WO2018095507A1

WO2018095507A1 - A method for scheduling field devices in a wireless network of an industrial process system

Info

Publication number: WO2018095507A1
Application number: PCT/EP2016/078382
Authority: WO
Inventors: Ewa Hansen; Johan ÅKERBERG; Jonas Neander; Krister Landernäs; Niclas Ericsson; Tomas Lennvall
Original assignee: Abb Schweiz Ag
Priority date: 2016-11-22
Filing date: 2016-11-22
Publication date: 2018-05-31

Abstract

A method (30) is provided of scheduling field devices (14, 16, 18) in a wireless network (20) of an industrial process system (1), the wireless network (20) providing communication using a wireless bandwidth. The method (30) is performed in a scheduling device (15) and comprises scheduling (31) real-time traffic on a first part of the bandwidth using a first scheduling algorithm, the first part of the bandwidth being dedicated for the real-time traffic, and scheduling (32) non-real-time traffic on a second part of the bandwidth using a second scheduling algorithm, the second part of the bandwidth being dedicated for the non-real-time traffic.A scheduling device (15), computer program and computer program products are also provided.

Description

A method for scheduling field devices in a wireless network of an industrial process system

Technical field

The technology disclosed herein relates generally to the field of scheduling in wireless networks, and in particular to a method of scheduling field devices in a wireless network of an industrial process system, a scheduling device, computer program and computer program product.

Background

Internet of Things (IoT) is designed for offering advanced connectivity for many types of devices provided with e.g. sensors, actuators, software and network connectivity. It may be expected that such IoT devices will be introduced in different types of networks, also in industrial process systems.

In the industrial process system there are often field devices, e.g. actuators, with which the communication is time-critical. Such field devices may, for instance, be controlled using a first network implementing a protocol such as e.g. WirelessHart. If IoT devices are to be introduced in such an industrial process system, an additional network might be needed for this type of traffic, which may be less time-critical.

However, having two or more separate communication networks is costly in terms of installation and maintenance. Should instead a single network be used it may be difficult to predict the amount of traffic in the network, in particular in view of an increasing number of different types of devices and the planning of network resources is instead rendered difficult.

Summary

An objective of the present invention is to address and improve various aspects for scheduling in wireless industrial process systems. A particular objective is to ensure that time-critical traffic is handled in a timely manner even in scenarios wherein a high number of devices, e.g. IoT devices, are introduced. This objective and others are achieved by the method, scheduling device, computer programs and computer program products according to the appended independent claims, and by the embodiments according to the dependent claims. The objective is according to an aspect achieved by a method of scheduling field devices in a wireless network of an industrial process system, the wireless network providing communication using a wireless bandwidth. The method is performed in a scheduling device and comprises scheduling real-time traffic on a first part of the bandwidth using a first scheduling algorithm, the first part of the bandwidth being dedicated for the real-time traffic, and scheduling non-real-time traffic on a second part of the bandwidth using a second scheduling algorithm, the second part of the bandwidth being dedicated for the non-real-time traffic.

The method provides a number of advantages. For instance, by dedicating a part of the wireless bandwidth for the real-time traffic it is ensured that time-critical traffic is scheduled in time, even when other types of devices, e.g. IoT devices, are introduced. At the same time, the non-real-time traffic is also handled properly by having its own dedicated part of the bandwidth, preferably the remaining part of the available bandwidth. Further, the real-time traffic and the non-real-time traffic can be scheduled using a scheduling algorithm best suited for the respective traffic types.

In some embodiments, the bandwidth dedicated for the non-real-time traffic is further divided, wherein the respective sub-divisions of the bandwidth are used for scheduling different types of traffic. This enables a still improved scheduling in that tailored scheduling algorithms can be used best suited for the intended type of traffic.

The objective is according to an aspect achieved by a computer program for a scheduling device. The computer program comprises computer program code, which, when run on processing circuitry of the scheduling device causes the scheduling device to perform the method as above.

The objective is according to an aspect achieved by a computer program product for a scheduling device. The computer program product comprises a computer program as above and a computer readable means on which the computer program is stored.

The objective is according to an aspect achieved by a scheduling device for scheduling field devices in a wireless network of an industrial process system, the wireless network providing communication using a wireless bandwidth. The scheduling device is configured to: schedule real-time traffic on a first part of the bandwidth using a first scheduling algorithm, the first part of the bandwidth being dedicated for the real-time traffic, and schedule non-real-time traffic on a second part of the bandwidth using a second scheduling algorithm, the second part of the bandwidth being dedicated for the non-real-time traffic.

Further features and advantages of the embodiments of the present invention will become clear upon reading the following description and the accompanying drawings.

