Method and system for synchronizing time-division-duplexed transceivers

• US 6,134,283 A
• Filed: 11/18/1997
• Issued: 10/17/2000
• Est. Priority Date: 11/18/1997
• Status: Expired due to Term

• Current Assignee: Amati Communications Corp. (Texas Instruments, Inc.)
• Original Assignee: Amati Communications Corp. (Texas Instruments, Inc.)
• Inventors: Sands, Nicholas P., Bingham, John A. C.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Fan, Chieh M.
• Application Number:
  US08/972,842
• Time in Patent Office: 1,064 Days
• Field of Search: 375/203, 375/219, 375/354, 375/357, 375/362, 375/364, 375/365, 375/368, 370/337, 370/347, 370/350, 370/503, 370/506, 370/507, 370/509, 370/510, 370/512, 370/514, 704/253
• US Class Current: 375/354
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601
• CPC Class Codes: H04L 5/1492 with time compression, e.g. operating according to the ping-pong technique

Abstract

An improved techniques for synchronizing transmissions and receptions of a data transmission system utilizing time division duplexing is disclosed. The improved synchronization techniques utilize the time-varying nature of the energy of the received data to obtain synchronization. In one embodiment, the improved synchronization technique uses the output signals from a multicarrier modulation unit (FFT unit) and thus provides the ability to avoid frequency tones that are susceptible to RF interference. The improved synchronization techniques can also utilize crosstalk interference levels to obtain synchronization. Remote receivers in the data transmission system are able to synchronize to central transmitters, central receivers in the data transmission system are able to synchronize to remote transmitters, and central transmitters are able to synchronize with one another.

Claims

1. A method for adjusting an alignment for a first transceiver to receive frames of data transmitted from a second transceiver over a transmission medium to the first transceiver, the first transceiver and the second transceiver being associated with a data transmission system providing two-way data communication using time division duplexing, said method comprising the acts of:

measuring an energy amount for each of a plurality of consecutive frames of received data;

detecting an edge in the plurality of consecutive frames of the received data based on the measured energy amounts, the edge detected being a burst edge, said detecting including at least the acts of;

computing successive energy differences in the plurality of the measured energy amounts; and

identifying a largest one of the successive energy differences, the largest one of the successive energy difference corresponding to the burst edge; and

determining an alignment error estimate using the edge detected in the plurality of consecutive frames.

2. A method as recited in claim 1, wherein the data transmission system transmits data using a superframe structure having a plurality of frames, a first set of the frames in the superframe transmit data in a first direction, and a second set of the frames in the superframe transmit data in a second direction.

3. A method as recited in claim 2, wherein the first transceiver uses a frame boundary pointer to identify a beginning of a frame in the superframe being received, and

wherein said method further comprises:

adjusting the frame boundary pointer in accordance with the alignment error estimate.

4. A method as recited in claim 3, wherein the alignment error estimate is an estimated alignment error as a fraction of a frame.

5. A method as recited in claim 3, wherein said method further comprises:

comparing the alignment error estimate with a threshold amount;

repeating said measuring through said determining until said comparing indicates that the alignment error estimate is less than the threshold amount.

6. A method as recited in claim 5, wherein said method further comprises:

outputting superframe identification information.

7. A method as recited in claim 1, wherein said determining comprises:

identifying a prior energy difference and a subsequent energy difference, the prior energy difference being the one of the successive differences immediately preceding the largest one of the successive energy differences, and the subsequent energy difference being the one of the successive differences immediately following the largest one of the successive energy differences; and

determining the alignment error estimate based on the prior energy difference and the subsequent energy difference.

8. A method as recited in claim 7, wherein said determining of the alignment error estimate computes a difference amount between the subsequent energy difference and the prior energy difference.

9. A method as recited in claim 7, wherein said determining of the alignment error estimate computes a difference amount between the subsequent energy difference and the prior energy difference, and then normalizes the difference amount to produce the alignment error estimate.

10. A method for adjusting an alignment for a first transceiver to receive frames of data transmitted from a second transceiver over a transmission medium to the first transceiver, the first transceiver and the second transceiver being associated with a data transmission system providing two-way data communication using time division duplexing, the first transceiver uses a frame boundary pointer to identify a beginning of a frame in the superframe being received, said method comprising the acts of:

measuring an energy amount for each of a plurality of consecutive frames of received data;

detecting an edge in the plurality of consecutive frames of the received data based on the measured energy amounts;

determining an alignment error estimate using the edge detected in the plurality of consecutive frames; and

adjusting the frame boundary pointer in accordance with the alignment error estimate.

11. A method as recited in claim 10, wherein the alignment error estimate is an estimated alignment error as a fraction of a frame.

12. A method as recited in claim 10, wherein said method further comprises:

comparing the alignment error estimate with a threshold amount;

repeating said measuring, detecting, determining, and until said comparing indicates that the alignment error estimate is less than the threshold amount.

