Method and system for determining symbol boundary timing in a multicarrier data transmission system

• US 7,643,582 B2
• Filed: 06/09/2004
• Issued: 01/05/2010
• Est. Priority Date: 06/09/2004
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell World Trade Limited (Marvell Technology Group Limited)
• Inventors: Leung, Pak Hei Matthew, Sands, Nicholas Phllip, Luk, King-Fuk, Tang, Eugene Yuk-Yin, Chow, Jacky S.
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): Wong; Linda
• Application Number:
  US10/866,327
• Publication Number:
  US 20050276340A1
• Time in Patent Office: 2,036 Days
• Field of Search: 370/465, 370/480, 370/485, 370/498, 370/500, 370/515, 370/516, 370/525, 370/526, 37524002-24007, 375229-236, 375/261, 375/269, 375/271, 375/274, 375/268, 375/298, 375/300, 375/302, 375/308, 375/320, 375/322, 375/326, 375/329, 375/338, 375/341, 375/343, 375/346, 375/355, 375/240.26, 375/240.28, 375/278, 375/285
• US Class Current: 375/335
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2691 involving interference determination or cancellation

Abstract

Improved techniques for acquiring symbol boundary timing at a receiver of a multicarrier data transmission system during a training sequence are disclosed. One aspect is symbol boundary determination at a receiver wherein minimal interference is used as a criterion in selecting from a plurality of potential symbol boundary timings. The symbol boundary determination at the receiver can be performed in a time domain or a frequency domain manner. Another aspect pertains to an improved training sequence wherein pairs of identical symbols are transmitted by a transmitter. These symbols can be supplied to the transmitter in a time domain or a frequency domain manner.

Claims

1. A method for detecting received symbol boundary timing in a multicarrier system, said method comprising:

retrieving a first training symbol and a second training symbol from a storage device;

computing a difference, on a processor, between (1) the retrieved first training symbol and (2) the retrieved second training symbol to produce a difference value, wherein the computing comprises;

subtracting a first sample value of the first training symbol from a second sample value of the second training symbol to produce the difference value;

accumulating the difference value with a previously computed difference value; and

repeating the subtracting and accumulating over at most a factor of a symbol length;

estimating noise due to inter-carrier and inter-symbol interference for different choices of symbol boundary timing; and

selecting, based on the accumulated difference value produced by the repeating, the choice of symbol boundary timing with substantially a least estimated noise due to inter-carrier and inter-symbol interference.

2. A method as recited in claim 1, wherein the multicarrier data transmission system includes at least one transmitter that transmits a training sequence such that at least two identical training symbols are preceded or succeeded by different symbols.

3. A method as recited in claim 2, wherein each of the training symbols being transmitted twice are transmitted in pairs.

4. A method as recited in claim 3, wherein the pairs are transmitted as consecutive pairs.

5. A method as recited in claim 3, wherein the training symbols are Quadrature Amplitude Modulation (QAM) symbols or Phase Shift Keying (PSK) symbols.

6. A method as recited in claim 1, wherein the multicarrier data transmission system is a digital subscriber line system.

7. A method as recited in claim 6, wherein the training symbols include at least one of a cyclic prefix and a cyclic suffix.

8. A method as recited in claim 1, wherein the training symbols have a random or pseudo-random characteristic.

9. A method as recited in claim 1, wherein said selecting selects, as the selected symbol timing, the choice of symbol boundary timing so as to minimize the noise due to inter-carrier and inter-symbol interference.

10. A method as recited in claim 1, wherein the noise is estimated by determining difference values between two consecutive training symbols.

11. A method as recited in claim 1 further comprising:

initializing a buffer offset value;

computing difference values for the two training symbols, wherein the computing comprises;

retrieving the first sample value from a first buffer position, wherein the first sample value corresponds to a first of the two training symbols;

retrieving the second sample value from a second buffer position, wherein the second sample value corresponds to a second of the two training symbols and the second buffer position is at least one symbol length away from the first buffer position; and

incrementing the buffer offset value;

wherein the repeating comprises;

repeating the computing difference values while the buffer offset value is less than twice a symbol length; and

wherein the selecting comprises;

selecting the symbol boundary timing based on the buffer offset value associated with a lowest accumulated difference value.

12. A method as recited in claim 11, wherein initializing comprises setting the buffer offset value and a variable value to zero.

13. A method as recited in claim 12, further comprising:

incrementing the variable value; and

repeating the computing difference values and incrementing the variable value until the variable value reaches a value equal to twice a number of subcarriers within one of the training symbols minus one.

14. A method as recite in claim 1, further comprising:

retrieving a first sample of the first training symbol from the storage device;

retrieving a first sample of the second training symbol from the storage device; and

subtracting the first sample value of the first training symbol from the first sample value of the second training symbol to obtain the difference value; and

accumulating the difference value with a previously stored difference value.

15. A method as recited in claim 1, further comprising:

retrieving a first plurality of samples of the first training symbol from the storage device;

retrieving a second plurality of samples of the second training symbol from the storage device;

computing difference values between pairs of samples in the first and second plurality of samples, wherein a pair comprises one sample from the first plurality of samples and one sample from the second plurality of samples;

determining a lowest computed difference value associated with one of the pairs of samples; and

selecting the choice of symbol boundary timing based on the lowest computed difference value.

