EP2898634A1

EP2898634A1 - Communications method in a communications system

Info

Publication number: EP2898634A1
Application number: EP13739982.0A
Authority: EP
Inventors: Volker Blaschke; Timo Lothspeich; Andreas Mueller
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-09-19
Filing date: 2013-07-19
Publication date: 2015-07-29
Also published as: WO2014044434A1; US10003643B2; DE102012216716A1; US20150229716A1

Abstract

The invention relates to a communications method that comprises the step of sending a query message (22) from a central entity (10) to at least one node (K₁, K₂, ..., K_N). For every queried node, the central entity determines a node-specific time window based on a node-specific response time (T₁, T₂, ..., T_N). The central entity filters out a response message (A₁, A₂,..., A_N, B₁, B₂,..., B_N), sent from the queried node, from the signals received during this time window. Based on the node-specific time window (Δ₂), the central entity assigns the response message to the queried node. The invention also relates to a computing unit that is configured to operate as a central entity, to a communications system, as well as to a computer program and a computer-readable storage program with said computer program.

Description

Description title

Communication method in a communication system

The present invention relates to two communication methods in communication systems, a computation unit adapted to be incorporated into a communication system, a communication system, a computer program, and a machine-readable storage medium.

State of the art

Known packet-based communication systems include multiple nodes (also referred to as "nodes"), a central entity (also called a "master" or "coordinator") and a shared transmission medium (also referred to as a "shared transmission medium" or "shared medium").

A principal problem with such a packet based communication system is the control of access to the "shared medium", because the concurrent use of the same resources from different nodes usually makes a successful (i.e., error free) transmission very unlikely. There are a variety of different degrees of freedom and possible manifestations and many different directions of optimization, for example, in terms of throughput, fairness, real-time capability, etc.

In general, a distinction between competing and coordinated media access methods is possible.

In the case of competing methods, it may in principle occur that two or more nodes simultaneously access the "shared medium" and want to transmit corresponding data, which then results in a collision on the common transmission medium. Examples of this type of method are slotted ALOHA, carrier sense multiple access (CSMA) and CSMA Collision detection (CSMA / CD, used among others in the Ethernet variants

10BASE5 and 10BASE2).

In competing media access methods such as CSMA / CD is in principle a very fast access to the "shared medium" possible, but at the same time there is no guarantee that a successful access (in terms of access, which brings a successful transfer) within a predetermined time can take place. This is due to the fact that collisions can occur at any time, even during normal operation, which normally causes a faulty transmission. This collision probability typically increases with an increasing number of nodes and increasing data traffic, i. it correlates with the utilization of the common transmission medium. Therefore, such methods are generally not or only partially suitable for real-time critical data that must be transmitted within a certain time.

In addition, such competing methods may also be regarded as very critical if all or at least some of the nodes are to be powered by the shared medium (eg via a wired bus), or if all or at least some of the nodes of the same energy source (eg a battery) are fed. In such a case, depending on the system design, it could happen that the entire system or a part of it fails due to too high an energy requirement if too many nodes want to access the "shared medium" at the same time. This is essentially due to the fact that the power consumption of a

Node is generally higher in transmit mode than in receive mode or in non-transmit mode.

In contrast to competing methods, in coordinated error-free media access, there should be no simultaneous collisions

Access multiple nodes on the "shared medium" occur. Coordination of the media access can be static, e.g. at static

Time-division multiplexing method in which each node is allowed to periodically use the "shared medium" for transmission for a certain period of time. This can be For example, with the help of a statically fixed schedule known to all nodes, in conjunction with temporal synchronization of all nodes, or, alternatively, the coordination can be realized by means of central instance control, such as a classical polling method In addition, however, a distributed coordination is possible, which is used, for example, in methods such as "token ring" or "token bus".

