Increasing reliability and reducing latency in a wireless network

• US 8,798,084 B2
• Filed: 04/10/2008
• Issued: 08/05/2014
• Est. Priority Date: 04/13/2007
• Status: Active Grant

• Current Assignee: FieldComm Group, Inc.
• Original Assignee: Hart Communication Foundation (FieldComm Group, Inc.)
• Inventors: Pratt, Wallace A. Jr., Nixon, Mark J., Rotvold, Eric D., Pramanik, Robin S., Lennvall, Tomas P., Blevins, Terrence L.
• Primary Examiner(s): Sefcheck, Gregory
• Assistant Examiner(s): YOUNG, STEVE R
• Application Number:
  US12/100,927
• Publication Number:
  US 20080279204A1
• Time in Patent Office: 2,308 Days
• Field of Search: None
• US Class Current: 370/406
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 56/002 Mutual synchronization
• CPC Class Codes: H04W 80/00 Wireless network protocols or protocol adaptations to wireless operation

Abstract

A mesh communication network for use in, for example, process control plants includes a plurality of network devices transmitting and receiving data according to a network schedule defined as a set of concurrent overlapping superframes, and along a set of graphs defining communication paths between pairs of network devices. A network manager residing in or outside the communication network develops a routing scheme for the network by analyzing the topology of the network and defining a set of graphs for use in routing or transmitting data between various nodes of the network, each graph including one or more communication paths between pairs of network devices. Concurrently or consequently, the network manager defines the network schedule in view of at least transmission requirements, power availability, and signal quality at each network device. If desired, the network manager may begin to define the network schedule upon completing the definition of the graphs of the communication network, so that the network manager may define the network schedule in view both the defined graphs and the transmission, power, etc. parameters associated with each network device.

Claims

1. A method of reliably transferring data in a communication network having a plurality of network devices and operating in a process control environment, wherein the method is executed in a computer that manages the communication network, the method comprising:

(i) generating a first routing graph having a multiplicity of nodes and a set of edges based on a topology of the communication network, including;

associating each of the multiplicity of nodes with a respective one of the plurality of network devices; and

associating each edge in the set of edges with a respective direct connection between two of the plurality of network devices;

(ii) defining a communication schedule of the communication network based on at least the first routing graph, including;

defining a communication timeslot of a fixed predetermined duration;

defining a superframe with a number of communication timeslots, a first portion of the number of communication timeslots of the superframe used for delivery of first process data using the first routing graph, and a second portion of the number of communication timeslots of the superframe used for delivery of second process data using a second routing graph, wherein at least one of the first process data or the second process data is generated based on a physical control function performed by a field device to control a process in the process control environment;

defining a superframe length based on a predetermined periodic update rate of a first one of the plurality of network devices; and

assigning a respective communication timeslot associated with the superframe to the each edge in the set of edges of the first routing graph according to a predetermined order,

wherein at least one of the generating the first routing graph or the defining the communication schedule is based on a set of requirements corresponding to delivery of the first process data from a source network device to a destination network device via at least one intermediate network device, the source network device, the destination network device and the at least one intermediate network device included in the plurality of network devices; and

(iii) communicating, to the first one of the plurality of network devices and to another one of the plurality of network devices, a respective portion of the first routing graph and respective one or more communication timeslots included in the first portion of the number of communication timeslots of the superframe,

wherein the first one of the plurality of network devices transmits, via the communication network and using the respective portion of the first routing graph and the respective one or more communication timeslots, the first process data to the another one of the plurality of network devices and third process data to a gateway in connection with another communication network operating in the process control environment.

2. The method of claim 1, wherein generating the first routing graph includes generating a directed graph defining a unidirectional flow of data from exactly one source node to a destination node;

and wherein the first one of the plurality of network devices is one of the exactly one source node or the destination node of the directed graph.

3. The method of claim 2, wherein assigning the respective communication timeslot to the each edge in the set of edges of the first routing graph according to the predetermined order includes allocating the respective communication timeslot to the each edge in the set of edges of the first routing graph in an order of traversal of the first routing graph from the exactly one source node toward the destination node.

