DE102014214459B4 - Collision-free media access method - Google Patents

Abstract

Station (2-1) for serial data transmission by means of data frames (data frame) in a communication network (1) with a plurality of stations (2-1, 2-2, 2-3, 2-4, 2-5, 2-6 ...), in particular in a time division multiplex method (TDMA), in which each station (2-1, 2-2, 2-3, 2-4, 2-5, 2-6, ...) has time access slots (S1, S2, S3, S4, S5, S6, ...) are assigned for a shared data transmission medium (3), comprising: a first processing device, set up to check whether in an access slot (S1, S2, S3, S4 , S5, S6, ...), which precedes the access slot (S1) assigned to the station, there is a data transmission on the data transmission medium (3), the station (2-1) being set up to transmit at least if there is no data transmission a first data frame of a first message (N1), the sequence of the access slot allocation being changed (106b), the arrangement of a second being effected by the first station (2-1) ordered access slot (S1) depends on the number of access slots (S1, S2, S3, S4, S5, S6, ...) which are required for the transmission of the first data frame of the first message (N1), with an inverse arrangement of the Access slots (..., S6, S5, S4, S3, S2, S1) is used.

Description

The invention relates to a station for data transmission by means of data frames in a communication network with a plurality of stations and a corresponding method, in particular a time division multiplex method (TDMA).

The number of electronic systems in motor vehicles has increased significantly over the past few decades. The technical devices of motor vehicles therefore now have a large number of electronic systems which control the motor vehicle and which in some cases replace mechanical systems.

Since a line is required for each piece of information in conventional cabling, the length and weight of the cable harness and the number of connections to the control units increase as the functionality of the vehicle electronics increases. A data bus, in particular a CAN bus (Controller Area Network), which transmits all information over two lines, has provided a remedy. Such a data bus connects a large number of control units that work together in a vehicle. The connected control units can exchange information with one another via the data bus. The individual control units are networked with one another in the bus system for data transmission. If a station or a control device transfers information into the bus system by means of a data frame, other stations or control devices can monitor or "listen in" to this information. Stations for which the information in the data frame is relevant will use this, other stations ignore this data frame.

With the progressive increase in control devices that are supposed to communicate via the bus systems in the motor vehicle, in particular from the fields of telematics, media and audio and vehicle automation, the problem arises that more and more data volumes and thus data frames are transmitted via the existing bus systems have to. Because of the serial mode of transmission, this often results in an overload or "congestion" with the data traffic of such a communication network.

Regardless of this, there is a desire on the part of vehicle manufacturers, from an economic and ecological point of view, especially against the background of the increasing electrification of the drive system for motor vehicles, to save the weight of motor vehicles and to merge systems or even the power lines that are used to supply power to the stations or control units To use the bus system, ie to use a so-called PowerLAN, dLAN (direct LAN) or Powerline Communication (PLC) via this power supply, in particular according to the IEEE 1901 standard.

The IEEE 1901 standard uses, for example, a multiple access with carrier check collision avoidance method (CSMA / CA) as the access method. This has the disadvantage that the overhead is comparatively large. In addition, collisions can occur when sending messages that include the data frames. To avoid collisions, a back-off mechanism, i.e. a collision avoidance mechanism, is used in radio transmissions (IEEE 802.11) or PowerLAN communication according to the standard mentioned. Each station randomly selects one of several possible times during an access slot in order to start the transmission. The station that selects the earliest transmission time comes into play during the transmission, whereas the other stations determine that a transmission is already taking place via the communication network.

If two or more stations accidentally select the same point in time for the start of a transmission, a collision has occurred and a transmission error results for this access slot. The back-off mechanism cannot completely rule out collisions. Collisions or transmission errors are generally recognized by the fact that there is no acknowledgment (ACK) for a data frame by the receiver. In this case, the data frame is generally retransmitted. This procedure according to such a protocol is not deterministic and no statement can be made about maximum delay times. If a message with a data frame to be transmitted from a station collides several times in the communication network with other messages from other stations, this is generally discarded after a certain time or after a maximum number of transmission attempts has been exceeded. In particular, when there is a large number of stations or participants in a communication, such as those reached in modern vehicles, collision avoidance mechanisms no longer work satisfactorily, since collisions occur despite these mechanisms.