Coordinated methods typically have more deterministic (i.e., more predictable) behavior than competing methods, and maximum access times to the shared medium can usually be guaranteed, at least to some extent. However, in particular in the case of methods in which the coordination takes place by a central authority, these guaranteed maximum access times can be relatively large, above all with a large number of nodes and / or a high traffic volume. For example, in a cyclic polling procedure, the central entity cyclically grants each node access to the shared medium, with the maximum cycle time and thus the guaranteed maximum access time to the shared medium generally directly proportional to the number of nodes and the maximum possible Traffic is.

Therefore, with the conventional coordinated methods, severe timing demands on at least a portion of the data to be transmitted (e.g., in terms of comparatively short maximum access times) can only be realized for systems having a relatively small number of nodes.

Another object in the design and implementation of communication systems with a central control / monitoring instance (eg in the case of corresponding systems with coordinated media access methods) is the supply of this central instance with information about the nodes, for example with regard to the current status of a node or on certain parameters. In conventional systems, special control messages are usually exchanged between the central entity and the individual nodes. These control messages usually consist of a suitable one Preamble for synchronization, a message header and the actual control data together and therefore often have a fairly large overhead, especially if only one or a few information / control bits (s) is to be transmitted. In addition, prior to transmitting such a message, a node must first gain access to the shared medium. For this, in principle, the options already described above come into consideration, but the cost of obtaining even simple information content is therefore often relatively high. Object of the present invention is to provide a communication method for a

To provide a communication system that enables high transmission reliability at relatively low cost and in particular is suitable to be used in communication systems with many nodes. It is also an object to enable a quick query of states (in particular send requests) while at the same time minimizing the energy consumption of the nodes.

Disclosure of the invention

The present invention relates to the communication method according to claims 1 and 2, the arithmetic unit according to claim 12, the communication system according to claim 13, the computer program according to claim 14 and the computer readable medium according to claim 15.

Both communication methods according to the invention are to be applied in a communication system comprising a central entity, a plurality of nodes and a communication medium which the central entity and the nodes share for communication. The communication medium may be, for example, a linear or annular bus or a wireless transmission channel.

The first communication method according to the invention comprises sending a query message from the central entity to one or more nodes in the communication system (which will be referred to as the "polled node"). can all nodes (different from the central instance) in the communication system or a selection of all nodes. If multiple nodes are queried, the query message can be transmitted, for example, from the central entity to each interrogated node in the communication system or passed from one interrogated node to the next, so that the one (ie in particular the once sent) query message reaches all interrogated nodes.

The query message may include, for example, a state (such as a send request or the priority of the send request, or the priority of the highest priority send request) or certain other parameters or properties of the addressed (polled) node (eg, whether the node is powering its own source (eg a battery) or the energy must be obtained via the common transmission medium) interrogate.

In the case of the transmission of the priority of the highest priority message to be transmitted, the central entity may determine it and allocate the transmission authority to the individual nodes according to the respective priority, for example by first granting access to the one / ones indicating a high priority transmission request have, then the one / those with a medium priority send request, etc.

The first communication method according to the invention further comprises for each node polled determining a node-specific time window based on a node-specific response time and filtering out a response message sent by the polled node from signals received during the node-specific time window. On the basis of the respective node-specific time window, the central instance assigns the response message to the or the individual nodes polled.

Preferably, the node specific response time is a time difference, specific to the particular node, between receiving the query message and sending the node a reply message; while the time point of the end or the beginning of the receipt of the query message or any other clearly defined reference time. The node-specific response time can be set automatically or manually by an appropriate configuration, for example with the aid of one or more configuration file (s) and / or in the course of network planning and / or installation. The node-specific response time (s) of the one interrogated node or of the several interrogated nodes may have been previously announced to the central entity. Alternatively, the central entity may itself allocate and / or communicate to the node (s) its respective node-specific airtime, as described further below.

A node-specific time window is preferably larger than the actual response time. Thus, uncertainties regarding the required signal propagation times can be compensated. Node-specific time windows of different nodes preferably do not overlap one another.