4. The method of claim 2, wherein generating the first routing graph further includes selecting a graph node from a set of candidate nodes based on a type of power supply available at each node in the set candidate nodes;

and wherein each node in the set candidate nodes can serve as an intermediate node between the exactly one source node and the destination node.

5. The method of claim 2,

wherein the first routing graph is a first directed routing graph, the multiplicity of nodes is a first multiplicity of nodes, the set of edges is a first set of edges, the exactly one source node is a first exactly one source node, and the destination node is a first destination node;

wherein the second routing graph is a second directed routing graph having a second multiplicity of nodes and a second set of edges based on the topology of the communication network, the second directed routing graph having a second exactly one source node and a second destination node and one or more intermediate nodes; and

wherein one of the second exactly one source node or the second destination node of the second directed routing graph is the same as a corresponding one of the first exactly one source node or the first destination node of the first directed routing graph; and

wherein defining the communication schedule of the communication network is based on at least the first directed routing graph and the second directed routing graph.

6. The method of claim 1, wherein the communication network is a wireless network;

and wherein associating the each edge in the set of edges with the respective connection between the two of the plurality of network devices includes selecting a connection from a set of candidate connections based on a signal quality associated with the connection.

7. The method of claim 1, wherein the superframe is a first superframe, the superframe length is a first superframe length, the number of communication timeslots is a first number of communication timeslots, and wherein defining the communication schedule of the communication network further includes:

defining a second superframe with a second number of communication timeslots defining a second superframe length based on a predetermined periodic update rate at which a second one of the plurality of network devices generates fourth process data to be transmitted to the another one of the plurality of network devices or receives the fourth process data from the another one of the plurality of network devices;

wherein the second superframe length is not equal to the first superframe length.

8. The method of claim 1, wherein the superframe is a first superframe, the superframe length is a first superframe length, the number of communication timeslots is a first number of communication timeslots, and wherein the method further comprises defining a second superframe with a second number of communication timeslots defining a second superframe length;

wherein defining the communication schedule of the communication network further includes associating the second superframe with network management data.

9. The method of claim 1, wherein defining the communication schedule of the communication network includes defining a plurality of superframes, each of the plurality of superframes including a repeating sequence of cycles of a number of consecutively scheduled communication timeslots, wherein the number can be expressed as 2x such that x is an integer number.

10. The method of claim 1, wherein defining the communication schedule of the communication network further includes assigning a primary communication timeslot and a secondary communication timeslot to the each edge;

wherein a transmitting network device associated with a particular edge transmits data to a receiving network device associated with the particular edge during the primary communication timeslot to generate a transmission result; and

conditionally transmits data to the receiving network device during the secondary communication timeslot based on the transmission result.

11. The method of claim 1, further comprising:

allocating one of a plurality of channels to each edge to which a communication timeslot is allocated.

12. The method of claim 11, wherein each of the plurality of channels is a radio band associated with a respective central frequency.

13. The method of claim 1, further comprising:

distributing device specific schedule information to at least some of the plurality of network devices, including;

specifying, for each direct connection to a different network device of the plurality of network devices, a timeslot, one of a plurality of communication channels, and one of a transmit mode or a receive mode.

33. The method of claim 1, wherein:

one of the communication network or the another communication network is a wireless communication network, and the other one of the communication network or the another communication network is a wired communication network.

34. The method of claim 1, wherein a first protocol used in the communication network and a second protocol used in the another communication network are different protocols and are each based on a common, standard process control industry protocol.

35. The method of claim 34, wherein the common, standard process control industry protocol is the Highway Addressable Remote Transmitter (HART) Communication Foundation protocol.

39. The method of claim 1, wherein the set of requirements includes a latency requirement.

40. The method of claim 1, wherein the set of requirements includes a delay tolerance requirement.

41. The method of claim 1, further comprising dynamically and automatically performing superframe management based on a change in the communication network, performing the superframe management including at least one of:

destroying the superframe;

deactivating the superframe without destroying the superframe;

modifying the superframe;

creating a new superframe;

modifying the communication schedule;

or

modifying the first routing graph.

