MULTI-CHANNEL TDOA SYSTEM

• US 20080037512A1
• Filed: 08/08/2007
• Published: 02/14/2008
• Est. Priority Date: 08/08/2006
• Status: Active Grant

• Current Assignee: Aeroscout Limited (Stanley Black & Decker, Inc.)
• Original Assignee: Aeroscout Limited (Stanley Black & Decker, Inc.)
• Inventors: Amsalem, Reuven, Aljadeff, Daniel, Lavi, Amir
• Granted Patent: US 8,576,829 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04W 4/12 Messaging; Mailboxes; Announcements
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A wireless network has at least one wireless unit which transmits messages in multiple channels. The messages are synchronously transmitted using a transmit clock signal. The at least one wireless unit starting transmission of the messages at intervals consisting of at least one of one or multiple periods of the transmit clock signal. A plurality of location receivers are used for receiving the messages at different channels transmitted by the wireless units within the wireless network and determining a time of arrival for the received messages. At least one master unit is used for receiving the time of arrival from each of the location units. The location of the wireless unit is to be determined on the Time Difference Of Arrival (TDOA) of the transmitted messages at the location units.

Claims

1. A wireless network comprising:

at least one wireless unit which transmits messages in multiple channels, wherein the messages are synchronously transmitted using a transmit clock signal, the at least one wireless unit starting transmission of the messages at intervals consisting of at least one of one or multiple periods of the transmit clock signal;

a plurality of location receivers for receiving the messages in one of at least two different channels, said messages transmitted by the wireless units within the wireless network and determining a time of arrival for the received messages; and

at least one master unit for receiving the time of arrival from each of the location receivers, whereby said location of the wireless unit is be determined on the Time Difference Of Arrival (TDOA) of the transmitted messages at the location receivers.

2. A wireless network in accordance with claim 1 wherein the at least one wireless unit comprises:

a communication controller which generates data to be transmitted;

a transmitter coupled to the communication controller to modulate the data and transmit the messages in a programmed channel, the transmitter starting transmission of the messages at intervals consisting of at least one of one or multiple periods of the transmit clock signal;

3. A wireless network in accordance with claim 2 wherein the at least one wireless unit further comprising:

a counter coupled to the communication controller to count cycles of the transmit clock signal; and

wherein the communication controller clears and enables the counter to start counting when transmission of a first message starts, the communication controller samples and reads a counter value when transmission of a second message on a different channel starts, the counter continuing counting clock cycles.

4. A wireless network in accordance with claim 1 further comprising a timing circuit coupled to the transmitter to provide synchronization of the transmit messages.

5. A wireless network in accordance with claim 4 wherein the timing circuit comprises:

a clock divider coupled to the transmit clock signal for generating a window clock signal, wherein the window clock signal and the transmit clock signal are synchronized;

a flip-flop device coupled to the communication controller, the flip flop device receiving start and stop transmission signals and outputting the synchronized start transmission signal on an edge of the window clock.

6. A wireless network in accordance with claim 1 wherein the plurality of Location Receivers comprises means for estimating clock frequency of the wireless unit.

7. A wireless network in accordance with claim 1 wherein said transmitted messages by said wireless unit include information related to the interval between two or more transmitted messages.

8. A wireless network in accordance with claim 1 wherein said transmission intervals consist of one or more periods of a window clock, said window clock being derived from the transmit clock and synchronized to it.

9. A wireless network in accordance with claim 7 wherein said window clock period is programmable and said programmable period is transmitted as part of the message data.

10. A wireless network in accordance with claim 1 wherein said transmission intervals are fixed and wherein the CCA process is done on the first channel only.

11. A wireless network in accordance with claim 1 wherein said transmitted messages are transmitted in a variable order of channels.

12. A wireless network in accordance with claim 11 wherein said transmitted messages include information on the next channel to be used.

13. A wireless network in accordance with claim 1 wherein said transmitted messages are transmitted as a response to an external request or event.