13. A method as recited in claim 12, wherein said method further comprises:

outputting superframe identification information.

14. A method for adjusting an alignment for a first transceiver to receive frames of data transmitted from a second transceiver over a transmission medium to the first transceiver, the first transceiver and the second transceiver being associated with a data transmission system providing two-way data communication using time division duplexing, the data transmission system transmits data using a superframe structure having a plurality of frames, a first set of the frames in the superframe transmit data in a first direction, a second set of the frames in the superframe transmit data in a second direction, and some of the frames contain a cyclic prefix for the superframe structure, said method comprising the acts of:

(a) measuring an energy amount for each of a plurality of consecutive frames of received data, said measuring (a) of the energy amounts including at least the acts of;

measuring energy amounts of a first set of consecutive frames of received data for the superframe structure;

measuring energy amounts of a second set of consecutive frames of received data for the superframe structure, the second set of the consecutive frames being offset from and overlapped with the first set of the consecutive frames; and

combining together the energy amounts from respective consecutive frames from the first and second sets of the consecutive frames to produce the energy amounts; and

(b) detecting an edge of the superframe structure within the plurality of consecutive frames of received data using the measured energy amounts.

15. A method as recited in claim 14, wherein the first transceiver is a remote unit and the second transceiver is a central unit.

16. A method as recited in claim 14, wherein the second transceiver is a remote unit and the first transceiver is a central unit.

17. A method as recited in claim 14, wherein the energy amount is a power amount.

18. A method as recited in claim 14, wherein the number of frames in the first and second sets of the consecutive frames is equal to the length of the superframe structure less the length of the cyclic prefix.

19. A method as recited in claim 18, wherein said combining determines mean energy amounts for each of the frames of the superframe structure including the cyclic prefix.

20. A computer readable medium containing program instructions for adjusting an alignment for a first transceiver to receive frames of data transmitted from a second transceiver over a transmission medium to the first transceiver, the first transceiver and the second transceiver being associated with a data transmission system providing two-way data communication using time division duplexing, said computer readable medium comprising:

first computer readable code devices for measuring an energy amount for each of a plurality of consecutive frames of received data; and

second computer readable code devices for computing an alignment error estimate using the measured energy amounts, said second computer readable code devices including at least;

computer readable code devices for detecting an edge in the plurality of consecutive frames of the received data based on the measured energy amounts, said computer readable code devices for detecting the edge including at least computer readable code devices for computing successive energy differences in the plurality of the measured energy amounts, and computer readable code devices for identifying a largest one of the successive energy differences, the largest one of the successive energy difference corresponding to a burst edge; and

computer readable code devices for determining the alignment error estimate using the edge detected in the plurality of consecutive frames.

21. A computer readable medium as recited in claim 20, wherein said second computer readable medium comprises:

computer readable code devices for identifying a prior energy difference and a subsequent energy difference, the prior energy difference being the one of the successive differences immediately preceding the largest one of the successive energy differences, and the subsequent energy difference being the one of the successive differences immediately following the largest one of the successive energy differences;

computer readable code devices for determining the alignment error estimate based on the prior energy difference and the subsequent energy difference.

22. A computer readable medium containing program instructions for adjusting an alignment for a first transceiver to receive frames of data transmitted from a second transceiver over a transmission medium to the first transceiver, the first transceiver and the second transceiver being associated with a data transmission system providing two-way data communication using time division duplexing, the data transmission system transmits data using a superframe structure having a plurality of frames, some of the frames transmit data in a first direction, some of the frames transmit data in a second direction, and some of the frames contain a cyclic prefix for the superframe structure, said computer readable medium comprising:

first computer readable code devices for measuring an energy amount for each of a plurality of consecutive frames of received data, said second computer readable code devices including at least;

computer readable code for measuring energy amounts of a first set of consecutive frames of received data for the superframe structure;

computer readable code for measuring energy amounts of a second set of consecutive frames of received data for the superframe structure, the second set of the consecutive frames being offset from and overlapped with the first set of the consecutive frames; and

computer readable code for combining together the energy amounts from respective consecutive frames from the first and second sets of the consecutive frames to produce the energy amounts for said second computer readable code devices; and

second computer readable code devices for computing an alignment error estimate using the measured energy amounts, said second computer readable code devices including at least;

computer readable code devices for detecting an edge in the plurality of consecutive frames of the received data based on the measured energy amounts; and

computer readable code devices for determining the alignment error estimate using the edge detected in the plurality of consecutive frames.

23. A computer readable medium as recited in claim 22, wherein said combining determines mean energy amounts for each of the frames of the superframe structure including the cyclic prefix.

24. A computer readable medium as recited in claim 23, wherein the number of frames in the first and second sets of the consecutive frames is equal to the length of the superframe structure less the length of the cyclic prefix.