42. The method of claim 1,

wherein the source network device is a first source network device and the destination network device is a first destination network device;

and

wherein the set of requirements further corresponds to transmitting the second process data from a second source network device directly to a second destination network device, the second source network device and the second destination network device included in the plurality of network devices.

14. A method of increasing reliability of a wireless mesh network in a process control system including a plurality of nodes, wherein the method is executed in a computer that manages the wireless mesh network, the method comprising:

(i) establishing a plurality of direct connections, wherein each of the plurality of direct connections is a unidirectional wireless connection having a transmitting node and a receiving node;

(ii) generating a plurality of directed graphs defining communication paths between pairs of nodes based on a topology of the wireless network, wherein;

each directed graph includes at least two of the plurality direct connections,

each directed graph has exactly one source node, a destination node, and one or more intermediate nodes,

the source node of a particular directed graph is associated with only one or more outbound communication connections on the particular directed graph, and

the destination node of the particular directed graph is associated with only one or more inbound communication connections on the particular directed graph;

(iii) defining a multiplicity of concurrent superframes as repeating cycles of consecutively scheduled communication timeslots of a single predefined duration, wherein;

a first portion of the communication timeslots of a first superframe included in the multiplicity of concurrent superframes is used for delivery of a first set of data packets over a first directed graph included in the plurality of directed graphs,

a second portion of the communication timeslots of the first superframe included in the multiplicity of concurrent superframes is used for delivery of a second set of data packets over a second directed graph included in the plurality of directed graphs,

the first set of data packets and the second set of data packets include process control data generated by or provided to control a set of physical control functions performed by a set of field devices to control a process in the process control system,

a number of timeslots in each of the multiplicity of concurrent superframes defines a length of the superframe, and

defining the multiplicity of concurrent superframes includes assigning at least one of the consecutively scheduled communications timeslots based on a predetermined periodic update rate of at least one of the plurality nodes;

(iv) defining a plurality of primary links to generate a communication schedule of the wireless mesh network including, for each directed graph;

associating each primary link with one of the plurality of direct connections of the each directed graph, wherein the one of the plurality of direct connections is associated with a primary fixed communication path from the source node to the destination node, wherein at least one intermediate node of the each directed graph, in response to a failure to deliver a data packet along the primary link, transmits the data packet along a secondary link associated with another one of the plurality of direct connections, and

allocating a different individual timeslot associated with one of the plurality of superframes to each primary link of the each directed graph so that the allocated individual timeslots are scheduled in the order in which packets travel through the each directed graph,

wherein at least one of the generating the plurality of directed graphs or the defining the plurality of primary links to generate the communication schedule is based on a set of requirements corresponding to delivery of process control data from a particular source node to a particular destination node; and

(v) communicating, to each source node, each intermediate node, and each destination node, one or more portions of one or more respective directed graphs and one or more respective different individual timeslots corresponding to one or more respective primary links,

wherein a first node of the plurality of nodes included in the wireless mesh network transmits, in accordance with a respective one or more portions of the one or more respective directed graphs and the one or more respective different individual timeslots, respective process control data to a second node of the plurality of nodes and other process control data to a gateway in connection with another communication network operating in the process control system.

15. The method of claim 14, wherein generating the plurality of directed graphs includes:

designating a first one of the plurality of nodes as a head node of the wireless mesh network;

generating at least one inbound graph defining a flow of data in an inbound direction of the head node along a first subset of direct connections; and

generating at least one outbound graph defining a flow of data in an outbound direction away from the head node along a second subset of direct connections.

