Scheduling communication frames in a wireless network

• US 8,356,431 B2
• Filed: 04/10/2008
• Issued: 01/22/2013
• 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., Zats, Yuri, Blevins, Terrence L.
• Primary Examiner(s): Rinehart, Mark
• Assistant Examiner(s): HOPKINS, MATTHEW A
• Application Number:
  US12/101,074
• Publication Number:
  US 20090046675A1
• Time in Patent Office: 1,748 Days
• Field of Search: 370/337
• US Class Current: 37/337
• CPC Class Codes: H04J 4/00 Combined time-division and frequency-division multiplex systems H04J13/00 takes precedence ; data transmission H04L5/26; telemetry G08C15/00
• CPC Class Codes: H04W 72/12 Wireless traffic scheduling
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A method of scheduling communications in a multi-node wireless mesh network which has a first network device and a second network device includes defining a communication timeslot of a predetermined duration, defining a first superframe having a repeating superframe cycle including a first number of the communication timeslots, defining a second superframe having a repeating superframe cycle including a second number of the communication timeslots, aligning the first superframe with the second superframe, so that one of the timeslots of the first superframe begins simultaneously with one of the timeslots of the second superframe, and associating the first and the second superframes with a network schedule, so that the first network device and the second network device transmit data according to the network schedule.

Claims

1. A method of scheduling communications in a multi-node wireless mesh network including a first network device and a second network device, the method comprising:

defining a communication timeslot of a predetermined duration;

defining, by a centralized network manager, a first superframe including a first number of the communication timeslots including respective transmit segments;

defining, by the centralized network manager, a second superframe including a second number of the communication timeslots including respective transmit segments;

aligning the first superframe with the second superframe, so that one of the timeslots of the first superframe begins simultaneously with one of the timeslots of the second superframe; and

associating, by the centralized network manager, the first and the second superframes with a network schedule for the multi-node wireless mesh network, the multi-node wireless mesh network operating in conjunction with a process plant,

wherein;

at least one of the first network device or the second network device performs a physical control function included in a control loop corresponding to a process being controlled by the process plant,

the first network device and the second network device each transmit data according to the network schedule, and

the data transmitted by the at least one of the first network device or the second network device is used to control the process.

2. The method of claim 1, wherein the first number of communication timeslots is not equal to the second number of communication timeslots.

3. The method of claim 2, wherein the first number corresponds to a transmission rate of the first network device and the second number of timeslots corresponds to a transmission rate of the second network device.

4. The method of claim 3, wherein the first superframe includes a repeating sequence of cycles, each cycle including the first number of consecutively scheduled communication slots, wherein the first network device transmits data in one of the timeslots of the first superframe during each cycle of the first superframe.

5. The method of claim 1, wherein the first network device receives data during at least one timeslot of the second superframe, and wherein the second network device transmits data during at least one timeslot of the second superframe.

6. The method of claim 1, wherein at least one timeslot of the first superframe is associated with a first radio frequency and at least one other timeslot of the first superframe is associated with a second radio frequency different from the first radio frequency.

7. The method of claim 1, wherein the first network device and the second network device each perform one of a control or a measurement function in the process control environment.

8. The method of claim 1, wherein the first superframe is associated with the first network device and the second superframe is associated with a second network device, the method further comprising:

defining a first individual device schedule for use by the first network device, wherein the first individual device schedule includes information related to the timeslots in the first superframe or the second superframe during which the first network device transmits or receives data;

defining a second individual device schedule for use by the second network device, wherein the second individual device schedule includes information related to the timeslots of the first superframe or the second superframe during which the second network device transmits or receives data; and

communicating the first individual device schedule to the first network device and second individual device schedule to the second network device.

9. A method of scheduling communications in a multi-node mesh network including a first network device and a second network device, the method comprising:

defining a communication timeslot of a predetermined duration;

defining, by a centralized network manager, a first superframe including a first number of the communication timeslots including respective transmit segments, wherein the first number corresponds to a transmission rate of the first network device;

defining, by the centralized network manager, a second superframe including a second number of the communication timeslots including respective transmit segments, wherein the second number of timeslots corresponds to a transmission rate of the second network device, and wherein the second number of communication timeslots is not equal to the first number of communication timeslots;

aligning the first superframe with the second superframe, so that one of the timeslots of the first superframe begins simultaneously with one of the timeslots of the second superframe; and

associating, by the centralized network manager, the first and the second superframes with a master network schedule for the multi-node mesh network, wherein;

the multi-node mesh network operates in conjunction with a process control environment,

at least one of the first network device or the second network device performs a physical control function corresponding to a process being controlled by the process control environment,

the first network device transmits data in at least one timeslot of the first superframe and during at least one timeslot of the second superframe according to the master network schedule, and

the data is used in a control scheme to control the process.

