Method for Operating a Radio Communication System for an Industrial Automation System, Radio Communication System, Base Station and Subscriber Station

Abstract

A method for operating a radio communication system for an industrial automation system, which includes at least one base station and a plurality of subscriber stations, wherein at predefined transmission times the base station cyclically polls datagrams to be transmitted by the subscriber stations, where the base station predefines for the subscriber stations the transmission times, within a polling cycle, for transmitting the datagrams to be transmitted, where the transmission times are each determined from a preceding transmission time by adding a polling cycle duration and subtracting a delay time, while the at least one datagram to be transmitted prior to the preceding transmission time is already in the corresponding subscriber station and ready for transmission, and where the subscriber stations transmit information to the base station regarding the corresponding delay time to determine the transmission times.

Claims

1.-15. (canceled)

16. A method for operating a radio communication system for an industrial automation system, in which the radio communication system comprises at least one base station and a plurality of subscriber stations, the method comprising: polling cyclically, by the at least one base station, at predefined transmission times, for respective datagrams which are to be transmitted by the plurality of subscriber stations; polling, by the at least one base station, for selected subscriber stations of the plurality of subscriber stations or for each individual subscriber station of the plurality of subscriber stations, for the respective datagrams to be transmitted at individual transmission times for every subscriber station of the plurality of subscriber stations in accordance with a station sequence predefined by the at least one base station; predefining, by the at least one base station, within a polling cycle, for the plurality of subscriber stations, the transmission times for transmitting the datagrams to be transmitted, the transmission times being ascertained from a respective preceding transmission time plus a polling cycle period and minus a waiting period, during which at least one datagram to be transmitted prior to the preceding transmission time was already present and ready for transmission in a respective subscriber station; and transmitting, by the plurality of subscriber stations information about the respective waiting period to the at least one base station to ascertain the transmission times.

17. The method as claimed in claim 16, wherein the at least one base station ascertains the respective waiting period from a recorded minimum waiting period plus a constant or continuously recorded delay.

18. The method as claimed in claim 17, wherein the delay is ascertained from waiting period variances recorded over multiple polling cycles.

19. The method as claimed in claim 16, wherein the plurality of subscriber stations transmit the information about the respective waiting period together with the datagrams to be transmitted at a respective current or subsequent transmission time.

20. The method as claimed in claim 16, wherein the plurality of subscriber stations ascertain an averaged waiting period over each multiple polling cycles; and wherein the information transmitted to the at least one base station about the respective waiting period comprises the averaged waiting period.

21. The method as claimed in claim 16, wherein the plurality of subscriber stations transmit the information about the respective waiting period only at a request of the at least one base station.

22. The method as claimed in claim 16, wherein each of the plurality of subscriber stations is associated to form a station group; and wherein, for station groups, the at least one base station polls for the respective datagrams to be transmitted at individual transmission times for every station group in accordance with at least one of a group and station sequence predefined by the base station.

23. The method as claimed in claim 22, wherein an individual ratio channel that a channel bundle associated with a respective station group comprises is utilized for polling for and transmitting the respective datagrams to be transmitted for every subscriber station associated with the station group.

24. The method as claimed in claim 22, wherein the at least one base station ascertains the respective waiting period for each station group from a recorded minimum waiting period within the station group plus the delay.

25. The method as claimed in claim 23, wherein the at least one base station ascertains the respective waiting period for each station group from a recorded minimum waiting period within the station group plus the delay.

26. The method as claimed in claim 16, wherein the plurality of subscriber stations are out of sync with one another; and wherein a station sequence and the transmission times are continuously stipulated in accordance with the waiting periods recorded for every polling cycle.

27. The method as claimed in claim 16, wherein selected subscriber stations each have at least one of a plurality of terminals and a plurality of field devices connected to said selected subscriber stations; wherein respective datagrams to be transmitted by the at least one of the plurality of terminals and the plurality of field devices connected to the same subscriber station are transmitted to the at least one base station as summed datagrams; and wherein a waiting period for summed datagrams corresponds to a period of time during which at least one summed datagram to be transmitted prior to a preceding transmission time was already present and ready for transmission in a respective subscriber station.

28. A radio communication system comprising: at least one base station; and a plurality of subscriber stations; wherein the at least one base station is configured to: cyclically poll, at predefined transmission times, for respective datagrams which are to be transmitted by the plurality of subscriber stations; poll, for selected subscriber stations of the plurality of subscriber station or poll individually for each subscriber station of the plurality of subscriber stations, for the respective datagrams to be transmitted at individual transmission times for every subscriber station of the plurality of subscriber stations in accordance with a station sequence predefined by the at least one base station; and predefine for the plurality of subscriber stations, within a polling cycle, the transmission times for transmitting the datagrams to be transmitted, the transmission times corresponding to a respective preceding transmission time plus a polling cycle period and minus a waiting period, during which at least one datagram to be transmitted prior to the preceding transmission time was already present and ready for transmission in a respective subscriber station; wherein the plurality of subscriber stations are configured to transmit information about the respective waiting period to the at least one base station to ascertain the transmission times.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is explained more thoroughly below using an exemplary embodiment with reference to the drawing, in which:

