DE102019106156A1 - Method for the optimal termination of a motor vehicle bus system and motor vehicle bus system - Google Patents

Abstract

A method for optimal termination of a motor vehicle bus system (10) is described which comprises several nodes (12) which are each set up to communicate with one another by means of an orthogonal frequency division multiplexing method (OFDM method). The signal strength and the signal-to-noise ratio are measured between the nodes (12) of a first pair of nodes (12) in both directions. The signal strength and the signal-to-noise ratio of a bus signal are calculated in both directions between the nodes (12) of at least one other pair of nodes. That node (12) is identified at which there is a poor signal-to-noise ratio with a simultaneously high signal strength. The termination of the identified node (12) is adjusted. A motor vehicle bus system (10) is also described.

Description

The invention relates to a method for optimal termination of a motor vehicle bus system with a plurality of nodes which are each set up to communicate with one another by means of an orthogonal frequency division multiplex method (OFDM method). The invention also relates to a motor vehicle bus system having a plurality of nodes which are each set up to communicate with one another by means of an orthogonal frequency division multiplex method (OFDM method).

Different bus systems are known from the prior art, which are used, among other things, in a motor vehicle in order to exchange or communicate data via nodes of the bus system, also called participants. These bus systems can connect comparatively few nodes with one another and moreover have relatively low bit rates if they are physically contacted on the same medium, for example. In order to achieve higher bit rates or to connect more nodes, it is known from the prior art to use so-called switches or gateways in order to logically connect nodes to different physical media. However, this increases the effort, which in turn increases the costs.

Also known from the prior art are bus systems in which the nodes communicate with one another using the orthogonal frequency division multiplexing method (OFDM method), with the nodes all being terminated in the same way, for example, depending on the arrangement of the nodes or the design of the bus system, i.e. with one ohmic resistance of the same resistance value are terminated. This leads to an increasing attenuation of the bus signal of around 3 dB per node or branch from the bus line, so that the maximum signal attenuation is already reached at 15 to 16 nodes, which corresponds to the maximum number of usable nodes in the bus system.

Another possibility for termination, which is known from the prior art, is to terminate the line only at the beginning and the end. The nodes between the start and end nodes can then be connected with very short stub lines so that a reflection at the non-terminated end of the stub line does not disturb the signal. This leads to restrictions in the cable routing or bus topology.

The object of the invention is to increase the number of possible nodes in the bus system in a cost-effective manner and to avoid restrictions in the bus topology.

• - Messen der Signalstärke und des Signal-Rausch-Abstands eines Bus-Signals zwischen den Knoten eines ersten Paars von Knoten in beide Richtungen,
• - Messen der Signalstärke und des Signal-Rausch-Abstands eines Bus-Signals in beide Richtungen zwischen den Knoten zumindest eines weiteren Paars von Knoten,
• - Identifizieren desjenigen Knotens, an dem ein schlechter Signal-Rausch-Abstand bei gleichzeitig hoher Signalstärke vorliegt, und
• - Anpassen der Terminierung des identifizierten Knotens.

The object is achieved according to the invention by a method for the optimal termination of a motor vehicle bus system with several nodes, each of which is set up to communicate with one another by means of an orthogonal frequency division multiplex method (OFDM method), with the following steps:

• - Measuring the signal strength and the signal-to-noise ratio of a bus signal between the nodes of a first pair of nodes in both directions,
• - Measuring the signal strength and the signal-to-noise ratio of a bus signal in both directions between the nodes of at least one other pair of nodes,
• - Identifying the node at which there is a poor signal-to-noise ratio with a simultaneously high signal strength, and
• - Adjusting the termination of the identified node.

The method according to the invention ensures that the existing motor vehicle bus system is adapted with regard to the termination of the individual nodes in such a way that no signal peaks (poor signal-to-noise ratio with simultaneously high signal strength) occur at the individual nodes which would lead to that the respective node would be overridden. In other words, there would be a poor signal-to-noise ratio at such a node, also known as the signal-to-noise ratio (SNR), although the signal power is due to the signal increase, i.e. negative attenuation of the bus Signal is relatively high.

Using the measured signal strength and the measured signal-to-noise ratio, nodes in the motor vehicle bus system can be determined where the signal-to-noise ratio is poor despite good signal strength. The termination, that is to say the ohmic resistance, of the respective node at which the signal excess has been identified can then be adapted accordingly in order to compensate or suppress the signal excess.

