USING DME FOR TERRESTRIAL TIME TRANSFER

• US 20160356891A1
• Filed: 03/04/2016
• Published: 12/08/2016
• Est. Priority Date: 03/06/2015
• Status: Active Grant

• Current Assignee: Iposi, Inc.
• Original Assignee: Iposi, Inc.
• Inventors: LEE, RICHARD M., DERBEZ, ERIC
• Granted Patent: US 9,715,017 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01S 19/11 wherein the cooperating elements are pseudolites or satellite radio beacon positioning system signal repeaters
• CPC Class Codes: G01S 19/23 Testing, monitoring, correcting or calibrating of receiver elements
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset
• CPC Class Codes: G01S 19/31 Acquisition or tracking of other signals for positioning
• CPC Class Codes: G04F 1/00 Apparatus which can be set and started to measure-off predetermined or adjustably-fixed time intervals without driving mechanisms, e.g. egg timers
• CPC Class Codes: G04R 20/02 the radio signal being sent by a satellite, e.g. GPS
• CPC Class Codes: G04R 20/26 the radio signal being a near-field communication signal

Abstract

Techniques for allowing a remote or fielded receiver to derive a precise time reference (such as Coordinated Universal Time (UTC)) when the fielded receiver is not able to derive time directly from received GPS signals. One or more fixed DME reference stations are located within range of DME beacon signals from an existing DME beacon station, the DME reference stations also having the capability to receive GPS signals and derive UTC therefrom. Based on the known distance between the DME reference station and the DME beacon station, the DME reference station can determine the time of transmission from the DME beacon station of each DME beacon signal. This time tag information is then provided to the fielded receiver, which is also within range of DME beacon signals from the DME beacon station. With this time tag information, the fielded receiver can correlate that with the received DME beacon signals and derive UTC to within an acceptably small margin.

GLOSSARY 3GPP Third Generation Partnership Program AWGN additive white Gaussian noise ASF Additional Secondary Factor alpha filter roll off factor BCCH broadcast control channel C carrier power CCCH common control channel CI coherent integration dB decibel DME Distance Measuring Equipment E911 Enhanced 911 E_b Energy per bit E_c Energy per chip E_s energy per symbol EIRP effective isotropic radiated power IF Intermediate Frequency FCC Federal Communications Commission GHZ gigahertz GNSS global navigation by satellite system GNSS Global Position System KHz kilohertz Km kilometer LTE Long Term Evolution MHz megahertz m meter ms milliseconds N₀ noise power spectral density NCI non coherent integration ns nanosecond NTP Network Time Protocol OCXO oven-controlled crystal oscillator PTP Precision Time Protocol Rx receive SNR signal to noise ratio spc samples per chip sps samples per symbol SV satellite vehicle TCXO temperature-controlled crystal oscillator Tx transmit

Claims

1. A method for deriving a precise time reference when GNSS signals are not directly available, comprising:

determining that GNSS signals are not directly available;

receiving a plurality of DME beacon signals from a DME beacon station;

receiving precise timing information from a DME reference station, the precise timing information including time tags for each DME beacon signal received by the DME reference station from the DME beacon station, the time tag including a precise time reference for the time that the DME beacon station sent the respective DME beacon signal; and

deriving a precise time reference from the DME beacon signals received from DME beacon station and the time tags received from the DME reference station corresponding to the received DME beacon signals.

2. A method as defined in claim 1, wherein the deriving does not require any knowledge of the position of the DME reference station or the distance to the DME reference station.

3. A method as defined in claim 1, wherein multiple DME beacon signals are received from the DME beacon station within a two-second period, and wherein the deriving includes integrating over the multiple received DME beacon signals to improve the signal-to-noise ratio.

4. A method as defined in claim 1, further including calculating a time tag for a time of transmission of each of the plurality of received DME beacon signals, based on a known travel time from the DME beacon station.

5. A method as defined in claim 4, wherein the deriving includes finding a correlation between the received plurality of DME beacon signals and the DME beacon signals received by the DME reference station.

6. A method as defined in claim 5, wherein finding the correlation includes performing a series of correlations as the time that the plurality of DME signals were believed to have been received is shifted by predetermined time increments.

7. A method as defined in claim 1, wherein the derived precise time reference includes UTC time.

8. A method as defined in claim 1, wherein the derived precise time reference is used to help reacquire GNSS signals.

9. A method as defined in claim 1, wherein signals received from the DME reference station and the plurality of DME beacon signals received from the DME beacon station are stored in one or more buffers for subsequent processing.

10. A method as defined in claim 1, wherein the plurality of DME beacon signals received from the DME beacon station are integrated.

11. A method as defined in claim 10, wherein the integration is selectively performed based on the signals received from the DME reference station.

12. A method for deriving a precise time reference when another precise time reference is not available, comprising:

receiving DME beacon signals from a DME beacon station; and

receiving precise timing information from a DME reference station;

wherein when the another precise time reference is not available, deriving a precise time reference from the DME beacon signals received from local DME beacon station and the precise timing information received from the DME reference station.

13. A method as defined in claim 12, wherein the precise timing information received from the DME reference station includes time tags for each DME beacon signal received by the DME reference station from the DME beacon station, the time tag including a precise time reference for the time that the DME beacon station sent the respective DME beacon signal.

14. A method as defined in claim 12, wherein the another precise time reference is GNSS time.

15. A method as defined in claim 12, wherein the another precise time reference is GPS time.

16. A system for deriving a precise time reference with the aid of DME beacon signals from a DME beacon station, comprising:

a DME reference station located within range of the DME beacon signals from the DME beacon station, the DME reference station receiving GNSS signals and determining a precise time reference therefrom, the DME reference station also receiving DME beacon signals from the DME beacon station and determining the time of transmission of one or more of the DME beacon signals from the DME beacon station based at least in part on the distance between the DME beacon station and the DME reference station; and

a receiver also located within range of the DME beacon signals from the DME beacon station, the receiver being in communication with the DME reference station to receive from the DME reference station the time of transmission of the one or more DME beacon signals, wherein the receiver derives a precise time reference based at least in part on the received DME beacon signals and their time of transmission from the DME beacon station.

17. A system as defined in claim 16, wherein the derivation by the receiver is also based on the distance between the DME beacon station and the receiver.

18. A method for providing timing information to a remote receiver, in part by utilizing DME beacon signals from a DME beacon station, comprising:

receiving DME beacon signals from a DME beacon station at a DME reference station;

determining the time of transmission of one or more DME beacon signals from the DME beacon station based at least in part on the distance between the DME beacon station and the DME reference station; and

communicating the time of transmission of the one or more DME beacon signals to a remote receiver.

19. A method as defined in claim 18, wherein the DME reference station also receives GNSS signals from which a precise time reference is determined.

20. A method as defined in claim 18, wherein the time of transmission of DME beacon signals from the DME beacon station includes UTC time.