Limiting the impact of cellular networks on latency in industrial automation systems

Abstract

In an industrial automation system comprising a first and a second wireless communication device (16a, 16b) communicating with each other via a cellular network (10), when the first wireless communication device (16a) is attached to a first base station (36a) of the cellular network (10), the first wireless communication device (16a) obtains knowledge about which base station the second wireless communication device (16b) is attached to, and if the second wireless communication device (16b) is attached to a second allowable base station (36b), the first wireless communication device (16a) detaches from the first base station (36a) and attaches to the second base station (36b).

Description

TECHNICAL FIELD

[0001] The present application relates generally to an industrial automation system. More specifically, the present application relates to a method, a computer program and a computer program product for establishing communication between a first wireless communication device and a second wireless communication device of an industrial automation system via a cellular network, and to the first wireless communication device in such an industrial automation system. BACKGROUND

[0002] With the development of 4G and 5G cellular networks, it has become of interest to use these cellular networks for communication in industrial automation systems.

[0003] One example of this is given in EP 3540991, where a cellular network is used for communication between intelligent electronic devices (IEDs) in a power system.

[0004] One example of a parameter that can need to be considered in an industrial automation system is latency. In many applications, this must be very low and / or limited. Other examples of important parameters are jitter and reliability.

[0005] When a cellular network is used for communication between wireless communication devices of an industrial automation system, the network has an impact on the above-mentioned parameters. Therefore, it is often of interest to limit this impact of the cellular network as much as possible.

[0006] WO 2011 / 109027 describes cellular controlled device-to-device (D2D) communication. In this document, a first wireless communication device and a second wireless communication device initially communicate with each other in a D2D session via a first base station. When the second wireless communication device is handed over to a second base station, it informs the first wireless communication device about the second base station, and if the quality is sufficient, the first wireless communication device is handed over to the second base station by a handover.

[0007] US 2015 / 0282028 likewise discusses cellular controlled D2D communication, where at least one of the two wireless communication devices can be handed over to a second, new cell, and the other can follow or remain connected to the first cell.

[0008] US 2014 / 0355444 describes how a first wireless communication device receives a discovery signal from a second wireless communication device, which discovery signal comprises a cell ID of the second wireless communication device. The first wireless communication device then investigates whether the cell ID can be found in a list, and if so, the first wireless communication device triggers the establishment of a local routing path. SUMMARY

[0009] It is therefore an object of the present application to limit the negative impact of a cellular network on one or more parameters of the communication between wireless communication devices of an industrial automation system, while allowing the wireless communication devices to adapt to situations where such negative impact cannot be limited. The negative impact can be a negative impact on latency, jitter and / or reliability.

[0010] According to a first aspect, the object is achieved by a method of establishing communication between a first wireless communication device and a second wireless communication device of an industrial automation system via a cellular network, the method being performed in the first wireless communication device and comprising:

[0011] receiving, from the second wireless communication device via a first base station to which the first wireless communication device is attached, a first message comprising base station identification information identifying a base station to which the second wireless communication device is attached,

[0012] investigating the base station identification information of the first message in order to identify the base station to which the second wireless communication device is attached,

[0013] if the second wireless communication device is attached to a second base station, then further performing

[0014] investigating whether the first wireless communication device fulfils one or more conditions for being attached to the second base station, wherein one condition is that the second base station is admissible, and

[0015] sending a response to the first message that the first wireless communication device is able to be attached to the second base station,

[0016] wherein if the one or more conditions are fulfilled, the method further comprises

[0017] disconnecting from the first base station, and

[0018] attaching to the second base station.

[0019] According to a second aspect, the object is achieved by a first wireless communication device in an industrial automation system, the device being configured to communicate via a cellular network and comprising

[0020] a radio circuit for wirelessly communicating with other wireless communication devices of the industrial automation system via the cellular network, and

[0021] a communication handling block configured to

[0022] receive, from a second wireless communication device via a first base station to which the first wireless communication device is attached, a first message comprising base station identification information identifying a base station to which the second wireless communication device is attached,

[0023] investigate the base station identity information of the first message in order to identify the base station to which the second wireless communication device is attached,

[0024] if the second wireless communication device is attached to the second base station, further configure the communication handling block to investigate whether the first wireless communication device fulfils one or more conditions for attaching to the second base station, wherein one condition is that the second base station is allowable, and

[0025] instruct the radio circuit to send a response to the first message, the response to the first message being about the ability of the first wireless communication device to attach to the second base station,

[0026] wherein if the one or more conditions are fulfilled, the communication handling block is further configured to

[0027] instruct the radio circuit to detach from the first base station, and

[0028] instruct the radio circuit to attach to the second base station.

