Method and apparatus for maintaining synchronization in a communication system

• US 20040202202A1
• Filed: 03/26/2004
• Published: 10/14/2004
• Est. Priority Date: 04/09/2003
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Currivan, Bruce, Pantelias, Niki, Kolze, Thomas
• Granted Patent: US 8,457,040 B2
• Time in Patent Office: Days
• US Class Current: 370/503
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43
• CPC Class Codes: H04J 3/0688 Change of the master or reference, e.g. take-over or failure of the master
• CPC Class Codes: H04L 1/004 by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00
• CPC Class Codes: H04L 7/048 using the properties of error detecting or error correcting codes, e.g. parity as synchronisation signal

Abstract

A central entity and/or a remote device in a communication system are designed to address the problem of maintaining upstream synchronization in the remote device after loss of the downstream signal. One issue of particular importance is maintaining upstream transmissions from the remote device in an S-CDMA (or perhaps S-TDMA) mode that do not degrade performance of the communication system via poor upstream timing or a need for re-ranging. By providing novel functionality at the central entity for synchronizing first and second downstream signals and/or by providing novel functionality at the remote device for determining a symbol clock offset between a first terminated downstream signal and a second re-acquired downstream signal, embodiments of the present invention facilitate maintenance of synchronization through the loss of the downstream signal, thereby minimizing the need for re-ranging and avoiding poorly timed upstream bursts.

Claims

1. A method for maintaining synchronization in a communication system wherein a central entity transmits a signal containing timing information to one or more remote devices, the one or more remote devices using the timing information for scheduling transmissions, the method comprising:

synchronizing a first symbol clock and a second symbol clock;

transmitting a first signal to the one or more remote devices, wherein the first signal includes timing information based on the first symbol clock; and

upon termination of transmission of the first signal to the one or more remote devices, transmitting the second signal to the one or more remote devices, wherein the second signal includes timing information based on the second symbol clock.

2. The method of claim 1, further comprising:

transmitting a notification message to the one or more remote devices indicating that the first signal will be terminated prior to the termination of transmission of the first signal.

3. A method for maintaining synchronization in a communication system wherein a central entity transmits a signal containing timing information to one or more remote devices, the one or more remote devices using the timing information for scheduling transmissions, the method comprising:

synchronizing a first symbol clock and a second symbol clock;

transmitting a first signal to the one or more remote devices, wherein the first signal includes timing information based on the first symbol clock and data having a first forward error correction (FEC) alignment; and

upon termination of transmission of the first signal to the one or more remote devices, transmitting the second signal to the one or more remote devices, wherein the second signal includes timing information based on the second symbol clock and data having a second FEC alignment that is synchronized with the first FEC alignment.

4. The method of claim 3, further comprising:

transmitting a notification message to the one or more remote devices indicating that the first signal will be terminated prior to the termination of transmission of the first signal.

5. A method for maintaining synchronization in a communication system wherein a central entity transmits a signal containing timing information to one or more remote devices, the one or more remote devices using the timing information for scheduling transmissions, the method comprising:

synchronizing a first symbol clock and a second symbol clock;

transmitting a first signal to the one or more remote devices, wherein the first signal includes timing information based on the first symbol clock and data having a first forward error correction (FEC) alignment;

generating a second signal that includes timing information based on the second symbol clock and data having a second forward error correction (FEC) alignment;

transmitting calibration information relating to a difference between the first FEC alignment and the second FEC alignment to the one or more remote devices; and

upon termination of transmission of the first signal to the one or more remote devices, transmitting the second signal to the one or more remote devices.

6. The method of claim 5, further comprising:

generating the calibration information by comparing the first FEC alignment to the second FEC alignment.

7. The method of claim 5, further comprising:

generating the calibration information, wherein generating the calibration information comprises generating first calibration data by comparing the first FEC alignment to a reference FEC alignment and generating second calibration data by comparing the second FEC alignment to the reference alignment.

8. The method of claim 5, further comprising:

transmitting a notification message to the one or more remote devices indicating that the first signal will be terminated prior to the termination of transmission of the first signal.

9. An apparatus in a communication system, the apparatus comprising:

a first transmitter adapted to transmit a first signal to one or more remote devices, wherein the first signal includes first timing information based on a first symbol clock;

a second transmitter adapted to transmit a second signal to the one or more remote devices in response to the first transmitter terminating transmission of the first signal, wherein-the second signal includes second timing information based on a second symbol clock; and

a synchronization element adapted to synchronize the first symbol clock and the second symbol clock.

10. The apparatus of claim 9, wherein the first transmitter transmits a notification message to the one or more remote devices indicating that the first signal will be terminated prior to termination of transmission of the first signal.

11. The apparatus of claim 9, wherein the apparatus is a cable modem termination system (CMTS).

12. An apparatus in a communication system, the apparatus comprising:

a first transmitter adapted to transmit a first signal to one or more remote devices, wherein the first signal includes first timing information based on a first symbol clock and first data having a first forward error correction (FEC) alignment;

a second transmitter adapted to transmit a second signal to the one or more remote devices in response to the first transmitter terminating transmission of the first signal, wherein the second signal includes second timing information based on a second symbol clock and second data having a second FEC alignment that is synchronized with the first FEC alignment; and

a synchronization element adapted to synchronize the first symbol clock and the second symbol clock.

13. The apparatus of claim 12, wherein the first transmitter transmits a notification message to the one or more remote devices indicating that the first signal will be terminated prior to termination of transmission of the first signal.

14. The apparatus of claim 12, wherein the apparatus is a cable modem termination system (CMTS).

15. An apparatus in a communication system, the apparatus comprising:

a first transmitter adapted to transmit a first signal to one or more remote devices, wherein the first signal includes first timing information based on a first symbol clock and first data having a first forward error correction (FEC) alignment;

a second transmitter adapted to transmit a second signal to the one or more remote devices in response to the first transmitter terminating transmission of the first signal, wherein the second signal includes second timing information based on a second symbol clock and second data having a second FEC alignment that is synchronized with the first FEC alignment; and

a synchronization element adapted to synchronize the first symbol clock and the second symbol clock;

wherein at least one of the first transmitter and the second transmitter is adapted to transmit calibration information relating to a difference between the first FEC alignment and the second FEC alignment to the one or more remote devices.

16. The apparatus of claim 15, further including a calibration element adapted to generate the calibration information by comparing the first FEC alignment and the second FEC alignment.

17. The apparatus of claim 15, further including a calibration element adapted to generate the calibration information by comparing the first FEC alignment to a reference FEC alignment and by comparing the second FEC alignment to the reference alignment.

18. The apparatus of claim 15, wherein the first transmitter transmits a notification message to the one or more remote devices indicating that the first signal will be terminated prior to termination of transmission of the first signal.

19. The apparatus of claim 15, wherein the apparatus is a cable modem termination system (CMTS).