Apparatus and method for synchronization in a multiple-carrier communication system by observing energy within a guard band

• US 6,389,087 B1
• Filed: 06/14/2000
• Issued: 05/14/2002
• Est. Priority Date: 06/23/1999
• Status: Expired due to Term

• Current Assignee: AT&T Mobility II LLC (AT&T, Inc.)
• Original Assignee: AT&T Wireless Services Incorporated (AT&T, Inc.)
• Inventors: Heinonen, Jari M., Hirano, Michael R.
• Primary Examiner(s): DEPPE, BETSY LEE
• Application Number:
  US09/593,449
• Time in Patent Office: 699 Days
• Field of Search: 375/354, 375/260, 375/130, 375/147, 375/136, 375/224, 375/316, 375/326, 375/344, 375/377, 375/367, 370/203, 370/204, 370/208, 370/503, 370/509, 370/516, 370/319, 370/344
• US Class Current: 375/354
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2678 using cyclostationarities, e.g. cyclic prefix or postfix

Abstract

A method, apparatus and system detects a loss of synchronization between a transmitter and a receiver in a multiple-carrier communication system such as an OFDM system. A guard band synchronization detector provides a synchronization indicator based on the energy detected within a guard band where a pilot tone is transmitted adjacent to the guard band. A timing error results in energy leakage into one or more guard bands. In one embodiment, a plurality of synchronization indicators are observed to determine whether a loss of synchronization between a transmitter and a receiver in the wireless system has occurred.

Claims

1. A method of determining a loss of synchronization between a receiver and a transmitter, the method comprising:

measuring an energy level of a pilot signal within a frequency guard band, the pilot signal transmitted adjacent to the frequency guard band; and

detecting a loss of synchronization between a transmitter transmitting the pilot signal and a receiver in accordance with the energy level.

2. A method in accordance with claim 1, further comprising:

determining loss of synchronization if the energy level within the guard band is above a threshold.

3. A method in accordance with claim 1, further comprising:

measuring another energy level of another pilot signal within another frequency guard band, the another pilot signal transmitted adjacent to the another frequency guard band, wherein detecting loss of synchronization comprises comparing a threshold to a ratio of the energy level to the another energy level.

4. A method in accordance with claim 3, wherein comparing the ratio comprises:

detecting loss of synchronization if the ratio is greater than a threshold.

5. A method in accordance with claim 3, wherein comparing the ratio comprises:

detecting loss of synchronization if the ratio is less than a threshold.

6. A method in accordance with claim 3, wherein comparing the ratio comprises:

detecting loss of synchronization if the ratio is outside a range.

7. A method in accordance with claim 1, further comprising:

detecting a loss of synchronization based on a timing error measured by a phase detector; and

determining loss of synchronization if the energy within the guard band is above an energy threshold and the timing error is larger than a timing threshold.

8. A method in accordance with claim 7, wherein the detecting the loss of synchronization based on the timing error comprises:

measuring a timing error of a received time slot within a series of received time slots.

9. A method in accordance with claim 1, further comprising:

detecting a loss of synchronization based on a slope of a line defined by a relationship between a frequency and a phase of a plurality of pilot signals; and

determining loss of synchronization if the energy within the guard band is above an energy threshold and the slope is greater than a timing threshold.

10. A method in accordance with claim 9, wherein detecting loss of synchronization comprises detecting loss of synchronization based on a number of slope threshold-exceeding occurrences within a time period.

11. A method of detecting a loss of synchronization between a transmitter and a receiver comprising:

measuring a first energy within a first guard band, wherein a first pilot signal is transmitted adjacent to the first guard band;

measuring a second energy within a second guard band, wherein a second pilot signal is transmitted adjacent to the second guard band; and

detecting a loss of synchronization between the transmitter and the receiver based on a ratio of the first energy to the second energy.

12. A method in accordance with claim 11, wherein detecting comprises:

detecting loss of synchronization if the ratio exceeds a guard band energy threshold.

13. A method in accordance with claim 11, wherein detecting comprises:

detecting loss of synchronization when the ratio is outside a range.

14. A method in accordance with claim 13, further comprising:

detecting loss of synchronization based on a relationship between a phase to a frequency of a plurality of pilot tones.

15. A method of detecting a loss of synchronization between a transmitter and a receiver in a multiple-carrier communication system, the method comprising:

measuring a phase-to-frequency relationship for a plurality of pilot tones received at the receiver from the transmitter;

measuring a first energy within a first guard band, wherein a first pilot signal is transmitted adjacent to the first guard band;

measuring a second energy within a second guard band, wherein a second pilot signal is transmitted adjacent to the second guard band; and

detecting a loss of synchronization between the transmitter and the receiver based on a ratio of the first energy to the second energy and the phase-to-frequency relationship.

16. A guard band energy synchronization detector comprising:

an energy detector adapted to measure an energy level of a pilot signal within a frequency guard band, the pilot signal transmitted adjacent to the frequency guard band; and

a controller adapted to determine a loss of synchronization between a transmitter transmitting the pilot signal and a receiver in accordance with the energy level.

17. A guard band energy synchronization detector in accordance with claim 16, wherein the controller is further adapted to determine loss of synchronization if the energy level within the guard band is above a threshold.

18. A guard band energy synchronization detector in accordance with claim 16, wherein the energy detector is further adapted to measure another energy level of another pilot signal within another frequency guard band, the another pilot signal transmitted adjacent to the another frequency guard band, the controller further adapted to detect loss of synchronization by comparing a threshold to a ratio of the energy level to the another energy level.

19. A guard band energy synchronization detector in accordance with claim 18, wherein the controller is further adapted to compare the ratio by detecting loss of synchronization if the ratio is greater than a threshold.

20. A guard band energy synchronization detector in accordance with claim 18, wherein the controller is further adapted to compare the ratio by detecting loss of synchronization if the ratio is less than a threshold.

21. A guard band energy synchronization detector in accordance with claim 18, wherein the controller is further adapted to compare the ratio by detecting loss of synchronization if the ratio is outside a range.

22. A guard band energy synchronization detector in accordance with claim 16, further comprising:

a phase-frequency slope synchronization detector configured to measure a timing error, the controller further adapted to determine loss of synchronization if the energy within the guard band is above an energy threshold and the timing error is larger than a timing threshold.