Wireless communication system and related methods

• US 20060239333A1
• Filed: 04/21/2006
• Published: 10/26/2006
• Est. Priority Date: 04/22/2005
• Status: Active Grant

• Current Assignee: Zenner Performance Meters, Inc. (Zenner International GmbH & Co. KG)
• Original Assignee: Axiometric, LLC
• Inventors: Albert, David, Martinez, John, Cornelius, Steve
• Granted Patent: US 8,126,488 B2
• Time in Patent Office: Days
• US Class Current: 375/130
• CPC Class Codes: H04W 56/002 Mutual synchronization
• CPC Class Codes: H04W 72/20 Control channels or signalling for resource management
• CPC Class Codes: H04W 8/005 Discovery of network devices, e.g. terminals
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A method of operating a wireless mesh network comprises generating a pseudorandom sequence element in a transmitting device and a receiving device of the network using information shared by the transmitting and receiving devices. The pseudorandom sequence element is then used to calculate a communication channel/timeslot assignment for communication between the transmitting wireless device and the receiving wireless device.

Claims

1. A method of coordinating communication between a plurality of wireless devices, the method comprising:

generating a pseudorandom sequence element in a transmitting wireless device by operation of a first pseudorandom sequence generator (PSG) located in the transmitting wireless device;

generating a pseudorandom sequence element in a receiving wireless device by operation of a second PSG located in the receiving wireless device;

calculating a communication channel/timeslot assignment for communication between the transmitting wireless device and the receiving wireless device based on the pseudorandom sequence element;

transmitting data from the transmitting wireless device to the receiving wireless device according to the communication channel/timeslot assignment;

wherein the first and second pseudorandom sequence generators are seeded with information that is shared by the plurality of wireless devices.

2. The method of claim 1, wherein the information that is shared by the plurality of wireless devices comprises:

a combination of a reference clock time and a plurality of unique device identifiers.

3. The method of claim 2, wherein the reference clock time is derived from a common global reference clock time that is shared by the plurality of wireless devices.

4. The method of claim 3, wherein each of the plurality of wireless devices contains a local clock adapted to maintain the reference clock time;

wherein maintaining the reference clock time comprises;

receiving a transmission encoding a global reference clock time and a new timing age indicating an amount of elapsed time since the global reference clock time was transmitted from a global reference clock time source;

determining whether the new timing age is less than a current timing age associated with the local clock;

upon determining that the new timing age is less than the current timing age, updating the local clock with the global reference clock time and updating the current timing age with the new timing age; and

,

incrementing the local clock and the current timing age at regular time intervals.

5. The method of claim 4, wherein maintaining the reference clock time further comprises:

incrementing the timing age each time the local clock is updated with the global reference clock time.

6. The method of claim 4, further comprising:

expanding a timeslot window for transmitting or receiving data in at least one of the plurality of wireless devices to compensate for drift of the local clock.

7. The method of claim 6, wherein expanding the timeslot window comprises:

determining a rate of the local clock drift;

measuring an elapsed time since a last update of the timeslot window; and

,

expanding the size of the timeslot window by an amount proportional to the elapsed time multiplied by the rate of the local clock drift.

8. The method of claim 6, further comprising:

by operation of the transmitting wireless device, determining a timing age associated with an adjacent wireless device; and

,

transmitting data from the transmitting wireless device to the adjacent wireless device based on whether the current timing age is greater than or less than the respective timing ages of other adjacent wireless devices.

9. The method of claim 6, further comprising:

by operation of the receiving wireless device, determining a timing age associated with an adjacent wireless device; and

,

processing data from the adjacent wireless device based on whether the current timing age is greater than or less than the respective timing ages of other adjacent wireless devices.

10. The method of claim 1, wherein the first and second PSGs each comprise a maximal-length pseudorandom sequence generator.

11. The method of claim 4, further comprising:

disregarding the received time if the timing age exceeds a predetermined threshold value.