Basically, local signal peaks can occur, i.e. negative attenuation of the bus signal, if the bus signal is reflected on the bus line at the nodes, branches and transitions and there is positive overlap or interference at other points .

To measure the signal strength and / or the signal-to-noise ratio, at least one node, in particular each node, of the motor vehicle Bus system at least partially comprise an (integrated) measurement module which is set up to measure the signal strength and the signal-to-noise ratio online, that is, during operation.

Such a measurement module can otherwise be provided in order to adapt the modulation of the corresponding node that uses the OFDM method for communication to a transmission channel, as is known from power line communication, i.e. power line communication (PLC).

Such a measurement module can comprise a receiver of a first node, which determines the signal strength or the signal power and can measure the noise power on the bus line. In addition, a transmitter (transmitter) can be provided in a second node, which generates a test signal that is received by the first node. The process can be coordinated by one of the nodes or by a central node that performs the network management.

The measurements can be carried out for all pairs of nodes on the same physical medium, i.e. all nodes. For M nodes, this results in a maximum number of “M ² - M” measurements, since the nodes are not measured with themselves.

The respective pairs each form a channel so that all channels can be measured in order to identify the termination of a node that needs to be adjusted.

In specially structured topologies of the motor vehicle bus system, the number of measurements can be reduced on the basis of previous knowledge, so that not all pairs of nodes necessarily have to be measured.

Basically, a pair of nodes comprises a first node and a second node, that is to say two different nodes.

As explained above, the corresponding permutations of the possible pairs of nodes thus result for all pairs, i.e. for example with three nodes the following pairs of nodes: The first pair includes the first node and the second node, the second pair includes the first node and the third node and the third pair includes the second node and the third node.

One aspect provides for the termination to be adapted by incorporating a lower termination. In this respect, the termination of the node at which the signal excess has been identified is changed manually by installing a termination at the corresponding node that is lower than the previous one. This makes it possible to compensate or suppress a signal increase that occurs at the node so that it no longer occurs.

A further aspect provides that the termination of the node is automatically adapted in that a variable termination unit of the node automatically provides an adapted termination. The node accordingly has a variable termination unit which is designed to automatically adapt the termination. Alternatively, the variable termination unit can be assigned to the node. In any case, the variable termination unit can comprise several, in particular different, terminations which can be switched independently of one another. Depending on the required termination, different terminations can be linked to one another or switched to one another in order to arrive at the desired termination, that is to say the desired value of the termination at which the identified excessive signal no longer occurs.

In other words, the variable termination unit comprises several, in particular different, ohmic resistors which can each be switched in order to set or adapt the resistance value at the corresponding node.

Furthermore, the nodes of the motor vehicle bus system can each have a variable impedance, the nodes each having a transmit mode and a receive mode, and the variable impedance in the receive mode being at least one order of magnitude higher than in the transmit mode, in particular at least three orders of magnitude, for example six orders of magnitude. Due to the different impedances of the nodes in the transmit and receive mode, a significantly higher number of nodes can be achieved with OFDM technology on coaxial and twisted lines that are used in a bus system, in particular the motor vehicle bus system. Due to the low impedance in the transmit mode, the node designed as a transmitter can operate long lines and many nodes accordingly, since the other nodes, i.e. the nodes designed as receivers, do not attenuate the bus signal as much due to their high impedance in the receive mode .

The node set up as a transmitter can, for example, have an impedance of 10 Ω, whereas the node set up as a receiver has an impedance of 10 kΩ to 10 MΩ.

In other words, the node has an impedance of 10 Ω if it is in the transmit mode, whereas the impedance of the node is between 10 kΩ and 10 MΩ if it is in the receive mode.

The different impedances in the transmit and receive mode lead to the fact that the bus signals are reflected more strongly to the node designed as a receiver, since the impedance in the receive mode is correspondingly higher, which leads to the local signal peaks the negative attenuation of the bus signal.

Another aspect provides that the measurement of the signal strength and the signal-to-noise ratio are repeated recursively for the pairs of nodes, the termination of the respectively identified node being adapted. The procedure is therefore repeated for the previously measured pairs of nodes, in particular for all nodes on the same medium, until a desired overall optimum is found. In the overall optimum, the signal strength and the signal-to-noise ratio for the respective nodes should be on the same level.

