Frequency tracking device for a receiver of a multi-carrier communication system

• US 20020021715A1
• Filed: 05/31/2001
• Published: 02/21/2002
• Est. Priority Date: 06/05/2000
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Matheus, Kirsten, Wachsmann, Udo, Dettmar, Uwe
• Granted Patent: US 7,009,932 B2
• Time in Patent Office: Days
• US Class Current: 370/480
• CPC Class Codes: H04L 27/2657 Carrier 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 frequency tracking device (FTD) in particular for use in a OFDM communication system comprises a selector (SEL) which selects on the basis of N channel coefficients (C_est) a number M of subcarriers corresponding to the M channel coefficients (C_est) having the largest absolute values. An evaluator (EVAL) of the frequency tracking device (FTD) determines a frequency deviation estimate (f_off,est) on the basis of the selected M subcarriers and the selected M channel coefficients. In addition to or instead of a feedback correction unit (CORR1) provided upstream of a multi-carrier filter bank (8; FFT), the frequency tracking device (FTD) can also comprise a feed forward correction unit (CORR2) provided downstream of the receiver multi-carrier filter bank (8). In this case the selector (SEL) and the feed forward correction unit (CORR2) operate on the same data symbols such that the correction unit (CORR2) corrects the same data symbols which are subject to the selection and evaluation process in the selector (SEL) and the evaluator (EVAL). Based on the selection and evaluation processes frequency deviations (f_off) which are introduced into multi-carrier symbols when being transmitted between a transmitter multi-carrier filter bank (4; IFFT) and a receiver multi-carrier filter bank (8; FFT) can be corrected more efficiently, e.g. with a reduced computational complexity.

Claims

1. Frequency tracking device (FTD) for a receiver (RC) of a multi-carrier communication system (MC-SYS), for evaluating and correcting frequency deviations (f_off) which are introduced into multi-carrier symbols when being transmitted between a transmitter multi-carrier filter bank (4;

IFFT) and receiver multi-carrier filter bank (8;

FFT), comprising;

a) a selector (SEL) adapted to receive a set of N complex data symbols output by the receiver multi-carrier filter bank (8;

FFT) and N channel coefficients (C_est) corresponding to each sub-carrier as estimated by a channel estimator (12) of said receiver (RC), where N is the number of used sub-carriers in the multi-carrier system (MC-SYS), and adapted to select, on the basis of the N channel coefficients (C_est), a number M of sub-carriers corresponding to the M channel coefficients (C_est) having the largest absolute values, where M≦

N;

b) an evaluator (EVAL) adapted to determine, on the basis of the M selected sub-carriers and their corresponding M channel coefficients (C_est), an estimate (f_off,est) of the frequency deviation (f_off) introduced into the multi-carrier symbols; and

c) a corrector (CORR;

CORR2) for correcting the frequency deviation introduced into the multi-carrier symbols on the basis of the determined frequency deviation estimate (f_off,est).

2. Frequency tracking device (FTD) according to claim 1,

wherein

said selector (SEL) adaptively adjusts the number M at adjustment time intervals including at least one multi-carrier symbol duration.

3. Frequency tracking device (FTD) according to claim 1,

wherein

said corrector (CORR1;

CORR2) includes a first correction unit (CORR1) arranged upstream the receiver multi-carrier filter bank (8) and adapted to rotate each received multi-carrier symbol with a different phase shift depending on the frequency deviation estimate (f_off,est) and the sample index (k) within the multi-carrier symbol.

4. Frequency tracking device (FTD) according to claim 1 or 3, wherein

said corrector (CORR1;

CORR2) includes a second correction unit (CORR2) arranged downstream of the receiver multi-carrier filter bank (8) and adapted to rotate all data symbols output by the receiver multi-carrier filter bank (8) with the same phase shift depending on the frequency deviation estimate (f_off,est).

5. Frequency tracking device (FTD) according to claim 4,

wherein

said second correction unit (CORR2) performs a correction of the same set of N data symbols which are subjected to the selection by said selector (SEL).

6. Frequency tracking device (FTD) according to claim 1,

wherein

said corrector (CORR1;

CORR2) includes;

a first correction unit (CORR1) arranged upstream the receiver multi-carrier filter bank (8) and adapted to rotate each received multi-carrier symbol with a different phase shift depending on the frequency deviation estimate (f_off,est) and the sample index (k) within the multi-carrier symbol; and

a second correction unit (CORR2) arranged downstream of the receiver multi-carrier filter bank (8) and adapted to rotate all data symbols output by the multi-carrier filter bank (8) with the same phase shift depending on the frequency deviation estimate (f_off,est).

