Method and apparatus for eliminating ionospheric delay error in global positioning system signals

• US 5,903,654 A
• Filed: 08/06/1997
• Issued: 05/11/1999
• Est. Priority Date: 08/06/1997
• Status: Expired due to Term

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Rockwell Science Center, Inc.
• Inventors: Meyer, Ron, Milton, Kevin
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US08/907,294
• Time in Patent Office: 643 Days
• Field of Search: 342/357, 342/457, 342/352, 342/460, 380/2, 380/9, 380/49, 380/59, 701/207, 701/213, 701/214, 701/215, 701/216
• US Class Current: 342/357.23
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/32 Multimode operation in a single same satellite system, e.g. GPS L1/L2

Abstract

A method and apparatus for determining and removing the error in the SPS measurement of the Global Positioning System due to ionospheric delay. The disclosed technique utilizes semi-codeless technique to provide high accuracy GPS measurements. The delay of the P code is varied and the signals are cross correlated until a maximum value is reached. When the cross correlation of the L1 and L2 signals is at a peak value, the relative delay between the L1 and L2 signals is proportional to the ionospheric delay. The derived ionospheric delay may be accounted for in measurement analysis of the L1 signal to provide for a high precision position solution. The semi-codeless correlator also provides the L1-L2 carrier phase measurement for wide-lane applications.

Claims

1. A method for eliminating ionospheric delay error due to an ionospheric delay from the signals of a global positioning system signal including the L1 and L2 signals without knowledge of the Y code signal due to encryption of the L1 and L2 signals to determine a high precision position solution, the method comprising:

receiving the L1 and L2 signals, said L1 and L2 signals being modulated by a predetermined high precision code;

filtering the high precision code from said L1 and L2 signals;

cross-correlating said L1 and L2 signals;

determining the ionospheric delay by varying the relative delay between said L1 and L2 signals until a predetermined correlation value is reached wherein the relative delay is proportional to the ionospheric delay; and

eliminating the ionospheric delay error from the position solution by correcting the position solution according to the determined ionospheric delay during measurement analysis of the position solution.

2. The method according to claim 1 wherein said filtering step includes filtering said L1 and L2 signals with a precorrelation filter having a bandwidth based upon the bandwidth of the encryption code of the L2 signal.

3. The method according to claim 1 wherein said filtering step includes filtering said L1 and L2 signals with a precorrelation filter having a bandwidth equal to the bandwidth of the encryption code of the L2 signal.

4. The method according to claim 1 wherein said filtering step includes filtering with an integrate and dump filter.

5. The method according to claim 1 wherein said predetermined correlation value is equal to a relative maximum correlation value.

6. The method according to claim 1 further comprising the step of generating an L2 carrier phase measurement from an L1 carrier phase measurement and a semi-codeless cross correlator L1-L2 carrier phase measurement.

7. The method according to claim 1, further comprising the step of generating a wide-lane L1-L2 carrier phase measurement for reconstructing the L2 carrier phase.

9. A processor as claimed in claim 7 further comprising a post detection processor for providing a semi-codeless cross correlator L2-L1 carrier phase measurement whereby a wide-lane signal is constructed for resolving L1 and L2 carrier phase ambiguity and for reconstructing L2 carrier phase.

8. A processor for eliminating ionospheric delay error due to an ionospheric delay from the signals of a global positioning system signal including the L1 and L2 signals without knowledge of the Y code signal due to encryption of the L1 and L2 signals to determine a high precision position solution, the processor comprising:

a first precorrelation filter for filtering the encryption code from a signal comprising the L1 signal multiplied with a high precision code, said L1 signal being previously encoded with said high precision code, said first precorrelation filter providing an output;

a second precorrelation filter and a high precision code delay unit having a high precision code delayed output;

said second precorrelation filter for filtering the encryption code from a signal comprising the L2 signal multiplied with said high precision code delayed output, said second precorrelation filter providing an output;

a predetection filter for filtering a signal comprising said output of said first precorrelation filter multiplied with said output of said second precorrelation filter, said predetection filter providing an output;

a tracking commands unit receiving said output of said predetection filter for processing tracking commands, said tracking commands unit providing an output to said high precision code delay unit; and

a post detection filter receiving said output of said predetection filter for providing an output proportional to the ionospheric delay based upon the cross correlation of the L1 and L2 signals.