In particular, the measurements are repeated recursively until a predefined overall optimum with regard to the termination is reached. As already explained, the predefined overall optimum can be defined in such a way that the attenuation, that is to say the signal strength, is the same for all nodes on the same medium with essentially the same signal-to-noise ratio. In other words, the signal strength and the signal-to-noise ratio for the respective nodes are at the same level.

Furthermore, the object is achieved according to the invention by a motor vehicle bus system with a plurality of nodes which are each set up to communicate with one another by means of an orthogonal frequency division multiplex method (OFDM method), at least one node having a variable impedance, the at least one node having a transmission Mode and a receiving mode, and wherein the variable impedance in the receiving mode is at least one order of magnitude higher than in the transmitting mode.

Due to the different impedances in the transmit and receive mode, it is possible to increase the number of nodes in the motor vehicle bus system accordingly, since the bus signal sent by the node set up as a transmitter is less attenuated, which means that it is sent to more nodes can be compared to a bus system with the same terminations.

One aspect provides that the at least one node comprises at least partially a measurement module which is set up to measure the signal strength and the signal-to-noise ratio of a bus signal. The measurement module can be a measurement module that measures the signal strength and the signal-to-noise ratio in order to adapt a modulation to a corresponding transmission channel of the bus system, provided that the respective node communicates using the OFDM method.

Another aspect provides that the measurement module is set up to identify a signal excess on the basis of the measured signal strength and the measured signal-to-noise ratio. From the signal strength and the signal-to-noise ratio, it is possible to infer a signal excess at a node of the motor vehicle bus system, the termination of which is to be adapted in order to compensate for or suppress the signal excess. In this respect, the measuring module can identify the signal increase.

According to a further aspect, the at least one node comprises a variable termination unit which is set up to automatically provide an adapted termination as a function of the measured signal strength and the measured signal-to-noise ratio. The variable termination unit is accordingly designed to automatically provide adapted termination to the node at which the signal excess has been identified so that the signal excess is compensated or suppressed. In other words, the termination of the node at which the signal excess has been identified is adapted in order to suppress or compensate for the signal excess.

The variable termination unit can have several, in particular different, terminations that can be switched independently of one another. The variable termination unit can accordingly set the termination in a simple manner so that the variable termination unit switches the multiple terminations in a certain way in order to arrive at an overall termination that is adapted to the measured signal strength and / or the measured signal-to-noise ratio . For this purpose, the variable termination unit can communicate with the measuring module in order to receive information or data on the measured signal strength and / or the signal-to-noise ratio.

Furthermore, the variable impedance in the receive mode can be at least three orders of magnitude, in particular six orders of magnitude, higher than in the transmit mode. Due to the different impedances in the receive or transmit mode, several nodes can be integrated into the vehicle Integrate the bus system, since the higher impedance in the receive mode of the nodes set up as receivers means that the bus signal sent by the node set up as a transmitter is less attenuated. As a result, the transmitted bus signal can be sent over a greater distance and accordingly several nodes, since the maximum signal attenuation occurs significantly later.

If a variable termination unit is assigned to all nodes, the termination can be adjusted in a simple and automated manner until a predetermined overall optimum is found.

For this purpose, the measurements described above are carried out for the respective pairs of nodes, with the termination of the identified node being adapted, for example the node with the greatest signal increase. The termination can be adjusted automatically via the variable termination unit so that the next loop of measurements can be carried out automatically.

This procedure is repeated until the predetermined overall optimum has been found in the motor vehicle bus system.

• - 1 eine schematische Darstellung eines erfindungsgemäßen Kraftfahrzeug-Bussystems, und
• - 2 eine schematische Darstellung, die das erfindungsgemäße Verfahren zur optimalen Terminierung eines Kraftfahrzeug-Bussystems verdeutlicht.

Further advantages and properties of the invention emerge from the following description and the drawings, to which reference is made. In the drawings show:

• - 1 a schematic representation of a motor vehicle bus system according to the invention, and
• - 2 a schematic representation that illustrates the inventive method for optimal termination of a motor vehicle bus system.

In 1 is a motor vehicle bus system 10 shown the multiple knot 12 which are each set up to communicate with one another by means of an orthogonal frequency division multiplexing method (OFDM method). The knots 12 are each via a bus line 14th interconnected through which the nodes 12 can communicate using bus signals.