[0029] According to a third aspect, the object is achieved by a computer program for establishing communication between a first wireless communication device and a second wireless communication device of an industrial automation system via a cellular network, the computer program comprising computer program code which, when run by a processor of a communication handling block of the first wireless communication device, causes the communication handling block to:

[0030] receive, from the second wireless communication device via a first base station to which the first wireless communication device is attached, a first message comprising base station identity information identifying a cellular network base station to which the second wireless communication device is attached,

[0031] investigate the base station identity information of the first message in order to identify the base station to which the second wireless communication device is attached,

[0032] if the second wireless communication device is attached to the second base station, further cause the communication handling block to investigate whether the first wireless communication device fulfils one or more conditions for attaching to the second base station, wherein one condition is that the second base station is allowable, and

[0033] instruct the radio circuit to send a response to the first message, the response to the first message being about the ability of the first wireless communication device to attach to the second base station,

[0034] wherein if the one or more conditions are fulfilled, further cause the communication handling block to

[0035] instruct the radio circuit to detach from the first base station, and

[0036] instruct the radio circuit to attach to the second base station.

[0037] According to a fourth aspect, the object is achieved by a computer program product for establishing communication between a first wireless communication device and a second wireless communication device of an industrial automation system via a cellular network, the computer program product comprising a data carrier having computer program code according to the third aspect.

[0038] The allowable base station can be a base station with which the first wireless communication device is allowed to communicate via the cellular network and / or via the industrial automation system.

[0039] The industrial automation system can be an electric power system, and the first wireless communication device can be a smart electronic device. In one variant, the smart electronic device is a phasor measurement unit. In a further variant, it is a phasor data concentrator. Also, the second wireless communication device can be a smart electronic device, such as a phasor measurement unit or a phasor data concentrator. When the second wireless communication device is a phasor data concentrator, the first wireless communication device can be a phasor measurement unit. When the second wireless communication device is a phasor measurement unit, the first wireless communication device can be a phasor measurement unit or a phasor data concentrator.

[0040] The first message can be information sent between the first wireless communication device and the second wireless communication device over a link established between the first wireless communication device and the second wireless communication device via the cellular network.

[0041] The base station identification information can comprise data broadcast by the base station, such as in a pilot signal, which identifies the base station. The base station identification information can comprise information such as a cell ID, a network ID, and a tracking area ID, etc.

[0042] As mentioned above, the attaching and disconnecting can only be performed if the first wireless communication device fulfils one or more conditions for attaching to the second base station.

[0043] One condition can be that the first wireless communication device does not participate in a communication session with any other wireless communication device.

[0044] According to a first variant of the first aspect, the method thus further comprises investigating whether there is an ongoing communication session with a further wireless communication device of the industrial automation system via the first base station, and performing the disconnecting and attaching only if there is not.

[0045] According to a corresponding variant of the second aspect, the communication handling block is further configured to investigate whether there is an ongoing communication session with a further wireless communication device of the industrial automation system via the first base station, and to instruct the disconnecting and attaching only if there is not.

[0046] As mentioned previously, one condition can be that the second base station is allowable for the first wireless communication device, i.e. that the first wireless communication device is allowed to communicate with the second base station.

[0047] According to a second variant of the first aspect, the method thus further comprises investigating the allowability of the second base station, and performing the disconnection and attachment only if the second base station is allowable.

[0048] According to a corresponding variant of the second aspect, the communication handling block is further configured to investigate the allowability of the second base station and to instruct the disconnection and attachment only if the second base station is allowable.

[0049] The investigation of the allowability can comprise investigating whether the second base station is on a list of approved base stations associated with the first wireless communication device. The investigation of the allowability can also involve an investigation of the cellular network. The investigation of the allowability can also comprise investigating the availability of the second wireless communication, such as whether the first wireless communication device is able to communicate therewith.

[0050] However, a further condition can be that a link quality between the first wireless communication device and the second base station meets a link quality criterion.

[0051] According to a third variant of the first aspect, the method thus further comprises investigating a quality of a wireless link between the first wireless communication device and the second base station, and performing the disconnection and attachment only if the link quality meets a link quality criterion.

[0052] According to a corresponding variant of the second aspect, the communication handling block is further configured to investigate a quality of a wireless link between the first wireless communication device and the second base station, and to instruct the disconnection and attachment only if the link quality meets a link quality criterion.

[0053] If the one or more conditions are met, the response can be a positive response to the first message sent.

[0054] The positive response to the first message is a response indicating that the first wireless communication device can be attached to the second base station.

[0055] If the one or more conditions are not met, the response can be a negative response to the first message sent as an alternative response.

[0056] The negative response to the first message is a response indicating that the first wireless communication device cannot be attached to the second base station.

[0057] According to a fourth variant of the first aspect, the method can further comprise, when the response is a negative response, sending a positive response to the first message if the one or more conditions are met.

[0058] According to a corresponding variant scheme of the second aspect, in the same situation, the communication handling block can be further configured to instruct the radio circuitry to transmit a positive response to the first message in case the one or more conditions are fulfilled.

[0059] According to a fifth variant scheme of the first aspect, the method further comprises transmitting a second message to the second wireless communication device, the second message comprising base station identification information identifying the first base station, and receiving a response to the second message from the second wireless communication device, the response to the second message pertaining to a capability of the second wireless communication device to attach to the first base station.

[0060] According to a corresponding variant scheme of the second aspect, the communication handling block is further configured to instruct the radio circuitry to transmit a second message to the second wireless communication device, the second message comprising base station identification information identifying the first base station, and receive a response to the second message from the second wireless communication device, the response to the second message pertaining to a capability of the second wireless communication device to attach to the first base station.