[0025] FIG. 1 shows a radio communication system for an industrial automation system with a WLAN access point and multiple WLAN clients in accordance with the invention;

[0026] FIG. 2 shows a time characteristic for a data transmission from the WLAN clients to the WLAN access point without optimized polling in accordance with the invention;

[0027] FIG. 3 shows a time characteristic for a data transmission from the WLAN clients to the WLAN access point with optimized polling in accordance with the invention; and

[0028] FIG. 4 is a flowchart of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0029] The radio communication system shown in FIG. 1 comprises a WLAN access point 100 as a radio base station and multiple WLAN clients 101, 102, 103, wirelessly connectable thereto, as radio subscriber stations. In the present exemplary embodiment, the WLAN clients 101, 102, 103 each have multiple automation or field devices 111, 112, 113, 121, 122, 123, 131, 132, 133 of an industrial automation system connected to them. Automation devices include in particular programmable logic controllers, input/output units (I/O modules) or operating and observation stations of the industrial automation system.

[0030] Programmable logic controllers typically each comprise a communication module, a central processing unit and at least one input/output unit. Input/output units may fundamentally also be configured as local peripheral modules arranged remotely from a programmable logic controller. The communication module thereof can be used to connect a programmable logic controller to a switch or router or additionally to a field bus, for example. The input/output unit is used for interchanging control and measured variables between a programmable logic controller and a sensor, or a controlled machine or installation, connected to the programmable logic controller. A sensor or a machine or installation can fundamentally also be connected to a programmable logic controller via the radio communication system. The central processing unit of a programmable logic controller is provided in particular for ascertaining suitable control variables from captured measured variables. The above components of a programmable logic controller can be connected to one another via a backplane bus system, for example.

[0031] An operating and observation station is used in particular to visualize process data or measured and control variables that are processed or captured by programmable logic controllers, input/output units or sensors. In particular, an operating and observation station is used to display values of a control loop and to alter control parameters. Operating and observation stations comprise at least a graphical user interface, an input device, a processor unit and a communication module.

[0032] The WLAN access point 100, on the one hand, and the WLAN clients 101, 102, 103, on the other hand, are in particular configured and set up to interchange data frames 10, 20 with one another. In the present exemplary embodiment, the data frames 10, 20 comprise firstly polling messages 10 and secondly control data 20, in particular process data or measured and control variables, which are associated with controllers, actuators, sensors, machines or installations connected to the WLAN clients 101, 102, 103 and which the WLAN access point 100 polls the WLAN clients 101, 102, 103 for via the polling messages 10.

[0033] The WLAN access point 100 uses the polling messages 10, P.sub.M, P.sub.M+1 to cyclically poll, at predefined transmission times t.sub.P.N, t.sub.P.N+1, for respective control data 20, D.sub.M, D.sub.M+1 to be transmitted by the WLAN clients 101, 102, 103 (see also FIGS. 2 and 3).

[0034] Within a polling cycle, the WLAN access point 100 predefines for the WLAN clients 101, 102, 103 the transmission times t.sub.P.N, t.sub.P.N+1 for transmitting the control data 20, D.sub.M, D.sub.M+1 to be transmitted. In the present exemplary embodiment, the polling cycle corresponds to an automation cycle within which the automation or field devices 111, 112, 113, 121, 122, 123, 131, 132, 133, FD connected to the WLAN clients 101, 102, 103 provide control data 20, D.sub.M, D.sub.M+1.

[0035] In contrast to the time characteristic without optimized polling that is shown in FIG. 2, the WLAN access point 100 in the present exemplary embodiment in accordance with FIG. 3 ascertains the transmission times t.sub.P.N, t.sub.P.N+1 from a respective preceding transmission time t.sub.P.N−1, t.sub.P.N plus a polling cycle period t.sub.c and minus a waiting period t.sub.W.M, t.sub.W.M+1, during which control data 20, D.sub.M, D.sub.M+1 to be transmitted prior to the preceding transmission time t.sub.P.N−1, t.sub.P.N were already present and completely ready for transmission in the respective WLAN client 101. Overall, a respective next transmission time t.sub.P.N+1 is obtained in the case of the optimized polling shown in FIG. 3 in accordance with the following relationship:

t.sub.P.N+1=t.sub.P.N+t.sub.c−t.sub.W.M.   Eq. 1

[0036] In order to ascertain the transmission times t.sub.P.N, t.sub.P.N+1, the WLAN clients 101-103 transmit information about the respective waiting period t.sub.W.M, t.sub.W.M+1 to the WLAN access point 100.

[0037] The WLAN access point 100 can ascertain the respective waiting period t.sub.W.M, t.sub.W.M+1 from a recorded minimum waiting period t.sub.W.min plus either a constant or continuously recorded delay t.sub.D. The delay t.sub.D is preferably ascertained from waiting period variances t.sub.W.Jitter recorded over multiple (x) polling cycles. The respective next transmission time t.sub.P.N+1 is therefore obtained in accordance with the following relationship:

t.sub.P.N+1=t.sub.P.N+t.sub.c−t.sub.W.min+t.sub.D   Eq. 2

[0038] where

t.sub.D=x*t.sub.W.Jitter(x>0).