Due to the assignment of a response message to a node on the basis of its node-specific receiving window, the content of the response message does not need to be considered during the assignment. In particular, the reply message need not contain any information about its sender.

The second inventive communication method comprises steps performed by a node, namely receiving an interrogation message sent by the central entity, which is preferably still directed to at least one further node in the communication system. It includes sending a response message to a node-specific response time to the central entity. Preferably, the node-specific response time is or was explicitly or implicitly assigned to the node by the central entity and / or communicated, or each node is / were manually configured with regard to its node-specific response time.

The methods according to the invention each comprise steps which execute the "central instance" or "node" from the various components are. They can be combined with each other and each allow a message exchange, which has the following advantages in particular:

The inventive methods allow very short transmission times for the answers, since almost no overhead is needed (for example, no preambles, destination addresses or other control / header information). In addition, since the interrogation of several different nodes occurs simultaneously with a single query message, thus a lower average power consumption, a reduction in the maximum transmission latency, an increase in the possible throughput and a quick query possible, especially in

Compared to conventional polling methods. In the latter case, each node is usually interviewed individually, which would usually take much more time. In contrast to a competing media access method, such as

CSMA, one has a deterministic behavior and can therefore ensure that each interrogated node within a given time in any case can send a response message, for example, to indicate a send request. In addition, in the error-free case there is no risk that the network or at least a part of it collapses if too many nodes have a transmission request at the same time and the power supply of these nodes via the shared transmission medium, e.g. a wired bus is realized, or if too many nodes have a simultaneous transmission request and all nodes or a part of the nodes from the same source are supplied with energy.

Due to the time sequence of the response messages, which is clearly defined via the node-specific response times or time windows, the overhead required for the individual response messages can be kept to a minimum. In particular, no additional synchronization mechanisms and measures are required, such as the use of preambles. Since only state information can be transmitted and each node can decide for itself whether this information is relevant to it or, alternatively, always only the central entity evaluates the corresponding state information In addition, no additional header information needed, which usually specify, among other things, for example, the recipient of a message.

The methods according to the invention are very well suited to be able to meet certain quality of service requirements (in particular latency and jitter) even for systems with a relatively large number of nodes.

In preferred embodiments, the respective response message is only a short burst that does not include a preamble and a header. The received (for example) from the central instance (receive) signals can contain not only the response message but also sections / samples without useful signal, which thus contain only noise, interference and / or other interference signals.

The arithmetic unit according to the invention is set up to be integrated into a communication system as a central entity and to carry out some or all steps of the method described above or below. The communication system according to the invention accordingly comprises a central instance thus set up and / or one or more nodes, which are set up to carry out some or all of the steps mentioned here.

Said methods may be implemented in the form of one or more computer programs which, when executed on a computer, cause the execution of the respective method. The computer program (s) may be stored on one or more machine-readable storage media.

Preferred embodiments are disclosed in the subclaims.

Advantageously, the two methods according to the invention are combined. The node performing the said steps is a polled node, that is, one who has received the query message from the central entity.

The node-specific response times of the individual nodes are or were preferably chosen such that, despite possible differences in the transit time between the individual nodes, individual transmissions, no collisions of different response messages can occur on the common transmission medium and the central entity can uniquely assign to each node a node-specific time window within which the central entity receives the response message of the corresponding node. This in turn makes it possible to uniquely assign a reply message to a specific node.

Preferably, the central entity implicitly or explicitly notifies the interrogated nodes of each node-specific response time for the response message and / or with, e.g. during a special initialization phase.

An implicit allocation can be realized in such a way that the central entity only specifies a logical order of the various nodes and only notifies each node of its position within this sequence. Each node (as well as the central instance) can then calculate the respective response time with the help of a predefined calculation rule.

In the case of an explicit allocation, the central entity can directly assign each node its node-specific response time.