[0061] Furthermore, the second message can be a message transmitted between the first wireless communication device and the second wireless communication device over a link established between the first wireless communication device and the second wireless communication device over the cellular network.

[0062] In case the second wireless communication device finds that the one or more conditions for the second wireless communication device to be attached to the first base station are not fulfilled, the response can be a negative response, wherein the negative response indicates that the second wireless communication device cannot be attached to the first base station.

[0063] Alternatively or in addition, in case the second wireless communication device finds that the one or more conditions for the second wireless communication device to be attached to the first base station are fulfilled, a positive response can be received from the second wireless communication device, wherein the positive response indicates that the second wireless communication device can be attached to the first base station.

[0064] When the response is a negative response, according to a sixth variant scheme of the first aspect, the method can further comprise receiving a positive response to the second message from the second wireless communication device in case the second wireless communication device finds that the one or more conditions for the second wireless communication device to be attached to the first base station are fulfilled.

[0065] According to a corresponding variant scheme of the second aspect, the communication handling block is further configured to receive a positive response to the second message from the second wireless communication device in case the second wireless communication device finds that the one or more conditions for the second wireless communication device to be attached to the first base station are fulfilled.

[0066] According to a seventh variant of the first aspect, the method further comprises, after being attached to the second base station, starting to transmit data to and / or receive data from the second wireless communication device via the radio circuitry and the second base station.

[0067] According to a corresponding variant of the second aspect, the communication handling block is further configured to, after being attached to the second base station, start to transmit data to and / or receive data from the second wireless communication device via the radio circuitry and the second base station.

[0068] The present application has many advantages. For example, the present application does indeed ensure that the contribution from the cellular network to the delay is kept to a minimum. If the wireless communication devices are involved in control in an automation system, the control loop used can be simplified, which can result in less jitter. Also, the reliability can be improved since fewer devices and components are involved. The application can be connected to a single base station, which can also simplify commissioning / provisioning. If the first base station is to be taken out of service, the movement of the first wireless communication device to the second base station can also be performed in advance. By receiving the first message and sending a negative response, the two wireless communication devices can adapt their communication to the knowledge that they are connected to the same base station or different base stations. For example, the control loop can adapt to changes in latency and / or jitter.

[0069] It should be emphasized that the term "comprises / comprising", when used in this specification, is taken to specify the presence of stated features, integers, steps, or components but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. BRIEF DESCRIPTION OF DRAWINGS

[0070] The present application will now be described in more detail in relation to the enclosed drawings, in which:

[0071] Figure 1 An automation system is schematically illustrated, which comprises a first wireless communication device and a second wireless communication device that communicate with each other via a cellular network,

[0072] Figure 2 A first wireless communication device is schematically illustrated, which comprises a first implementation of a communication handling block,

[0073] Figure 3 A first wireless communication device is schematically illustrated, which comprises a second implementation of a communication handling block,

[0074] Figure 4 A first wireless communication device is schematically illustrated, which is attached to a first base station of a cellular network, and a second wireless communication device is schematically illustrated, which is attached to a second base station of the cellular network,

[0075] Figure 5A flow chart is shown with a number of method steps in a first embodiment of a method of establishing a communication between a first wireless communication device and a second wireless communication device,

[0076] Figure 6 A flow chart is shown with a number of method steps in a second embodiment of a method of establishing a communication between a first wireless communication device and a second wireless communication device, and

[0077] Figure 7 A computer program product according to an embodiment of the application is schematically shown in the form of a CD ROM disc on which a computer program for implementing the communication handling block is provided. DETAILED DESCRIPTION

[0078] 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 of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

[0079] The present application is generally directed to using a cellular network for communication between devices in an industrial automation system.

[0080] Figure 1 is a schematic diagram showing an environment in which embodiments presented herein can be applied. The power transmission line 12 can be an alternating current (AC) power line for transferring power in a power system or grid, where a power system is a type of industrial automation system. The power transmission line 12 can transfer power in any direction. In the case of AC, the power transmission line 12 can comprise separate cables for separate phases, e.g. three phases. The transmission can be a medium voltage (MV) transmission. For the purpose of this disclosure, medium voltage (MV) refers to voltages higher than 1 kV AC and lower than 72 kV AC.

[0081] There are a first substation 14a and a second substation 14b. Each of the substation 14a, 14b obtains power measurements of the power transmission line 12. Both the first substation 14a and the second substation 14b are power substations for managing the power transfer through the power transmission line. For example, the substations can comprise components for power conversion and / or power distribution. The power measurements are related to voltage and / or current and are expressed as phasors. To collect these phasors, each substation can comprise an intelligent electronic device (IED), which can in turn be a phasor measurement unit (PMU). In alternative implementations of the power system, one of the IEDs is a PMU, while the other is a phasor data concentrator (PDC) that can communicate with several PMUs. It should also be appreciated that the IEDs are not limited to the substations or to a particular power transmission line, and can be placed anywhere in the power system.

