to system time. The clock drift is typically a fault of the quartz. The clock rate is typically a dynamic change in the error of the crystal, that is, for example, a slow change in the crystal frequency, which is mainly influenced by aging and temperature. The confidence interval serves in particular for an accuracy estimate and corresponds, for example, to the expected maximum error of the time. The specified drift can be, for example, the drift value explained above.

The procedure described herein allows further calculation of the system time after loss of a GNSS signal, satellite signal or other synchronization signal. Other controllers may decide for themselves, based on the confidence interval, if the required accuracy is still sufficient, and the method can largely compensate for the quartz error. The possibility with drift correction has the particular advantage that it still delivers a very accurate time with a good accuracy estimate even with long GNSS signal failures. The drift-correction option typically provides a likely, but not necessarily greater, time error (depending on the actual quartz error or drift) with a poorer accuracy estimate, but is easier to implement.

The possibility with drift correction can be used in particular if the internal clock drift can be measured on the basis of an absolute reference, for example based on a GNSS time. The non-drift option is more universal and can be applied to systems without corresponding synchronization capabilities.

Mentioned steps of the method according to the invention can be carried out in the order given. However, they can also be executed in a different order. In one of its embodiments, for example with a specific set of steps, the method according to the invention can be carried out in such a way that no further steps are carried out. However, in principle also further steps can be carried out, even those which are not mentioned.

In general, it should be pointed out that vehicle-to-X communication in particular means direct communication between vehicles and / or between vehicles and infrastructure facilities. For example, this may be vehicle-to-vehicle communication or vehicle-to-infrastructure communication. If, in the context of this application, reference is made to communication between vehicles, this can in principle be carried out, for example, in the context of vehicle-to-vehicle communication, which typically takes place without being mediated by a mobile radio network or a similar external infrastructure and which is therefore the result of other solutions which, for example, build on a mobile network, is to be distinguished. For example, vehicle-to-X communication may be performed using the IEEE 802.11p or IEEE 1609.4 standards. Vehicle-to-X communication may also be referred to as C2X communication. The subareas can be referred to as C2C (Car-to-Car) or C2I (Car-to-Infrastructure). However, the invention explicitly does not exclude vehicle-to-X communication with switching, for example via a mobile radio network.

The claims belonging to the application do not constitute a waiver of the achievement of further protection.

If, in the course of the procedure, it turns out that a feature or a group of features is not absolutely necessary, it is already desired on the applicant side to formulate at least one independent claim which no longer has the feature or the group of features. This may, for example, be a subcombination of a claim present at the filing date or a subcombination of a claim limited by further features of a claim present at the filing date. Such newly formulated claims or feature combinations are to be understood as covered by the disclosure of this application.

It should also be noted that embodiments, features and variants of the invention, which are described in the various embodiments or embodiments and / or shown in the figures, can be combined with each other as desired. Single or multiple features are arbitrarily interchangeable. Resulting combinations of features are to be understood as covered by the disclosure of this application.

Recoveries in dependent claims are not to be understood as a waiver of obtaining independent, objective protection for the features of the dependent claims. These features can also be combined as desired with other features.

Features that are disclosed only in the specification or features that are disclosed in the specification or in a claim only in conjunction with other features may, in principle, be of independent significance to the invention. They can therefore also be included individually in claims to distinguish them from the prior art.

Claims (15)

A method for outputting a time by means of a continuous counter (36), the method comprising the steps of: Setting an output time, wherein the counter (36) has an output counter reading at the output time, Outputting the time based on a current count of the counter (36), the output count and the output time, and Calculating a confidence interval of the output time based on a difference between the output time and the output time. Method according to Claim 1 , wherein the time without drift correction of the counter (36) is output. Method according to Claim 2 - wherein the confidence interval is calculated as the sum of - an accuracy in the determination of the output time, and - a product of a maximum drift of the counter (36) multiplied by the difference between the output time and the output time. Method according to Claim 1 , - wherein the time is output with drift correction of the counter (36). Method according to Claim 4 in which a drift value used for drift correction has been determined by means of satellite signals prior to outputting the time as follows: - receiving a first reference time pulse of a satellite signal, the first reference time pulse indicating a first reference time, responsively storing a current first count of the counter (36) in one Register (34), - receiving a second reference time pulse of a satellite signal, wherein the second reference time pulse indicates a second reference time, the counter (36) having a current second count upon receiving the second reference time pulse, - calculating a counter difference between the second count and the first Counter reading, calculating a drift value based on the counter difference and a time difference between the second reference time and the first reference time. Method according to Claim 5 , wherein the drift value indicates a deviation between a time calculated by means of the counter difference and the time difference between the second reference time and the first reference time. Method according to one of Claims 5 or 6 in which the drift correction is effected by adding a correction value, which is calculated as the product of the drift value and a difference between the current counter reading and the output counter reading, before outputting the time. Method according to one of Claims 4 to 7 - where the confidence interval is the sum of - an accuracy in determining the starting time, and - is calculated from a measurement accuracy of the drift value multiplied by the difference between the output time and the output time. Method according to one of Claims 4 to 7 - the confidence interval being the sum of - an accuracy in the determination of the output time, and - a product of a measurement accuracy of the drift value multiplied by the difference between the output time and the output time, and - a product of a drift change multiplied by the squared difference between the output time and the output time. Method according to one of Claims 3 . 8th . 9 or a claim dependent thereon, wherein the accuracy in the determination of the output time is calculated as the sum of an accuracy of a satellite-based reference time pulse and an accuracy of a measurement of the satellite-based reference time pulse. Method according to one of the preceding claims, - wherein the outputting of the time during an interruption of reception of satellite signals or other synchronization signals is performed. Method according to one of the preceding claims, - Wherein the counter (36) is driven by a quartz oscillator (38). Method according to one of the preceding claims, - where the output time is determined by means of satellite signals. Method according to one of the preceding claims, - comparing the confidence interval with a threshold, and - where the time spent is discarded when the confidence interval exceeds the threshold. Method for sending vehicle-to-X messages, wherein each vehicle-to-X message is provided with a time issued by a method according to any one of the preceding claims; and or Method for receiving vehicle-to-X messages, wherein each vehicle-to-X message is provided with a time which is compared with a system time, the system time having been issued by a method according to one of the preceding claims.

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