Symmetric chirp communications acquisition method and apparatus

• US 6,396,866 B1
• Filed: 05/01/1998
• Issued: 05/28/2002
• Est. Priority Date: 05/01/1998
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Smith, Martin P., Kolze, Thomas J., Brown, Kenneth L., Upton, Eric L.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Ha, Dac V.
• Application Number:
  US09/071,574
• Time in Patent Office: 1,488 Days
• Field of Search: 375/139,142,152,343,369 370/503,515,350
• US Class Current: 375/139
• CPC Class Codes: H04L 2027/0095 in a preamble or similar structure
• CPC Class Codes: H04L 27/2278 using correlation techniques, e.g. for spread spectrum signals

Abstract

A method of acquiring a communications signal is provided. The method includes the steps of storing a forward chirp sync segment (106) of an auto-correlating forward chirp sync (102) and storing a reverse chirp sync segment (108) of a symmetric auto-correlating reverse chirp sync (104). A header comprising of either a forward chirp sync FCS (102) or a reverse chirp sync RCS (104), a predetermined number of data blocks comprising a data frame (308), and the symmetric auto-correlating trailer is received. The header, the data blocks, and the symmetric trailer are susceptible to frequency error. The method correlates the FCS segment (106) with the auto-correlating FCS (102) to provide a FCS correlation signal (312) and correlates the RCS segment (104) with the auto-correlating RCS (108) to provide a RCS correlation signal (314). The method determines the frequency error, symbol timing, and frame timing based upon the FCS correlation signal (312) and the RCS correlation signal (314).

Claims

1. A method of acquiring a communications signal, the method comprising the steps of:

a) storing a segment of an auto-correlating forward chirp sync waveform (FCS);

b) storing a segment of a symmetric auto-correlating reverse chirp sync waveform (RCS);

c) receiving said auto-correlating FCS, a predetermined number of symbols comprising a data frame, and said symmetric auto-correlating RCS, said auto-correlating FCS, said symbols, and said symmetric auto-correlating RCS susceptible to frequency error;

d) correlating said FCS segment with said auto-correlating FCS to provide a FCS correlation signal;

e) correlating said RCS segment with said auto-correlating RCS to provide a RCS correlation signal; and

f) determining said frequency error based upon said FCS correlation signal and said RCS correlation signal.

2. The method of claim 1, further comprising the step of:

g) determining symbol timing for said symbols based upon said FCS correlation signal and said RCS correlation signal.

3. The method of claim 2, further comprising the step of:

h) determining frame timing for said data frame based upon said FCS correlation signal and said RCS correlation signal.

4. The method of claim 1, further comprising the step of:

g) determining frame timing for said data frame based upon said FCS correlation signal and said RCS correlation signal.

5. The method of claim 1, wherein said receiving step receives a forward chirp sync waveform representing said auto-correlating FCS.

6. The method of claim 5, wherein said receiving step receives a reverse chirp sync waveform representing said symmetric auto-correlating RCS.

7. The method of claim 6, further comprising the step of:

g) determining symbol timing for said symbols based upon said FCS correlation signal and said RCS correlation signal.

8. The method of claim 6, further comprising the step of:

g) determining frame timing for said data frame based upon said FCS correlation signal and said RCS correlation signal.

9. The method of claim 8, further comprising the step of:

h) determining symbol timing for said symbols based upon said FCS correlation signal and said RCS correlation signal.

10. The method of claim 1, wherein said correlating step comprises the steps of:

a) providing a first Bragg grating written with said FCS segment; and

b) detecting energy returned by said first Bragg grating in response to said auto-correlating FCS.

11. The method of claim 10, wherein said correlating step comprises the further steps of:

c) providing a second Bragg grating written with said RCS segment; and

d) detecting energy returned by said second Bragg grating in response to said symmetric auto-correlating RCS.

12. The method of claim 1, wherein said correlating step comprises the steps of:

a) providing a surface acoustic wave material;

b) forming a first series of detection fingers on said surface acoustic wave material, said first series of detection fingers representing said FCS reference; and

c) detecting energy returned by said first series of detection fingers in response to said auto-correlating FCS.

13. The method of claim 12, wherein said correlating step comprises the further steps of:

a) forming a second series of detection fingers on said surface acoustic wave material, said second series of detection fingers representing said RCS reference; and

b) detecting energy returned by said second series of detection fingers in response to said symmetric auto-correlating RCS.

14. A synchronization processor comprising:

a memory storing a plurality of received signal segments;

an address counter connected to said memory;

a forward sync correlator connected to said memory and responsive to a first plurality of coefficients representing an auto-correlating header segment;

a reverse sync correlator connected to said memory and responsive to a second plurality of coefficients representing a symmetric auto-correlating trailer segment;

a peak detection circuit connected to said forward sync correlator and said reverse sync correlator; and

an arithmetic logic unit connected to said peak detection circuit.

15. The synchronization processor of claim 14, wherein said forward sync correlator comprises a first delay line, a first plurality of multipliers connected to said first delay line, and a first summer connected to said first plurality of multipliers.

16. The synchronization processor of claim 15, wherein said reverse sync correlator comprises a second delay line, a second plurality of multipliers connected to said second delay line, and a summer connected to said second plurality of multipliers.

17. The synchronization processor of claim 14, wherein a digital signal processor comprises said memory, said address counter, said forward sync correlator, said reverse sync correlator, said peak detection circuit, and said arithmetic logic unit.

18. The synchronization processor of claim 14, wherein said peak detection circuit comprises a first comparison circuit connected to said forward sync correlator, and a second comparison circuit connected to said second sync correlator.

19. The synchronization processor of claim 18, wherein said peak detection circuit further comprises a predetermined threshold input connected to said first comparison circuit and said second comparison circuit.

20. The synchronization processor of claim 16, wherein said auto-correlating header segment is a forward chirp sync segment and wherein said symmetric auto-correlating trailer segment is a reverse chirp sync segment.

21. A method of generating a signal for transmission centered at a predetermined carrier frequency comprising:

generating an auto-correlating header sweeping in frequency an expected frequency error range of the predetermined carrier frequency;

generating a predetermined number of symbols comprising a first data block following the auto-correlating header,

generating a symmetric auto-correlating trailer following the data block; and

generating after the symmetric auto-correlating trailer, a series of additional data blocks, each additional data block followed by at least one of an additional auto-correlating header and trailer, wherein the auto-correlating header, first data block, auto-correlating trailor, additional data blocks, and additional auto-correlating headers and trailers form a pseudorandom noise sequence.

22. A method of generating a signal for transmission centered at a predetermined carrier frequency comprising:

generating an auto-correlating header sweeping in frequency an expected frequency error range of the predetermined carrier frequency;

generating a predetermined number of symbols comprising a first data block following the auto-correlating header;

generating a symmetric auto-correlating trailer following the data block; and

generating after the symmetric auto-correlating trailer, a series of additional data blocks, each additional data block followed by at least one of an additional auto-correlating header and trailer, wherein the auto-correlating header, first data block, auto-correlating trailer, additional data blocks, and additional auto-correlating headers and trailers form a frame synchronization code.