[0082] The PMUs communicate with each other via the cellular network CN 10. Thus, the PMU in the first substation 14a is a first wireless communication device WCDa 16a, while the PMU in the second substation 14b is a second wireless communication device WCDb 16b. In the following, the first wireless communication device 16a and the second wireless communication device 16b will be referred to as WCDa and WCDb, respectively. Figure 1 As can be seen in Fig. 1, the communication can involve the second wireless communication device 16b sending a first message Ml to the first wireless communication device 16a via the cellular network 10, and the first wireless communication device 16a sending a second message M2 to the second wireless communication device 16b via the cellular network 10. These messages Ml and M2 will be described in more detail later.

[0083] Each of the first wireless communication device 16a and the second wireless communication device 16b comprises a respective radio circuit comprising hardware and software to allow the device 16a, 16b to act as a cellular terminal, also known as a user equipment (UE), for communication with the cellular network 10. The cellular network can for example comply with any one or a combination of LTE (Long Term Evolution), such as 4G LTE or the next generation mobile networks (Fifth Generation, 5G) or any other current or future wireless network, as long as the principles described in the following are applicable.

[0084] Figure 2 Fig. 2 is a schematic diagram illustrating components of an embodiment of the wireless communication device 16, which is applicable to both the first wireless communication device 16a and the second wireless communication device 16b.

[0085] The wireless communication device 16 comprises a radio circuit 18 comprising appropriate analog and digital components to allow signal transmission Tx and signal reception Rx with the cellular network 10 using one or more antennas ANT 20.

[0086] The wireless communication device 16 further comprises a communication handling block CHD 24, which in a first variant is implemented as a block comprising a connection investigation unit CIU 26 and a data handling unit DHU 28.

[0087] The operation of the communication handling block 24 will be described in more detail later.

[0088] The wireless communication device 16 can further comprise an input / output (I / O) interface 22 for communication with other external entities. Optionally, the I / O interface 22 also comprises a user interface.

[0089] The communication handling block 24 can be implemented as one or more application specific integrated circuits (ASICs), digital signal processors (DSPs) or field programmable gate arrays (FPGAs).

[0090] Figure 3 A wireless communication device 16 according to another implementation is shown. In this case, the radio circuitry 18, the antenna 20 and the I / O interface 22 are the same as in Figure 2 However, the communication handling block 24 has another implementation. It is implemented as a processor 30 acting on computer instructions 34 in a memory 32. The processor 30 can be any combination of one or more of a central processing unit (CPU), a multi-processor, a microcontroller, etc., capable of executing software instructions 34 stored in the memory 34.

[0091] The memory 32 can be any combination of random access memory (RAM) and / or read only memory (ROM). The memory 32 can also include persistent storage, which can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The software instructions 34 can be in the form of one of several software applications executable by the processor 30.

[0092] Wireless communication devices of an industrial automation system can need to communicate with each other for a number of reasons. In Figure 1 In the example, the first and second wireless communication devices 16a, 16b can for example need to communicate phasors between the two substations 14a, 14b. This can be used for a protection function, where the phasors are compared for detecting possible faults. For such fault detection, a line differential analysis can be performed, which is known per se in the art. This analysis can be performed in the respective relays of the substations 14a, 14b. It should be appreciated here that this is just one example of a possible need for communication between IEDs, another example being for power oscillation damping.

[0093] However, in order to perform the desired functions in an industrial automation system, the latency can need to be very low, which can be particularly critical for some applications such as protection. It can therefore be necessary to ensure that the contribution of the cellular network 10 to the latency is as low as possible.

[0094] Aspects of the present invention are directed to such ensuring.

[0095] The cellular network 10 typically comprises a plurality of base stations with which wireless communication devices communicate in order to exchange data, such as phasors, between each other. In 4G and 5G networks, the base stations are typically denoted as eNodeBs or gNodeBs.

[0096] Figure 4 One example is shown with a first base station BSa 36a having a first coverage range (indicated with a dashed line) and a second base station BSb 36b having a second coverage range (indicated with a solid line). In this example, the first wireless communication device 16a is attached to the second base station (36b).

[0097] 15. A method for communicating via a cellular network (10) between a first wireless communication device 16a and a second wireless communication device 16b. The first wireless communication device 16a is attached to a first base station 36a. It can also be seen that the first wireless communication device 16a is also within the coverage range of a second base station 36b. It is therefore within the coverage range of both the first base station 36a and the second base station 36b. In contrast, the second wireless communication device 16b is only within the coverage range of the second base station 36b.

[0098] In the cellular network 10, the base stations communicate with each other via a core network, sometimes referred to as the evolved packet core (EPC). The core network can be co-located with the base stations, meaning that it can be located in the same physical location as one of the base stations. However, by this it is also placed in a different location from the other base stations. By this, data transmitted between two wireless communication devices connected to two different base stations will need to go through the core. This will typically affect the communication latency between the wireless communication devices. Latency is one example of a communication parameter that can be affected. Other examples are jitter and reliability.

[0099] In many cellular networks, communication between two UEs attached to the same base station does not need to go through the core network. This means that in order to ensure that the contribution of the cellular network to the latency is as low as possible, it would be advantageous to have the wireless communication devices attached to the same base station. Even if the communication between the wireless communication devices attached to the same base station goes through a co-located core, a considerable latency limitation will be achieved compared to the communication that would go between the core and a distant base station. This can also have an impact on the jitter.