Brief description of the drawings

Figure l illustrates an environment in which embodiments according to the present invention may be implemented.

Figures 2a and 2b illustrate exemplary splits of available bandwidth according to the invention.

Figure 3 illustrates a flow chart over steps of an embodiment of a method in a scheduling device in accordance with the present invention.

Figure 4 illustrates schematically a scheduling device and means for implementing embodiments of the method in accordance with the present invention.

Detailed description

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description with unnecessary detail. Same reference numerals refer to same or similar elements throughout the description.

Figure 1 illustrates an environment in which embodiments according to the present invention may be implemented. The environment may, for instance, be an industrial process system 1. Computer controlled process control systems are used for controlling and/or monitoring industrial processes in many different types of industries and utilities such as automotive, chemical, pharmaceutical, food, metal, mines, steel mills, consumer products, power generation, power distribution, pure and waste water handling, oil refineries, gas pipe-lines and off-shore platforms. An example of a process control system (PCS) architecture is SCADA (Supervisory Control And Data Acquisition), and another example is a distributed control system (DCS). The traffic to and from the control system (e.g. SCADA) may comprise realtime and/or non-real-time traffic. Figure 1 also illustrates a programmable logic controller (PLC) 21, which is an industrial digital computer for process control having high reliability. The traffic to and from the PLC 21 may also comprise real-time and/or non-real-time traffic.

Field devices 14, 16, 18, e.g. instruments or actuators such as motors, valves, valve positioners and sensors of different types, perform functions within the process such as driving conveyor belts, opening or closing valves, and measuring various process control parameters. Controllers perform control functions to monitor and control the field devices 14, 16, 18. Such control functions may involve receiving signals indicating process control measurements, processing the received information and generating control signals that are transmitted to the field device(s) 14, 16, 18 in order to control and/or monitor the operation of the process. The field devices 14, 16, 18 may thus be of many different types and may have very different requirements. A first field device may run an application requiring frequent uplink transmission and downlink transmission, while a second field device only occasionally needs to report e.g. a measurement value (i.e. only has an uplink). To some of the field devices time- critical data has to be delivered (e.g. control commands for quickly shutting a valve) or have such data to send (e.g. alarms). Other field devices have less time-critical communication needs.

In an industrial process system 1 an operator is generally able to perform desired operations with respect to a process by means of an operator workstation 2, 4 that is communicatively connected to receive process information from the field devices 14, 16, 18 and various controllers 5a, 5b. The operator may for instance be able to view the current state of the process via a user interface, perform evaluations of the process and modify the operation of the process by using the operator workstation 2, 4. Controllers 5a, 5b and workstations 2, 4 are generally connected via a

communications network to a server 6 providing control and monitoring of the process and a database 8 where data, such as historical data relating to control and monitoring of the process is stored. Such communications network may, as in the illustrated case, comprise a first bus (Bus 1 in the figure) to which the operator workstations 2, 4 are connected and a second bus (Bus 2 in the figure). The server 6 and the database 8 are, in this case, connected between the first and second buses. The second bus may be connected to one or more gateways 12 (only one illustrated) via wired or wireless interfaces. The gateway 12 may in turn be connected to (or be part of) a wireless network 20, which may be a wireless industrial network. The wireless network 20 may also comprise access points 13a, 13b interfacing the gateway 12 and providing a communication point for the field devices 14, 16, 18. Such access points 13a, 13b may, for instance, enable redundant communication paths for the gateway 12. In an embodiment, the wireless network 20 is a time division multiple access TDMA-based wireless field device network. The wireless network 20 may be a multi-hop network, i.e. the field devices 14, 16, 18 may use one, two or more hops to convey information to a destination.

With the introduction of IoT, devices may communicate with cloud computing nodes, e.g. application servers, of a cloud environment 25. A sensor may, for instance, communicate its data to such application server and receive commands, management and configuration data from it. This type of traffic is typically non-real-time traffic.

Figure 2a illustrates an exemplary split of available bandwidth according to an aspect of the invention. The wireless network 20 may use Time Division Multiple Access (TDMA) or Carrier Sense Multiple Access (CSMA) as mechanism for the field devices 14, 16, 18 to access a shared medium (a wireless bandwidth). TDMA divides the available bandwidth into time slots and assigns time slots to different field devices in which they can communicate. Determining which field devices should be assigned which TDMA slot (one or more) for communication is known as scheduling. CSMA scheduling solutions on the other hand are usually distributed (i.e. a node uses only its own information) and are based on the idea that a node can communicate anytime the medium is free.