16. The method of claim 14, wherein:

the predetermined periodic update rate is a scan rate;

a first at least a portion of the plurality of nodes of the wireless mesh network are field devices each performing a respective control function in the process control system;

a second at least a portion of the plurality of nodes of the wireless mesh network are field devices each performing a respective measurement function in the process control system; and

nodes included in the first at least the portion of the plurality of nodes and nodes included in the second at least the portion of the plurality of nodes each publish report data at respective scan rates; and

wherein defining the multiplicity of concurrent superframes includes;

defining a first superframe according to a scan rate of a first field device having a first number of timeslots corresponding to a first length; and

defining a second superframe according to a scan rate of a second field device having a second number of timeslots corresponding to a second length;

wherein the first length is smaller than the second length.

17. The method of claim 16, including allocating timeslots within the first superframe prior to allocating time slots within the second superframe.

18. The method of claim 14, further comprising:

allocating a plurality of carrier radio frequencies for use by the wireless network, wherein each of the plurality of carrier radio frequencies is identified by a unique channel offset; and

wherein defining the plurality of primary links to generate the communication schedule further includes associating each link with one of the channel offsets.

19. The method of claim 14, further comprising:

defining a plurality of secondary links as part of generating the communication schedule, wherein at least one of the plurality of direct connections included in at least one of the plurality of directed graphs is associated with a primary link and a secondary link, and wherein distinct timeslots in a particular superframe are allocated to the primary link and the secondary link.

20. The method of claim 19, further comprising allocating consecutive timeslots to one of the primary links and to one of the secondary links.

21. The method of claim 19, wherein generating the plurality of directed graphs includes defining duplicate communication paths between pairs of nodes including a primary and secondary communication path, wherein the primary communication path and the secondary communication path differ in at least one direct connection.

22. The method of claim 14, wherein establishing the set of direct connections includes establishing unidirectional wireless connections between two nodes according to a strength of a radio signal detected by a first of the two nodes and transmitted by a second of the two nodes.

23. The method of claim 14, wherein each directed graph defines a fixed primary communication path to be taken by communication packets when traveling along the each directed graph from the source node to the destination node of the each directed graph.

24. The method of claim 14, wherein defining the communication schedule of the wireless mesh network includes assigning communication timeslots to each edge in the set of edges of the first directed graph so that the communication timeslots are associated with the set of edges according to a predetermined order of traversal of the first directed graph from the source node to the destination node.

36. The method of claim 14, wherein the process control system includes a plurality of field devices including at least one sensing device, at least one valve device, and at least one switch device;

and wherein each field device corresponds to a different node of the plurality of nodes.

43. The method of claim 14, wherein the set of requirements includes at least one of a latency requirement, a delay tolerance requirement, a transmission requirement, a signal strength requirement, a signal quality requirement, or a power availability requirement.

44. The method of claim 14, further comprising modifying at least one of the plurality of directed graphs or the plurality of primary links based on a changed network condition.

45. The method of claim 44, wherein the changed network condition includes at least one of a data burst, congestion, a block transfer, or a change in network topology.

25. A method of reliably transferring data in a wireless communication network operating in a process control environment and including a plurality of network devices, wherein the method is executed in a computer-based centralized network manager that manages the wireless communication network, the method comprising:

(i) generating a routing scheme of the wireless communication network, including defining a plurality of routing graphs based on a topology of the wireless communication network, each of the plurality of routing graphs having a plurality of nodes and a set of edges, each of the plurality of nodes corresponding to a respective one of the plurality of network devices;

(ii) defining a multiplicity of superframes each having a set of consecutively numbered communication timeslots of a predetermined duration based on predetermined regular communication requirements of at least some of the plurality of network devices, wherein a first portion of the communication timeslots of a first superframe included in the multiplicity of superframes is used for delivery of first process data using a first routing graph included in the plurality of routing graphs, and a second portion of the communication timeslots of the first superframe included in the multiplicity of superframes is used for delivery of second process data using a second routing graph included in the plurality of routing graphs, and wherein at least one of the first process data or the second process data is generated by or provided to control a physical control function performed by a field device to control a process in the process control environment; and