[0100] How this latency and / or jitter limitation can be achieved will now be described, also with reference to Figure 5Fig. 1 shows a flow chart illustrating a first embodiment of a method of establishing communication between a first wireless communication device 16a and a second wireless communication device 16b, wherein the method steps of the method are performed in the first wireless communication device 16a.

[0101] Here it is assumed that the first wireless communication device 16a is attached to a first base station 36a and that the second wireless communication device 16b is attached to a second base station 36b, and that at least one of the devices needs to send data to the other, such as a phasor.

[0102] The method starts by the connection investigating unit 26 of the first wireless communication device 16a receiving a first message M1 from the second wireless communication device 16b, step 38.

[0103] The content of the first message M1 is then continued and investigated, step 39. The first message M1 can comprise base station identification information BSII identifying to which base station the second wireless communication device 16b is attached. The investigation can thus involve investigating the base station identification information BSII in order to find out to which base station the second wireless communication device 16b is attached.

[0104] The second wireless communication device 16b is either attached to the first base station 36a or to another base station, where any such other base station to which the second wireless communication device 16b is attached is the second base station 36b. The second wireless communication device 16b must thus be attached to the first base station 36a if it is not attached to the second base station 36b, step 40. In this case the delay and / or the jitter caused by the cellular network 10 is already as low as possible. From this the data handling unit 28 can continue and order the radio circuit 18 to start sending data to and / or receiving data from the second wireless communication device 16b, step 50.

[0105] However, if the second wireless communication device 16b is attached to the second base station 36b, step 40, the connection investigating unit 26 continues and investigates whether the first wireless communication device 16a fulfils one or more conditions for being attached to the second base station 36b, one of the conditions being that the second base station 36b is allowable. In this embodiment the condition that the second base station 36b is an allowable or approved base station is the only condition that is investigated.

[0106] If the first wireless communication device 16a has the second base station 36b listed as allowable to communicate with, step 42, the data handling unit 28 can continue and order the radio circuit 18 to start sending data to and / or receiving data from the second wireless communication device 16b, step 50.

[0107] If the second base station 36b is not allowable, step 42, the connection investigation unit 26 instructs the radio circuit 18 to send a negative response to the first message Ml to the second wireless communication device 16b, step 43, and then ends the method, step 44, whereupon the first wireless communication device 16a continues to be attached to the first base station 36a.

[0108] If the second base station 36b is not allowable, step 42, the connection investigation unit 26 instructs the radio circuit 18 to send a negative response to the first message Ml to the second wireless communication device 16b, step 43, and then ends the method, step 44, whereupon the first wireless communication device 16a continues to be attached to the first base station 36a.

[0109] The negative response to the first message Ml is a response indicating that the first wireless communication device 16a cannot be attached to the second base station 36b.

[0110] However, if the second base station 36b is an allowable base station, step 42, the connection investigation unit 26 instructs the radio circuit 18 to send a positive response to the first message Ml to the second wireless communication device 16b, step 45, to be detached from the first base station 36a, step 46, and to be attached to the second base station 36b, step 48, where the attachment and detachment can be performed by executing a handover procedure from the first base station to the second base station, which handover can in addition be a so-called soft handover.

[0111] The positive response to the first message Ml is a response indicating that the first wireless communication device 16a can be attached to the second base station 36b.

[0112] After the first wireless communication device 16a has been attached to the second base station 36b, the data handling unit 28 can command the radio circuit 18 to start sending data and / or receiving data from a corresponding data handling unit of the second wireless communication device 16b, step 50, which data can be, as an example, phasor data.

[0113] By using both the first wireless communication device 16a and the second wireless communication device 16b with the second base station 36b, the use of the core network can be avoided and thereby the delay contribution from the cellular network 10 kept at a minimum. If the wireless communication devices are involved in control in the automation system, the control loop used can be simplified, which can result in less jitter. Also, the reliability of the automation system can be improved since fewer devices and components are involved. Furthermore, the application can be allowed to connect to a single base station, which can also simplify commissioning / pre-configuration. If the first base station 36a is to be taken out of service, e.g. due to maintenance, software update, the movement of the first wireless communication device 16a to the second base station 36b can also be performed in advance.

[0114] By receiving the first message, the first wireless communication device knows whether the second wireless communication device is connected to the same base station. Also, by investigating the one or more conditions, the first wireless communication device also knows whether it can be attached to the second base station. By sending a response, whether a positive or a negative response, the second wireless communication device also knows whether the first wireless communication device can be attached to the second base station. Thereby, the wireless communication devices can adapt their communication based on their knowledge of whether they are connected to the same cell or different base stations. This means that the control loop involving both the first wireless communication device and the second wireless communication device can adapt to changes in jitter and / or delay caused by the wireless communication devices being attached to the same or different base stations.

[0115] It should be realized here that only one type of response can be sent, which can advantageously be a negative response. Thus, the first wireless communication device can send a negative response in case it cannot be attached to the second base station, but no response or remain silent in case it can be attached to the second base station. Thus, the positive response can be omitted and vice versa.