16. A computer readable medium encoded with computer program code for detecting received symbol boundary timing in a multicarrier system, said computer readable medium comprising:

Computer program code for retrieving a first training symbol and a second training symbol from a storage device;

Computer program code for computing a difference, on a processor, between (1) the retrieved first training symbol and (2) the retrieved second training symbol to produce a difference values, wherein the computing comprises;

subtracting a first sample value of the first training symbol from a second sample value of the second training symbol to produce the difference value;

accumulating the difference value with a previously computed difference value; and

repeating the subtracting and accumulating over at most a factor of a symbol length;

Computer program code for estimating noise due to inter-carrier and inter-symbol interference for different choices of symbol boundary timing; and

Computer program code for selecting, based on the accumulated difference value produced by the repeating, the choice of symbol boundary timing with substantially a least estimated noise due to inter-carrier and inter-symbol interference.

17. A computer readable medium as recited in claim 16, wherein the multicarrier system includes at least one transmitter that transmits a training sequence such that at least two identical training symbols are preceded or succeeded by different symbols.

18. A computer readable medium as recited in claim 17, wherein each of the training symbols being transmitted twice are transmitted in pairs.

19. A computer readable medium as recited in claim 18, wherein the pairs are transmitted as consecutive pairs.

20. A computer readable medium as recited in claim 18, wherein the training symbols are Quadrature Amplitude Modulation (QAM) symbols or Phase Shift Keying (PSK) symbols.

21. A computer readable medium as recited in claim 16, wherein the multicarrier system is a digital subscriber line system.

22. A computer readable medium as recited in claim 21, wherein the training symbols include at least one of a cyclic prefix and a cyclic suffix.

23. A computer readable medium as recited in claim 16, wherein the training symbols have a random or pseudo-random characteristic.

24. A computer readable medium as recited in claim 16, wherein said computer program code for selecting selects, as the selected symbol timing, the choice of symbol boundary timing so as to minimize the noise due to inter-carrier and inter-symbol interference.

25. A computer readable medium as recited in claim 16, wherein the noise is estimated by determining difference values between two consecutive training symbols.

26. A computer readable medium as recited in claim 16 further comprising:

computer program code for initializing a buffer offset value;

computer program code for computing difference values for the two training symbols, wherein the computing comprises;

computer program code for retrieving the first sample value from a first buffer position, wherein the first sample value corresponds to a first of the two training symbols;

computer program code for retrieving the second sample value from a second buffer position, wherein the second sample value corresponds to a second of the two training symbols and the second buffer position is at least one symbol length away from the first buffer position; and

computer program code for incrementing the buffer offset value;

wherein the repeating comprises;

computer program code for repeating the computing difference values while the buffer offset value is less than twice a training symbol length; and

wherein the selecting comprises;

computer program code for selecting the symbol boundary timing based on the buffer offset value associated with a lowest accumulated difference value.

27. A system as recited in claim 26, wherein the comparator is utilized to select, as the selected symbol timing, the choice of symbol boundary timing so as to minimize the noise due to inter-carrier and inter-symbol interference.

28. A computer readable medium as recited in claim 27, further comprising:

computer program code for incrementing the variable value; and

computer program code for repeating the computing difference values and incrementing the variable value until the variable value reaches a value equal to twice a number of subcarriers within one of the training symbols minus one.

37. A computer readable medium as recited in claim 26, wherein initializing comprises setting the buffer offset value and a variable value to zero.

29. A system for detecting received symbol boundary timing in a multicarrier system, said system comprising:

a storage device that stores a first training symbol and a second training symbol;

a processor that;

retrieves the stored first training symbol and the stored second training symbol from the storage device;

computes a difference between (I) the retrieved first training symbol and (2) the retrieved second training symbol to produce a difference value, wherein computes a difference comprises;

subtracting a first sample value of the first training symbol from a second sample value of the second training symbol to produce the difference value;

accumulating the difference value with a previously computed difference value; and

repeating the subtracting and accumulating over at most a factor of a symbol length;

estimates noise due to inter-carrier and inter-symbol interference for different choices of symbol boundary timing; and

comparator circuitry that is utilized to select, based on the accumulated difference value produced by the repeating, the choice of symbol boundary timing with substantially a least estimated noise due to inter-carrier and inter-symbol interference.

30. A system as recited in claim 29 further comprising at least one transmitter that transmits a training sequence such that at least two identical training symbols are preceded or succeeded by different symbols.

31. A system as recited in claim 30, wherein each of the training symbols being transmitted twice are transmitted in pairs.

32. A system as recited in claim 31, wherein the pairs are transmitted as consecutive pairs.

33. A system as recited in claim 31, wherein the training symbols are Quadrature Amplitude Modulation (QAM) symbols or Phase Shift Keying (PSK) symbols.

34. A system as recited in claim 29, wherein the multicarrier system is a digital subscriber line system.

35. A system as recited in claim 34, wherein the training symbols include at least one of a cyclic prefix and a cyclic suffix.

36. A system as recited in claim 29, wherein the training symbols have a random or pseudo-random characteristic.

38. A system as recited in claim 29, wherein the noise is estimated by determining difference values between two consecutive training symbols.

39. A system as recited in claim 29, the wherein the processor:

initializes a buffer offset value;

computes difference values for the two training symbols by;

retrieving a first sample value from a first buffer position, wherein the first sample value corresponds to a first of the two training symbols;

retrieving a second sample value from a second buffer position, wherein the second sample value corresponds to a second of the two training symbols and the second buffer position is at least one symbol length away from the first buffer position; and

incrementing the buffer offset value;

wherein repeating comprises;

repeat the computing difference values while the buffer offset value is less than twice a training symbol length; and

wherein selecting comprises;

select the symbol boundary timing based on the buffer offset value associated with a lowest accumulated difference value.

40. A system as recited in claim 39, wherein the processor sets the buffer offset value and a variable value to zero.

41. A system as recited in claim 40, the wherein the processor:

increments the variable value; and

repeats the computing difference values and incrementing the variable value until the variable value reaches a value equal to twice a number of subcarriers within one of the training symbols minus one.