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

• US 20050276340A1
• Filed: 06/09/2004
• Published: 12/15/2005
• Est. Priority Date: 06/09/2004
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Hong Kong Applied Science And Technology Research Institute Co., Ltd., Industrial Technology Research Institute
• Inventors: Sands, Nicholas Phillip, Leung, Pak Hei Matthew, Tang, Eugene Yuk-Yin, Chow, Jacky S., Luk, King-Fuk
• Granted Patent: US 7,643,582 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• 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:

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

selecting the choice of symbol boundary timing with the least 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 for detecting received symbol boundary timing in a multicarrier system, said method comprising:

(a) receiving a series of received training signals over a wire-based channel;

(b) storing at least three of the series of received training signals to a buffer;

(c) determining difference values for a pair of consecutive received training signals stored in the buffer;

(d) selecting one of the difference values; and

(e) determining the received symbol boundary timing based on the selected one of the difference values.

11. A method as recited in claim 10, wherein said selecting (d) operates to select the smallest of the difference values.

12. A method as recited in claim 10, wherein the multicarrier data transmission system is a digital subscriber line system.

13. A method as recited in claim 12, wherein the training symbols are Quadrature Amplitude Modulation (QAM) symbols or Phase Shift Keying (PSK) symbols.

14. A method as recited in claim 13, wherein the training symbols include at least one of a cyclic prefix and a cyclic suffix.

15. A method as recited in claim 10,

wherein the difference values can be accumulated or averaged over a plurality of different pairs of received training symbols, and

wherein said selecting (d) selects one of the accumulated or averaged difference values.

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

(a) receiving a series of received training signals over a wire-based channel;

(b) determining a plurality of correlation values for a plurality of pairs of received training signals, where each respective pair of training symbols were identical when transmitted;

(c) selecting one of the correlation values; and

(e) determining the received symbol boundary timing based on the selected one of the correlation values.

17. A method as recited in claim 16, wherein the correlation values represent correlation values for each of the plurality of pairs accumulated or averaged over the plurality of pairs.

18. A method as recited in claim 16, wherein said determining (b) of the plurality of correlation values is performed with time domain processing.

19. A method as recited in claim 16, wherein each of the correlation values is obtained in accordance with the following equation:

$G<br><br>\left(x\right)=\underset{n=0}{\overset{2*\mathrm{Nsc}-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{abs}<br><br>\left[r<br><br>\left(x+{\mathrm{dmtsymbol}}_{\mathrm{—<br><br>}}<br><br>\mathrm{length}+n\right)-r<br><br>\left(x+n\right)\right]$

where r represents buffer contents storing the received training symbols, abs represents taking the absolute value, Nsc is the number of subcarriers, and the search is performed over x=0 to dmtsymbol_length−

1.

20. A method as recited in claim 16, wherein said determining (b) of the plurality of correlation values is performed with frequency domain processing.

21. A method as recited in claim 16, wherein each of the correlation values is obtained in accordance with the following equation:

$G<br><br>\left(x\right)=\underset{k\in <br><br>I}{\sum <br><br>}<br><br>f<br><br>\left[\mathrm{R1}<br><br>\left(k\right)-\mathrm{R0}<br><br>\left(k\right)\right]$

where I is the set of tone indices that contains the training symbols, where the function f[.] is one of an absolute value and an absolute value squared function, and where, for a delay index x, two sequences in the frequency domain are defined as follows;

R0(x,k)=FFT{r(x+n),n=0,1,2, . . . ,2·

Nsc−

1}k=0,1,2, . . . ,2·

Nsc−

1
R1(x,k)=FFT{r(x+dmtsymbol_length+n), n=0,1,2, . . . ,2·

Nsc−

1}k=0,1,2, . . . ,2·

Nsc−

1

where r represents buffer contents storing the received training symbols, Nsc is the number of subcarriers, and FFT represents a fast Fourier transform operation.

22. A multicarrier data transmission system, comprising:

at least one transmitter, said transmitter including at least;

a line encoder that encodes data into symbols to be transmitted;

training symbols;

a switch that selects symbols for transmission either said training symbols or the symbols pertaining to the encoded data from said line encoder;

a multicarrier modulation unit for modulating the symbols into modulated symbols; and

a digital-to-analog converter for converting the modulated symbols into analog signals; and

at least one receiver, said receiver including at least;

an analog-to-digital converter for converting the analog signals into digital samples;

a symbol timing unit for examining the analog signals to produce correlation values for a plurality of different potential symbol timing boundaries;

a multicarrier demodulation unit for demodulating the digital samples into symbols; and

a line decoder that decodes the symbols into data,

wherein said transmitter transmits pairs of identical training symbols, and

wherein said symbol timing unit produces the correlation values with respect to the pairs of identical training symbols as received at said receiver.

23. A multicarrier data transmission system as recited in claim 22, wherein the correlation values pertain to estimated noise due to inter-carrier and inter-symbol interference for the different potential symbol timing boundaries.

24. A multicarrier data transmission system as recited in claim 23, wherein said symbol timing unit selects the one of the different potential symbol timing boundaries with the least estimated noise due to inter-carrier and inter-symbol interference as a selected symbol timing boundary.

25. A multicarrier data transmission system as recited in claim 22, wherein said multicarrier data transmission system further comprises another switch that supplies symbols from either the training symbols or system information to said switch, and

wherein said switch that selects symbols for transmission operates to select either the symbols pertaining to the encoded data from said line encoder or from the symbols provided by said another switch.

26. A multicarrier data transmission system as recited in claim 25, wherein said transmitter further comprises a control unit, and

wherein said switch and said another switch are controlled by said control unit.

27. A multicarrier data transmission system as recited in claim 22, wherein said another switch is used to interleave training symbol information with the system information.

28. A multicarrier data transmission system as recited in claim 22, wherein said symbol timing unit determines the correlation values for the plurality of different potential symbol timing boundaries based on time domain processing.

29. A multicarrier data transmission system as recited in claim 22, wherein said symbol timing unit determines the correlation values for the plurality of different potential symbol timing boundaries based on frequency domain processing.

30. A computer readable medium including at least computer program code for detecting received symbol boundary timing in a multicarrier system, said computer readable medium comprising:

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 the choice of symbol boundary timing with the least noise due to inter-carrier and inter-symbol interference.