Adaptive Scheduling in a Wireless Network

• US 20080279155A1
• 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 8,325,627 B2
• Time in Patent Office: Days
• US Class Current: 370/336
• CPC Class Codes: H04L 12/66 Arrangements for connecting between networks having differing types of switching systems, e.g. gateways
• CPC Class Codes: H04W 40/20 based on geographic position or location
• CPC Class Codes: H04W 72/0446 Resources in time domain, e.g. slots or frames
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method of adaptively scheduling communications in a wireless mesh network including a plurality of network nodes includes generating a network routing scheme based on a topology of the wireless mesh network, generating a communication schedule for the wireless mesh network, and automatically updating the communication schedule in response to detecting a change in a transmission requirement of at least one of the plurality of network nodes. The act of generating a communication schedule includes defining a communication timeslot of a predefined duration and defining a plurality of superframes as repeating cycles of a certain number of consecutively scheduled communication timeslots.

Claims

1. A method of adaptively scheduling communications in a wireless mesh network including a plurality of network nodes, the method comprising:

generating a network routing scheme based on a topology of the wireless mesh network;

generating a communication schedule for the wireless mesh network, including;

defining a communication timeslot of a predefined duration; and

defining a plurality of superframes as repeating cycles of a certain number of consecutively scheduled communication timeslots;

automatically updating the communication schedule in response to detecting a change in a transmission requirement of at least one of the plurality of network nodes.

2. The method of claim 1, wherein detecting a change in a transmission requirement of at least one of the plurality of network nodes includes detecting at least one of addition of a new network node to the plurality of network nodes or a removal of one of the plurality of network nodes from the wireless mesh network.

3. The method of claim 1, wherein generating a network routing scheme based on a topology of the wireless mesh network includes:

defining a plurality of direct wireless connections between pairs of the plurality of network nodes based on at least one of a strength, a minimum number of hops between a source network node and a destination network node, or a quality of a respective wireless signal; and

creating a plurality of directed graphs, each graph connecting a source node and destination node and including one or more of the plurality of direct wireless connections.

4. The method of claim 3, wherein at least some of the plurality of network nodes are wireless field devices operating in a process control environment;

and wherein creating a plurality of directed graphs includes associating one of the source node or the destination node of each of the plurality of directed graphs with a gateway connecting the wireless mesh network to a plant automation network.

5. The method of claim 3, wherein creating a plurality of directed graphs includes, for each of the plurality of directed graphs, creating a redundant graph between the source node and the destination node having at least one direct wireless connection distinct from each of the direct wireless connections associated with the directed graph;

and wherein detecting a change in a transmission requirement of at least one of the plurality of network nodes includes;

detecting a failure to communicate with the one of the plurality of network nodes associated with a directed graph; and

routing a message indicative of the failure using a redundant graph corresponding to the directed graph.

6. The method of claim 1, wherein automatically updating the communication schedule includes:

periodically exchanging keep-alive messages between pairs of the plurality of network nodes sharing a direct wireless connection;

propagating a path down indication indicative of a failure of a certain direct wireless connection to a network manager responsible for updating the network routing scheme and the communication schedule in the wireless mesh network; and

removing the certain direct wireless connection from the network routing scheme.

7. The method of claim 1, wherein defining a plurality of superframes includes defining lengths of at least some of the plurality of superframes based on update rates of at least some of the network nodes.

8. The method of claim 7, wherein automatically updating the communication schedule includes:

detecting a temporary increase in a bandwidth requirement at one of the plurality of network nodes; and

creating a superframe for transferring traffic associated with the temporary increase in the bandwidth requirement.

9. A method of adaptively scheduling communications in a wireless mesh network including a plurality of network nodes, wherein at least some of the plurality of nodes are field devices operating in a process control environment;

the method comprising;

generating a communication schedule for the wireless mesh network, including;

defining a communication timeslot of a predefined duration;

defining a plurality of superframes as repeating cycles of a certain number of consecutively scheduled communication timeslots; and

associating each of the field devices with at least one of the plurality of superframes, including selecting the at least one of the plurality of superframes based on rate of scheduled publishing of process data at the field device;

automatically updating the communication schedule in response to detecting a change in performance of the wireless mesh network without restarting the wireless mesh network.