In the case of time division multiplex data transmission, collisions are excluded because the access slots are permanently assigned to the stations participating in the communication and can only be predicted by maximum delays, but this method is relatively inflexible. For example, valuable transmission time is lost when time slots are not required or not be used. The time-division multiplexing methods for data transmission are rather inefficient, especially when there are sporadic communication requests from the participants.

DE 41 29 205 A1 relates to a method for building messages for the exchange of data and / or synchronization of processes in data processing systems, with a message comprising at least one element or start bit field (SOF), identification and data, with a bit field (IDE bit having at least one bit ) is provided to mark the length of the identifier.

DE 698 07 235 T2 relates to a method of reducing the number of messages required to send messages in a deterministic manner between multiple nodes communicatively connected by a bus using the Controller Area Network (CAN) serial communication protocol.

It is an object of the invention to specify a flexible, collision-free and, in particular, deterministic access method for serial data transmission.

This object is achieved by a station according to claim 1 and a method for serial data transmission by means of data frames in a communication network according to claim 5. Advantageous refinements are claimed in the subclaims.

The station according to the invention for serial data transmission by means of data frames in a communication network with a plurality of stations, in particular a time division multiplex method (TDMA), in which each station is assigned time access slots for a shared data transmission medium, has a first processing device, set up to check whether there is a data transmission on the data transmission medium in an access slot which precedes the access slot assigned to the station. Furthermore, if there is no data transmission, the station is preferably set up to transmit at least a first data frame of a first message.

The method according to the invention for serial data transmission by means of data frames in a communication network to a plurality of stations, in particular a time division multiplex method in which time access slots for a shared data transmission medium are assigned to each station, has the following working steps when the plurality of stations communicate with each other: Check whether there is a data transmission on the data transmission medium in an access slot which precedes an access slot assigned to a first station; and transmitting, if there is no data transmission, at least a first data frame of a first message.

A data frame within the meaning of the invention is a data unit of a protocol. A data frame preferably consists of destination and source addresses, control information for data flow control, user data of a data packet and / or a checksum to ensure data integrity.

A station within the meaning of the invention is a participant in a communication in a communication network.

A data transmission medium within the meaning of the invention is any type of medium which can be used jointly by a plurality of stations, preferably a radio connection, an electrical connection or an optical connection.

A message within the meaning of the invention is a self-contained data transmission unit defined by a data transmission protocol, which preferably has a data frame as well as further information and elements that are necessary for the orderly flow of communication in serial data transmission.

The invention is based on the approach of making the use of stations permanently assigned access slots more flexible. If there is no data transmission in a communication network or on the data transmission medium used jointly by several stations, a station may start a transmission in the access slot assigned to it. In contrast to known transmission methods, however, the duration of the transmission can be longer than an access slot, so that during the transmission, access slots assigned to other stations are blocked for transmission by this station. As a result, the duration of the access slots can be significantly shortened compared to conventional time division multiplexing methods. By means of the method according to the invention, the number of unused access slots can be significantly reduced and collisions on a data transmission medium can be completely avoided.

In an advantageous embodiment of the station according to the invention, it has a second processing device, set up to skip at least one subsequent access slot assigned to the station, the number of access slots to be skipped depending on the number of access slots which are used for the Transmission of the at least one first data frame of the first message are required.

By skipping or omitting access slots that would actually be assigned to the station, it can be ensured that imbalances that arise from the transmission of messages with data frames across access slots can be compensated. If a station with a pending transmission does not get to work because another station occupies many access slots, it can rely on the fact that it will be given the opportunity to start a transmission at a later point in time.

The aspect of the invention described above and the associated features disclosed for developing the station according to the invention also apply accordingly to the aspects of the invention described below and the associated features disclosed for developing the method according to the invention, and vice versa.

In an advantageous embodiment of the method according to the invention, the duration of an access slot is shorter than the transmission duration of a message, in particular the first message, preferably a fraction of the transmission duration of the message.

