Time transfer utilizing ultra wideband signals

• US 7,649,925 B2
• Filed: 05/28/2005
• Issued: 01/19/2010
• Est. Priority Date: 06/14/1999
• Status: Expired due to Term

• Current Assignee: Humatics Corporation
• Original Assignee: Time Domain Corporation (Humatics Corporation)
• Inventors: Fullerton, Larry W., Richards, James, Roberts, Mark
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): Guarino; Rahel
• Application Number:
  US11/140,535
• Publication Number:
  US 20060291537A1
• Time in Patent Office: 1,697 Days
• Field of Search: 375/145, 375/149, 375/130, 375/219, 375/342, 375/295, 370/503, 370/208, 370/508, 713/400, 713/176, 342/64, 342/85, 342/88, 342/105, 342/137, 342/357.06, 342/357.08, 342/357.12
• US Class Current: 375/145
• CPC Class Codes: G01S 13/0209 Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
• CPC Class Codes: G01S 13/765 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 7/4052 by simulation of echoes
• CPC Class Codes: G01S 7/4065 involving a delay line
• CPC Class Codes: G01S 7/4069 involving a RF signal injection
• CPC Class Codes: G01S 7/4082 using externally generated reference signals, e.g. via remote reflector or transponder
• CPC Class Codes: G06K 7/10306 ultra wide band
• CPC Class Codes: H04B 1/7183 Synchronisation

Abstract

Time is transferred from an ultra wideband (UWB) transmitter to UWB receiver by transmitting a signal structure having an associated timing reference point together with a time value for the timing reference point. The UWB receiver receives the timing signal structure by synchronizing a receiver time base to the signal structure, demodulating the time value information, and using the demodulated time value information to set a receiver clock value. Propagation delay information is used to adjust the receiver clock value by advancing the receiver clock value to account for the propagation delay. In one embodiment, propagation delay is determined from a known distance between the transmitter and receiver. In another embodiment, the transmitter and receiver are part of a two-way link wherein propagation delay is measured by round trip timing measurements.

Claims

1. A method utilizing a first transceiver and a second transceiver for transferring timing between a first time clock and a second time clock comprising:

transmitting a first ultra wideband signal by said first transceiver, said ultra wideband signal having a signal structure comprising a time reference point and conveying digital time information for said time reference point, said time reference point and said digital time information established in accordance with said first time clock;

receiving the first ultra wideband signal by said second transceiver;

synchronizing a receiver time base of said second transceiver with the received first ultra wideband signal;

generating a first detected signal versus delay time multipath pattern of said first ultra wideband signal as received at said second transceiver;

transmitting a return ultra wideband signal by said second transceiver, said return ultra wideband signal having predetermined timing relationship to the receiver time base of said second transceiver;

generating a second detected signal versus delay time multipath pattern of said return ultra wideband signal as received at said first transceiver;

determining a round trip propagation delay from said first transceiver to said second transceiver and back to said first transceiver in part by comparing said first detected signal versus delay time multipath pattern to said second detected signal versus delay time multipath pattern;

determining a propagation delay from said first transceiver to said second transceiver based on said round propagation trip delay;

determining by said second transceiver a received time reference point and said received digital time information from the signal structure of the first received ultra wideband signal; and

setting said second time clock in accordance with said received digital time information, said received time reference point, and said propagation delay.

2. The method of claim 1, further including the step of sending the first detected signal versus delay time multipath pattern to the first transceiver;

and wherein the step of comparing said first detected signal versus delay time multipath pattern to said second detected signal versus delay time multipath pattern is performed by said first transceiver.

3. The method of claim 1, wherein the step of determining a round trip propagation delay from said first transceiver to said second transceiver and back to said first transceiver in part by comparing said first detected signal versus delay time multipath pattern to said second detected signal versus delay time multipath pattern includes correlation matching of said first detected signal versus delay time multipath pattern with said second detected signal versus delay time multipath pattern.

4. The method of claim 1, wherein the step of determining a round trip propagation delay from said first transceiver to said second transceiver and back to said first transceiver in part by comparing said first detected signal versus delay time multipath pattern to said second detected signal versus delay time multipath pattern includes pattern matching of said first detected signal versus delay time multipath pattern with said second detected signal versus delay time multipath pattern.

5. The method of claim 1 wherein the signal structure includes a code and the synchronizing step uses the code to synchronize the time base with the signal structure.

6. The method of claim 5 wherein the code is periodically changed to effectively extend the code repeat length.

7. The method of claim 5 wherein the code is applied to groups of pulses and the spacing between groups of pulses is changed to effectively extend the code repeat length.

8. The method as in claim 1, wherein said received UWB signal results from a direct path between a transmitting UWB radio and a receiving UWB radio.

9. The method as in claim 1, wherein said received UWB signal results from an indirect path between a transmitting UWB radio and a receiving UWB radio.

10. The method of claim 1, wherein the calculation of propagation delay includes a process for correcting internal errors, said process comprising the steps of:

receiving a portion said return ultra wideband signal by said second transceiver;

determining the relative timing of said portion of said return ultra wideband signal relative to said first ultra wideband signal as received by said second transceiver; and

using said relative timing of said portion of said ultra wideband signal to correct said round trip propagation delay.

11. The method of claim 10, wherein the portion of said return ultra wideband signal comprises a reflection related to an antenna impedance mismatch for said second transceiver.

12. The method of claim 10, wherein the portion of said return ultra wideband signal is delayed by a delay line internal to said second transceiver and coupled to a receiver input of said second transceiver.

13. The method of claim 10, wherein the step of using the timing of said portion of said ultra wideband signal to correct said round trip propagation delay includes adjusting the second transceiver transmitter timing.

14. The method of claim 1, further including the step of updating said second time clock in accordance with said time base of said second transceiver.

15. The method of claim 1, wherein said ultra wideband signal comprises a coded pulse train and said time reference point refers to a particular pulse of said coded pulse train.

16. The method of claim 15, wherein each pulse of said coded pulse train includes an identifiable reference cycle for resolving cycle ambiguity and enabling time resolution to less than one radio frequency cycle.

17. A system utilizing a first transceiver and a second transceiver for transferring timing between a first time clock and a second time clock comprising:

a first transceiver transmitting a first ultra wideband signal, said first ultra wideband signal having a signal structure comprising a time reference point and conveying digital time information for said time reference point, said time reference point and said digital time information established in accordance with said first time clock;

a second ultra wideband transceiver receiving said first ultra wideband signal;

said second transceiver having a time base synchronized with said received first ultra wideband signal;

said second ultra wideband transceiver generating a first scanning receiver data comprising a sequential set of signal strength measurements versus delay time for said received first ultra wideband signal;

said second ultra wideband transceiver transmitting a return ultra wideband signal, said return ultra wideband signal having predetermined timing relationship to a receiver time base of said second transceiver;

said first ultra wideband transceiver generating a second scanning receiver data comprising a sequential set of signal strength measurements versus delay time for said return ultra wideband signal as received at said first ultra wideband transceiver;

said system determining a round trip propagation delay from said first transceiver to said second transceiver and back to said first transceiver in part by comparing said first scanning receiver data to said second scanning receiver data;

said second ultra wideband receiver determining said time reference point and said digital time information from the signal structure of the first received ultra wideband signal; and

said second time clock being set in accordance with said received digital time information, said received time reference point, and said propagation delay.