10. The method of claim 9, further comprising monitoring the performance of the wireless mesh network by collecting statistical data related to a transfer of data packets between pairs of network nodes along one or more direct wireless connections, each connecting two of the plurality of network nodes.

11. The method of claim 10, wherein collecting statistical data includes at least one of counting a number of packets successfully delivered between at least one pair of the plurality of network nodes, counting a number of packets received at each of the plurality of network nodes, counting a number of packets transmitted at each of the plurality of network nodes, and calculating a delay associated with a delivery of a data packet between at least one pair of the plurality of network nodes.

12. The method of claim 10, wherein the method further comprises creating a routing scheme for the wireless mesh network, including:

defining a plurality of directed graphs between the field devices and a gateway device connecting the wireless mesh network to an external network; and

wherein collecting statistical data related to a transfer of data packets between pairs of network nodes includes separately maintaining separate statistics for each of the plurality of directed graphs.

13. The method of claim 10, wherein detecting a change in performance of the wireless network includes:

collecting health reports from at least some of the plurality of network nodes, wherein each health report from a network node includes data related to direct wireless connections between the network node and other ones of the plurality of network nodes; and

determining a change in the direct wireless connections available at the network node relative to a previous health report.

14. The method of claim 9, wherein the method further comprises creating a routing scheme for the wireless mesh network, including:

defining a plurality of directed graphs between the field devices and a plurality of network access points associated with a gateway device connecting the wireless mesh network to an external network;

wherein each of the plurality of directed graphs is associated with at least one respective communication timeslot in at least one respective superframe included in the plurality of superframes, and wherein each of the plurality of directed graphs independently supports a communication path to the gateway device.

15. The method of claim 9, wherein detecting a change in performance of the wireless mesh network includes receiving a message from one of the plurality of network nodes requesting a change in bandwidth allocation.

16. A method of optimizing a transfer of data in a wireless communication network operating in a process control environment and including a plurality of wireless network devices, the method comprising:

generating a routing scheme including a plurality of directed routing graphs, each graph connecting two of the plurality of wireless network devices and having a source node and a destination node, including;

defining a plurality of direct wireless connections between pairs of the plurality of network devices; and

associating each of the plurality of directed routing graphs with one or more direct wireless connections;

generating a communication schedule for the wireless mesh network, including;

defining a communication timeslot of a predefined duration;

defining a plurality of superframes as repeating cycles of a certain number of consecutively scheduled communication timeslots; and

associating each of the field devices with at least one of the plurality of superframe, including selecting the at least one of the plurality of superframes based on rate of scheduled publishing of process data at the field device; and

optimizing the routing scheme and the communication schedule during an operation of the wireless network by monitoring at least a health of each of the plurality of direct wireless connections.

17. The method of claim 16, wherein monitoring the health of each of the plurality of direct wireless connections includes:

receiving a health report from at least one of two network devices associated with the direct wireless connection; and

undefining the direct wireless connection if the health report indicates a low signal level.

18. The method of claim 16, wherein optimizing the routing scheme and the communication schedule during an operation of the wireless network includes routing less data through battery-powered network devices than through network devices having access to a constant power source.

19. The method of claim 16, further comprising allocating additional bandwidth in response to receiving a request from one of the plurality of network devices.

20. The method of claim 16, further comprising allocating additional bandwidth in response to receiving a request from a gateway connecting the wireless communication network to a plant automation network;

wherein the gateway requests additional bandwidth to set up a data pipe between an external application and one of the plurality of network devices.

21. The method of claim 20, wherein allocating additional bandwidth includes creating a temporary superframe for use by the one of the plurality of network devices, wherein the temporary superframe has a shorter length than a superframe corresponding to the rate of scheduled publishing of process data at the one of the plurality of network devices.