Granted Patent B2

US 7,889,803 · App. 12/034,717 · Granted Feb 15, 2011

Abstract

Claims (105)

1. A method of timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said method comprises:

estimating timing and frequency offsets by more than one estimation process, wherein the estimation process comprises a scatter pilot based timing and frequency offset estimating process;

assigning weights to said timing and frequency offsets based on a condition of said channel;

said scatter pilot based timing and frequency offset estimating process comprises:

calculating timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

calculating a phase difference between two received scatter pilots spaced four OFDM symbols apart; and

approximating the timing and frequency offset using Δφ k ≈4(ΔfT u +ξk), where T u is an OFDM symbol time, Δf is a frequency offset, ξ=ΔT/T is a timing offset in percentage, and k is a sub-carrier (bin) index.

2. The method of claim 1 , wherein said weights are assigned based on channel conditions.

3. A method of timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said method comprises:

estimating timing and frequency offsets by more than one estimation process, wherein the estimation process comprises a Transmission Multiplexing Configuration Control (TMCC) based timing and frequency offset estimating process;

assigning weights to said timing and frequency offsets based on a condition of said channel;

said TMCC based timing and frequency offset estimation process comprises:

calculating timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

approximating a phase difference of a TMCC bin over two adjacent symbols as Δφ k ≈ΔfT u +ξk+Ph tmcc , where T u is a OFDM symbol time, Δf is a frequency offset, ξ=ΔT/T is a timing offset in percentage, k is a sub-carrier (bin) index, and Ph tmcc reflects TMCC data modulated on TMCC bins;

locking TMCC information for each said symbol;

subtracting modulated TMCC data, Ph tmcc , from said approximated phase difference;

relating a mean of said phase difference with frequency offset; and

using a slope of said phase difference to indicate said timing offset.

4. The method of claim 3 , wherein said weights are assigned based on channel conditions.

5. A method of timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said method comprises:

estimating timing and frequency offsets by more than one estimation process, wherein the estimation process comprises an auxiliary channel (AC) based timing and frequency offset estimating process;

assigning weights to said timing and frequency offsets based on a condition of said channel;

said AC based timing and frequency offset estimating process comprises:

calculating timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

approximating a phase difference of an AC bin over two adjacent symbols as Δφ k ≈ΔfT u +ξk+Ph ac , where T u is a OFDM symbol time, Δf is a frequency offset, ξ=ΔT/T is a timing offset in percentage, k is a sub-carrier (bin) index, and Ph ac is AC data modulated on AC bins;

estimating a value of said Ph ac ;

subtracting said estimated value of Ph ac from said phase difference;

relating a mean of said phase difference with frequency offset; and

using a slope of said phase difference to indicate said timing offset.

6. The method of claim 5 , wherein said weights are assigned based on channel conditions.

7. A method of timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said method comprises:

estimating timing and frequency offsets by more than one estimation process, wherein the estimation process comprises a channel estimated based timing and frequency offset estimating process;

assigning weights to said timing and frequency offsets based on a condition of said channel;

said channel estimated based timing and frequency offset estimating process comprises:

calculating timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

interpolating channel estimates on each sub-carrier using scatter pilots;

calculating a phase difference on said channel estimate on each sub-carrier over two adjacent symbols;

relating a mean of said phase difference with frequency offset; and

using a slope of said phase difference to indicate said timing offset.

8. The method of claim 7 , wherein said weights are assigned based on channel conditions.

9. A method of timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said method comprises:

estimating timing and frequency offsets by more than one estimation process, wherein the estimation process comprises a time-domain correlation based frequency offset estimating process;

assigning weights to said timing and frequency offsets based on a condition of said channel;

said time-domain correlation based timing and frequency offset estimating process comprises:

calculating timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

correlating a currently received symbol with a conjugate of a previous symbol received one symbol time (T u ) prior to said currently received symbol;

passing said correlated symbol through a moving average filter, wherein the filter comprises a window length equal to the time for a guard interval (T g );

integrating an output of said moving average filter over N symbols with a window size of (T u +T g ); and

detecting a peak of the integrator outputs with a phase of said peak indicating frequency offset.