As a further alternative to implicit or explicit signaling by the central entity, node-specific response times may also be set at each node during commissioning of the communication system by one person (e.g., by setting appropriate values in a mass storage). The assignment of response times and corresponding unique identifiers or addresses of the individual nodes can then be stored in the central instance.

For the assignment of the response message, the central entity can advantageously determine a node-specific reception time already in advance (ie before receiving the response messages) from the node-specific response time. At or during this time, the central entity expects a response from the associated node and correspondingly assigns the reply message received at or at that time to the node. Preferably, the central entity determines for each node polled a time or space to or at which it expects a response from the node. A reply message arriving at or during this time then assigns the central instance to the corresponding node.

Depending on the topology or type of common transmission medium considered, a lack of certainty regarding the time at which the response message of a particular node is expected can exist at the central entity due to unknown transit time differences.

For example, in the case of a linear bus or a wireless transmission channel, it may happen that the central entity can limit the expected time of reception only to a specific time window, without being able to tell exactly in advance exactly when within this time window, the central entity the response message of this node Will be received.

In the case of a perfectly terminated linear bus, the central authority for assigning the response messages to the polled nodes may each determine or use an upper limit of the maximum expected (simple) signal propagation time, which is or has been determined, for example, based on the bus length and propagation speed.

For the special case of a ring topology, in which the central authority on the one hand put a message on the bus and at the same time can receive messages from the bus on the other side, there is no such blurring, because here the various response messages always just sequentially strung together from the central instance are received.

Preferably, the response messages each comprise only a single (modulation) symbol, such as a wave train with a certain frequency, or only a sequence of a few (for example, a maximum of 10) (modulation) symbols, such as a sequence of individual wave trains with possibly different frequencies. In a preferred embodiment, the response messages are differentially modulated. This offers the advantage that, despite the possible blurring due to propagation time differences, a high transmission reliability can be ensured, but at the same time for additional overhead for establishing a temporal synchronization (for example in the form of a special preamble, which in the case of a reply message is the actual information bit or modulation symbol could be preceded) can be omitted. In a further preferred embodiment, a reply message corresponds to a constant length wave train of a predetermined frequency selected from a set of predefined frequencies depending on the state to be transmitted; this corresponds on the transmitter side to a multilevel frequency shift keying, also referred to as "Multi-Level Frequency Shift Keying". In this case, a spectral analysis of the signal received during the node-specific time window can then be carried out on the receiver side (eg with the aid of a fast / discrete Fourier transformation), so that a determination of the transmission frequency of the signal train and thus of the indicated state of the node is possible on the receiver side.

A differential transmission can take place, for example, by means of a differential binary frequency shift keying. For this purpose, the node in question transmits a wave-shaped (for example, cosine (or sinusoidal) signal) first with a first frequency and then with a second frequency f ₂ different from the first frequency. The central instance then only has to determine whether within the associated (fuzzy) receive window, a transition from a low to a high frequency occurs or vice versa. It can thus relatively easily determine relatively reliably whether the node has a send request or not.