10. The method of claim 9, wherein the multi-node mesh network is a wireless process control network, wherein the communication timeslot is a Time Division Multiple Access (TDMA) timeslot, the method further comprising:

allocating a plurality of radio channels, wherein each radio channel is associated with a unique radio frequency;

associating one of the timeslots of the first superframe with a first of the plurality of radio channels; and

associating another one of the timeslots of the first superframe with a second of the plurality of radio channels.

11. The method of claim 9, wherein defining a communication timeslot of a predetermined duration includes:

allocating a first segment of the timeslot for assessing availability of the communication timeslot;

allocating a second segment of the communication timeslot for a transmitting a data packet; and

allocating a third segment of the communication timeslot for transmitting an acknowledgement associated with the data packet;

wherein none of the first, second, or third segment overlaps another one of the first, second, or third segment.

12. The method of claim 11, wherein defining a communication timeslot of a predetermined duration further includes:

defining a dedicated communication timeslot, wherein no more than one source network device transmits data during the dedicated communication timeslot; and

defining a shared communication timeslot, wherein a plurality of source network devices transmit data during the shared communication timeslot;

wherein each of the first and second superframes includes at least one shared communication timeslot and at least one dedicated communication timeslot.

13. The method of claim 9, further comprising:

receiving a bandwidth increase request from the first network device, wherein the first network device sends a bandwidth increase request in response to detecting a temporary increase in the transmission rate of the first network device;

defining a third superframe in response to receiving the bandwidth increase request from the first network device, wherein the third superframe is associated with the temporary increase in the transmission rate of the first network device;

temporarily adding the third superframe to the master network schedule without restarting the multi-node mesh network, wherein the first network device transmits data during at least one timeslot of the third superframe according to the master network schedule.

14. The method of claim 13, further comprising:

deactivating the third superframe in response to detecting a deactivation command from the first network device, whereby each network device participating in the third superframe stops transmitting or receiving data in each of the timeslots of the third superframe.

15. The method of claim 13, further comprising:

deleting the third superframe from the master network schedule in response to detecting a delete command from the first network device.

16. The method of claim 9, further comprising:

defining a management superframe for transmitting management information related to the multi-node mesh network, wherein the management information is transmitted to the first and the second network devices during only one of the timeslots of the management superframe, and wherein the management information is transmitted from a network manager device servicing the multi-node mesh network.

17. The method of claim 9, wherein the second network device is a transient device having a low update rate relative to other network devices, wherein the second network device does not route data traveling to or from other network devices, the method further comprising:

maintaining the second network device in a sleep mode during most of a period in which the second network device is not communicating in the second superframe; and

restoring communication between the second network device and the multi-node mesh network without transmitting additional commands by waking up the second network device prior to an occurrence of a timeslot of the second superframe during which the second network device is scheduled to communicate.

18. The method of claim 9, wherein maintaining the second network device in a sleep mode includes not receiving keep-alive messages during the period in which the second network device is not communicating in the second superframe.

19. The method of claim 9, further comprising:

defining a first individual device schedule for use by the first network device, wherein the first individual device schedule includes only information related to the timeslots of the first superframe or the second superframe during which the first network device transmits or receives data;

defining a second individual device schedule for use by the second network device, wherein the second individual device schedule includes only information related to the timeslots of the first superframe or the second superframe during which the second network device transmits or receives data; and

communicating the first individual device schedule to the first network device and second individual device schedule to the second network device.

20. The method of claim 9, further comprising allocating a plurality of radio channels, wherein each radio channel is associated with a unique radio frequency;

associating a first timeslot of the first superframe with at least two of the plurality of radio channels, wherein the first timeslot of the first superframe occurs on a first of the at least two of the plurality of radio channels during a first frame cycle of the first superframe and wherein the first timeslot of the first superframe occurs on a second of the at least two of the plurality of radio channels during a second frame cycle of the first superframe.

21. A multi-node mesh wireless network including a plurality of network devices and operating in a process control environment, the network comprising:

a first network device;

a second network device corresponding to a physical control function included in a control loop corresponding to a process being controlled by the process control environment;

a plurality of wireless connections between pairs of the plurality of network devices, including a first wireless connection between the first network device and the second network device; and

a network manager storing a network schedule for use by the first network device and the second network device, the network schedule including;

a first superframe including a first number of timeslots of a predefined duration including respective transmit segments, the first number of timeslots cyclically repeating to define a first plurality of frame cycles; and

a second superframe including a second number of timeslots of a predefined duration including respective transmit segments, the second number of timeslots cyclically repeating to define a second plurality of frame cycles,

wherein the first network device and the second network device are each assigned at least one respective timeslot in which to transmit respective data used to control the process.