10. The method of claim 9 , wherein said weights are assigned based on channel conditions.

11. A system for performing timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said system comprises:

an estimator configured to estimate timing and frequency offsets by different estimation processes, wherein said estimator comprises a scatter pilot based timing and frequency offset estimator; and

a processor configured to:

assign weights to said timing and frequency offsets based on condition of said channel;

said scatter pilot based timing and frequency offset estimator configured to:

calculate timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

calculate phase difference between two received scatter pilots spaced four OFDM symbols apart; and

approximate the timing and frequency offset using Δφ k ≈4(ΔfT u +ξk), where T u is an OFDM symbol time, Δf is a frequency offset, ξ=ΔT/T is a timing offset in percentage, and k is a sub-carrier (bin) index.

12. The system of claim 11 , wherein said weights are assigned based on channel conditions.

13. A system for performing timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said system comprises:

an estimator configured to estimate timing and frequency offsets by different estimation processes, wherein said estimator comprises a Transmission Multiplexing Configuration Control (TMCC) based timing and frequency offset estimator; and

a processor configured to:

assign weights to said timing and frequency offsets based on condition of said channel;

said TMCC based timing and frequency offset estimator configured to:

calculate timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

approximating a phase difference of a TMCC bin over two adjacent symbols as Δφ k ≈ΔfT u +ξk+Ph tmcc , where T u is a OFDM symbol time, Δf is a frequency offset, ξ=ΔT/T is a timing offset in percentage, k is a sub-carrier (bin) index, and Ph tmcc reflects TMCC data modulated on TMCC bins;

lock TMCC information for each said symbol;

subtract modulated TMCC data, Ph tmcc , from said approximated phase difference;

relate a mean of said phase difference with frequency offset; and

use a slope of said phase difference to indicate said timing offset.

14. The system of claim 13 , wherein said weights are assigned based on channel conditions.

15. A system for performing timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said system comprises:

an estimator configured to estimate timing and frequency offsets by different estimation processes, wherein said estimator comprises an auxiliary channel (AC) based timing and frequency offset estimator; and

a processor configured to:

assign weights to said timing and frequency offsets based on condition of said channel;

said AC based timing and frequency offset estimator configured to:

calculate timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

approximating a phase difference of an AC bin over two adjacent symbols as Δφ k ≈ΔfT u +ξk+Ph ac , where T u is a OFDM symbol time, Δf is a frequency offset, ξ=ΔT/T is a timing offset in percentage, k is a sub-carrier (bin) index, and Ph ac is AC data modulated on AC bins;

estimate a value of said Ph ac ;

subtract said estimated value of Ph ac from said phase difference;

relate mean of said phase difference with frequency offset; and

use a slope of said phase difference to indicate said timing offset.

16. The system of claim 15 , wherein said weights are assigned based on channel conditions.

17. A system for performing timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said system comprises:

an estimator configured to estimate timing and frequency offsets by different estimation processes, wherein said estimator comprises a channel estimated based timing and frequency offset estimator; and

a processor configured to:

assign weights to said timing and frequency offsets based on condition of said channel;

said channel estimated based timing and frequency offset estimator configured to:

calculate timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

interpolate channel estimates on each sub-carrier using scatter pilots;

calculate a phase difference on said channel estimate on each sub-carrier over two adjacent symbols;

relate a mean of said phase difference with frequency offset; and

use a slope of said phase difference to indicate said timing offset.

18. The system of claim 17 , wherein said weights are assigned based on channel conditions.

19. A system for performing timing and frequency offset estimation for a channel in an orthogonal frequency division multiplexing (OFDM) environment, wherein said system comprises:

an estimator configured to estimate timing and frequency offsets by different estimation processes, wherein said estimator comprises a time-domain correlation based frequency offset estimator; and

a processor configured to:

assign weights to said timing and frequency offsets based on condition of said channel;

said time-domain correlation based timing and frequency offset estimator configured to:

calculate timing and frequency offsets using said estimates of timing and frequency offsets and said weights;

correlate a currently received symbol with a conjugate of a previous symbol received one symbol time (T u ) prior to said currently received symbol;

pass said correlated symbol through a moving average filter, wherein the filter comprises a window length equal to the time for a guard interval (T g );

integrate an output of said moving average filter over N symbols with a window size of (T u +T g ); and

detect a peak of the integrator outputs with a phase of said peak indicating frequency offset.

20. The system of claim 19 , wherein said weights are assigned based on channel Conditions.

Assignments (23)