Alternatively, non-differential transmission can be done with binary or multilevel frequency shift keying. In such a non-differential transmission by means of a binary or multistage frequency shift keying, the respective interrogated node transmits to the node-specific response node assigned to it. time a wavy (eg cosine or sinusoidal) signal with a frequency f, e {fi, f ₂ , ..., fivi}, which is selected depending on the information to be transmitted or the state to be transmitted and where M the degree of modulation corresponds, ie the number of distinguishable by means of a (modulation) symbols states. In the special case of a binary frequency shift keying, ie for M = 2, the respective interrogated node could, for example, transmit a sinusoidal signal at a first frequency or at a second frequency f ₂ different from the first frequency at its associated node-specific response time, as the case may be. whether he has a send request or not. The detection of this signal at the central instance can then be realized for example with the aid of a correlation receiver, or - as previously described - by means of a spectral analysis (eg using a fast / discrete Fourier transformation) of the received signal received during the respective node. In addition, there are a variety of other ways in which such a response message can be transmitted. In principle, the use of all common modulation methods is conceivable. In particular, instead of a single modulation symbol (which may be modulated as described above, for example with the aid of a binary or multilevel frequency shift keying), sequences of such modulation symbols may also be transmitted, eg, sequences of individual cosine or sinusoidal signal trains having different or equal frequencies, depending on which data to be transferred. In an advantageous embodiment, the query message at the at least one node to which it is addressed asks for a send request. It is therefore asked if the interviewed node (s) have to transmit one or more messages. Preferably, the response messages merely indicate whether or not the corresponding node has a send request. This information can be represented using a single bit. Advantageously, an embodiment in which the query only send requests for time-critical messages to be sent, ie messages that need to be transmitted within a certain time. In a further advantageous embodiment, a polled node can transmit the priority of the highest priority message that the node would like to transmit. For this purpose, for example, three priority levels (low, medium, high) can be defined, with each message to be transmitted having exactly one such priority level. The assignment of priority levels to messages can be done, for example, by the respective application or according to precisely defined criteria (eg depending on the previous waiting time or depending on a corresponding priority level / QoS class higher protocol layers, such as IP). In addition, a node can indicate in its response that it does not currently have a send request. In this case, there are thus four different possible answers, which corresponds to two bits in terms of information theory. Advantageously, the transmission of the response then takes place as described above with the aid of a multilevel frequency shift keying, ie the node transmits a signal train of fixed length with a frequency f, e {fi, f ₂ , f ₃ , f}, the choice of the frequency being dependent from the state to be transmitted

(e.g., low priority send request, medium priority send request, high priority send request, no send request).

Based on the response messages, the central entity can determine one or more polled nodes that have requested a send request, and him

(or sequentially) grant exclusive access to the shared transmission medium, which the respective node can then use to send its message (s) to another node or to the central entity. Preferably, the central entity informs each discovered node in advance by a special message about this grant. The determined nodes can preferably be addressed by the central entity via an identifier, such as a MAC address.

Preferably, an exclusive accessibility for a determined node is limited to send request and ends with the transfer of at least one

Message or after a specified period of time. Thereafter, for example, the central entity may grant exclusive access to the shared transmission medium to another discovered node, or it may send a new query message or may resort to another media access method, such as For example, CSMA, change. Such a change preferably announces it by sending a message to the at least two interrogated nodes. An embodiment of the invention comprises a combination of some or all of the above steps with an alternative media access method, such as Carrier Sense Multiple Access (CSMA) or a cyclic polling method. For example, the central authority can determine at regular intervals whether one or more nodes have to send time-critical messages, for example those whose timely transmission with the aid of the basic access method may not be guaranteed. If a node indicates a send request for one or more such time-critical messages, the central entity can grant it exclusive access to the common communication medium for this purpose. For non-time critical messages, the base media access method (eg CSMA) can also be used.

This embodiment of the method is particularly suitable for better fulfilling given (hard) quality of service (QoS) requirements for different packet transmissions. In particular, transmission requests with hard time requirements for individual packets can be recognized and preferably treated.

Preferably, the response messages of the queried nodes each comprise only one bit. Alternatively, they may consist of several bits, each unique combination of bits preferably being associated with one quality of service class. Advantageously, the nodes may then indicate which quality of service class has a highest priority packet pending for transmission.

In a preferred embodiment, the method comprises a step of determining, by the central entity, that a predetermined number of

Node in the communication system is reached or exceeded. This allows to ensure that the further steps, such as sending a query message and the assignment of the response messages, are appropriate in the given case. Accordingly, the arithmetic unit to be used as the central instance can be set up to check the number of nodes present in the communication system, to select a basic access method (such as ALOHA, CSMA or CSMA / CD) in the case of a number below a predetermined limit, and otherwise some or all to execute the method steps described here.

