Suspending transmissions in a wireless network

• US 8,169,974 B2
• Filed: 04/10/2008
• Issued: 05/01/2012
• 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.
• Primary Examiner(s): Mills, Donald
• Assistant Examiner(s): CHOUDHRY, SAMINA F
• Application Number:
  US12/101,011
• Publication Number:
  US 20080273518A1
• Time in Patent Office: 1,482 Days
• Field of Search: None
• US Class Current: 370/332
• 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 method of increasing operational safety of a wireless communication network operating in a process control environment and having a plurality of network devices includes detecting a first triggering condition associated with an increased operational risk due to a wireless transmissions by at least one of the plurality of network devices, sending a suspend command to at least some of the plurality of network devices, suspending transmissions at the at least some of the plurality of network devices; and resuming transmissions at the at least some of the plurality of network devices upon occurrence of a second triggering condition.

Claims

1. A method of increasing operational safety of a wireless communication network operating in a process control environment and having a plurality of network devices, comprising:

maintaining an absolute slot number counter indicative of a number of communication timeslots of a predetermined duration scheduled since a formation of the wireless communication network;

wherein each of the plurality of network devices communicates with at least one other of the plurality of network devices according to a communication schedule having a plurality of concurrent superframes, each defined as a repeating sequence of timeslots;

detecting a first triggering condition associated with an increased operational risk due to a wireless transmissions by at least one of the plurality of network devices;

sending a suspend command to at least some of the plurality of network devices;

specifying, in the suspend command, a suspend time at which a recipient network device must suspend transmissions, including specifying an absolute slot number;

suspending transmissions at the at least some of the plurality of network devices; and

resuming transmissions at the at least some of the plurality of network devices upon occurrence of a second triggering condition.

2. The method of claim 1, wherein sending a suspend command includes

specifying, in the suspend command, a resume time at which the recipient network device is allowed to resume transmissions.

3. The method of claim 2,

wherein the absolute slot number is a first absolute slot number, and wherein the method further comprises

specifying the resume time include specifying a second absolute slot number.

4. The method of claim 1, wherein sending a suspend command includes

specifying, in the suspend command, a quiet time interval during which the recipient network device is not allowed to resume transmissions.

5. The method of claim 1, further comprising pre-configuring each of the plurality of network devices with a quiet time interval during which the network device is not allowed to resume communications following a reception of the suspend command.

6. The method of claim 1, wherein sending a suspend command includes broadcasting the suspend command to each of the plurality of network devices from a gateway device connecting the wireless communication network to an external network.

7. The method of claim 6, wherein broadcasting the suspend command from the gateway device includes receiving a suspension request from an external host operating outside the wireless communication network and communicatively coupled to the gateway.

8. The method of claim 6, wherein broadcasting the suspend command from the gateway device includes receiving a suspension request from a handheld device operating in the wireless communication network as one of the plurality of network devices.

9. The method of claim 1, further comprising:

starting a timer at each of the at least of the plurality of network devices to which the suspend command is sent; and

wherein

the second triggering condition is an expiration of the timer.

10. The method of claim 1, further comprising:

sending a resume command to the at least some of the plurality of network devices to which the suspend command is sent after a suspension period;

wherein

the second triggering condition is a reception of the resume command at the at least some of the plurality of network devices.

11. A method of temporarily suspending communications in a wireless communication network operating in a process control environment and having a plurality of network devices, comprising:

maintaining an absolute slot number counter indicative of a number of communication timeslots of a predetermined duration scheduled since a formation of the wireless communication network;

specifying, in a suspend command, a suspend time at which a recipient network device must suspend transmissions, including specifying an absolute slot number;

sending the suspend command to each of the plurality of network devices;

suspending transmissions at the each of the plurality of network devices;

starting a quiet time timer at the each of the plurality of network devices; and

resuming transmissions at the each of the plurality of network devices upon expiration of the quiet time timer.

12. The method of claim 11, wherein sending a suspend command to each of the plurality of network devices includes sending a suspend command in response to detecting a condition associated with an elevated safety risk due to transmissions by one or more of the plurality of network devices.

13. The method of claim 11, wherein sending a suspend command to each of the plurality of network devices includes sending at least one of a transmission stop time, a transmission resume time, and a quiet time interval;

wherein the quiet time interval defines a duration of the quiet time timer.

14. The method of claim 11, further comprising:

defining a network communication schedule of the wireless communication network as a plurality of concurrent overlapping superframes, wherein each of the plurality of concurrent overlapping superframes is a repeating sequence of cycles, each cycle having a number of communication timeslots defining a length of the superframe, each timeslot win each cycle sequentially numbered to have relative slot numbers in a range from zero to the certain number minus one; and

associating wireless communications at each of the plurality of network devices with at least one communication timeslot in at least one of the plurality of concurrent overlapping superframes;

wherein

resuming transmissions at each of the plurality of network devices includes synchronizing each of the plurality of network devices with the network communication schedule, including calculating a relative slot number within a corresponding one of the plurality of concurrent overlapping superframe based on the absolute slot number.

15. The method of claim 14, wherein synchronizing each of the plurality of network devices with the network communication schedule includes performing a modulo division of a value of the absolute slot number counter into the length of one of the plurality of concurrent overlapping superframes to obtain a current relative slot number within the one of the plurality of concurrent overlapping superframes.

16. The method of claim 14, wherein suspending transmissions at each of the plurality of network devices includes maintaining the absolute slot number counter at each of the plurality of network devices while the quiet time timer is running.

17. The method of claim 11, wherein starting a quiet time timer at each of the plurality of network devices includes setting a duration of the quiet time timer to a preconfigured value stored at each of the plurality of network devices.

18. A method of temporarily suspending wireless communications in communication network operating in a process control environment and having a plurality of network devices, comprising:

maintaining an absolute slot number counter at each of the plurality of network devices, wherein the absolute slot number counter is indicative of a number of communication timeslots scheduled since the wireless mesh network was formed;

defining a communication schedule having a plurality of links, each link specifying a communication timeslot of a predetermined duration, at least one sender, and at least one receiver, wherein the at least one sender and the at least one receiver are included in the plurality of network devices and wherein each of plurality of network devices communicates according to the communication schedule;

detecting a condition associated with a increase in operational risk of the process control network; and

suspending wireless communications in the wireless mesh network, including transmitting a first broadcast message to each of the plurality of network devices requesting each device to temporarily suspend wireless communications, the first broadcast message including a suspend time corresponding to an absolute slot number at which to temporarily suspend wireless communications.

19. The method of claim 18, wherein defining a communication schedule includes allocating timeslots to each of the field devices according to rates at which the field devices transmit process control or measurement data.

20. The method of claim 18, wherein detecting a condition associated with a increase in operational risk of the process control network includes detecting a condition associated with an elevated risk of explosion in an environment in which the process control network is operating.

21. The method of claim 18, wherein suspending wireless communications includes specifying to each network device a amount of time during which the wireless communications are to be suspended, and wherein each of the plurality of network devices is allowed to resume wireless communications after the specified amount of time.

22. The method of claim 18, further comprising resuming wireless communications in the wireless mesh network, including broadcasting a second message to each of the plurality of network devices requesting each device to resume wireless communications.