According to the invention, the available wireless bandwidth is divided into a first part, which is dedicated for real-time traffic, and a second part, which is dedicated for non-real-time traffic. The second part of the wireless bandwidth may in turn be divided into a number of sub-parts, each given to a particular traffic class. In the figure 2a three such non-real-time traffic classes are indicated: first, second and third traffic class. For instance, the first traffic class may comprise Internet traffic, the second traffic class may comprise streamed traffic and the third traffic class may comprise network management traffic, although it is noted that any number of classes may be provided for many different types of traffic.

Figure 2b illustrates another exemplary split of the available bandwidth according to an aspect of the invention. The first part of the bandwidth, i.e. the part that is dedicated for real-time traffic may be a continuous part of the available bandwidth as illustrated in figure 2a, but in other embodiments, the first part of the bandwidth comprises two or more non-connected parts of the available bandwidth as illustrated in figure 2b. That is, the first part comprises a first sub-part RTi and a second subpart RT2 of the available bandwidth. Correspondingly, the second part, i.e. the part that is dedicated for non-real-time traffic, may (but need not) comprise a first subpart NRTi and a second sub-part NRT2 of the available bandwidth. Any combination of these embodiments is also conceivable, e.g. the first part may be a continuous part of the available bandwidth, while the second part comprises two non-connected parts of the available bandwidth.

Figure 3 illustrates a flow chart over steps of embodiments of a method in a scheduling device in accordance with the present invention. A method 30 is provided of scheduling field devices 14, 16, 18 in a wireless network 20 of an industrial process system 1. The wireless network 20 provides communication using a wireless bandwidth, e.g. timeslots in a TDMA system. The method 30 may be performed in a scheduling device 15.

The method 30 comprises scheduling 31 real-time traffic on a first part of the bandwidth using a first scheduling algorithm, the first part of the bandwidth being dedicated for the real-time traffic.

The method 30 comprises scheduling 32 non-real-time traffic on a second part of the bandwidth using a second scheduling algorithm, the second part of the bandwidth being dedicated for the non-real-time traffic.

Dedicating part of the total available wireless bandwidth in the wireless network 20 to real-time traffic enables the remaining part to be used for non-real-time traffic, wherein the non-real-time traffic can be scheduled using another type of scheduling algorithm than the real-time traffic. Thereby each traffic type can be scheduled using a scheduling algorithm best suited for it. The first dedicated part should be allocated such as to ensure that the real-time traffic can indeed be timely delivered. The allocation can be made in a semi-static way; the allocation may, for instance, be made at deployment of the wireless network 20 and if additional time critical field devices are introduced over time, the allocation of the first dedicated part may be reviewed so as to ensure that real-time traffic can still be delivered timely.

The part of the bandwidth that is dedicated to the real-time traffic is denoted "first part of the bandwidth" and the bandwidth that is dedicated to the non-real-time traffic is denoted "second part of the bandwidth" as a way of indicating that the bandwidth is divided between these different traffic types, and does not indicate an order in which the steps of the method 30 occur. An allocation of the wireless bandwidth may thus first be made, and the different traffic classes may then be scheduled. That is, it is noted that the scheduling steps 31, 32 of the method 30 can be made in any order, i.e. the real-time traffic and the non-real time traffic may be scheduled in any order. In some embodiments, the method 30 comprises

determining a first share of the wireless bandwidth to be dedicated to the real-time traffic and determining a second share of the wireless bandwidth to be dedicated to the non-real-time traffic. The first share is then used as the first part when scheduling the real-time traffic, and the second share is used as the second part when scheduling the non-real-time traffic. The second part is preferably the remaining part of the available bandwidth when the first share has been determined, but in other embodiments the second part is less than the remaining part of the available bandwidth when the first share has been determined. The determining of bandwidth share dedicated to the different types of traffic may, for instance, be based on one or more of: available possibly predefined configuration data, application requirements such as period time and/or priority, expected amount of traffic of the different types. The determining may be repeated regularly or upon need, e.g. when a number of new field devices and/or other devices has been introduced and require bandwidth.

In some embodiments, a support feature is provided for performing or assisting in the determining of the different bandwidth shares. For instance, the user may enter e.g. data about the applications that are to use the available bandwidth, e.g. data such as application requirements. The support feature, taking this data as input, then determines an appropriate bandwidth share for the real-time traffic and non-real- time traffic, respectively. Further, the support feature may also suggest a proportional split of the second share, i.e. the share dedicated for use for the non-real-time-traffic. This proportional split may comprise determining which sub-share of the second part of the bandwidth that the respective traffic classes should be given.