[0116] A second embodiment addressing the delay and / or jitter limitation will now be described with reference to Figure 6 Fig. 4, which illustrates a flowchart of a method of establishing communication between a first wireless communication device 16a and a second wireless communication device 16b according to the second embodiment, wherein the method steps of the method are performed in the first wireless communication device 16a. Here, the conditions shown in Fig. 2 also apply. Figure 4

[0117] In this case, the connection investigating unit 26 of the first wireless communication device 16a instructs or commands the radio circuit 18 to send a second message M2 to the second wireless communication device, step 52, which the radio circuit 18 then sends to the second wireless communication device 16b via the antenna 20 and the first base station 36a and the second base station 36b.

[0118] ​The connection investigating unit 26 also receives the first message Ml via the radio circuit 18, the antenna 20 and the first base station 36a and the second base station 36b, step 54.

[0119] It should be noted here that the first message and the second message are not synchronization messages of the cellular network 10, such as the synchronization messages used between UEs and base stations. The first message and the second message are messages sent between the first wireless communication device 16a and the second wireless communication device 16b over a link established between the two devices through the cellular network 10.

[0120] The message comprises base station identification information BSII, which is information about the base station to which the wireless communication device in question is attached. It is thus information about the base station to which the sending wireless communication device is attached. This information can comprise information such as cell ID, network ID and tracking area ID, and can for example be obtained by the wireless communication device listening to a pilot signal broadcast by the base station. The cell ID is here the identity of the cell provided by the base station, the network ID is the identity of the cellular network, and the tracking area ID is the identity of a cell set comprising the cell with the cell ID.

[0121] The connection investigating unit 26 of the first wireless communication device 16a then investigates this base station identification information BSII of the first message Ml, step 56, where the investigation can be an investigation of which base station the second wireless communication device is attached to.

[0122] Also in this case, the second wireless communication device 16b is either attached to the first base station 36a or to another base station, where any such other base station to which the second wireless communication device 16b is attached is the second base station 36b. Thus, if it is not attached to the second base station 36b, step 58, the second wireless communication device 16b must be attached to the first base station 36a. In this case, the delay caused by the cellular network 10 has been as low as possible. From this, the data handling unit 28 can continue and instruct the radio circuit 18 to start sending data to and / or receiving data from the second wireless communication device, step 74.

[0123] However, if the second wireless communication device 16b is attached to the second base station 36b, step 58, the connection investigating unit 26 continues and investigates whether the first wireless communication device 16a fulfils various conditions for being attached to the second base station 36b.

[0124] One condition can be that the first wireless communication device 16a is not involved in a communication session with any other wireless communication device.

[0125] Thus, the connection investigating unit 26 can investigate whether there is an ongoing communication session with another communication device, such as whether the first wireless communication device 16a is exchanging phasors with another wireless communication device than the second wireless communication device 16b.

[0126] If the first wireless communication device 16a is engaged in such a session, step 60, the connection investigating unit 26 proceeds and instructs the radio circuit 18 to send a negative response to the first message Ml, which can be done by sending a negative acknowledgement NACK of the first message Ml to the second wireless communication device 16b via the radio circuit 18 and the antenna 20, step 66.

[0127] A further condition can be that the second base station is available to the first wireless communication device.

[0128] Thus, if no session is ongoing, step 60, the connection investigating unit 26 can investigate whether the second base station 36b is allowable for the first wireless communication device 16a, such as whether the first wireless communication device 16a has the second base station 36b on a list of available base stations where handover can be made. The second base station 36b can be allowable if the first wireless communication device 16a is able to receive signals and extract base station identification information from such signals, such as a pilot signal broadcasted by the second base station 36b. A further possible investigation is to investigate whether the second base station 36b belongs to the same cellular network as the first base station 16a. Yet another possible investigation is whether the second base station 36b is on a white list associated with the first wireless communication device 16a as mentioned earlier, where the second base station 36b is allowable if it belongs to the same network and / or is on the white list.

[0129] If the second base station 36b is not allowable, step 62, the connection investigating unit 26 proceeds and instructs the radio circuit 18 to send a negative response to the first message Ml to the second wireless communication device 16b, step 66.

[0130] However, a further condition can be that a link quality LQ between the first wireless communication device 16a and the second base station 36b fulfils a link quality criterion LQC.

[0131] Thus, if the second base station 36b is allowable, step 62, the connection investigating unit 26 can proceed and investigate whether the quality of the communication link between the first wireless communication device 16a and the second base station 36b fulfils a link quality criterion LQC. The criterion can be provided in the form of one or more threshold values. For example, the link quality LQ can comprise a signal strength and / or a bit error rate of the base station transmission, which can be compared to a corresponding threshold value. The link quality criterion LQC can be fulfilled if the measured link quality LQ is to the right of the corresponding threshold value. The link quality criterion LQC can be fulfilled when the signal strength is above a corresponding threshold value, and for the bit error rate below a corresponding threshold value. It should be realized that other link quality criteria can be used, such as a carrier-to-interference ratio (CIR) and a block error rate (BLER). It can also be decided based on the number of retransmissions.

[0132] If the link quality criterion is not fulfilled, step 64, the connection investigating unit 26 proceeds and instructs the radio circuit 18 to send a negative response to the first message Ml to the second wireless communication device, step 66.