22. The network of claim 21, wherein the first network device is associated with a first update rate and the second network device is associated with a second update rate and wherein the first number of timeslots corresponds to the first update rate and the second number of timeslots corresponds to the second update rate;

and wherein the first network device transmits data during at least one timeslot in each of the first plurality of frame cycles and the second network device transmits data during at least one timeslot in each of the second plurality of frame cycles.

23. The network of claim 21, wherein the first network device includes a first memory unit that stores a first fragment of the network schedule and the second network device includes a second memory unit that stores a second fragment of the network schedule different from the first fragment of the network schedule.

24. The network of claim 21, further including a plurality of wireless channels;

wherein at least one timeslot in the first superframe is associated with a first one of the plurality of wireless channels and at least another one timeslot in the first superframe is associated with a second plurality of wireless channels.

25. A multi-node mesh wireless network adapted to dynamically schedule communications between a plurality of network devices, the network comprising:

a first network device corresponding to a physical control function corresponding to a process being controlled by a process control environment, and the first network device associated with a first update rate corresponding to a frequency of transmitting, from the first network device, process data used in a control scheme for the process;

a second network device associated with a second update rate corresponding to a frequency of transmitting data from the second network device;

a plurality of wireless connections between pairs of the plurality of network devices, including a wireless connection between the first network device and the second network device; and

a network manager responsible for defining and scheduling communication resources in the multi-node mesh network, the communication resources including;

a plurality of communication channels;

a first superframe including a first number of timeslots of a fixed predefined duration including respective transmit segments, wherein the first number of timeslots corresponds to the first update rate; and

a second superframe including a second number of timeslots of a fixed predefined duration including respective transmit segments, wherein the second number of timeslots corresponds to the second update rate;

wherein the network manager associates at least one of the first number of timeslots with a first one of the plurality of communication channels and at least another one of the first number of timeslots with a second one of the plurality of communication channels.

26. A computing device in communicative connection with a wireless mesh network including a plurality of network devices, the computing device embodied with a network manager software routine comprising computer-executable instructions including:

a first procedure to define a plurality of concurrent overlapping superframes, wherein each of the superframes includes repeating superframe cycles defined by a fixed number of communication timeslots of a fixed time duration and including respective transmit segments, and wherein the superframe cycle for at least one of the plurality of concurrent overlapping superframes includes a different number of communication timeslots than the superframe cycle for another one of the concurrent overlapping superframes, and wherein each of the plurality of concurrent overlapping superframes is associated with one or more of the plurality of network devices;

a second procedure to define a management superframe for shared use by the plurality of network devices; and

a third procedure to define a plurality of device specific schedules, wherein;

each of the plurality of device specific schedules is associated with one of the plurality of network devices,

each of the plurality of device specific schedules specifies at least one timeslot during which the network device is allowed to transmit data and at least one timeslot during which the network device is allowed to receive data,

none of the network devices transmits or receives data in a communication timeslot not included in the device specific schedule of the network device,

at least one of the plurality of network devices performs a physical control function included in a control loop corresponding to a process being controlled within a process control network, and

the data transmitted by the at least one of the plurality of network devices is used to control the process.

27. A method of scheduling communications in a multi-node mesh network including a first network device and a second network device, the method comprising:

defining a communication timeslot of a predetermined duration;

defining, by a centralized network manager, a first superframe having a first repeating superframe cycle including a first number of the communication timeslots including respective transmit segments, wherein the first number corresponds to a transmission rate of the first network device and wherein the first network device transmits first process data associated with the first network device during at least one of the communication timeslots of the first superframe, the first process data used to control a process being controlled by a process control environment corresponding to the multi-node mesh network;

defining, by the centralized network manager, a second superframe having a second repeating superframe cycle including a second number of the communication timeslots including respective transmit segments, wherein the second number of timeslots corresponds to a transmission rate of the second network device, wherein the second network device transmits second process data associated with the second network device during at least one of the communication timeslots of the second superframe, the second process data used to control the process, and wherein the first network device does not transmit the first process data associated with the first network device using any of the timeslots of the second superframe;

defining, by the centralized network manager, a management superframe including a third number of the communication timeslots, wherein none of the first network device or the second network device transmits, respectively, the first process data or the second process data using any of the communication timeslots of the management superframe and wherein at least one of the communication timeslots of the management superframe is reserved for network management data; and

aligning the first superframe, the second superframe, and the management superframe so that one of the timeslots of the first superframe begins simultaneously with one of the timeslots of the second superframe and with one of the timeslots of the management superframe,

wherein at least one of the first network device or the second network device corresponds to a physical control function corresponding to the process.