The central authority can thus autonomously and dynamically adapt the use of one of the described methods to the respective situation.

The initiation of the methods described here is preferably carried out by the central entity. This allows easy configuration and control.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawings and will be described in detail below with reference to the drawings.

Brief description of the drawings

Figure 1 shows an example of a communication system in which the present invention can be used.

FIG. 2 shows by way of example a typical arrangement of components in a communication system with a linear bus structure. FIG. 3 shows by way of example a basic message exchange according to an embodiment of the present invention.

FIG. 4 shows a time window which a central entity can consider for assigning a response message to a node.

Figure 5 shows a message transmission in a ring structure of the common communication medium, which is suitable for a method according to the invention.

FIG. 6 schematically shows a communication method according to an embodiment of the present invention.

FIGS. 7a and 7b illustrate an information transmission with differential binary frequency shift keying, as can be used for the communication according to the invention.

The communication system 1 shown in Figure 1 comprises a control entity 10, a plurality of nodes K ^ K ₂ , K ₃ , K ₄ , K ₅ , K ₆ and a common communication medium 11, via which the nodes and the control entity can communicate with each other.

The common transmission medium may be, for example, a linear bus to which all nodes and the central entity are connected. This is sketched by way of example in FIG. 2; at the points 11 a and 1 1 b ends the bus 1 1, for example, with appropriate bus terminations. The bus terminations are typically impedances equal to the characteristic impedance of the line to avoid reflections. In addition, however, a variety of other forms of shared transmission medium are conceivable, such as a wireless transmission channel, a ring-shaped bus, etc. The only requirement is that the various nodes can use all the same resources for data transmission, in principle, for example the same frequencies on an electrical line, the same wavelengths in an optical fiber, etc. 3 shows a sequence diagram according to an embodiment of the invention by way of example in its time sequence (shown from top to bottom). The system considered here comprises, in addition to the central entity 10, in total the N nodes K 1 K ₂ , K ₃ ,... K _N , where N represents a natural number.

The diagram shows a phase 20 in which a fast status request is made by the central entity and a phase 21 in which exclusive access to the common communication medium is granted.

Phase 20 may be preceded by a phase, not shown, in which the communication system uses a basic access method, such as CSMA. Alternatively or additionally, after phase 21, the central entity may send a message (not shown) to all nodes Ki to K _N announcing a transition to a basic media access procedure which may then be used.

In phase 20, the central instance 10 of the system first initiates a quick poll of the send requests of the individual nodes by sending a poll message 22 received from all nodes Κ K ₂ , K ₃ , ... K _N. For n = 1, ..., N sends each node K _n , after the complete receipt of the query message 22 its node-specific response time T _{n has} expired, a corresponding response message A _n . In the message A _n , the node K _n respectively informs the central entity whether it has a transmission request or not; As mentioned above, in one embodiment of the invention, only such send requests are communicated which relate to a time-critical message. Alternatively or additionally, the node K _n in the message A _n can convey the priority of the highest-priority message to be transmitted (eg with the distinction in {low, medium, high} and / or indicating that it has no transmission request.

After evaluating the responses of the individual nodes, the central entity 10 then grants those nodes which have requested a send request, explicitly exclusive access to the common communication medium so that these nodes can transmit their respective messages. For this purpose, the central entity sends a special message to the respective node, which may then itself transmit a message. As mentioned above, the central entity can take the respective priority into account

In the example shown in FIG. 3, it is assumed that the nodes Ki and K ₃ each communicate a send request. In the message, the central authority notifies the node Ki that it is granted exclusive access to the common communication medium. The node Ki then sends the

Data D ^ are directed to the central instance 10 in the example shown. The central entity then informs analogously to the node N ₃ in the message Z ₃ that now exclusive access to the common communication medium is granted to it, which then uses the node K ₃ for the transmission of his data D ₃ , in the illustrated Example also be sent to the central instance.

