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US 7,889,803 B2Granted
Time and frequency domain based approaches for fine timing and frequency estimations
AssigneeNewport Media, Inc.
InventorsYongru Gu, Jun Ma
Life of this patent
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Abstract
A method and apparatus for estimating timing and frequency offsets in an ISDB-T and ISDB-TSB receiver. In different embodiments, the method comprises estimating timing and frequency offsets by different estimation processes; assigning weights to the timing and frequency offsets according to the channel condition; and calculating timing and frequency offsets using the estimates of timing and frequency offsets and the weights.
Claims20
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 Δφk≈4(ΔfTu+ξk), where Tu 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.
4 more elements
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 Δφk≈ΔfTu+ξk+Phtmcc, where Tu 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 Phtmcc reflects TMCC data modulated on TMCC bins;
- locking TMCC information for each said symbol;
- subtracting modulated TMCC data, Phtmcc, 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.
7 more elements
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 Δφk≈ΔfTu+ξk+Phac, where Tu 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 Phac is AC data modulated on AC bins;
- estimating a value of said Phac;
- subtracting said estimated value of Phac 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.
7 more elements
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.
6 more elements
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 (Tu) 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 (Tg);
- integrating an output of said moving average filter over N symbols with a window size of (Tu+Tg);
- and
- detecting a peak of the integrator outputs with a phase of said peak indicating frequency offset.
6 more elements
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 Δφk≈4(ΔfTu+ξk), where Tu 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.
6 more elements
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 Δφk≈ΔfTu+ξk+Phtmcc, where Tu 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 Phtmcc reflects TMCC data modulated on TMCC bins;
- lock TMCC information for each said symbol;
- subtract modulated TMCC data, Phtmcc, 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.
9 more elements
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 Δφk≈ΔfTu+ξk+Phac, where Tu 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 Phac is AC data modulated on AC bins;
- estimate a value of said Phac;
- subtract said estimated value of Phac 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.
9 more elements
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.
8 more elements
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 (Tu) 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 (Tg);
- integrate an output of said moving average filter over N symbols with a window size of (Tu+Tg);
- and
- detect a peak of the integrator outputs with a phase of said peak indicating frequency offset.
8 more elements
Dependencies are inferred from the claim text.