Synchronization burst processor for a processing satellite

• US 6,434,361 B1
• Filed: 09/29/1999
• Issued: 08/13/2002
• Est. Priority Date: 09/29/1999
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Wright, David A., Moretti, Vincent C., Caso, Gregory S., Carrozza, Dominic P.
• Primary Examiner(s): To, Doris H.
• Assistant Examiner(s): Orgad, Edan
• Application Number:
  US09/408,261
• Time in Patent Office: 1,049 Days
• Field of Search: 455/12.1, 455/13.2, 455/427, 455/428, 455/430, 370/315, 370/316, 370/321, 370/345, 370/505, 370/347, 370/324, 370/350, 375/343, 375/367, 375/149, 375/150, 375/152, 375/142, 375/354
• US Class Current: 455/13.2
• CPC Class Codes: H04B 7/2125 Synchronisation
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15

Abstract

A synchronization burst processor (56) used in a processing satellite (12) in a satellite based communications system (10) is provided with a sync burst memory (72), a first double correlator (74), a second double correlator (76) and a modulus module (78). The sync burst memory (72) stores at least one sync burst (52) transmitted from a terrestrial terminal (14) to the processing satellite (12) where the sync burst (52) is formed from a quadrature pair sample set {p, q}. The first double correlator (74) performs an early correlation and a late correlation of the p samples relative to a sync burst slot (50) to generate an early correlation Pe and a late correlation Pl. The second double correlator (76) performs an early correlation and a late correlation of the q samples relative to the sync burst slot (50) to generate an early correlation Qe and a late correlation Ql. The modulus module (78) determines an early modulus Re and a late modulus Rl from the early correlations Pe and Qe and from the late correlations Pl and Ql. The early modulus Re and the late modulus Rl are used to determine if the sync burst (52) is present in the sync burst slot (50) and if the sync burst (52) is early or late relative to the sync burst slot (50).

Claims

1. A synchronization burst processor for use in a processing satellite in a satellite based communications system, said synchronization burst processor comprising:

a sync burst memory operable to store at least one sync burst transmitted from at least one terrestrial terminal to the processing satellite, said sync burst formed from a quadrature pair sample set {p, q};

a first double correlator operable to perform an early correlation and a late correlation of said p samples relative to a sync burst slot to generate an early correlation Pe and a late correlation Pl;

a second double correlator operable to perform an early correlation and a late correlation of said q samples relative to said sync burst slot to generate an early correlation Qe and a late correlation Ql; and

a modulus module operable to determine an early modulus Re and a late modulus Rl from said early correlations Pe and Qe and from said late correlations Pl and Ql, wherein said early modulus Re and said late modulus Rl are used to determine if said sync burst is present in said sync burst slot and if said sync burst is early or late relative to said sync burst slot.

2. The synchronization burst processor as defined in claim 1 further comprising a test functions module operable to perform tests on said early modulus Re and said late modulus Rl to determine if said sync burst is present in said sync burst slot and if said sync burst is early or late relative to said sync burst slot.

3. The synchronization burst processor as defined in claim 2 wherein said test functions module performs an energy test on a sum of said early modulus Re and said late modulus Rl, said sum being compared to a threshold, whereby if said threshold is not exceeded, an absent outcome is declared.

4. The synchronization burst processor as defined in claim 3 wherein said test functions module further performs a ratio test if said energy test is passed, said ratio test compares ABS [LOG[Re/Rl]] to a second threshold, whereby if said second threshold is exceeded then an absent outcome is declared.

5. The synchronization burst processor as defined in claim 4 wherein said test function module performs a third test if said energy test is passed and said ratio test is passed, said third test determines if said sync burst is early or late by comparing said early modulus Re with said late modulus Rl, whereby if said early modulus Re is greater than said late modulus Rl, then said sync burst is early, otherwise said sync burst is late.

6. The synchronization burst processor as defined in claim 1 wherein said quadrature pair sample set (p, q) stored in said sync burst memory are odd samples of said sync burst.

7. The synchronization burst processor as defined in claim 1 wherein said first double correlator and said second double correlator perform said early correlations and said late correlations against a sync burst template sequence which is loaded from an onboard processor on the processing satellite.

