Carrier frequency offset estimating device and system

1. A carrier frequency offset estimating device for estimating frequency offsets of a multi-carrier signal, comprising:

a transforming circuit for receiving the multi-carrier signal, and transforming the multi-carrier signal into single-carrier signals having cosine effects;

a cosine effect eliminating circuit for eliminating the cosine effects in the single-carrier signals to form single-carrier signals without the cosine effects;

a model creating circuit for creating linear data models according to the single-carrier signals without the cosine effects; and

an estimating circuit for estimating frequency offsets of the multi-carrier signal according to the linear data models.

2. The carrier frequency offset estimating device as claimed in claim 1 , wherein the multi-carrier signal comprises an orthogonal frequency division multiplexing signal.

3. The carrier frequency offset estimating device as claimed in claim 1 , wherein the transforming circuit further multiplies the multi-carrier signal by a conjugation of a training sequence to transform the multi-carrier signal into the single-carrier signals.

4. The carrier frequency offset estimating device as claimed in claim 3 , wherein the training sequence comprises M-ary phase shift keying signals.

5. The carrier frequency offset estimating device as claimed in claim 1 , wherein the cosine effect eliminating circuit comprises:

a time delay circuit for delaying two neighboring single-carrier signals transformed by the transforming circuit for a predefined time period;

a conjugating circuit for conjugating the two delayed neighboring single-carrier signals for the predefined time period from the time delay circuit;

a multiplying circuit for multiplying the two neighboring single-carrier signals transformed by the transforming circuit respectively by two conjugated neighboring single-carrier signals from the conjugating circuit;

an adding circuit for adding the two neighboring single-carrier signals multiplied by the multiplying circuit to obtain single-carrier sum signals; and

a dividing circuit for dividing the single-carrier sum signals by two to obtain single-carrier quotient signals.

6. The carrier frequency offset estimating device as claimed in claim 5 , wherein the conjugating circuit further conjugates two neighboring single-carrier signals transformed by the transforming circuit.

7. The carrier frequency offset estimating device as claimed in claim 6 , wherein the multiplying circuit further multiplies two delayed neighboring single-carrier signals for the predefined time period respectively by two conjugated neighboring single-carrier signals from the conjugating circuit.

8. The carrier frequency offset estimating device as claimed in claim 5 , wherein the model creating circuit comprises:

a phasing circuit for retrieving phases of the two neighboring single-carrier quotient signals generated by the dividing circuit; and

a subtracting circuit for subtracting the phases of the two neighboring single-carrier quotient signals to create the linear data models.

9. The carrier frequency offset estimating device as claimed in claim 1 , wherein the estimating circuit further multiplies the linear data models by a weighting function to estimate the frequency offsets of the multi-carrier signal.

10. The carrier frequency offset estimating device as claimed in claim 8 , wherein the weighting function comprises

A

T

⁢

C

-

1

A

T

⁢

C

-

1

⁢

A

,

and A is an m×1 order matrix of 1, A T is the transpose of A, C is an m×m order covariance matrix, and C −1 is the reflexive matrix of C.

11. A carrier frequency offset estimating system, comprising:

a signal transmitter for appending a training sequence to a multi-carrier signal and transmitting the multi-carrier signal with the training sequence over a communication channel;

a signal receiver for receiving the multi-carrier signal with the training sequence from the signal transmitter over the communication channel; and

a carrier frequency offset estimating device for estimating frequency offsets of multi-carrier signal received by the signal receiver, the carrier frequency offset estimating device comprising:

a transforming circuit for transforming the multi-carrier signal received by the signal receiver to single-carrier signals having cosine effects;

a cosine effect eliminating circuit for eliminating the cosine effects in the single-carrier signals to form single carrier effects without the cosine effects;

a model creating circuit for creating linear data models according to the single-carrier signals without the cosine effects; and

an estimating circuit for estimating the frequency offsets of the multi-carrier signal with the training sequence according to the linear data models.

12. The carrier frequency offset estimating system as claimed in claim 11 , wherein the communication channel comprises an additive white Gaussian noise channel.

13. The carrier frequency offset estimating system as claimed in claim 11 , wherein the transforming circuit further multiplies the multi-carrier signal received by the signal receiver by a conjugation of the training sequence to transform the multi-carrier signal received by the signal receiver to the single-carrier signals.

14. The carrier frequency offset estimating system as claimed in claim 11 , wherein the cosine effect eliminating circuit comprises:

a time delay circuit for delaying the two neighboring single-carrier signals transformed by the transforming circuit for a predefined time period;

a conjugating circuit for conjugating the two delayed neighboring single-carrier signals from the time delay circuit;

a multiplying circuit for multiplying the two neighboring single-carrier signals transformed by the transforming circuit respectively by the two conjugated neighboring single-carrier signals from the conjugating circuit;

an adding circuit for adding the two multiplied neighboring single-carrier signals from the multiplying circuit to obtain single-carrier sum signals; and

a dividing circuit for dividing the single-carrier sum signals by two to obtain single-carrier quotient signals.

15. The carrier frequency offset estimating system as claimed in claim 14 , wherein the conjugating circuit further conjugates the two neighboring single-carrier signals transformed by the transforming circuit.

16. The carrier frequency offset estimating system as claimed in claim 15 , wherein the multiplying circuit further multiplies the two delayed neighboring single-carrier signals from the time delay circuit respectively by two conjugated neighboring single-carrier signals from the conjugating circuit.

17. The carrier frequency offset estimating system as claimed in claim 14 , wherein the model creating circuit comprises:

a phasing circuit for retrieving phases of the two neighboring single-carrier quotient signals generated by the dividing circuit; and

a subtracting circuit for subtracting the phases of two neighboring single-carrier quotient signals to create the linear data models.

18. The carrier frequency offset estimating system as claimed in claim 11 , wherein the estimating circuit further multiplies the linear data models by a weighting function to estimate the frequency offsets of the multi-carrier signal.

19. The carrier frequency offset estimating system as claimed in claim 18 , wherein the weighting function comprises

A

T

⁢

C

-

1

A

T

⁢

C

-

1

⁢

A

,

and A is an m×1 order matrix of 1, A T is the transpose of A, C is an m×m order covariance matrix, and C −1 is the reflexive matrix of C.