Method for checking a message in a communication system

Abstract

A method for checking a message in a communication system, in which multiple users are connected to a communication medium that includes two signal lines and exchange messages via same. A time difference between points in time of reception of a message that is sent on the communication medium is ascertained at two different, predefined positions on the communication medium, and based on a comparison of the time difference to at least one reference time difference, it is determined whether the message originates from a verified user. During the ascertainment of the time difference at the two positions, in each case a difference signal is formed from signals that have resulted on the two signal lines due to the message.

Claims

1. A method for checking a message in a communication system, in which multiple users are connected to a communication medium that includes two signal lines and exchange messages via the communication medium, the method comprising the following steps: ascertaining a time difference between points in time of reception of a message that is sent on the communication medium at two different, predefined positions on the communication medium; based on a comparison of the time difference to at least one reference time difference, determining whether the message originates from a verified user; and during the ascertainment of the time difference at the two positions, at each of the two positions, forming a difference signal from signals that resulted on the two signal lines due to the message.

2. The method as recited in claim 1, wherein a voltage level of the difference signal is adapted to a time-to-digital converter (TDC) using a voltage divider.

3. The method as recited in claim 1, wherein at at least one of the two positions, a threshold value for a signal level is predefined during the detection of the difference signal, and the difference signal is assumed to be recognized when the threshold value is exceeded.

4. The method as recited in claim 3, wherein a comparator is used via which the difference signal is compared to the threshold value.

5. The method as recited in claim 3, wherein the threshold value is individually predefined for each of the at least one of the two positions, and is also automatically determined.

6. The method as recited in claim 5, wherein the threshold value is predefined using a digital-to-analog converter.

7. The method as recited in claim 1, wherein a signal transceiver or a dedicated subtraction logic system is used to form the difference signal.

8. The method as recited in claim 1, wherein the communication medium is a CAN bus, or a CAN FD bus, or a CAN XL bus, or a 10BASE-T1S bus.

9. A processing unit configured to check a message in a communication system, in which multiple users are connected to a communication medium that includes two signal lines and exchange messages via the communication medium, the processing unit configured to: ascertain a time difference between points in time of reception of a message that is sent on the communication medium at two different, predefined positions on the communication medium; based on a comparison of the time difference to at least one reference time difference, determine whether the message originates from a verified user; and during the ascertainment of the time difference at the two positions, at each of the two positions, a difference signal is formed from signals that resulted on the two signal lines due to the message.

10. A non-transitory machine-readable memory medium on which is stored a computer program for checking a message in a communication system, in which multiple users are connected to a communication medium that includes two signal lines and exchange messages via the communication medium, the computer program, when executed on a processing unit, causing the processing unit to perform method comprising the following steps: ascertaining a time difference between points in time of reception of a message that is sent on the communication medium at two different, predefined positions on the communication medium; based on a comparison of the time difference to at least one reference time difference, determining whether the message originates from a verified user; and during the ascertainment of the time difference at the two positions, at each of the two positions, forming a difference signal from signals that resulted on the two signal lines due to the message.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a communication system in which a method according to the present invention may be carried out.

(2) FIG. 2 shows a diagram including reference time differences as may be used in a method according to an example embodiment of the present invention.

(3) FIG. 3 shows a circuit system for carrying out a method of the present invention in one preferred specific embodiment.

(4) FIG. 4 shows signal patterns for explaining a method according to the present invention in a further preferred specific embodiment.

(5) FIG. 5 shows a circuit system for carrying out a method according to the present invention in a further preferred specific embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(6) FIG. 1 schematically illustrates a communication system in which a method according to the present invention may be carried out. For this purpose, communication system 100 is shown with two users 110, 112 by way of example, which are connected or attached to a communication medium 120. Users 110, 112 may be, for example, control units in a vehicle. Communication medium 120, which is a CAN bus, for example, includes two signal lines 120.sub.H and 120.sub.L, which in the case of the CAN bus are also denoted as CAN high and CAN low.

(7) In addition, a processing unit or circuit system 130 is shown which is configured and used for ascertaining a time difference between points in time of reception of a message that is sent on the communication medium, at two different, predefined positions P.sub.1 and P.sub.2 on communication medium 120 (these positions are valid in each case for both signal lines, which in practice are usually twisted). The message is indicated here by reference numeral 200. The two points in time of reception are indicated by reference symbols t.sub.1 and t.sub.2, and in particular with user 110 as sender. For this purpose, processing unit 130 may be connected to communication medium 120 or to the two signal lines at positions P.sub.1 and P.sub.2 in order to receive the signals in question.