(iii) combining the routing scheme with the definition of the multiplicity of superframes to define a communication schedule of the wireless communication network, including, for at least the first superframe included in the multiplicity of superframes and a respective particular routing graph in the plurality of routing graphs;

assigning communication timeslots within the at least the first superframe to edges of the respective particular routing graph so that the communication timeslots are associated with the set of edges of the respective particular routing graph according to a predetermined order from the source node to the destination node of the respective particular routing graph, and

communicating, to each of the plurality of network devices corresponding to respective nodes included in the respective particular routing graph, one or more portions of the respective particular routing graph and one or more respective communication timeslots,

wherein;

at least a portion of at least one of the defining the plurality of routing graphs or the defining the multiplicity of superframes is based on one or more requirements corresponding to delivery of the first process data from a source node to a destination node by way of at least one intermediate node, the source node, the destination node and the at least one intermediate node included in the plurality of nodes, and

a first network device transmits, via the wireless communication network and according to a respective one or more portions of the respective particular routing graph and the one or more respective communication timeslots, respective process data to a second network device of the plurality of network devices to control the process and other process data to a gateway in connection with another communication network operating in the process control environment.

26. The method of claim 25, wherein defining the plurality of routing graphs includes:

defining a first unidirectional routing graph connecting a first source node to a first destination node; and

defining a second unidirectional routing graph connecting a second source node to a second destination node;

wherein the first source node and the second source node correspond to a same one of the plurality of network devices.

27. The method of claim 25, further comprising:

updating the definition of the at least the first superframe while the wireless communication network is active, including adjusting the length of the at least the first superframe; and

assigning communication timeslots within at least the first superframe to edges of the particular routing graph without updating the definition of the particular routing graph.

37. The method of claim 25, wherein the first network device transmits the respective process data to the second network device using a protocol based on the Highway Addressable Remote Transmitter (HART) Communication Foundation protocol.

46. The method of claim 25, further comprising modifying at least one of the multiplicity of superframes based on a detected change in the wireless communication network, the detected change included in a set of changes to the wireless communication network comprising a data burst, congestion, a block transfer, a particular network device entering or leaving the network, or a change in network topology.

47. The method of claim 25, wherein the one or more requirements include at least one of a latency requirement, a delay tolerance requirement, a transmission requirement, a signal strength requirement, a signal quality requirement, or a power availability requirement.

28. A method of reliably transferring data in a communication network operating in a process control environment, wherein the method is executed in a computer-based centralized network manager that manages the communication network, the method comprising:

(i) generating a first routing graph having a plurality of nodes and a set of edges based on a topology of the communication network, including;

associating each of the plurality of nodes with a respective one of a plurality of network devices participating in the communication network;

associating each edge in the set of edges with a respective connection between two of the plurality of network devices participating in the communication network;

associating a first one of the plurality of nodes with a source of the first routing graph; and

associating a second one of the plurality of nodes with a destination of the first routing graph, wherein the source of the first routing graph and the destination of the first routing graph are separated by at least one intermediate node; and

(ii) generating a communication schedule of the communication network, including;

(a) selecting a superframe of a particular length for transmitting data from the source of the first routing graph, wherein;

the superframe includes a number of consecutively scheduled communication timeslots defining the length of the superframe,

a first portion of timeslots in the superframe are used for delivery of first process control data using the first routing graph,

a second portion of communication timeslots in the superframe are used for delivery of second process control data using a second routing graph,

at least one of the first process control data or the second process control data is generated based on a physical control function performed by a field device to control a process in the process control environment, and

the length of the superframe is selected based on a criterion associated with one of the source or the destination of the first routing graph or one of the source of the destination of the second routing graph; and

(b) assigning at least some of the communication timeslots of the superframe to the set of edges of the first routing graph according to a predetermined order of traversal of the first routing graph from the source to the destination,

wherein at least one of the generating the first routing graph or the generating the communication schedule is based on a set of requirements corresponding to delivery of the first process control data from a source network device via one or more intermediate network devices to a destination network device, the source network device, the destination network device and the one or more intermediate network devices included in the plurality of network devices; and

(iii) communicating, to network devices corresponding to the plurality of nodes of the first routing graph, respective one or more portions of the first routing graph and one or more respective communication timeslots,

wherein a first network device transmits, via the communication network and according to a respective one or more portions of the first routing graph and the one or more respective communication timeslots, respective process control data to a second network device node for performing a control function in the process control environment and other respective process control data to a gateway in connection with another communication network operating in the process control environment.

