Multi-carrier transmission systems

• US 6,363,128 B1
• Filed: 06/23/1999
• Issued: 03/26/2002
• Est. Priority Date: 09/02/1996
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: STMicroelectronics NV
• Inventors: Bahlenberg, Gunnar, Isaksson, Anders, Okvist, Goran, Ljunggren, Lis-Marie, Isaksson, Mikael, Nordstrom, Tomas, Johansson, Magnus, Isaksson, Lars-Ake, Tonvall, Harry, Bengtsson, Daniel, Olsson, Lennart, Hakansson, Siwert, Stefansson, Tomas, Wen, Ye, Ohman, Hans
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/147,746
• Time in Patent Office: 1,007 Days
• Field of Search: 375/355, 375/376, 375/260, 370/509, 370/480
• US Class Current: 375/355
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

A multi-carrier transmission system, such as a DMT system. A receiver must be able to recover a sampling clock that is very accurately synchronized to a transmitter sampling clock. Typically, synchronization is achieved by using a reserved carrier, the pilot carrier, which is transmitted with a fixed phase. The receiver sampling clock is then phase locked to the pilot carrier. Frame timing can be recovered by using a correlation technique. Thus an improved method of recovering a sample clock and phase locking the sampling clock to a pilot carrier is provided.

Claims

1. A receiver, for use with a multi-carrier transmission system using orthogonal carriers, in which a receiver sampling clock is synchronized with a transmitter sampling clock by phase locking said receiver sampling clock to a pilot carrier, characterised in that said receiver includes:

a first feedback loop adapted to align said receiver'"'"'s frame timing by using a frame timing deviation signal to control an oscillator means adapted to produce said receiver sampling clock; and

a second feedback loop adapted to compensate for channel effects by using a signal representative of an argument estimate of said pilot carrier to control said oscillator means.

2. A receiver, as claimed in claim 1, characterised in that said oscillator means is a VCXO.

3. A receiver, as claimed in claim 1, characterised in that said multi-carrier transmission system is a DMT transmission system.

4. A receiver, as claimed in claim 1, characterised in that said multi-carrier transmission system is a DMT based VDSL system.

5. A receiver, as claimed in claim 1, characterised in that said receiver includes correlator means connected to peak position estimator means adapted to produce said frame timing deviation signal.

6. A receiver, as claimed in claim 1, characterised in that said receiver includes pilot argument estimation means adapted to produce said signal representative of said pilot argument estimate.

7. A receiver, as claimed in claim 6, characterised in that said peak position estimation means and said pilot argument estimation means are each connected to feedback controller means which are connected, via a D/A, to said oscillator means.

8. A receiver, as claimed in claim 7, characterised in that said feedback controller means comprises two feedback controllers whose outputs are summed to produce a control signal for said oscillator means.

9. A receiver, as claimed in claim 1, characterised in that said signal representative of said pilot argument estimate functions as an equaliser parameter and causes said oscillator means to be adjusted in a manner which compensates for channel effects.

10. A receiver, as claimed in claim 1, characterised in that said receiver operates in accordance with a synchronization process having the following elements:

frame alignment by adjustment of said oscillator means in response to a frame timing deviation signal;

equalisation by adjustment of said oscillator means in response to said signal representative of said pilot carrier argument; and

after a settling down period has elapsed, adjustment of said oscillator means in response to said signal representative of said pilot carrier argument estimate, only.

11. A receiver, as claimed in claim 1, characterised in that said signal representative of said pilot carrier argument estimate is employed to equalize time variations in channel characteristics for a channel over which said pilot carrier is transmitted.

12. A receiver, as claimed in claim 1, characterised in that monitoring means are provided to monitor frame timing deviations and to initiate resynchronization if said frame timing deviations exceed a large predetermined value.

13. A transceiver, including a transmitter and a receiver, characterised in that said receiver is a receiver as claimed in claim 1.

14. A multi-carrier transmission system using orthogonal carriers, in which a receiver sampling clock is phase locked to a pilot carrier, characterised in that said multi-carrier transmission system includes two transceivers as claimed in claim 13.

15. A transceiver, multi-carrier transmission system, or method, as claimed in claim 13, characterised in that said multi-carrier transmission system is a DMT system.

16. A transceiver, multi-carrier tranmission system, or method, as claimed in claim 15, characterised in that said multi-carrier transmission system is a DMT based VDSL system.

17. In a multi-carrier system in which a transmitter and a receiver are synchronised by means of a pilot carrier transmitted by said transmitter to said receiver, a method of recovering, at said receiver, said transmitter'"'"'s sampling clock from said pilot signal and synchronising said transmitter with said receiver, characterised by the steps of:

deriving a frame timing deviation signal;

using said frame timing deviation signal to align a received frame structure with a transmitted frame structure; and

deriving an estimate of said pilot carrier'"'"'s argument and using it as an equalisation parameter to compensate for channel influence.

18. In a multi-carrier transmission system using orthogonal carriers, in which a receiver sampling clock is synchronized with a transmitter sampling clock by phase locking said receiver sampling clock to a pilot carrier transmitted by said transmitter, a method of synchronising said receiver'"'"'s sampling clock to said transmitter sampling clock, characterised by the steps of:

aligning said receiver'"'"'s frame timing by using a frame timing deviation signal to control said receiver'"'"'s sampling clock; and

compensating for channel effects by using a signal representative of an argument estimate of said pilot carrier to control said receiver'"'"'s sampling clock.

19. A method, as claimed in claim 18, characterised in that said multi-carrier transmission system is a DMT transmission system.

20. A method, as claimed in claim 18, characterised in that said multi-carrier transmission system is a DMT based VDSL system.

21. A method, as claimed in claim 18, characterised by deriving said frame timing deviation signal, by correlation, from a stream of received time domain data.

22. A method, as claimed in claim 18, characterised by adding said frame timing deviation signal to said signal representative of an argument estimate of said pilot carrier to produce a receiver sampling clock control signal.

23. A method, as claimed in claim 18, characterised by said signal representative of said pilot argument estimate functioning as an equaliser parameter and causing said oscillator means to be adjusted in a manner which compensates for channel effects.

24. A method, as claimed in claim 18, characterised by said method including the following elements:

frame alignment, between said receiver and said transmitter, by adjustment of said receiver'"'"'s sampling clock in response to a frame timing deviation signal;

equalisation of a channel over which said pilot signal is transmitted by adjustment of said receiver'"'"'s sampling clock in response to said signal representative of said pilot carrier argument; and

after a settling down period has elapsed, adjustment of said receiver'"'"'s sampling clock in response to said signal representative of said pilot carrier argument, only.

25. A method, as claimed in claim 18, characterised by employing said signal representative of said pilot carrier argument estimate to equalize for time variations in channel characteristics in a channel over which said pilot carrier is transmitted.

26. A method, as claimed in claim 18, characterised by monitoring said frame timing deviations and initiating a resynchronization if said frame timing deviations exceed a large predetermined value.