FALSE LOCK DETECTION FOR PHYSICAL LAYER FRAME SYNCHRONIZATION

• US 20100150054A1
• Filed: 06/17/2009
• Published: 06/17/2010
• Est. Priority Date: 12/17/2008
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Thesling, William H., Becker, Donald W., Nimon, Matthew D.
• Granted Patent: US 8,401,038 B2
• Time in Patent Office: Days
• US Class Current: 370/316
• CPC Class Codes: H04B 7/18504 Aircraft used as relay or high altitude atmospheric platform
• CPC Class Codes: H04L 7/0016 correction of synchronization errors

Abstract

Systems, devices, processors, and methods are described which may be used for the reception of a wireless broadband signal at a user terminal from a gateway via a satellite. A wireless signal may include a series of physical layer frames, each frame including a physical layer header and payload. The received signal is digitized and processed using various novel physical layer headers and related techniques to synchronize the physical layer frames and recover data from physical layer headers for purposes of demodulation and decoding.

Claims

1. A terminal to process a plurality of physical layer frames of a received wireless signal, the terminal comprising:

a receiver module configured to receive a wireless signal comprising a plurality of physical layer frames;

a physical layer frame synchronization module, communicatively coupled with the receiver module, and configured to identify one or more start of frame locations for the plurality of physical layer frames to achieve frame synchronization;

a physical layer header decoder module, communicatively coupled with the physical layer frame synchronization module, and configured to decode at least a portion of a physical layer header of a selected one of the plurality physical layer frames according to a first decoding technique to identify signaling information attributable to a payload of the selected frame; and

an error identification module, communicatively coupled with the physical layer header decoder module, and configured to;

decode at least the portion of the physical layer header according to a second decoding technique;

compare results from the first technique to results of the second technique; and

generate an error value when the compared results do not match.

2. The terminal of claim 1, wherein the first decoding technique comprises finding a maximum likelihood transmitted data pattern across a plurality of sub-blocks of encoded data.

3. The terminal of claim 2, wherein the plurality of sub-blocks comprise one or more sub-blocks of the signaling information and one or more sub-blocks of parity information.

4. The terminal of claim 2, wherein,

the second decoding technique comprises performing a max bin search over each of the plurality of sub-blocks;

and

the error value is generated when each of the max bin searches does not match the maximum likelihood transmitted data pattern.

5. The terminal of claim 1, further comprising:

an error accumulator module, communicatively coupled with the error identification module, and configured to;

receive the generated error value; and

accumulate generated error values from the plurality of physical layer frames.

6. The terminal of claim 5, wherein the error accumulator module is further configured to:

determine that a false synchronization lock has occurred when the accumulated error value exceeds a threshold.

7. The terminal of claim 6, wherein the threshold is a user configurable parameter.

8. The terminal of claim 5, wherein the error accumulator module is further configured to:

weight a first set of error values from more recently received physical layer frames more heavily than a second set of error values from physical layer frames received before the more recently received physical layer frames.

9. The terminal of claim 5, wherein the error accumulator module is further configured to:

weight the generated error value in proportion to a degree of difference between the comparison of the results from the first technique to results of the second technique

10. The terminal of claim 5, wherein the error accumulator module comprises an infinite impulse response filter.

11. A device for processing a stream of physical layer frames, the device comprising:

means for identifying one or more start of frame locations for a subset of the physical layer frames to achieve frame synchronization;

means for decoding at least a portion of a physical layer header according to a first decoding technique to identify signaling information attributable to a payload of the frame;

means for decoding at least the portion of the physical layer header according to a second decoding technique;

means for comparing results from the first decoding technique to results of the second decoding technique; and

means for generating an error value when the compared results do not match.

12. A method for processing a plurality of physical layer frames, the method comprising:

acquiring frame synchronization for at least a subset of the plurality of physical layer frames;

decoding a code block of a physical layer header of a selected one of the plurality of physical layer frames according to a first decoding technique to identify signaling information attributable to a payload of the selected frame;

decoding the code block of the physical layer header according to a second decoding technique;

comparing results from the first decoding technique to results of the second decoding technique;

generating an error value when the compared results do not match; and

determining that a false synchronization lock has occurred when an accumulated error value exceeds a threshold.

13. The method of claim 12, further comprising:

re-initializing frame synchronization in response to the determination that the false synchronization lock has occurred.

14. The method of claim 12, wherein the first decoding technique comprises:

finding a maximum likelihood transmitted data pattern across a plurality of sub-blocks of encoded data comprising the physical layer header.

15. The method of claim 14, wherein each of the physical layer header comprises two Walsh code sub-blocks of the signaling information and one Walsh code sub-block of parity information.

16. The method of claim 14, further comprising:

utilizing the physical layer header to identify a start of frame.

17. The method of claim 14, wherein the second decoding technique comprises:

performing a max bin search over each of the plurality of sub-blocks, wherein the error value is generated when each of the max bin searches does not match the maximum likelihood transmitted data pattern.

18. The method of claim 12, further comprising:

accumulating error values from the plurality of physical layer frames, wherein the error values are weighted.

19. The method of claim 12, further comprising:

weighting error values from more recently received physical layer frames more heavily than error values from older physical layer frames.

20. The method of claim 12, further comprising:

weighting the generated error value in proportion to a degree of difference between the comparison of the results from the first technique to results of the second technique

21. The method of claim 12, wherein the threshold is a user configurable parameter.

22. A system for transmitting a wireless signal, the system comprising:

a gateway configured to;

generate a code block comprising a physical layer header of a selected physical layer frame, the code block identifying signaling information for a payload of the selected frame and further formatted to be useable by a receiver to identify a start of the frame; and

transmit a plurality of physical layer frames in a wireless signal, including the selected physical frame; and

a terminal, in communication with the gateway via satellite, and configured to;

receive the wireless signal;

synchronize at least a subset of the plurality of physical layer frames;

decode at least a portion of the physical layer header according to a first decoding technique to identify signaling information attributable to a payload of the selected frame;

decode at least the portion of the physical layer header according to a second decoding technique;

compare results from the first technique to results of the second technique; and

generate an error value when the compared results do not match.