In various embodiments, the method 30 comprises, prior to the scheduling 31, allocating a first part of the bandwidth for the real-time traffic and a second part of the bandwidth for the non-real-time traffic based on expected amount of real-time traffic.

The allocation is made such as to ensure timely delivery of the real-time traffic, e.g. based on the amount of real-time traffic. The remaining part may then be allocated for scheduling of non-real-time traffic.

In various embodiments, the first scheduling algorithm is different than the second scheduling algorithm.

In various embodiments, the second part of the bandwidth is divided into at least two traffic classes, each traffic class having a respective dedicated part of the second part of the bandwidth. In other embodiments, the non-real-time traffic is simply prioritized in each node of the wireless network 20. That is, communication resources of the part of the bandwidth that is dedicated to the non-real-time traffic (denoted second part of the bandwidth) are allocated to the non-real-time traffic, and each node may prioritize which non-real-time traffic packets to send. The prioritization should then be known (and used) by all nodes of the industrial process system 1.

In variations of the above embodiments, the traffic classes are divided based on one or more of: type of traffic, quality of service requirement, application requirement, period time and priority class. The field devices 14, 16, 18 and possibly IoT devices may having non-real-time traffic may have different requirements and may be grouped accordingly.

In variations of the above two set of embodiments, the method 30 comprises applying a respective scheduling algorithm for each traffic class. Different scheduling algorithms may be used for the different traffic classes and adapted to the particular requirements of the type of traffic. In various embodiments, the first scheduling algorithm comprises one of: a fixed- priority real-time scheduling, dynamic-priority real-time scheduling, deadline monotonic algorithm, earliest deadline first algorithm and constant bandwidth server type of algorithm. Many other scheduling algorithms may also be used.

In various embodiments, the second scheduling algorithm comprises one of: a best effort algorithm, a first come-first serve type of algorithm, and round-robin algorithm with quantum or priorities.

The scheduling device 15 may be a separate standalone device, or it may be an integrated part of another device or node, e.g. a network manager also responsible for e.g. managing routing tables and monitoring the wireless network 20.

The scheduling device 15 comprises a processor 40 comprising any combination of one or more of a central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit etc. capable of executing software instructions stored in a memory 41 which can thus be or form part of a computer program product. The processor 40 (or processing circuitry) can be configured to execute any of the various embodiments of the method 30 as described herein, for instance as described in relation to figure 3.

The memory 41 of the scheduling device 15 can be any combination of read and write memory (RAM) and read only memory (ROM), Flash memory, magnetic tape, Compact Disc (CD)-ROM, digital versatile disc (DVD), Blu-ray disc etc. The memory 41 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

The scheduling device 15 may comprise an interface 43 for communication with other devices and/or entities, e.g. with one or more of: other field devices 14, 16, 18, the gateway 12 and access points 13a, 13b. The interface 43 may, for instance, comprise a protocol stack, for wireless communication with other devices or entities. The interface may be used for receiving data input and for outputting data. A scheduling device 15 is provided for scheduling field devices 14, 16, 18 in a wireless network 20 of an industrial process system 1, the wireless network 20 providing communication using a wireless bandwidth. The scheduling device 15 is configured to:

- schedule real-time traffic on a first part of the bandwidth using a first scheduling algorithm, the first part of the bandwidth being dedicated for the real-time traffic, and

- schedule non-real-time traffic on a second part of the bandwidth using a second scheduling algorithm, the second part of the bandwidth being dedicated for the non- real-time traffic.

The scheduling device 15 may be configured to perform the scheduling e.g. by comprising one or more processors 40 and memory 41, the memory 41 containing instructions executable by the processor 40, whereby the scheduling device 15 is operative to perform the steps.

In some embodiments, the scheduling device 15 is configured to, prior to the scheduling, allocate a first part of the bandwidth for the real-time traffic and a second part of the bandwidth for the non-real-time traffic based on expected amount of realtime traffic.

In various embodiments, the second part of the bandwidth is divided into at least two traffic classes, each traffic class having a respective dedicated part of the second part of the bandwidth.

In various embodiments, the traffic classes are divided based on one or more of: type of traffic, quality of service requirement, application requirement, periodicity and priority class.

In various embodiments, the scheduling device 15 is configured to apply a respective scheduling algorithm for each traffic class.

In various embodiments, the first scheduling algorithm comprises one of: a fixed- priority real-time scheduling, dynamic-priority real-time scheduling, deadline monotonic algorithm, earliest deadline first algorithm and constant bandwidth server type of algorithm.

The present invention also encompasses a computer program 42 for a scheduling device 15. The computer program 42 comprises computer program code, which, when executed on at least one processor on the scheduling device 15, causes the scheduling device 15 to perform the method 30 according to any of the described embodiments.

