Time-hopping low-power wireless network for turning off and on fluorescent lamps

• US 8,184,674 B2
• Filed: 09/30/2009
• Issued: 05/22/2012
• Est. Priority Date: 09/30/2009
• Status: Active Grant

• Current Assignee: IXYS Intl Limited (Littelfuse Incorporated)
• Original Assignee: IXYS CH GmbH (Littelfuse Incorporated)
• Inventors: Pope, Steven M.
• Primary Examiner(s): WANG, TED M
• Application Number:
  US12/587,106
• Publication Number:
  US 20110076950A1
• Time in Patent Office: 965 Days
• Field of Search: 375/138, 375/135, 375/132, 375/219, 455/67.11, 315/138, 315/312
• US Class Current: 375/138
• CPC Class Codes: G08C 17/02 using a radio link
• CPC Class Codes: G08C 2201/12 Power saving techniques of remote control or controlled devices
• CPC Class Codes: H04W 52/0229 where the received signal is a wanted signal
• CPC Class Codes: H04W 74/085 collision avoidance
• CPC Class Codes: H04W 84/20 Master-slave selection or change arrangements
• CPC Class Codes: H05B 47/195 the transmission using visible or infrared light
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A low-power wireless network involves a master and a plurality of RF-enabled fluorescent lamp starter units. In each of a plurality of intervals, a starter wakes up and listens for a beacon, regardless of whether a beacon is transmitted during that interval or not. The starter operates in a low power sleep mode during the majority of the interval. The master can transmit during the beacon slot time of any interval, but typically only transmits frequently enough to maintain starter synchronization. If the master wishes to communicate with the starters with reduced latency, then the master can transmit a beacon in the next interval. Beacon slot time is varied within the interval (for example, from interval to interval or from group of intervals to group of intervals) in a pseudo-random time-hopping fashion known to both the starters and the master, thereby reducing persistence of collisions with similar networks.

Claims

1. A time-hopping wireless network system comprising:

a master unit; and

a remote lighting control unit, wherein the master unit is in wireless Radio Frequency (RF) communication with the remote lighting control unit, wherein the master unit transmits beacons in some but not all of a plurality of beacon slot times, wherein there is one beacon slot time in each of a corresponding one of a plurality of intervals, wherein the intervals of the plurality of intervals are all of identical duration, wherein the beacon slot times of a sequence of the plurality of intervals vary in time within their respective intervals from interval to interval in the sequence of intervals, and wherein the remote lighting control unit only transmits if commanded to by a beacon received from the master unit.

2. The time-hopping wireless network system of claim 1, wherein the remote lighting control unit wakes up and operates in a higher power receive mode during a portion of each interval to listen for a beacon even if the master unit does not transmit a beacon during said each interval, and wherein the lighting control unit operates in a lower power sleep mode for a majority of said each interval.

3. The time-hopping wireless network system of claim 2, wherein the beacon slot time of an interval has an offset time with respect to a time point within the interval, wherein the offset times of the beacon slot times of the sequence are varied in pseudo-random fashion from interval to interval in the sequence of intervals, and wherein the time point is taken from the group consisting of:

a start time of the interval, an end time of the interval, and a time point of the interval between the start time and the end time.

4. A method comprising:

(a) in each of a plurality of intervals placing a receiver of a receiver unit into a receive mode, and then listening for a beacon during a predefined beacon slot time within the interval, and operating the receiver in a low-power sleep mode for substantially all the rest of the interval, wherein beacons are received by the receiver during the beacon slot times of some of the intervals but wherein no beacon is received during the beacon slot times of others of the intervals, wherein the beacon slot time of an interval has an offset time with respect to a time point within the interval, and wherein the offset time is varied in pseudo-random fashion from interval to interval; and

(b) using the beacons received in (a) to synchronize the placing of the receiver into the receive mode with respect to the beacon slot times of the intervals.

5. The method of claim 4, wherein the receiver unit includes a transmitter, and wherein the receiver unit does not transmit from its transmitter unless being first commanded to by a beacon.