[0133] However, if the link quality criterion LCQ is fulfilled, step 64, the connection investigating unit 26 instructs the radio circuit 18 to send a positive response to the first message Ml to the second wireless communication device 16 via the radio circuit 18 and the antenna 20, step 68. The positive response can be sent as an acknowledgement or ACK of the first message Ml. The connection investigating unit 26 then instructs the radio circuit 18 to detach from the first base station 36a, step 70, and attach to the second base station 36b, step 72, where the attachment and detachment can be performed by executing a handover procedure from the first base station to the second base station, which handover can in addition be a so-called soft handover.

[0134] In this case, it is also possible that the only response to the first message Ml is a negative response or a positive response.

[0135] After the first wireless communication device 16a has been attached to the second base station 36b, the data handling unit 28 can instruct the radio circuit 18 to start sending data and / or receiving data to / from a corresponding data handling unit of the second wireless communication device 16b, step 74, which data can be, as an example, phasor data.

[0136] By both the first wireless communication device 16a and the second wireless communication device 16b using the second base station 36b, it is possible to avoid using the core network and thereby keep the latency contribution from the cellular network 10 at a minimum.

[0137] By using the first message and the response to the first message, both wireless communication devices can know whether they are connected to the same or different base stations. Both are thus able to adapt their communication to that knowledge. By sending the second information, both the first wireless communication device and the second wireless communication device know the other base station to which the other is attached, which allows adaptation also. By the response to the second information, both wireless communication devices can also know whether the other is able to connect to the same base station to which it is attached itself. This allows one wireless communication device to be attached to the other’s base station in case the other wireless communication device is unable to disconnect from its current base station.

[0138] As can be seen from the above IED example, in case a cellular communication network is used, the latency in the communication between the IEDs is limited by reducing the hop count between the base stations. This will also have a positive effect on possible jitter.

[0139] It should be recognized here that the second wireless communication device 16b can have the same type of operation as the first wireless communication device 16a. If it has the same type of operation, it will send a negative response to the second message M2 of the first wireless communication device 16a, as the first base station 36a is not available, as can be seen in the example according to Figure 4

[0140] The described operation can be a complement to the differentiated scheduling and edge computing mechanisms and will eliminate the time for a data packet to leave one base station and enter the EPC from where it is routed to a second base station. Instead, both wireless communication devices will try to belong to the same base station and can exploit the local breakout / core network for the routing of the packet.

[0141] In differentiated scheduling, user traffic is marked and can have priority during access to radio resources. This reduces latency when there is traffic from multiple sources in the network. However, some latency is added when the traffic is routed over multiple base stations. Similarly, in technologies such as edge computing, devices are served by a core network (edge computing node) or processing unit that is kept very close to the radio network, e.g. in the user plane, routing user packets.

[0142] In other words, it can be seen that a wireless communication device, possibly an IED, such as a PMU and / or a phasor data concentrator (PDC), has the following capabilities

[0143] 1. sending and receiving a message with base station identification information to and from a corresponding wireless communication device such as a PDC before starting to send phasor information or any other information that needs to be communicated between wireless communication devices

[0144] a. the message contains information such as network ID, tracking area ID, cell ID of the base station to which the wireless communication device is attached​

[0145] b. Upon receipt of the first message, the first wireless communication device checks whether it is at that moment in communication with the other wireless communication device

[0146] c. If so, the first wireless communication device sends a negative response to the second wireless communication device, indicating that it cannot change its base station in order to prevent interruption in the existing communication.

[0147] 2. Based on the network ID of the base station of the corresponding wireless communication device broadcast by the cellular network, determine the availability of the corresponding base station

[0148] 3. If no base station of the corresponding wireless communication device is found, send a negative response to the corresponding wireless communication device,

[0149] 4. If a corresponding base station is found, then determine whether the link quality meets the link quality criteria

[0150] 5. If the link quality meets the link quality criteria, attach to the base station of the corresponding node and send a positive response to the corresponding wireless communication device,

[0151] 6. If the link quality does not meet the link quality criteria, send a negative response to the corresponding wireless communication device,

[0152] 7. Start exchanging information

[0153] In the example given above, the communication is exemplified by the communication between two IEDs implemented as PMUs in a power system. However, it should be realized that other types of IEDs are possible. For example, the first wireless communication device can be a PMU and the second wireless communication device can be a PDC, e.g. implemented in an edge node, where the edge node also communicates with other PMUs. In this case, the PMU acting as the first wireless communication device can not send a synchronization message. In addition, the PDC acting as the second wireless communication device can not send any data to the PMU.

[0154] It should also be realized that the communication can also be provided in other types of industrial automation systems. For example, it can be used in a process control system, where two wireless field devices are to communicate with each other, or where a wireless field device is to communicate with a programmable logic controller (PLC) via a gateway.

[0155] The communication handling module described above is described as being provided in the form of a processor having an associated program memory comprising computer program code for performing the functions of the connection investigation unit and the data handling unit. The computer program code can also be provided on a data carrier, such as a CD ROM disc or a memory stick, which, when loaded into a computer, will implement the functions of the communication handling module.Figure 7 One such computer program product is shown schematically in Fig. 3 as a CD ROM disc 76 having a computer program code 34.