In the in 1 The embodiment shown is, for example, a linear motor vehicle bus system 10 . In principle, other motor vehicle bus systems are also conceivable, that is to say other topologies.

The knots 12 each have a variable impedance, since in the embodiment shown each of the nodes 12 have a send mode and a receive mode.

In receive mode is the variable impedance of the respective node 12 by at least one order of magnitude higher than in the send mode of the corresponding node 12 , as follows using the 2 will be explained.

For example, the impedance is in the transmit mode 10 Ω, whereas the impedance in receive mode 10 kΩ to 10 MΩ, i.e. three to six orders of magnitude higher than in the transmit mode.

Furthermore, the nodes include 12 in the embodiment shown, one measuring module each 16 , which is set up to measure the signal strength and the signal-to-noise ratio of a transmitted bus signal from a node set up as a transmitter 12 via the bus line 14th to one or more nodes designed as receivers 12 is sent.

In particular, a first node 12 a measuring module serving as a receiver 16 and a second knot 12 a measuring module serving as a transmitter 16 which can communicate with one another via a channel formed between them in order to determine the signal strength and the signal-to-noise ratio of the transmitted bus signal.

In principle, every measuring module 16 of a node 12 serve both as a receiver and as a transmitter or have the corresponding functions, so that between the pairs of nodes 12 formed channels can be measured in both directions, for example from the first node 12 to the second knot 12 and vice versa.

Using the measuring module 16 can thus be a signal increase at a corresponding node 12 identify. The signal strength and the signal-to-noise ratio can accordingly be determined, in particular simultaneously.

It also includes each node 12 a variable termination unit 18th (here only for one node for reasons of clarity 12 shown), which in the embodiment shown has multiple terminations 20th which can be switched independently of one another. The terminations 20th can be designed differently so that they depend on the circuit of the individual terminations 20th result in a different resulting termination value.

Via the variable termination unit 18th the respective node can thus be terminated as a function of the measured signal strength or the measured signal-to-noise ratio 12 , in which the signal increase has been identified, automatically adjust so that there is no manual adjustment of the termination of the corresponding node 12 requirement.

Alternatively, it can be provided that due to the detected signal increase, which is generated by means of the measuring module 16 has been determined, the respective termination of the node 12 adjusted manually by terminating the appropriate node 12 is changed or a different termination is installed that has a lower value than the previous termination. This ensures that the previously identified signal increase can be suppressed or compensated.

In principle, the variable termination unit 18th in the respective node 12 be integrated. Alternatively, the variable termination unit 18th the respective node 12 only be assigned, in particular separately from the node 12 be formed, the variable termination unit 18th with the corresponding node 12 but is electrically coupled to the node 12 terminate electrically.

The following is based on the 2 explains how an optimal termination of the motor vehicle bus system 10 is determined.

So it can be the motor vehicle bus system 10 basically adjust by taking a first step S1 the signal strength and the signal-to-noise ratio of a correspondingly transmitted bus signal at a node 12 is measured. So it is the signal strength and the signal-to-noise ratio of the bus signal between the nodes 12 a first pair of knots 12 measured in both directions.

The bus signal can come from a node designed as a transmitter 12 to one or more nodes designed as receivers 12 being sent to a node configured as a recipient 12 Will be received. These two knots 12 , so the node trained as a transmitter 12 and the node designed as a receiver 12 accordingly represent the pair of nodes 12 represent.

In a second step S2 the corresponding measurements, i.e. the measurement of the signal strength and the measurement of the signal-to-noise ratio, at least for another pair of nodes 12 carried out. So there are at least two pairs of nodes 12 has been measured.

The measured signal strength and the measured signal-to-noise ratio are then used in a third step S3 used to signal a cant at the at least one node 12 of the motor vehicle bus system 10 to identify, i.e. a poor signal-to-noise ratio with high signal strength at the same time.

In a fourth step S4 is the termination of the corresponding identified node 12 adjusted with the signal increase in step S3 has been established. This compensates or suppresses the previously determined signal increase so that it no longer occurs.

As already explained, the termination can easily be adjusted manually by installing a lower termination, that is, a termination with a lower value. The lower termination has the consequence that the signal excess that is sent to the corresponding node 12 has been identified, is compensated or suppressed.