The access slots are here preferably significantly shorter than the access slots which are usually used in time division multiplexing (TDMA). As a result, in relation to the length of the messages to be transmitted, there is a large number of access slots available in which transmission can begin. Due to the short duration of the access slots in relation to the messages, the overhead of data transmission due to unused transmission capacities can be significantly reduced, since access slots are available for all stations in a short period of time and therefore only a short time elapses until the next station, which is on wants to access the data transmission medium, a transmission can begin.

In a further advantageous embodiment of the method according to the invention, it also has the step of skipping at least one subsequent access slot assigned to the first station, the number of access slots to be skipped depending on the number of access slots used for the transmission of the first data frame of the first Message are needed.

As already explained, this can eliminate or even prevent imbalances in relation to the access of the stations, which can arise as a result of the method according to the invention.

In a further advantageous embodiment of the method according to the invention, it also has the working step of changing the sequence of the access slot allocation, the arrangement of a second access slot allocated to the first station depending on the number of access slots required for the transmission of the first data frame of the first message will.

In this way too, an imbalance in access to the data transmission medium by a large number of stations can be eliminated in that a station which has taken up the transmission time or transmission capacity is then postponed during transmission.

In a further advantageous embodiment of the method according to the invention, an inverse arrangement of the access slots is used when changing the sequence of the access slot allocation.

In a further advantageous embodiment of the method according to the invention, the number of access slots assigned to the first station at a predetermined time interval depends on the probability of a transmission request from the first station and / or a prioritization of the first station or the first data frame of the first station.

By giving certain stations several access slots in one interval, if the probability of this station requesting a transmission is higher than that of other stations, delay times for a transmission can be reduced. Furthermore, through this advantageous embodiment, the balance of access rights between the individual stations can in turn be balanced.

In a further advantageous embodiment of the method according to the invention, this furthermore has the working step of blocking the start of a data transmission at at least one access slot which is arranged in front of at least one access slot of cyclically sent information.

By providing blocked access slots, it can be ensured that cyclic or periodic data frames, which are necessary, for example, to control the communication network, can always be transmitted.

In a further advantageous embodiment of the method according to the invention, the Blocking the start of a data transmission, in particular the first data frame of a first message, is carried out when the expected transmission duration of the data transmission is longer than the cumulative duration of access slots up to the at least one access slot of cyclically sent information.

This ensures that a station does not “accidentally” start a transmission which, if the method according to the invention is followed, would lead to the blocking of access slots which are actually reserved for cyclically or periodically sent information.

In a further advantageous embodiment of the method according to the invention, it also has the steps of checking whether there is an access slot of cyclically sent information in the communication and skipping, before an access slot of cyclically sent information, the working step of checking data transmission is present.

Since the access slots for cyclically sent information are blocked for data transmission, the data transmission medium does not necessarily have to be checked for this in order to avoid collisions. And this saves computing capacity.

• 1 eine teilweise schematische Darstellung eines Kommunikationsnetzwerks, in welchem das erfindungsgemäße Verfahren Anwendung findet;
• 2 eine teilweise schematische Darstellung eines zeitlichen Verlaufs des Kommunikationsprotokolls des erfindungsgemäßen Verfahrens zur Datenübertragung;
• 3 eine teilweise schematische Darstellung des zeitlichen Ablaufs eines modifizierten Kommunikationsprotokolls des erfindungsgemäßen Verfahrens der Datenübertragung;
• 4 eine teilweise schematische Darstellung eines zeitlichen Ablaufs eines Kommunikationsprotokolls des erfindungsgemäßen Verfahrens zur Datenübertragung, wenn zyklische/periodische Datenrahmen übertragen werden sollen.
• 5 stellt ein teilweise schematisches Blockdiagramm des erfindungsgemäßen Verfahrens zur seriellen Datenübertragung dar.

