System and method for detecting packet synchronization

• US 8,559,413 B2
• Filed: 09/30/2010
• Issued: 10/15/2013
• Est. Priority Date: 09/30/2010
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Lee, Gaspar, Cheng, Hao-Jen
• Primary Examiner(s): NGUYEN, STEVEN H D
• Application Number:
  US12/895,757
• Publication Number:
  US 20120082187A1
• Time in Patent Office: 1,111 Days
• Field of Search: None
• US Class Current: 370/350
• CPC Class Codes: G01S 19/243 Demodulation of navigation message
• CPC Class Codes: G01S 19/27 creating, predicting or correcting ephemeris or almanac data within the receiver
• CPC Class Codes: G01S 19/33 Multimode operation in different systems which transmit time stamped messages, e.g. GPS/GLONASS
• CPC Class Codes: H04B 7/2125 Synchronisation

Abstract

A method of providing frame synchronization for GPS signals can include performing coherent bit extraction on the GPS bits and then performing coherent frame boundary detection based on the bits of the coherent bit extraction. Concurrently, differential bit extraction on the GPS bits and differential frame boundary detection based on bits of the differential bit extraction can be performed. Whichever of the coherent frame boundary detection and the differential frame boundary detection first finds a frame boundary, then that frame boundary is used for the frame synchronization. A method of providing string synchronization for GLONASS signals includes performing coherent and differential bit extraction on the GLONASS bits.

Claims

1. A method of providing frame synchronization for Global Positioning System (GPS) signals, the method comprising:

performing coherent bit extraction on GPS bits, including;

finding a first preamble of a first telemetry (TLM) word of a first GPS subframe, parity bits of the first TLM word and a first hand over word (HOW) word, a first time of week (TOW) of the first HOW word, and first subframe ID bits of the first HOW word, and

finding a second preamble of a second TLM word of a second GPS subframe, parity bits of the second TLM word and a second HOW word of the second GPS subframe, a second TOW of the second HOW word, and second subframe ID bits of the second HOW word;

performing coherent frame boundary detection based on bits of the coherent bit extraction, including;

checking validity of the first TLM word using the parity bits of the first TLM word,

checking validity of the first HOW word using the parity bits of the first HOW word,

declaring a TOW synchronization when a valid first HOW word follows a valid first TLM word,

checking validity of the second TLM word using the parity bits of the second TLM word,

checking validity of the second HOW word using the parity bits of the second HOW word, and

declaring a detected frame boundary when (1) a valid second HOW word follows a valid second TLM word, (2) the second TOW is equal to the first TOW +1, and (3) when the second subframe ID bits equal the first subframe ID bits +1;

performing differential bit extraction on the GPS bits;

performing differential frame boundary detection based on bits of the differential bit extraction, wherein said performing the differential frame boundary detection and said performing the coherent frame boundary detection are done concurrently; and

providing the frame synchronization, wherein whichever of the coherent frame boundary detection and the differential frame boundary detection first finds a frame boundary, that frame boundary is used for the frame synchronization.

2. The method of claim 1, further including proceeding with said performing the coherent and the differential frame boundary detection only when two words are stored.

3. The method of claim 2, further including deleting a first-in GPS bit of the two words and adding a new GPS bit as a last-in GPS bit of the two words, and repeating said performing the coherent and the differential bit extraction on the GPS bits as well as said performing the coherent and the differential frame boundary detection.

4. A method of providing frame synchronization for GPS signals, the method comprising:

performing coherent bit extraction on GPS bits;

performing coherent frame boundary detection based on bits of the coherent bit extraction;

performing differential bit extraction on the GPS bits, and finding a preamble of a telemetry (TLM) word of a GPS subframe, and a limited number of most significant bits (MSB) of a time of week (STOW) of a hand-over word (HOW) word;

performing differential frame boundary detection based on bits of the differential bit extraction, further comprising;

performing the differential and the coherent frame boundary detection concurrently,

identifying the TLM word using the preamble, and saving a limited number of survivor paths, wherein survivor paths are most likely locations for the frame boundary; and

providing the frame synchronization, wherein whichever of the coherent frame boundary detection and the differential frame boundary detection first finds the frame boundary, that frame boundary is used for the frame synchronization.