Alternatively, the termination of the node 12 can be adjusted automatically by the variable termination unit 18th of the corresponding node 12 automatically provides an adapted termination.

The variable termination unit 18th and the measuring module 16 communicate with each other so that the measuring module 16 measured signal strength and / or the measured signal-to-noise ratio to the variable termination unit 18th of the node 12 is transmitted so that the termination unit 18th automatically adjusts the termination accordingly.

After the termination of the node identified in a first loop 12 has been adjusted, follow the previous steps S1 to S4 repeated to re-tie a knot 12 to identify where the signal-to-noise ratio is poor and the signal strength is high.

Then the termination of the node identified in the next loop 12 adjusted accordingly.

The loops are repeated recursively, for example until an overall optimum is found with regard to the termination, that is to say at which the signal strength and the signal-to-noise ratio for the respective nodes 12 are on the same level.

Provided each knot 12 a variable termination unit 18th is assigned, the respective scheduling can be adjusted automatically. Furthermore, the loops described above can run automatically in order to achieve the overall optimum.

In any case, it is ensured that the number of in the motor vehicle bus system 10 used knot 12 can be maximized, since the maximum signal attenuation occurs significantly later than with identically terminated nodes.

This is achieved by making the knot 12 have a variable impedance, the impedance in the transmit mode being at least one order of magnitude smaller than in the receive mode, in particular by three to six orders of magnitude lower.

Due to the different termination of the nodes 12 Higher reflections that occur and lead to local signal peaks can be compensated or suppressed by a correspondingly lower termination.

Claims (12)

Method for optimal termination of a motor vehicle bus system (10) with several nodes (12), each of which is set up to communicate with one another by means of an orthogonal frequency division multiplex method (OFDM method), with the following steps: - Measuring the signal strength and the signal-to-noise ratio of a bus signal between the nodes (12) of a first pair of nodes (12) in both directions, - Measuring the signal strength and the signal-to-noise ratio of a bus signal in both directions between the nodes (12) of at least one further pair of nodes (12), - Identifying the node (12) at which there is a poor signal-to-noise ratio with a simultaneously high signal strength, and - Adjusting the termination of the identified node (12). Procedure according to Claim 1 , characterized in that the termination is adjusted by incorporating a lower termination. Procedure according to Claim 1 or 2 , characterized in that the termination of the node (12) is automatically adapted in that a variable termination unit (18) of the node (12) automatically provides an adapted termination. Method according to one of the preceding claims, characterized in that the nodes (12) of the motor vehicle bus system (10) each have a variable impedance, the nodes (12) each having a transmit mode and a receive mode, and the variable impedance in the receive mode is at least one order of magnitude higher than in the transmit mode, in particular at least three orders of magnitude, for example six orders of magnitude. Method according to one of the preceding claims, characterized in that the measurement of the signal strength and the signal-to-noise ratio are repeated recursively for the pairs of nodes, the termination of the respectively identified node being adapted. Procedure according to Claim 5 , characterized in that the measurements are repeated recursively until a predefined overall optimum with regard to the termination is reached. Motor vehicle bus system (10) with a plurality of nodes (12) which are each set up to communicate with one another by means of an orthogonal frequency division multiplexing method (OFDM method), at least one node (12) having a variable impedance, the at least one node (12 ) has a transmit mode and a receive mode, and wherein the variable impedance in the receive mode is at least one order of magnitude higher than in the transmit mode. Motor vehicle bus system (10) according to Claim 7 characterized in that the at least one node (12) at least partially comprises a measurement module (16) which is set up to measure the signal strength and the signal-to-noise ratio of a bus signal. Motor vehicle bus system (10) according to Claim 8 , characterized in that the measuring module (16) is set up to identify a signal increase based on the measured signal strength and the measured signal-to-noise ratio. Motor vehicle bus system (10) according to Claim 8 or 9 characterized in that the at least one node (12) comprises a variable termination unit (18) which is set up to automatically provide an adapted termination as a function of the measured signal strength and the measured signal-to-noise ratio. Motor vehicle bus system (10) according to Claim 10 , characterized in that the variable termination unit (18) comprises several, in particular different, terminations (20) which can be switched independently of one another. Motor vehicle bus system (10) according to one of the Claims 7 to 11 , characterized in that the variable impedance in receiving mode is around is at least three orders of magnitude, in particular six orders of magnitude, higher than in the transmit mode.

Images