Further features of advantageous possible applications of the invention emerge from the following description in conjunction with the figures. Show it

• 1 a partially schematic representation of a communication network in which the method according to the invention is used;
• 2 a partially schematic representation of a time course of the communication protocol of the method according to the invention for data transmission;
• 3 a partially schematic representation of the timing of a modified communication protocol of the data transmission method according to the invention;
• 4th a partially schematic representation of a time sequence of a communication protocol of the method according to the invention for data transmission when cyclic / periodic data frames are to be transmitted.
• 5 represents a partially schematic block diagram of the method according to the invention for serial data transmission.

In 1 an example of a communication network is shown in which the method according to the invention for serial data transmission is preferably used. This communication network has several stations 2-1 , 2-2 , 2-3 , 2-4 , 2-5 , 2-6 , ... on. These stations are, for example, control devices and are participants in a serial data transmission. The communication network is preferably a communication network of a vehicle, in particular a motor vehicle, and the stations or control devices 2-1 until 2-6 control or perform various functions for driving or other functions, such as multimedia functions of the vehicle. The individual stations are in the communication network 2-1 until 2-6 over a shared data transmission medium 3 connectable. The communication network is preferably a WLAN network, a CAN network, PowerLAN network, a radio network or the like, so that the data transmission medium 3 is implemented on the physical level by wire, radio, optically or acoustically.

2 represents a section of a time sequence of an embodiment of a communication protocol of the method according to the invention for serial data transmission. In the present case, six stations take place 2-1 until 2-6 in communication via the data transmission medium 3 in the communication network 1 part. The areas S1, S2 etc. each represent an access slot for the station 1 , station 2 etc. to access the data transmission medium 3 are reserved. The area S1 to S6 represents an interval in which each of the six stations has an access right to the data transmission medium 3 has by each of the six stations 2-1 until 2-6 has the option of data transmission via the data transmission medium 3 to start. In the present case, the first station 2-1 started transmitting the message N1. The message N1 or the data frame which is transmitted with this message N1, however, is longer than the access slot S ₁ . The transmission is therefore across access slots also in the time periods of the access slots S ₂ , S ₃ for two of the stations and the third station 2-3 continued. The access slot S ₄ is free again, but the fourth station can 2-4 here not with the transmission of a message N ₄ start because the access slot S ₃ which is the access slot, which is the fourth station 2-4 assigned, S ₄ , going ahead, was not free. In the present case, the fifth station can only be used again 2-5 in the access slot S ₅ with the transmission of the message N ₅ begin, which due to its length, the duration of the access slot S ₆ takes. In the right part of the 2 again shows a time interval in which access slots S ₁ until S ₆ , for all six stations 2-1 until 2-6 occurrence. There in that Access slot S ₁ no transmission takes place, the second station can 2-2 in the access slot S ₂ with the transmission of the message N ₂ begin, which is also based on the access duration of the access slots S ₃ and S ₄ extends, which is why neither the third station 2-3 , nor the fourth or fifth station 2-4, 2-5 can start a transmission. Only the sixth station 2-6 can after in the access slot S ₅ there was no transmission in the access slot S ₆ with the transmission of the message N ₆ kick off. It is necessary to leave an access slot free between the respective start of transmissions, since on the one hand it takes a certain amount of time to identify whether the data transmission medium is 3 is free, on the other hand must be the transceivers of the station 2-1 until 2-6 Allow a certain amount of time to switch from receiving (Rx) to sending (Tx).

In general, the method according to the invention can therefore be expressed as follows: An access slot that is permanently assigned to a station is shown with S _x designated. If there is a transmission request from a station X (which is the access slot S _x is assigned), then the station X must in particular the access slot S _x-1 monitor, i.e. the access slot before the access slot assigned to station X. If this access slot is "free", station X is allowed to use its access slot S _x begin a transfer. This transmission preferably extends in time beyond the duration of an access slot. Stations that have access slots immediately after the access slot S _x are therefore blocked by this transmission.

Due to the blocking of access slots of other stations during the transmission by a station, which can be referred to as a virtual collision, imbalances or an unfairness in the distribution of access slots can occur S ₁ until S ₆ come in which a transfer can be started. In the extreme case, the first station sends 2-1 news N ₁ each having the duration of five access slots S ₁ until S ₅ occupy so that the access slot S ₆ remains free. In this case it would come with incessant sending of messages N ₁ none of the other stations 2-2 until 2-6 for a transfer to the train.