7. Frequency tracking device (FTD) according to claim 1,

wherein

said evaluator (EVAL) is adapted to carry out a decision directed evaluation for said M sub-carriers.

8. Frequency tracking device (FTD) according to claim 1,

wherein

said evaluator (EVAL) is adapted to carry out a pilot carrier aided evaluation for said M sub-carriers.

9. Frequency tracking device (FTD) according to claim 1,

wherein

said evaluator (EVAL) is adapted to carry out a combination of a decision directed evaluation and a pilot carrier aided evaluation for said M subcarriers.

10. Frequency tracking device (FTD) according to claim 1,

wherein

the number of selected sub-carriers is M=N/4 to M=N/3 where N is the number of used subcarriers.

14. Receiver (RC) of a multi-carrier communication system (MC-SYS), comprising reception means (RM) for receiving multi-carrier symbols transmitted from a transmitter (TR) via a transmission channel (6), a receiver multi-carrier filter bank (8) for converting said multi-carrier symbols into complex data symbols, a data symbol sink (11) for receiving said data symbols and a frequency tracking device (FTD) in accordance with one or more of claims 1-10 or one or more of claims 11-13.

11. Frequency tracking device (FTD) for a receiver (RC) of a multi-carrier communication system (MC-SYS), for evaluating and correcting frequency deviations (f_off) which are introduced into multi-carrier symbols when being transmitted between a transmitter multi-carrier filter bank (4;

IFFT) and receiver multi-carrier filter bank (8;

FFT), comprising;

a) an evaluator (EVAL) adapted to receive a set of N complex data symbols output by the receiver multi-carrier filter bank (8;

FFT) and N channel coefficients (C_est) corresponding to each sub-carrier as estimated by a channel estimator (12) of said receiver (RC), where N is the number of used sub-carriers in the multi-carrier system (MCSYS), and to determine, on the basis of N sub-carriers and their corresponding N channel coefficients (C_est), an estimate (f_off,est) of the frequency deviation (f_off) introduced into the multi-carrier symbols, where N is the number of sub-carriers used in the transmitter;

b) a corrector (CORR1;

CORR2) for correcting the frequency deviation introduced into the multi-carrier symbols on the basis of the determined frequency deviation estimate (f_off,est); and

c) wherein said corrector (CORR1;

CORR2) comprises a corrector unit (CORR2) arranged downstream of the receiver multi-carrier filter bank (8) and adapted to rotate all data symbols output by the receiver multi-carrier filter bank (8) with the same phase shift depending on the frequency deviation estimate (f_off,est).

12. Frequency tracking device (FTD) according to claim 11,

wherein

said corrector (CORR1;

CORR2) further includes a correction unit (CORR1) arranged upstream the receiver multi-carrier filter bank (8) and adapted to rotate each received multi-carrier symbol with a different phase shift depending on the frequency deviation estimate (f_off,est) and the sample index (k) within the multi-carrier symbol.

13. Frequency tracking device (FTD) according to claim 11,

further comprising

a selector (SEL) adapted to receive a set of N complex data symbols output by the receiver multi-carrier filter bank (8;

FFT) and N channel coefficients (C_est) corresponding to each sub-carrier as estimated by a channel estimator (12) of said receiver (RC), where N is the number of used sub-carriers in the multi-carrier system (MCSYS), and adapted to select, on the basis of the N channel coefficients (C_est), a number M of sub-carriers corresponding to the M channel coefficients (C_est) having the largest absolute values, where M≦

N; and

wherein

said evaluator (EVAL) is adapted to determine, on the basis of the M selected sub-carriers and their corresponding M channel coefficients (C_est), an estimate (f_off,set) of the frequency deviation (f_off) introduced into the multi-carrier symbols.

15. A multi-carrier communication system (MC-SYS), comprising at least one transmitter (TR) including a data symbol source (1-3) generating complex data symbols, a transmitter multi-carrier filter bank (4) for generating multi-carrier symbols from said complex data symbols and a transmission means (TR) for transmitting said multi-carrier symbols onto a transmission channel (6), and at least one receiver (RC) in accordance with claim 14.