6. The method of claim 5, wherein the receiver unit is a fluorescent lamp starter unit, wherein one of the beacons includes a command, and wherein the command causes the receiver unit to turn off a fluorescent lamp.

7. The method of claim 5, wherein the receiver unit is a fluorescent lamp starter unit, wherein one of the beacons includes a command, and wherein the command causes the receiver unit to turn on a fluorescent lamp.

8. The method of claim 4, wherein the receiver unit implements a table lookup function, wherein a beacon is received onto the receiver unit, wherein the beacon includes a value, wherein the receiver unit supplies the value to the table lookup function such that the table lookup function outputs an offset control value, and wherein the offset control value is used to determine when to listen for a beacon within an interval.

9. The method of claim 8, wherein the time point is taken from the group consisting of:

a start time of the interval, an end time of the interval, and a time point of the interval between the start time and the end time.

10. The method of claim 4, wherein the receiver unit implements a table lookup function, wherein the table lookup function outputs a pseudo-random sequence of offset control values, and wherein each offset control value is used to determine when to listen for a beacon within an interval.

11. The method of claim 4, further comprising:

(c) in a synchronization mode using a sliding listening window technique in a plurality of intervals to detect a beacon.

12. The method of claim 4, further comprising:

(c) receiving a beacon, wherein the beacon includes an identifier that identifies the receiver unit, and wherein the receiver unit includes a transmitter; and

(d) using the identifier to determine that the receiver unit is to make a transmission, and then transmitting a signal from the receiver unit.

13. The method of claim 12, wherein the signal is indicative of whether the receiver unit is synchronized to beacons received onto the receiver unit in (a).

14. A system comprising:

an occupancy detector that transmits a plurality of beacons, wherein each beacon is transmitted in a beacon slot time of a respective one of a plurality of intervals, wherein the beacon slot time of an interval has an offset time with respect to a time point within the interval, wherein the offset time is varied in pseudo-random fashion from interval to interval, and wherein the occupancy detector transmits no beacon in some beacon slot times of some of the intervals but does transmit beacons in beacon slot times of other ones of the intervals; and

a fluorescent lamp starter unit that receives the beacons and uses the beacons to synchronize the placing of a receiver of the fluorescent lamp starter unit into a receive mode with respect to the beacon slot times of the intervals, wherein the receiver is placed into the receive mode during the beacon slot time of every one of the plurality of intervals.

15. The system of claim 14, wherein the time point is taken from the group consisting of:

a start time of the interval, an end time of the interval, and a time point of the interval between the start time and the end time.

16. An apparatus comprising:

a pair of terminals adapted to be coupled to a fluorescent lamp; and

means for turning on the fluorescent lamp and for using a time-hopping Radio Frequency (RF) network protocol to receive a plurality of beacons, wherein each of a plurality of intervals has a beacon slot time, wherein the plurality of beacons is received by the means during the beacon slot times of some of the intervals but wherein no beacon is received during the beacon slot times of others of the intervals, wherein the means wakes up and operates in a higher power receive mode during a portion of each interval to listen for a beacon even if there is no beacon to receive during said each interval, wherein the means operates in a lower power sleep mode during a majority of each interval, and wherein the beacon slot times of at least some of the intervals vary in time-position within their respective intervals.

17. The apparatus of claim 16, wherein at least one of the beacons includes a value, and wherein the means is also for using the value to determine when to start operating in the higher power receive mode.

18. The apparatus of claim 16, wherein the means is also for turning off the fluorescent lamp.

19. The apparatus of claim 16, wherein the beacon slot times of a first sequence of intervals all have a first time-position within their respective intervals, wherein the beacon slot times of a second sequence of intervals all have a second time-position within their respective intervals, and wherein the first and second time-positions are different.

20. The apparatus of claim 16, wherein beacon slot times of a sequence of intervals vary in time-position within their respective intervals from interval to interval throughout the sequence.