29. The method of claim 28, wherein the criterion is a regularly scheduled transmission requirement of the one of the source or the destination of the first routing graph.

30. The method of claim 28, wherein selecting the superframe of the particular length includes selecting the superframe in view of the first routing graph so that each edge of the first routing graph can be accommodated within the superframe.

38. The method of claim 28, wherein:

the communication network is a first communication network; and

one of the first communication network or the other communication network is a wireless communication network and the other one of the first communication network or the other communication network is a wired communication network.

48. The method of claim 28, further comprising modifying the superframe based on a detected change in the communication network, the detected change included in a set of changes to the communication network comprising a data burst, a detected congestion, a block transfer, a particular network device entering or leaving the network, or a change in a topology of the communication network.

49. The method of claim 28, wherein the set of requirements includes at least one of a latency requirement, a delay tolerance requirement, a transmission requirement, a signal strength requirement, a signal quality requirement, or a power availability requirement.

31. A multi-node mesh communication network operating in a process control environment, comprising:

a plurality of field devices to perform respective control functions in the process control environment and to define respective nodes of the multi-node mesh communication network;

a network device operating in the multi-node mesh communication network to define a node of the multi-node mesh communication network;

first computer-executable instructions stored on a computer-readable memory and executable to generate and store a routing scheme of the multi-node mesh communication network and a communication schedule of the multi-node mesh communication network, at least one of the routing scheme or the communication schedule based on a set of requirements corresponding to delivery of process data from a source field device to a destination field device,

the routing scheme including a multiplicity of directed graphs, each of the multiplicity of directed graphs connecting a respective pair of nodes of the multi-node mesh communication network via one or more intermediate nodes, wherein each direct connection between two nodes associated with a particular directed graph define an edge of the graph; and

the communication schedule including a superframe including a number of consecutively scheduled communication timeslots defining a length of the superframe, a first portion of the communication timeslots of the superframe used for delivery of first process data using a first directed graph in the multiplicity of directed graphs, and a second portion of the communication timeslots of the superframe used for delivery of second process data using a second directed graph in the multiplicity of directed graphs, wherein the length of the superframe is based on a predetermined periodic update rate of one of the plurality of field devices, and wherein at least one of the first process data or the second process data is generated based on a physical control function performed by a field device to control a process in the process control environment; and

second computer-executable instructions stored on the computer-readable memory and executable to communicate, to the one of the plurality of field devices, respective portions of a particular directed graph with which the one of the plurality of field devices is associated and respective one or more corresponding communication timeslots of the superframe for the one of the plurality of field devices to use for transmitting respective process data to a gateway in connection with another communication network operating in the process control environment.

32. The multi-node mesh communication network of claim 31, wherein the network device is a gateway device that provides an external interface to the multi-node mesh communication network;

and wherein the multiplicity of directed graphs includes;

a first unidirectional graph connecting a first one of the plurality of field devices defining a source of the first unidirectional graph to the gateway device defining a destination of the first unidirectional graph; and

a second unidirectional graph connecting a second one of the plurality of field devices defining a source of the second unidirectional graph to the gateway device defining a destination of the second unidirectional graph.

50. The multi-node mesh communication network of claim 31, wherein the set of requirements includes at least one of a latency requirement, a delay tolerance requirement, a transmission requirement, a signal strength requirement, a signal quality requirement, or a power availability requirement.

51. The multi-node mesh communication network of claim 31, further comprising third computer-executable instructions stored on the computer-readable memory and executable to dynamically and automatically perform superframe management based on a change in the multi-node mesh communication network, wherein superframe management includes at least one of:

destroying the superframe;

deactivating the superframe without destroying the superframe;

modifying the superframe;

creating a new superframe;

or

modifying at least one of the multiplicity of directed graphs.