[0039] In comparison with the time characteristic shown in FIG. 2 for a data transmission from the WLAN clients 101, 102, 103 to the WLAN access point 100, the optimized polling in accordance with FIG. 3 results in significantly reduced waiting periods or latencies. In addition, the WLAN clients 101, 102, 103 can transmit the information about the respective waiting period t.sub.W.M, t.sub.W.M+1 together with the control data D.sub.M or D.sub.M+1 to be transmitted at a respective current transmission time t.sub.P.N or at a subsequent transmission time t.sub.P.N+1. Transmitting the information about the respective waiting period together with the control data to be transmitted at a later transmission time presents a solution if the information about the respective waiting period can, for technical reasons, no longer be added to a data frame with the control data to be transmitted at the respective current transmission time. A further simplification is obtained if the WLAN clients 101, 102, 103 ascertain an averaged waiting period over each of the multiple polling cycles and the information transmitted to the WLAN access point 100 about the respective waiting period comprises the averaged waiting period. Here, the information about the respective waiting period is not transmitted to the WLAN access point 100 during each polling cycle. An even further reduction in complexity is possible if the WLAN clients 101, 102, 103 transmit the information about the respective waiting period to the WLAN access point 100 only at the explicit request of the latter.

[0040] For selected WLAN clients or for each WLAN client 101, 102, 103 individually, the WLAN access point 100 can fundamentally poll for the respective control data 20 to be transmitted at individual transmission times t.sub.P.N for every WLAN client in accordance with a station sequence predefined by the WLAN access point 100. Alternatively or additionally, each of the multiple WLAN clients may be associated to form a station group. Here, for station groups, the WLAN access point 100 polls for the respective control data 20 to be transmitted at individual transmission times t.sub.P.N for every station group in accordance with a group and/or station sequence predefined by the WLAN access point 100.

[0041] When multiple WLAN clients are associated to form a station group, an individual radio channel that a channel bundle associated with the respective station group comprises is preferably used for polling for and transmitting the respective control data 20 to be transmitted for every WLAN client. By way of example, in WLAN systems based on IEEE 802.11ax, multiple WLAN clients can transmit data in a shared multi-user uplink frame (MU-UL) at the same time after a multi-user downlink trigger frame (MU-DL). A station group based on IEEE 802.11ax can in particular comprise a maximum number of WLAN clients for every possible channel width, for example 20 MHz or 40 MHz. In the case of group-by-group polling, the WLAN access point 100 ascertains the respective waiting period, in the present exemplary embodiment, for each station group from a recorded minimum waiting period t.sub.W.M within the station group plus the delay t.sub.D.

[0042] It is fundamentally also possible for the WLAN clients 101-103 not to be, or not to have to be, in sync with one another. Here, the station sequence and the transmission times t.sub.P.N are continuously stipulated in accordance with the waiting periods t.sub.W.M recorded for every polling cycle.

[0043] Respective datagrams 21, 22, 23 to be transmitted by the terminals and/or field devices 111, 112, 113, 121, 122, 123, 131, 132, 133 connected to the same WLAN client 101, 102, 103 are advantageously transmitted to the WLAN access point 100 as summed datagrams. The waiting period t.sub.W.M for summed datagrams corresponds to a period of time during which at least one summed datagram to be transmitted prior to the preceding transmission time was already present and ready for transmission in the respective WLAN client 101, 102, 103.

[0044] FIG. 4 is a flowchart of the method for operating a radio communication system for an industrial automation system, where the radio communication system comprises at least one base station 100 and a plurality of subscriber stations 101, 102, 103.

[0045] The method comprises polling cyclically, by the at least one base station 100, at predefined transmission times tP.N, for respective datagrams 20 that are to be transmitted by the plurality of subscriber stations 101, 102, 103, as indicated in step 410.

[0046] Next, the at least one base station 100 polls, for selected subscriber stations of the plurality of subscriber stations 101, 102, 103 or for each individual subscriber station of the plurality of subscriber stations 101, 102, 103, for the respective datagrams to be transmitted at individual transmission times for every subscriber station of the plurality of subscriber stations 101, 102, 103 in accordance with a station sequence predefined by the at least one base station 100, as indicated in step 420.

[0047] Next, the at least one base station 100, within a polling cycle, for the plurality of subscriber stations 101, 102, 103, predefines the transmission times tP.N for transmitting the datagrams to be transmitted, as indicated in step 430. In accordance with the method of the invention, the transmission times tP.N are ascertained from a respective preceding transmission time tP.N−1 plus a polling cycle period tc and minus a waiting period tW.M, during which at least one datagram to be transmitted prior to the preceding transmission time was already present and ready for transmission in a respective subscriber station.

[0048] Next, the plurality of subscriber stations transmit 101, 102, 103 information about the respective waiting period to the at least one base station 100 to ascertain the transmission times, as indicated in step 440.

[0049] Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.