12. The method of claim 1, wherein transmitting data from the transmitting wireless device to the receiving wireless device according to the communication channel/timeslot assignment comprises:

tuning a transmitter of the transmitting wireless device and a receiver of the receiving wireless device to a communication channel specified by the communication channel/timeslot assignment; and

,

transmitting the data from the transmitting wireless device to the receiving wireless device during a timeslot specified by the channel/timeslot assignment.

13. The method of claim 1, wherein where the receiving wireless device has more than one adjacent wireless device transmitting data during a timeslot in which the receiving wireless device is receiving data, the receiving wireless device decides to receive data transmitted by the transmitting device using random selection or a heuristic technique.

14. A method of discovering devices in a wireless network, the method comprising:

tuning a receiver in a receiving wireless device to random frequencies for a plurality of respective timeslots until a transmission is received from a transmitting wireless device, wherein the transmission includes a device identifier for the transmitting wireless device and timing information for the wireless network;

upon receiving the transmission, synchronizing a local clock in the receiving wireless device with a local clock in the transmitting wireless device; and

,

recording a device identifier (ID) of the transmitting wireless device in a table in the receiving wireless device.

15. The method of claim 14, further comprising:

by operation of the receiving wireless device, transmitting data in a predetermined timeslot and communication channel reserved by the transmitting wireless device for discovering new devices.

16. The method of claim 15, wherein the communication channel reserved by the transmitting wireless device is the same communication channel on which the receiving wireless device received a transmission from the transmitting wireless device;

and,

the timeslot reserved by the transmitting wireless device has a predetermined offset from the timeslot in which the transmitting device last transmitted data.

17. A method of operating a wireless mesh network when a wireless device within the network has lost primary power, the method comprising:

using a secondary power source to operate the wireless device;

operating the wireless device on a reduced duty cycle;

performing synchronized transmission and reception with the wireless device based on a synchronized time.

18. The method of claim 17, wherein the synchronized time comprises:

a global reference clock time; and

,

wherein performing synchronized transmission and reception comprises transmitting and receiving data for a predetermined period of time using a predetermined schedule.

19. A method of aggregating data for transmission in a wireless mesh network comprising a plurality of wireless devices, the method comprising:

receiving and storing a table including a plurality of data items in a memory array located in a transmitting wireless device;

by operation of the transmitting wireless device, periodically transmitting the plurality of data items to adjacent devices;

wherein each of the data items has a source of origin that can be ascertained from the table.

20. The method of claim 19 wherein the table includes a unique identifier for each data item to indicate the source of origin of the data item.

21. The method of claim 19 wherein each source of origin is associated with a unique position in the table such that the source of origin for a data item in the table is ascertainable from the location of the data item within the table.

22. The method of claim 21 wherein the table further comprises compressed metadata indicating a number of empty rows in the table.

23. The method of claim 19 wherein the table further includes a timestamp for each data item;

wherein the source of origin of the data item sets the timestamp to indicate a time when the data item was first transmitted from the source of origin; and

,

wherein each data item in the table can only be updated by a data item from the same source of origin and having a newer timestamp.

24. The method of claim 23 wherein the timestamp is compressed by specifying it as an offset in timed units relative to a time when the data item was transmitted to the transmitting device.

25. The method of claim 23 wherein each data item further includes an acknowledgement indicator which is cleared by its source of origin device when transmitted and set when received by a destination device;

wherein any device receiving a transmitted version of a data item with an acknowledgement indicator set updates any stored version of the data item with the acknowledgment indicator cleared with the transmitted version of the data item; and

,

wherein any device receiving a transmitted version of the data item with the acknowledgement indicator cleared and whose stored version of the data item has the acknowledgement indicator set, transmits the stored data item in a subsequent transmission.

26. The method of claim 25, wherein a stored data item in the table having its acknowledgement indicator set may be replaced by a received new data item with the acknowledgement indicator cleared if the stored data item has been acknowledged for more than a predetermined period of time.