5. The method of claim 4, wherein the limited number of survivor paths is 10-12 locations out of a possible 300 locations.

6. The method of claim 4, further including performing the differential frame boundary detection using multiple TLM and HOW words and updating the survivor paths to reflect the most likely locations for the frame boundary.

7. The method of claim 6, further including adding +1 to a metric each time the TLM word is identified using the preamble.

8. The method of claim 7, further including storing a value of a last STOW, and setting a STOW flag to ON when a current STOW equals the last STOW.

9. The method of claim 8, wherein performing the differential frame boundary detection includes declaring a detected frame boundary when (1) the metric is greater than or equal to a threshold and the STOW flag is set to ON.

10. The method of claim 9, wherein the threshold is a function of time.

11. The method of claim 10, wherein the threshold is increased by “

1”

every 10 ms.

12. A method of providing string synchronization for GLONASS signals, the method comprising:

performing coherent bit extraction on GLONASS bits, including extracting 30 bits every 10 ms;

performing coherent string boundary detection based on bits of the coherent bit extraction, including correlating the 30 bits with a time mark of GLONASS without bit flipping;

performing differential bit extraction on the GLONASS bits;

performing differential string boundary detection based on bits of the differential bit extraction, wherein said performing the differential string boundary detection and said performing the coherent string boundary detection are done concurrently; and

providing the string synchronization, wherein whichever of the coherent string boundary detection and the differential string boundary detection first finds a string boundary, that string boundary is used for the string synchronization.

13. The method of claim 12, wherein said performing the coherent string boundary detection further includes assigning a metric for each correlation output value.

14. The method of claim 13, wherein said performing the coherent string boundary detection further includes accumulating the metric for each bit location every 2 seconds.

15. The method of claim 14, wherein said performing the coherent string boundary detection further includes identifying a limited number of survivor paths based on highest accumulated metrics.

16. The method of claim 15, wherein the limited number of survivor paths is 8.

17. The method of claim 15, wherein said performing the coherent string boundary detection further includes updating the survivor paths as necessary for each extracted sequence.

18. The method of claim 17, wherein said performing the coherent string boundary detection further includes determining whether a set of accumulated metrics is greater than or equal to a threshold, and if so, then declaring a time mark boundary detection, wherein the time mark boundary detection provides the string synchronization.

19. A method of providing string synchronization for GLONASS signals, the method comprising:

performing coherent bit extraction on GLONASS bits;

performing coherent string boundary detection based on bits of the coherent bit extraction;

performing differential bit extraction on the GLONASS bits, including extracting 30 bits every 10 ms;

performing differential string boundary detection based on bits of the differential bit extraction, performing the differential string boundary detection and the coherent string boundary detection concurrently, and correlating the 30 bits with a time mark of GLONASS with bit flipping; and

providing the string synchronization, wherein whichever of the coherent string boundary detection and the differential string boundary detection first finds a string boundary, that string boundary is used for the string synchronization.

20. The method of claim 19, wherein said performing the differential string boundary detection further includes assigning a metric for each correlation output value.

21. The method of claim 20, wherein said performing the differential string boundary detection further includes accumulating the metric for each bit location every 2 seconds.

22. The method of claim 21, wherein said performing the differential string boundary detection further includes identifying a limited number of survivor paths based on highest accumulated metrics.

23. The method of claim 22, wherein the limited number of survivor paths is 8.

24. The method of claim 22, wherein said performing the differential string boundary detection further includes updating the survivor paths as necessary for each extracted sequence.

25. The method of claim 24, wherein said performing the differential string boundary detection further includes determining whether a set of accumulated metrics is greater than or equal to a threshold, and if so, then declaring a time mark boundary detection, wherein the time mark boundary detection provides the string synchronization.