8. The synchronization burst processor as defined in claim 1 wherein said early modulus Re is determined by Re={square root over (Pe²+L +Qe²+L )} and said late modulus Rl is determined by Rl={square root over (Pl²+L +Ql²+L )}.

9. The synchronization burst processor as defined in claim 1 further comprising a select module operable to select a quadrature pair sample set {p, q} during a synchronization burst block, said quadrature pair sample set {p, q} including odd and even quadrature pair samples from a plurality of sync bursts.

10. A synchronization burst processor for use in a processing satellite in a satellite based communications system, said synchronization burst processor comprising:

a select module operable to select a quadrature pair sample set {p, q} during a synchronization burst block, said quadrature pair sample set {p, q} including odd and even samples from a plurality of sync bursts;

a sync burst memory operable to store said odd samples from said quadrature pair sample set {p, q} of said plurality of sync bursts;

a first double correlator operable to perform an early correlation and a late correlation of said p samples from said sync burst memory against a sequence template to generate an early correlation Pe and a late correlation Pl;

a second double correlator operable to perform an early correlation and a late correlation of said q samples from said sync burst memory against said sequence template to generate an early correlation Qe and a late correlation Ql; and

wherein said early correlations Pe and Qe and said late correlations Pl and Ql are used to determine if each of said sync bursts are present in a corresponding sync burst slot and if each of said sync bursts are early or late relative to said corresponding sync burst slot.

11. The synchronization burst processor as defined in claim 10 further comprising a modulus module operable to determine an early modulus Re and a late modulus Rl from said early correlations Pe and Qe and from said late correlations Pl and Ql, whereby said early modulus Re and said late modulus Rl are used to determine if each of said sync bursts is present in said corresponding sync burst slot and if each of said sync bursts is early or late relative to said corresponding sync burst slot.

12. The synchronization burst processor as defined in claim 11 wherein said early modulus Re is determined by Re={square root over (Pe²+L +Qe²+L )} and said late modulus Rl is determined by Rl={square root over (Pl²+L +Ql²+L )}.

13. The synchronization burst processor as defined in claim 10 further comprising a test functions module operable to determine if each of said sync bursts are present in said corresponding sync burst slot and if each of said sync bursts are early or late relative to said corresponding sync burst slot.

14. The synchronization burst processor as defined in claim 10 wherein said sequence template is loadable from an onboard control processor in the processing satellite.

15. A synchronization burst processor for use in a processing satellite in a satellite based communications system, said synchronization burst processor comprising:

a first double correlator operable to perform an early correlation and a late correlation of p samples from a quadrature pair sample set {p, q} of a sync burst to generate an early correlation Pe and a late correlation Pl;

a second double correlator operable to perform an early correlation and a late correlation of q samples from said quadrature pair sample set {p, q} of said sync burst to generate an early correlation Qe and a late correlation Ql;

a modulus module operable to determine an early modulus Re and a late modulus Rl from said early correlations Pe and Qe and from said late correlations Pl and Ql; and

a test functions module operable to determine if said sync burst is present in a sync burst slot and if said sync burst is early or late relative to said sync burst slot using said early modulus Re and said late modulus Rl.

16. The synchronization burst processor as defined in claim 15 wherein said test functions module performs an energy test on a sum of said early modulus Re and said late modulus Rl, said sum being compared to a threshold, whereby if said threshold is not exceeded, an absent outcome is declared.

17. The synchronization burst processor as defined in claim 16 wherein said test functions module further performs a ratio test if s aid energy test is passed, said ratio test compares ABS [LOG[Re/Rl]] to a second threshold, whereby if said second threshold is exceeded then an absent outcome is declared.

18. The synchronization burst processor as defined in claim 17 wherein said test function module performs a third test if said energy test is passed and said ratio test is passed, said third test determines if said sync burst is early or late by comparing said early modulus Re with said late modulus Rl, whereby if said early modulus Re is greater than said late modulus Rl, then said sync burst is early, otherwise said sync burst is late.

19. The synchronization burst processor as defined in claim 15 wherein said quadrature pair sample set {p, q} are odd samples of said sync burst.

20. The synchronization burst processor as defined in claim 15 wherein said first double correlator and said second double correlator perform said early correlations and said late correlations against a sync burst template sequence which is loaded from an onboard processor on the processing satellite.