In the general case, a node which has received exclusive access to the common communication medium through a corresponding message may selectively transmit its message to the central entity (as shown in Figure 3) or to any other node in the system. After the transfer, the control over the common communication medium is first of all again with the central entity, which thus, for example, can grant exclusive access to the next node or initiate a new query of the send requests.

FIG. 4 shows a time window Δ ₂ and its calculation by way of example for the node K ₂ with the node-specific response time T ₂ . In this time slot at the central instance 10 incoming reply messages are assigned according to node K ₂ . The central instance initially only knows that the response message of the node K _{2 is} received within this window, but does not know the exact time (blur of the order of 2 * T _prop + T _var ). The period of time Δ1 is required for the sending of the query message by the central entity to the node K ₂ . As explained above, the node K ₂ then waits for the node-specific response time T ₂ before sending a response message to the central entity 10. The earliest possible time at which the central entity can receive the response message from the node K ₂ is therefore after

Expiration of the specific response time T _{2 of} this node, measured from the beginning of the reception of the query message or from its complete transfer. The latest possible time at which the central entity can begin to receive the response message is T ₂ + 2 * T _prop + T _var after sending the query message, where T _{var is} a time interval that takes into account one or more practical effects can lead to temporal deviations, such as oscillator inaccuracies and / or drifts. T _var can be a fixed value (eg according to a specification) or can be determined dynamically by the central instance and communicated to the individual nodes. T _prop is the maximum expected (simple) signal propagation time; in the case of a wired linear bus, it results from the propagation speed on the medium and the length of the bus. The end time of the reception window accordingly (again measured from the completion of the full sending the query message) T ₂ + T _rep i _y + 2 * T _prop + T _var, with T _rep iy than the time period required for the actual transmission of the response message ,

FIG. 5 illustrates by way of example the special case that the nodes Ki to K ₆ and the central entity 10 are arranged in a ring topology. The central entity can on the one hand a message (eg the query message

22) on the bus while receiving messages from the bus on the other side. The answer messages Ai to A _{6 of} the various nodes can be appended to the query message one after the other in the ring pass.

In this case, the assignment of the response messages to the nodes can also take place without the determination of a time window, as shown in FIG. FIG. 6 schematically shows a communication method according to an embodiment of the present invention in its time sequence. The method comprises a phase 60 in which the communication system with the central entity 10 and nodes K ^ K ₂ , K ₃ , ... K _N uses a conventional media access method. In a subsequent phase 61, a fast parameter or status inquiry and detection by the central authority 10. This sends a query message 64 to all nodes in which they one or more parameters or a state, such as information about the power supply or requests a send request (for example, a send request whose priority reaches or exceeds a certain value).

As in the case of polling a send request (for n = 1, ..., N) sends each node K _n after its node-specific response time T _{n has} expired after the complete reception of the query message 64, a corresponding response message B _n , which queried the queried Contains information.

The system then reverts to a basic media access procedure in phase 62.

FIGS. 7a and 7b show possibilities of bit transmission by means of differential binary frequency shift keying. 7a shows this case, the bit '0' by a transition of a voltage waveform having a first frequency to a second frequency f _2. In figure 7b is reversed by the transition from the second frequency f ₂ to the first frequency, the bit represented 1 '. In the case shown, the frequency is higher than the frequency f ₂ , but it can be analog lower.

Claims

A communication method in a communication system (1) comprising a central entity (10), a plurality of nodes (K ^ K ₂ , K _N ) and a common communication medium (11), the communication process comprising the following steps performed by the central entity: sending a Polling message (22, 64) via the common communication medium to one or more polled nodes in the communication system; and

for the interviewed node or nodes

Determining a node-specific time window (Δ ₂ ) on the basis of a node-specific response time (ΤΊ, T ₂ , T _N );

Filtering out a response message (Ai, A ₂ , A _N , BL B ₂ , B _N ) sent by the polled node from signals obtained during the node-specific time window; and

Associate the answer message to the polled node based on the node-specific time window.

