Method and apparatus for frame alignment in discrete multitone transceivers

• US 7,042,969 B2
• Filed: 01/15/2002
• Issued: 05/09/2006
• Est. Priority Date: 01/15/2002
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Lai, Yhean-Sen
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): File, Erin M.
• Application Number:
  US10/047,177
• Publication Number:
  US 20030133525A1
• Time in Patent Office: 1,575 Days
• Field of Search: 375/229, 375/232, 375/290, 375/348, 455/296
• US Class Current: 375/348
• 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 27/2695 with channel estimation, e.g. determination of delay spread, derivative or peak tracking channel estimation H04L25/0202

Abstract

A method and apparatus for determining frame alignment in a discrete multitone transceiver by determining a rotation of the coefficients of the shortening channel impulse response for which inter symbol interference (ISI) is minimal. The ISI is determined by multiplying the average value of a transmitted discrete multitone symbol and multiplying it by the coefficients of the shortening channel impulse response in a given rotation.

Claims

1. A method of generating a shortening channel impulse response in a discrete multitone transceiver, said method comprising the steps of:

(1) determining an impulse response of a channel, said impulse response having a plurality of coefficients corresponding to a length of a symbol;

(2) rotating said impulse response coefficients to a rotation in which the first L+1 coefficients of said channel impulse response yield a substantially maximal energy, where L is a length of said cyclic prefix; and

wherein said rotation decreases inter-symbol interference.

2. A method of generating a shortening channel impulse response in a discrete multitone transceiver, said method comprising the steps of:

(1) determining an impulse response of a channel, said impulse response having a plurality of coefficients corresponding to a length of a symbol;

(2) rotating said impulse response coefficients to a rotation that decreases inter-symbol interference;

wherein said rotation step comprises rotating said impulse response coefficients to a rotation that starts with coefficient L+1, where L is a length of said cyclic prefix.

7. The method of claim 2 wherein step (2) comprises calculating

FINTF={overscore (C)}(|h′

_Y|(FV₁·

W)+|h′

_Y+1|(FV₂·

W)+ . . . +|h′

<sub>P−

1</sub>|(FV<sub>P−

Y</sub>·

W))

where

{overscore (C)}=an average value of a transmitted discrete multitone symbol,

h′

_i represent a series of coefficients in said shortening channel impulse response,

Y=an integer selected based on the number of the next to last coefficient of the series of consecutive coefficients,

P=the number of h′

_i coefficients

V_k=[1,1, . . . ,1,0,0, . . . , 0], in which there is a string of k ones and a string of (P−

k) zeroes,

W=is a weighting factor vector [w₀, w₁, w₂ . . . , w<sub>P−

1</sub>]^T, and

F represents the process of taking a Fast Fourier Transform.

8. The method of claim 7 wherein w₀, w₁ , . . . , w_L=0 and W_L+1, w_L+2 , . . . w_P−

1=1.

3. A method of generating a shortening channel impulse response in a discrete multitone transceiver, said method comprising the steps of:

(1) determining an impulse response of a channel, said impulse response having a plurality of coefficients corresponding to a length of a symbol;

(2) rotating said impulse response coefficients to a rotation that decreases inter-symbol interference wherein said rotating step comprises the steps of;

(2.1) selecting a plurality of rotations of said channel impulse response including and surrounding said rotation that starts with coefficient L+1, where L is a length of said cyclic prefix;

(2.2) calculating a value for inter-symbol interference based on each of said rotations; and

(2.3) selecting a one of said rotations of said channel impulse response that yields the lowest inter-symbol interference value.

4. The method of claim 3 wherein step (2.2) is performed in the frequency domain.

5. The method of claim 4 wherein step (2.2) comprises:

(2.2.1) generating Fourier transforms of said coefficients of said channel impulse response;

(2.2.2) calculating an average value of a transmitted discrete multitone symbol; and

(2.2.3) multiplying said Fourier transforms of said coefficients with said average.

6. The method of claim 5 wherein, in step (2.2.1), said Fourier transforms are generated by fast Fourier transform.

9. A method of frame alignment in a discrete multitone transceiver, said method comprising the steps of:

(1) determining an impulse response of a channel, said impulse response having a plurality of coefficients corresponding to a length of a symbol;

(2) rotating said impulse response coefficients to a rotation that decreases inter-symbol interference value; and

(3) using said rotation for frame alignment.

10. The method of claim 9 wherein step (2) comprises rotating said impulse response coefficients to a rotation in which the first L+1 coefficients of said channel impulse response yield a substantially maximal energy, where L is a length of said cyclic prefix.

11. The method of claim 9 wherein step (2) comprises the steps of:

(2.1) selecting a plurality of rotations of said channel impulse response including and surrounding said a rotation that starts with coefficient L+1, where L is a length of said cyclic prefix;

(2.2) calculating a value for inter-symbol interference based on each of said rotations; and

(2.3) selecting a one of said rotations of said channel impulse response that yields the lowest inter-symbol interference value.