(8) The signal of line 120.sub.H at position P.sub.1 is denoted by reference symbol S.sub.H1, the signal of line 120.sub.L at position P.sub.1 is denoted by reference symbol S.sub.L1, the signal of line 120.sub.H at position P.sub.2 is denoted by reference symbol S.sub.H2, and the signal of line 120.sub.L at position P.sub.2 is denoted by reference symbol S.sub.L2.

(9) For implementing the functions mentioned above, a component 132, by use of which the time difference on the communication medium may be determined, may be provided in processing unit 130. This component is also referred to below as a propagation difference determination component (PDDC). The PDDC could include, for example, a TDC or an independent circuit that measures the time difference between two signals at the two positions, for example also the ends, of the communication medium based on an internal timer, for example. Processing unit or circuit system 130 is explained in greater detail below, namely, in two different preferred variants.

(10) FIG. 2 illustrates a diagram by way of example, including reference time differences as may be used in a method according to the present invention, namely, as a probability distribution model of eight senders or users on the communication medium, using a Gaussian distribution. For this purpose, a probability density is plotted as a function of a time difference Δt (in ns by way of example). As an example, a reference time difference is denoted by reference symbol Δt.sub.R. If the time difference, ascertained for a message within the scope of the present invention, corresponds to one of the reference time differences or, for example, differs therefrom at least [by] less than a threshold value, it may be assumed that the message has been sent by a verified user.

(11) FIG. 3 illustrates a circuit system 130 for carrying out a method according to the present invention in one preferred specific embodiment. The circuit system may be circuit system or processing unit 130 shown in FIG. 1. In particular, the four incoming signals S.sub.H1, S.sub.L1, S.sub.H2, and S.sub.L2 are also shown. With the aid of detection means (i.e., detector(s)) such as CAN transceivers 136, 138, a difference or a difference signal S.sub.D1 or S.sub.D2 may be formed from signals that are in each case associated with a position. If the voltage level of the signals is appropriate for PDDC 132, the signals may be directly passed on to the PDDC, as indicated by dashed lines. Otherwise, in each case a voltage divider 140, 142 may be provided in order to appropriately adapt the voltage level.

(12) In this way, based on the two difference signals, the time difference for message 200 that is sent on the CAN bus may be ascertained in order to determine whether the message originates from a verified user. As mentioned above, this operation functions in particular when it may be assumed that the difference signals have comparable rising edges. If this is not the case, another variant may be used, as explained below.

(13) FIG. 4 illustrates signal patterns for explaining a method according to the present invention in a further preferred specific embodiment, namely, signal patterns of two difference signals S.sub.D1 and S.sub.D2 as voltage U plotted as a function of time t. The two signal patterns rise in a time-offset manner, but initially each with approximately the same slope. The time offset results, for example, from the different propagation times of the message up to the two positions, as mentioned above.

(14) However, as is further apparent, the slope of difference signal S.sub.D1 changes, so that this difference signal is even overtaken by difference signal S.sub.D2. If the CAN transceivers as shown in FIG. 2 or some other detection means regard the difference signal as recognized for a certain, fixedly predefined threshold value U.sub.S, the points in time of reception and thus the time difference may possibly be incorrectly recognized.

(15) FIG. 5 illustrates a circuit system 130′ for carrying out a method according to the present invention in a further preferred specific embodiment. This circuit system 130′ may likewise be used as processing unit or circuit system 130 shown in FIG. 1.

(16) Here as well, difference signals S.sub.D1 and S.sub.D2 are formed, initially with the aid of detection means (detectors) 150, 152, which are dedicated subtraction logic systems or corresponding circuits, for example. These difference signals are then supplied to a comparator 154 or 156, respectively, which also obtains a signal for a threshold value U.sub.S, above which the particular difference signal is to be considered as recognized. As indicated by the dashed line, this threshold value U.sub.S may also be dynamically determined and predefined with the aid of a digital-to-analog converter 158, for example.

(17) In this way, threshold value U.sub.S may be adapted and set, for example, to value U′.sub.S as shown in FIG. 4. It is also conceivable to use different threshold values for the two comparators 154, 156. The individual circumstances of the communication medium, which influences the signal propagation as shown in FIG. 4, may thus be taken into account.