A communication method in a communication system (1) comprising a central entity (10), a plurality of nodes (Κ ^ K ₂ , K _N ) and a common communication medium (11), the communication method comprising the following steps performed by one node of the plurality of nodes includes:

Receiving an interrogation message (22, 64) sent by the central entity, which is preferably still directed to at least one further node in the communication system;

Sending a response message (Ai, A ₂ , ..., A _N , B ^ B ₂ , B _N ) to a node-specific response time (ΤΊ, T ₂ , T _N ) to the central entity, preferably the node-specific response time to the node of the central instance is explicitly or implicitly allocated and / or notified or has been. The communication method according to claim 1, wherein the central entity (10) implicitly or explicitly allocates and / or notifies its node-specific response time (s) (ΤΊ, T ₂ ,..., T _N ) to the node or nodes being interrogated.

A communication method according to claim 1 or 3, further comprising the steps performed by a polled node of the plurality of nodes according to claim 2.

A communication method according to any one of claims 1 to 4, wherein the response messages (Ai, A ₂ , A _N , Bi, B ₂ , B _N ) are transmitted with differential and / or coherent binary or multilevel frequency shift keying.

A communication method according to any one of claims 1 to 5, wherein the central entity (10) additionally determines which of the polled nodes has a send request, or determines that none of the polled nodes has a send request;

and / or determines which priority occurs as the highest priority of messages to be sent from a polled node requesting transmission; and / or determines that a polled node has no send request

A communication method according to claim 6, wherein the central entity grants to a determined polled node with a transmission request for transmission (DL D ₃ ) at least one message an exclusive access to the common communication medium,

wherein preferably the central entity informs the determined polled node in advance by a special message (Z ^ Z ₃ ) about this grant.

A communication method according to claim 7, wherein the exclusive accessibility is temporary and ends with the transmission (DL D ₃ ) of the at least one message or after a specified period of time.

9. The communication method according to claim 8, wherein after the end of exclusive access

either the central entity (10) grants an exclusive access possibility to another polled node with a send request,

or the central entity switches the communication system to the use of another media access method, such as CSMA, and preferably announces this switching by sending a message to the at least two polled nodes.

10. Communication method according to one of the preceding claims, wherein the query message (64) state information and / or predetermined parameters interrogated and / or

wherein the response messages (Β ^ B ₂ , B _N ) contain state information and / or queried parameters.

1 1. A communication method according to any one of the preceding claims, further comprising determining, by a polled node, to send one or more time critical messages, and wherein the response message (Ai, A ₂ , A _N ) indicates a polling request of the polled node.

12. arithmetic unit (10) which is set up to be integrated in a communication system with a plurality of nodes (Κ ^ K ₂ , K _N ) and a common communication medium (1 1) and to act there as the central instance,

wherein the arithmetic unit is further adapted to carry out the steps to be executed by a central entity according to claim 1 or according to one of claims 3 to 9.

13. Communication system with at least two nodes (Κ ^ K ₂ , K _N ), a central entity (10) and a common communication medium (1 1), the central entity being set up to carry out the steps to be carried out by it according to one of claims 1 or 3 to 9,

and / or wherein at least one of the nodes is arranged to execute the steps to be executed by a node according to one of claims 2 to 10.

14. Computer program with program code means which cause a computer or a corresponding arithmetic unit to perform a method according to one of claims 1 to 9, when they are executed on the computer or the corresponding arithmetic unit, in particular according to claim 10.

15. A machine-readable storage medium having a computer program stored thereon and having program code means which cause a computer or a corresponding computing unit to perform a method according to one of claims 1 to 11 when executed on the computer or the corresponding computing unit.