12. The method of claim 10 wherein step 2 comprises calculating

FINTF={overscore (C)}(|h′

_Y|(FV₁·

W)+|h′

_Y+1|(FV₂·

W)+ . . . +|h′

<sub>P−

1</sub>|(FV<sub>P−

Y</sub>·

W))

where

{overscore (C)}=an average value of a transmitted discrete multitone symbol,

h′

_i represent a series of coefficients in said shortening channel impulse response,

Y=an integer selected based on the number of the next to last coefficient of the series of consecutive coefficients,

P=the number of h′

_i coefficients

V_k=[1,1, . . . ,1,0,0, . . . , 0], in which there is a string of k ones and a string of (P−

k) zeroes,

W=is a weighting factor vector [w₀, w₁, w₂ . . . , w<sub>P−

1</sub>]^T, and

F represents the process of taking a Fast Fourier Transform.

13. A discrete multitone transceiver comprising:

a transmitter;

a receiver;

a digital processing device adapted to generating a shortening channel impulse response by;

determining an impulse response of a channel, said impulse response having a plurality of coefficients corresponding to a length of a symbol; and

rotating said impulse response coefficients to a rotation that decreases inter-symbol interference value; and

a timing recovery circuit that aligns with a received frame using said rotation.

14. The transceiver of claim 13 wherein said digital processing device is adapted to determine said rotation by rotating said impulse response coefficients to a rotation in which the first L+1 coefficients of said channel impulse response yield a substantially maximal energy.

15. The transceiver of claim 13 wherein said digital processing device is adapted to determine said rotation by rotating said impulse response coefficients to a rotation that starts with coefficient L+1, where L is a length of said cyclic prefix.

16. The transceiver of claim 13 wherein said digital processing device is adapted to determine said rotation by:

selecting a plurality of rotations of said channel impulse response including and surrounding said a rotation that starts with coefficient L+1, where L is a length of said cyclic prefix;

calculating a value for inter-symbol interference based on each of said rotations; and

selecting a one of said rotations of said channel impulse response that yields the lowest inter-symbol interference value.

17. The transceiver of claim 16 wherein said digital processing device performs said calculation by:

generating Fourier transforms of said coefficients of said shortening channel impulse response;

calculating an average value of a transmitted discrete multitone symbol; and

multiplying said Fourier transforms of said coefficients with said average.

18. The transceiver of claim 16 wherein said processor calculates said inter-symbol interference, FINTF, by;

FINTF={overscore (C)}(|h′

_Y|(FV₁·

W)+|h′

_Y+1|(FV₂·

W)+ . . . +|h′

<sub>P−

1</sub>|(FV<sub>P−

Y</sub>·

W))

where

{overscore (C)}=an average value of a transmitted discrete multitone symbol,

h′

_i represent a series of coefficients in said shortening channel impulse response,

Y=an integer selected based on the number of the next to last coefficient of the series of consecutive coefficients,

P=the number of h′

_i coefficients

V_k=[1,1, . . . ,1,0,0, . . . , 0], in which there is a string of k ones and a string of (P−

k) zeroes,

W=is a weighting factor vector [w₀, w₁, w₂ . . . , w<sub>P−

1</sub>]^T, and

F represents the process of taking a Fast Fourier Transform.

19. A method of frame alignment in a discrete multitone transceiver, said method comprising the steps of:

(1) determining an impulse response of a channel, said impulse response having a plurality of coefficients corresponding to a length of a symbol;

(2) determining a set of consecutive samples of said channel impulse response of length L+1, where L is a length of said cyclic prefix, for which the channel impulse response energy is maximal;

(3) selecting a plurality of rotations of said shortening channel impulse response including and surrounding a rotation that starts with a first coefficient of said consecutive samples determined in step (3);

(4) calculating a value for inter-symbol interference based on each of said rotations; and

(5) selecting a one of said rotations selected is step (3) that decreases inter-symbol interference value.

20. The method of claim 19 wherein step (4) comprises:

(4.1) generating fast Fourier transforms of said coefficients of said channel impulse response;

(4.2) calculating an average value of a transmitted discrete multitone symbol; and

(4.3) multiplying said Fourier transforms of said coefficients with said average.

21. The method of claim 19 wherein step (5) comprises calculating

FINTF={overscore (C)}(|h′

_Y|(FV₁·

W)+|h′

_Y+1|(FV₂·

W)+ . . . +|h′

<sub>P−

1</sub>|(FV<sub>P−

Y</sub>·

W))

where

{overscore (C)}=an average value of a transmitted discrete multitone symbol,

h′

_i represent a series of coefficients in said shortening channel impulse response,

Y=an integer selected based on the number of the next to last coefficient of the series of consecutive coefficients,

P=the number of h′

_i coefficients

V_k=[1,1, . . . ,1,0,0, . . . , 0], in which there is a string of k ones and a string of (P−

k) zeroes,

W=is a weighting factor vector [w₀, w₁, w₂ . . . , w<sub>P−

1</sub>]^T, and

F represents the process of taking a Fast Fourier Transform.