[0156] While the application has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the application is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements. Therefore, the application should only be limited by the appended claims.

Claims

1. A method for establishing communication between a first wireless communication device and a second wireless communication device in an industrial automation system via a cellular network, the method being performed in the first wireless communication device and comprising: When the first wireless communication device is attached to a first base station of the cellular network, a first message is received from the second wireless communication device via the first base station. The first message includes base station identification information that identifies the base station of the cellular network to which the second wireless communication device is attached. The base station identification information of the first message is investigated in order to identify the base station to which the second wireless communication device is attached. If the second wireless communication device is attached to the second base station, then the following also applies: The investigation examines whether the first wireless communication device meets one or more conditions for attachment to the second base station, one of which is that the second base station is permissible, and Send a response to the first message, the response to the first message relating to the capability of the first wireless communication device to attach to the second base station. If one or more of the conditions are met, the method further includes... Disconnect from the first base station, and It is attached to the second base station.

2. The method of claim 1, wherein satisfying one of the conditions involves investigating whether there is an ongoing communication session between the first base station and another wireless communication device of the industrial automation system, and performing the disconnection and reconnection only if no such session exists.

3. The method according to claim 1 or 2, wherein the satisfaction of one of the conditions involves investigating the permissibility of the second base station, and the disconnection and attachment are performed only if the second base station is permissible.

4. The method of claim 3, wherein the investigation into the permissibility includes investigating whether the second base station is on the list of approved base stations.

5. The method according to claim 1 or 2, wherein satisfying one of the conditions involves investigating the quality of the wireless link between the first wireless communication device and the second base station, and performing the disconnection and reattachment only if the link quality meets the link quality standard.

6. The method of claim 1 or 2, wherein if one or more conditions are not met, the response includes a negative response to the first message.

7. The method of claim 1 or 2, wherein if one or more of the conditions are met, the response includes an affirmative response to the first message.

8. The method according to claim 1 or 2, further comprising: Send a second message to the second wireless communication device, the second message including base station identification information that identifies the first base station; And receiving a response to the second message from the second wireless communication device, the response to the second message relating to the capability of the second wireless communication device to attach to the first base station.

9. The method of claim 1 or 2, further comprising, after being attached to the second base station, initiating the transmission of data to the second wireless communication device and / or the reception of data from the second wireless communication device via the second base station.

10. A first wireless communication device in an industrial automation system, the first wireless communication device being configured to communicate via a cellular network and including... A radio circuit for wireless communication with other wireless communication devices in the industrial automation system via the cellular network, and The communication processing block is configured as follows When the first wireless communication device is attached to a first base station of the cellular network, a first message is received from the second wireless communication device via the first base station. The first message includes base station identification information that identifies the base station of the cellular network to which the second wireless communication device is attached. The base station identification information of the first message is investigated in order to identify the base station to which the second wireless communication device is attached. If the second wireless communication device is attached to the second base station, the communication processing block is further configured to... The investigation examines whether the first wireless communication device meets one or more conditions for attachment to the second base station, one of which is that the second base station is permissible, and The radio circuit is instructed to send a response to the first message, the response to the first message relating to the capability of the first wireless communication device to attach to the second base station. If one or more of the conditions are met, the communication processing block is further configured to... Instructing the radio circuit to disconnect from the first base station, and The radio circuit is instructed to be attached to the second base station.

11. The first wireless communication device of claim 10, wherein the investigation of one or more conditions involves investigating whether there is an ongoing communication session with another wireless communication device of the industrial automation system via the first base station, and the disconnection and attachment are performed only if no such session exists.

12. The first wireless communication device according to claim 10 or 11, wherein the communication processing block is further configured to: instruct the radio circuit to send a second message to the second wireless communication device, the second message including base station identification information identifying the first base station; and receive a response to the second message from the second wireless communication device, the response to the second message relating to the capability of the second wireless communication device to attach to the first base station.

13. The first wireless communication device according to claim 10 or 11, wherein the first wireless communication device is a smart electronic device, and the industrial automation system is a power system.

14. A computer-readable storage medium for establishing communication between a first wireless communication device and a second wireless communication device in an industrial automation system via a cellular network, the computer-readable storage medium comprising computer program code, which, when executed by a processor of a communication processing block of the first wireless communication device, causes the communication processing block to: When the first wireless communication device is attached to a first base station of the cellular network, a first message is received from the second wireless communication device via the first base station. The first message includes base station identification information that identifies the base station of the cellular network to which the second wireless communication device is attached. Investigate the base station identification information of the first message to identify the base station to which the second wireless communication device is attached. If the second wireless communication device is attached to the second base station, then the communication processing block is also enabled. The investigation examines whether the first wireless communication device meets one or more conditions for attachment to the second base station, one of which is that the second base station is permissible, and Send a response to the first message, the response to the first message relating to the capability of the first wireless communication device to attach to the second base station. If one or more of the conditions are met, then the communication processing block is also enabled. Instruct the radio circuit to be disconnected from the first base station, and The radio circuit is instructed to be attached to the second base station.

15. A computer program product for establishing communication between a first wireless communication device and a second wireless communication device in an industrial automation system via a cellular network, the computer program product comprising a computer-readable storage medium as described in claim 14.

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