14. A wireless network in accordance with claim 1 wherein said transmitted messages are transmitted within time slots as specified by a WLAN Access Point or any other element managing the traffic in the wireless network.

15. A wireless network in accordance with claim 1 wherein said at least one Location Receiver is part of a WLAN Access Point.

16. A wireless network in accordance with claim 1 wherein said at least one Location Receiver reports the estimated clock frequency of said wireless unit to a master unit, said master unit using this information to improve the TDOA accuracy.

17. A wireless network in accordance with claim 1 wherein said at least one wireless unit is a tag device.

18. A method for accurately measuring the TDOA of messages transmitted at different channels in a multiple-channel wireless data communication system comprising:

transmitting the messages in multiple channels by at least one wireless unit, wherein the messages are synchronized using a transmit clock signal, transmission of the messages at intervals consisting of at least one of one or multiple periods of the transmit clock signal;

receiving the messages transmitted by the wireless units device by a plurality of Location Receivers within the wireless network on at least two different channels;

determining a time of arrival data for the received messages by the plurality of Location Receivers; and

receiving time of arrival data by at least one master unit; and

determining location of the wireless unit by the Time Difference Of Arrival (TDOA) of the transmitted messages.

19. The method of claim 18 further comprising adding data related to an interval between the transmitted messages into the transmitted messages.

20. The method of claim 18 wherein transmitting the messages at intervals further comprises transmitting the messages at intervals wherein the intervals of transmission comprises at least one of one or more periods of a window clock, the window clock being derived from the transmit clock and synchronized to the transmit clock.

21. The method of claim 20 wherein the window clock period is programmable and the programmable period is transmitted as part of the message data.

22. The method of claim 18 wherein transmitting the messages at intervals further comprises transmitting the messages at intervals that are fixed and wherein a CCA process is done on a first channel.

23. The method of claim 18 wherein the transmitted messages are transmitted in a variable order of channels.

24. The method of claim 23 wherein said transmitted messages include information regarding the next channel to be used.

25. The method of claim 18 wherein the transmitted messages are transmitted as a response to an external request or event.

26. The method of claim 18 wherein said transmitted messages are transmitted within time slots as specified by a WLAN Access Point or any other element managing the traffic in the wireless network.

27. A method as specified in claim 18 wherein said at least one Location Receiver has means to estimate the transmitter clock frequency.

28. A method as specified in claim 27 wherein said at least one Location Receiver reports the estimated clock frequency of said wireless unit to a master unit, said master unit using this information to improve the TDOA accuracy.

29. A wireless unit for a multiple-channel wireless data communication system, wherein mobile units communicate with Location Receivers, and wherein the wireless communication system is intended to locate the wireless unit transmitting messages in multiple channels of the communication system, the transmitter comprising:

a communication controller which generates data to be transmitted;

a transmitter coupled to the communication controller to modulate the data and transmit the messages in a programmed channel, the transmitter starting transmission of the messages at intervals consisting of at least one of one or multiple periods of the transmit clock signal;

30. A wireless unit as specified in claim 29 wherein said wireless unit further comprising a counter coupled to the communication controller to count cycles of the transmit clock signal;

and

wherein the communication controller clears and enables the counter to start counting when transmission of a first signal starts, the communication controller samples and reads a counter value when transmission of a second signal on a different channel starts, the counter continuing counting clock cycles.

31. A wireless unit as specified in claim 29 further comprising a timing circuit coupled to the transmitter to provide synchronization of the transmit signals.

32. A transmitter as specified in claim 31 wherein the timing circuit comprises:

a clock divider coupled to the transmit clock signal for generating a window clock signal, wherein the window clock signal and the transmit clock signal are synchronized;

a flip-flop device coupled to the communication controller, the flip flop device receiving start and stop transmission signals and outputting the synchronized start transmission signal on an edge of the window clock.