17. A method according to claim 16,

wherein

said correction step (S5) includes a first correction (CORR1) carried out upstream a receiver multi-carrier filter bank (8) in which each received multi-carrier symbol is rotated with a different phase shift depending on the frequency deviation estimate (f_off,est) and the sample index (k) within the multi-carrier symbol.

18. A method according to claim 16,

wherein

said correction step (S5) includes a second correction (CORR2) carried out downstream a receiver multi-carrier filter bank (8) in which all data symbols output by the receiver multi-carrier filter bank (8) are corrected with the same phase shift depending on the frequency deviation estimate (f_off,est).

19. A method according to claim 16,

wherein

said correction step (S4) includes:

a first correction (CORR1) carried out upstream a receiver multi-carrier filter bank (8) in which each received multi-carrier symbol is rotated with a different phase shift depending on the frequency deviation estimate (f_off,est) and the sample index (k) within the multi-carrier symbol; and

a second correction (CORR2) carried out downstream a receiver multi-carrier filter bank (8) in which all data symbols output by the receiver multi-carrier filter bank (8) are corrected with the same phase shift depending on the frequency deviation estimate (f_off,est).

16. A method for evaluating and correcting frequency deviations (f_off) which are introduced into multi-carrier symbols when being transmitted between a transmitter multi-carrier filter bank (4;

IFFT) and receiver multi-carrier filter bank (8;

FFT), comprising the steps of;

a) determining (S1;

S2), in a receiver (RC) of a multi-carrier communication system (MC-SYS), a set of N complex data symbols output by the receiver multi-carrier filter bank (8;

FFT) and N channel coefficients (C_est) corresponding to each sub-carrier as estimated by a channel estimator (12) of said receiver (RC), where N is the number of used sub-carriers in the multi-carrier system (MCSYS); and

b) selecting (S3), on the basis of the N channel coefficients (C_est) a number M of sub-carriers corresponding to the M channel coefficients (C_est) having the largest absolute values, where M≦

N;

c) determining (S4), on the basis of the M selected sub-carriers and their corresponding M channel coefficients (C_est), an estimate (f_off,est) of the frequency deviation (f_off) introduced into the multi-carrier symbols; and

d) correcting (S5) the frequency deviation introduced into the multi-carrier symbols on the basis of the determined frequency deviation estimate (f_off,est).

20. A method for evaluating and correcting frequency deviations (f_off) which are introduced into multi-carrier symbols when being transmitted between a transmitter multi-carrier filter bank (4;

IFFT) and receiver multi-carrier filter bank (8;

FFT), comprising the steps of;

a) determining (S1′

, S2′

), in a receiver (RC) of a multi-carrier communication system (MC-SYS), a set of N complex data symbols output by the receiver multi-carrier filter bank (8;

FFT) and N channel coefficients (C_est) corresponding to each sub-carrier as estimated by a channel estimator (12) of said receiver (RC), where N is the number of used sub-carriers in the multi-carrier system (MCSYS), and

b) determining (S3′

;

S4′

), on the basis of N sub-carriers and their corresponding N channel coefficients (C_est), an estimate (f_off,est) of the frequency deviation (f_off) introduced into the multi-carrier symbols, where N is the number of sub-carriers used in the transmitter; and

c) correcting (S5′

) the frequency deviation (f_off) introduced into the multi-carrier symbols on the basis of the determined frequency deviation estimate (f_off,est); and

c) wherein said correction step (S3′

) comprises a correction (CORR2) carried out downstream of the receiver multi-carrier filter bank (8) in which all data symbols output by the receiver multi-carrier filter bank (8) are rotated with the same phase shift depending on the frequency deviation estimate (f_off,est).

21. A method according to claim 20,

wherein

said correction step (S5′

) further includes a correction step (CORR1) carried out upstream the receiver multi-carrier filter bank (8) in which each received multi-carrier symbol is rotated with a different phase shift depending on the frequency deviation estimate (f_off,est) and the sample index (k) within the multi-carrier symbol.

22. A method according to claim 20,

further including the steps of.

selecting (S2′

), on the basis of the N channel coefficients (C_est), a number M of sub-carriers corresponding to the M channel coefficients (C_est) having the largest absolute values, where M≦

N; and

wherein

determining (S4′

), on the basis of the M selected sub-carriers and their corresponding M channel coefficients (C_est), an estimate (f_off,set) of the frequency deviation (f_off) introduced into the multi-carrier symbols.