Increasing Reliability and Reducing Latency in a Wireless Network

• US 20080279204A1
• Filed: 04/10/2008
• Published: 11/13/2008
• Est. Priority Date: 04/13/2007
• Status: Active Grant

• Current Assignee: FieldComm Group, Inc.
• Original Assignee: Hart Communication Foundation (FieldComm Group, Inc.)
• Inventors: Blevins, Terrence L., Nixon, Mark J., Rotvold, Eric D., Pratt, Wallace A. JR., Pramanik, Robin S., Lennvall, Tomas P.
• Granted Patent: US 8,798,084 B2
• Time in Patent Office: Days
• 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 operating in a process control environment, the method comprising:

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; and

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; and

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

assigning communication timeslots to each edge in the set of edges of the first graph according to a predetermined order.

2. The method of claim 1, wherein generating a first routing graph includes generating a directed graph having a source node and a destination node so that data travels in only one direction from the source node toward the destination node using the directed graph.

3. The method of claim 2, wherein associating communication timeslots with each edge within the set of edges of the first graph according to a predetermined order includes allocating the communication timeslots in an order of traversal of the first graph from the source node toward the destination node.

4. The method of claim 2, wherein generating a 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 source node and the destination node.

5. The method of claim 2, further comprising generating a second directed routing graph having a plurality of nodes and a set of edges based on the topology of the communication network;

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

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

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

and wherein associating each edge in the set of edges with a respective connection between 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 defining a communication schedule of the communication network further includes:

using communication timeslots of a single predefined duration; and

defining a first superframe based on a transmission requirement of at least one of the nodes included in the first graph;

wherein the first superframe includes a repeating sequence of cycles, each cycle including a first number of consecutively scheduled communication timeslots defining a length of the first superframe;

wherein each communication timeslot assigned to an edge in the set of edges is associated with the first superframe.

8. The method of claim 7, wherein defining a communication schedule of the communication network further includes:

defining a second superframe including a repeating sequence of cycles, each cycle including a second number of consecutively scheduled communication timeslots defining a length of the second superframe;

wherein the second number is not equal to the first number.

9. The method of claim 8, wherein defining the second superframe is based on a transmission requirement of at least another one of the nodes included in the first graph;

wherein the method further comprises;

generating a second routing graph based on the topology of the communication network, the second routing graph having a different plurality of nodes than the first routing graph;

wherein defining a communication schedule includes assigning communication timeslots associated with the first superframe prior to assigning communication timeslots associated with the second superframe if the length of the first superframe is smaller than the length of the second superframe.

10. The method of claim 7, wherein defining a communication schedule of the communication network further includes associating the second superframe with network management data.

11. The method of claim 1, wherein defining a 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 2^x such that x is an integer number.

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

13. A method of generating a communication schedule for a mesh communication network having a plurality of nodes and operating in a process control environment, the method comprising:

defining communication timeslots of a fixed duration;

defining a first superframe as a repeating sequence of cycles, each cycle including a first number of consecutively scheduled communication timeslots defining a length of the first superframe; and

allocating the timeslots associated with the first superframe to direct connections between pairs of nodes of the communication network, wherein each connection to which a timeslot is allocated is associated with one of a set of routing graphs specifying one or more routing paths in the communication network.

14. The method of claim 13, further comprising:

allocating one of a plurality of channels to each direct connection to which a timeslot is allocated.

15. The method of claim 14, wherein each of the plurality of channels is a radio band associated with a respective central frequency.

16. The method of claim 13, wherein each graph in the set of routing graphs is a directed graph defining a unidirectional flow of data from a source node to a destination node.

17. The method of claim 16, wherein one of the source node or the destination node of each directed graph is a field device performing a process control function in the process control environment, and the other one of the source node or the destination node is a gateway device connecting the mesh communication network to an outside network.

18. The method of claim 17, wherein defining a first superframe includes selecting the length of the first superframe according to a rate of transmitting process control data between the field device and the gateway device.

19. The method of claim 13, further comprising:

defining a second superframe as a repeating sequence of cycles, each cycle including a second number of consecutively scheduled communication timeslots defining a length of the second superframe;

wherein the second superframe is associated with network management data of the communication network; and

wherein each of the plurality of nodes transmits and receives data in at least one timeslot of the second superframe.

20. The method of claim 19, wherein the communication network is a wireless network;

and wherein at least some of the timeslots of the second superframe are associated with a respective multicast session on one of a plurality of wireless channels.

21. The method of claim 19, wherein the communication network is a wireless network;

and wherein at least one of the timeslots of the second superframe is associated with a single receiving one of the plurality of nodes and one or more of potential nodes not participating in the communication network.

22. The method of claim 13, further comprising:

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

specifying, for each direct connection to another of the plurality of nodes, a timeslot, one of a plurality of communication channels, and one of a transmit or receive modes.

23. A method of increasing reliability of a wireless mesh network including a plurality of nodes, the method comprising:

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;

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 one of the plurality direct connections;

defining a plurality of concurrent superframes as repeating cycles of consecutively scheduled communication timeslots a single predefined duration, wherein a number of timeslots in each of the plurality of concurrent superframes defines a length of the superframe; and

defining a plurality of primary links to generate a communication schedule of the wireless mesh network, including;

associating each primary link with one of the plurality of direct connections associated with at least one of the plurality of directed graphs; and

allocating an individual timeslot associated with one of the plurality of superframes to each primary link.

24. The method of claim 23, wherein generating a 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.

25. The method of claim 23, wherein at least some of the plurality of nodes of the wireless mesh network are field devices performing a control function or a measurement function in a process control system and publishing report data at a particular scan rate, and wherein defining a plurality 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;

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.

26. The method of claim 25, wherein allocating a timeslot in one of the plurality of superframes to each primary link includes allocating a first timeslot to a first primary link for transmission of report data from the first field device prior to allocating a second timeslot to a second primary link for transmission of report data from the second field device, wherein the first primary link is associated with a direct connection originating from the first field device and the second primary link is associated with a direct connection originating from the second field device.

27. The method of claim 23, 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 a plurality of primary links to generate a communication schedule further includes associating each link with one of the channel offsets.

28. The method of claim 23, 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 are allocated to the primary link and the secondary link.

29. The method of claim 28, wherein consecutive timeslots are allocated to the primary links and the secondary links.

30. The method of claim 28, wherein generating a set 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 secondary communication path differ in at least one direct connection.

31. The method of claim 23, wherein establishing a 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.