In order to counteract such an imbalance, various mechanisms to be implemented in the data transmission method are possible. A preferred possibility is to vary the order in which the access slots are allocated in order to prevent some stations from receiving an unwanted predominance in the transmission when other stations also want to send messages. For example, such a variation in the allocation of the access slots as shown in FIG 3 represented by an inversion of the order of the access slots, in the present case the access slots S ₁ until S ₆ take place. Another preferred possibility to effect compensation is that a station which has used a plurality of access slots for a transmission must accordingly leave access slots assigned to it unused in subsequent intervals in order to allow other stations to preferentially send messages. In particular, the number of access slots to be skipped or unused can depend on the number of access slots that were required for the transmission of a message.

It can further preferably be provided in the method according to the invention that transmission is always guaranteed in some access slots. At least one access slot is used for this S _x-1 , in front of the affected access slot S _x , as in 4th shown blocked for transmission. This can ensure that the access slot S _x can always be used. Such a procedure can be necessary, for example, to provide guaranteed transmission times for cyclic or periodic data frames that are necessary for managing the communication or the communication network.

For this it may be necessary to additionally check whether a data frame of a message would extend into the at least one blocked access slot if a transmission started beforehand. If this is the case, the start of a transmission of the corresponding message should preferably be prevented before the blocked access slot.

With the method according to the invention it is also possible, via the distribution of the access slots for a specific station in an interval, to respond to the probabilities of a transmission request from a specific station and / or prioritization of a specific station or its messages or data frames. For example, if a station occurs twice as often in an interval as all other stations, it will also have twice as many options for sending messages.

5 represents a partially schematic block diagram of the method 100 according to the invention for serial data transmission. Optional work steps of the advantageous embodiments are preferably shown in dashed lines. The order is preferably as shown, but can also differ from this.

In the method according to the invention, it is preferably checked 101 whether an access slot S _x of cyclically sent information occurs in the communication. If this is the case, the start of a data transmission can optionally be in at least one access slot, which is before at least one access slot S _x of cyclically sent information is blocked 102. Thereafter, the cyclical information or its data frame is transmitted 105. If there is no access slot S _x of cyclically sent information, it is checked 104 whether there is a data transmission on the data transmission medium for an access slot preceding the access slot assigned to a station. If there is no data transmission, at least one data frame of a message from the station is transmitted 105. Finally, depending on the duration of the message that was transmitted, access slots of this station can subsequently be skipped 106a, the number of access slots to be skipped depending on the number of access slots which were required for the transmission of the data frame or the message. As an alternative to this, the order of the access slot allocation can be changed 106b, wherein the allocation or the arrangement of the access slots can also depend on the number of access slots which were required for the transmission of the data frame or the message. The aforementioned steps are preferably repeated until communication between the stations S1 to S6 has ended.

List of reference symbols

1

Communication network

2-1

First stop

2-2

Second stop

2-3

Third station

2-4

Fourth station

2-5

Fifth station

2-6

Sixth station

3

Data transmission medium

S1, S2, S3, S4, S5, S6

Access slots of the respective stations

N1, N2, N3, N4, N5, N6

Message from a respective station

Sx

Access slot for information sent cyclically

Sx-1

Previous access slot

Claims (12)