The present invention also encompasses computer program products 41 for a scheduling device 15 for scheduling field devices 14, 16, 18 in a wireless network 20. The computer program product 41 comprises the computer program 42 for implementing the embodiments of the methods as described, and a computer readable means on which the computer program 42 is stored. The computer program product, or the memory, thus comprises instructions executable by the processor 40. Such instructions may be comprised in a computer program, or in one or more software modules or function modules. The computer program product 41 may, as mentioned earlier, be any combination of random access memory (RAM) or read only memory (ROM), Flash memory, magnetic tape, Compact Disc (CD)-ROM, digital versatile disc (DVD), Blu-ray disc etc.

In other embodiments, the scheduling device 15 comprises function

modules/software modules. The function modules can be implemented using software instructions such as computer program executing in a processor and/or using hardware, such as application specific integrated circuits (ASICs), field programmable gate arrays, discrete logical components etc., and any combination thereof. Processing circuitry may be provided, which may be adaptable and in particular adapted to perform any of the steps of the method 30 that has been described in various embodiments.

The invention has mainly been described herein with reference to a few

embodiments. However, as is appreciated by a person skilled in the art, other embodiments than the particular ones disclosed herein are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A method (30) of scheduling field devices (14, 16, 18) in a wireless network (20) of an industrial process system (1), the wireless network (20) providing communication using a wireless bandwidth, the method (30) being performed in a scheduling device (15) and comprising:

- scheduling (31) real-time traffic on a first part of the bandwidth using a first scheduling algorithm, the first part of the bandwidth being dedicated for the realtime traffic, and

- scheduling (32) non-real-time traffic on a second part of the bandwidth using a second scheduling algorithm, the second part of the bandwidth being dedicated for the non-real-time traffic.

2. The method (30) as claimed in claim 1, comprising, prior to the scheduling (31), allocating a first part of the bandwidth for the real-time traffic and a second part of the bandwidth for the non-real-time traffic based on expected amount of real-time traffic.

3. The method (30) as claimed in claim 1 or 2, wherein the second part of the bandwidth is divided into at least two traffic classes, each traffic class having a respective dedicated part of the second part of the bandwidth.

4. The method (30) as claimed in claim 3, wherein the traffic classes are divided based on one or more of: type of traffic, quality of service requirement, application requirement, periodicity and priority class.

5. The method (30) as claimed in claim 3 or 4, comprising applying a respective scheduling algorithm for each traffic class.

6. The method (30) as claimed in any of the preceding claims, wherein the first scheduling algorithm comprises one of: a fixed-priority real-time scheduling, dynamic-priority real-time scheduling, deadline monotonic algorithm, earliest deadline first algorithm and constant bandwidth server type of algorithm.

7. The method (30) as claimed in any of the preceding claims, wherein the second scheduling algorithm comprises one of: a best effort algorithm, a first come-first serve type of algorithm, and round-robin algorithm with quantum or priorities.

8. A computer program (42) for a scheduling device (15), the computer program (42) comprising computer program code, which, when run on processing circuitry of the scheduling device (15) causes the scheduling device (15) to perform the method (30) according to any of claims 1-7.

9. A scheduling device (15) for scheduling field devices (14, 16, 18) in a wireless network (20) of an industrial process system (1), the wireless network (20) providing communication using a wireless bandwidth, the scheduling device (15) being configured to:

10. The scheduling device (15) as claimed in claim 9, configured to, prior to the scheduling, allocate a first part of the bandwidth for the real-time traffic and a second part of the bandwidth for the non-real-time traffic based on expected amount of realtime traffic.

11. The scheduling device (15) as claimed in claim 9 or 10, wherein the second part of the bandwidth is divided into at least two traffic classes, each traffic class having a respective dedicated part of the second part of the bandwidth.

12. The scheduling device (15) as claimed in claim 11, wherein the traffic classes are divided based on one or more of: type of traffic, quality of service requirement, application requirement, periodicity and priority class.

13. The scheduling device (15) as claimed in claim 11 or 12, configured to apply a respective scheduling algorithm for each traffic class.

14. The scheduling device (15) as claimed in any of claims 9-13, wherein the first scheduling algorithm comprises one of: a fixed-priority real-time scheduling, dynamic-priority real-time scheduling, deadline monotonic algorithm, earliest deadline first algorithm and constant bandwidth server type of algorithm.

15. The scheduling device (15) as claimed in any of claims 9-14, wherein the second scheduling algorithm comprises one of: a best effort algorithm, a first come-first serve type of algorithm, and round-robin algorithm with quantum or priorities.