Station (2-1) for serial data transmission by means of data frames (data frame) in a communication network (1) with a plurality of stations (2-1, 2-2, 2-3, 2-4, 2-5, 2-6 ...), in particular in a time division multiplex method (TDMA), in which each station (2-1, 2-2, 2-3, 2-4, 2-5, 2-6, ...) has time access slots (S1, S2, S3, S4, S5, S6, ...) are assigned for a shared data transmission medium (3), having: a first processing device set up to check whether there is a data transmission on the data transmission medium (3) in an access slot (S1, S2, S3, S4, S5, S6, ...) which precedes the access slot (S1) assigned to the station , the station (2-1) being set up, if there is no data transmission, to transmit at least a first data frame of a first message (N1), the sequence of the access slot allocation being changed (106b), the arrangement of a second of the first station (2-1) assigned access slot (S1) depends on the number of access slots (S1, S2, S3, S4, S5, S6, ...) which are required for the transmission of the first data frame of the first message (N1), an inverse arrangement of the access slots (..., S6, S5, S4, S3, S2, S1) is used. Station (2-1) Claim 1 , further comprising: a second processing device, set up to skip at least one subsequent access slot (S1) assigned to the station (2-1), the number of access slots (S1) to be skipped being dependent on the number of access slots (S1, S2, S3 , S4, S5, S6, ...) which are required for the transmission of the at least one first data frame of the first message (N1). Communication network (1), in particular for radio communication or power line communication, preferably using the time division multiplex method (TDMA), with a plurality of stations (2-1, 2-2, 2-3, 2-4, 2-5, 2-6, ...) after Claim 1 or 2 , with each station (2-1, 2-2, 2-3, 2-4, 2-5, 2-6, ...) time access slots (S1, S2, S3, S4, S5, S6, .. .) are assigned for a shared data transmission medium (3). Vehicle, in particular a motor vehicle, with a communication network (1) Claim 3 . Method (100) for serial data transmission by means of data frames in a communication network (1) with a plurality of stations (2-1, 2-2, 2-3, 2-4, 2-5, 2-6,. ..), in particular a time division multiplex method (TDMA), in which each station is assigned time access slots (S1, S2, S3, S4, S5, S6, ...) for a shared data transmission medium (3) which is used in a Communication of the plurality of stations (2-1, 2-2, 2-3, 2-4, 2-5, 2-6, ...) comprises the following work steps: Checking (104) whether there is a data transmission on the data transmission medium (3) in an access slot which precedes an access slot (S1) assigned to a first station (2-1); and if there is no data transmission, transmitting (105) at least a first data frame of a first message (N1), changing (106b) the order of the access slot allocation, the arrangement of a second access slot (S1) allocated to the first station (2-1) being different from the Number of access slots (S1, S2, S3, S4, S5, S6, ...) depends which are required for the transmission of the first data frame of the first message (N1), with an inverse arrangement of the access slots (..., S6 , S5, S4, S3, S2, S1) is used. Method (100) according to Claim 5 , the duration of an access slot (S1) being less than the transmission duration of a message (N1, N2, N3, N4, N5, N6, ...), in particular the first message (N1), preferably a fraction of the transmission duration of the message (N1, N2, N3, N4, N5, N6, ...). Method (100) according to Claim 5 or 6th , further comprising the following working step: skipping (106a) at least one subsequent access slot (S1) assigned to the first station (2-1), the number of access slots (S1) to be skipped being dependent on the number of access slots (S1, S2, S3, S4, S5, S6 ...) which are required for the transmission of the first data frame of the first message (N1). Method (100) according to one of the Claims 5 until 7th , wherein the number of the first station (2-1) assigned access slots (S1) in a predetermined time interval of the probability of a transmission request of the first station (2-1) and / or a prioritization of the first station (2-1) or the first data frame of the first station (2-1) depends. Method (100) according to one of the Claims 5 until 8th , further comprising the following working step: blocking (103) the beginning of a data transmission in at least one access slot (Sx-1) which is arranged in front of at least one access slot (Sx) of cyclically sent information. Method (100) according to Claim 9 , the blocking of a start of a data transmission, in particular the first data frame of a first message (N1), being carried out if the expected transmission duration of the data transmission is longer than the cumulative duration of access slots (S1, S2, S3, S4, S5, S6, ...) up to which there is at least one access slot (Sx) of cyclically sent information. Procedure according to Claim 9 or 10 , further comprising the following work steps: checking (101) whether an access slot (Sx) of cyclically sent information occurs in the communication before an access slot (Sx) of cyclically sent information, skipping (102) the working step of checking whether a Data transmission is available. Computer program having instructions which, when executed by a computer, cause the computer to carry out the steps of a method according to one of the Claims 5 until 11 carry out.

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