System and method for frequency synchronization of doppler-shifted subcarriers
View Patent ↗A method includes receiving an Orthogonal Frequency Division Multiplexing (OFDM) signal comprising a plurality of Doppler-shifted OFDM subcarriers and determining frequency-shift data corresponding to the plurality of Doppler-shifted OFDM subcarriers. The determining includes calculating frequency-shift data for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers, thereby yielding a plurality of subcarrier-specific frequency-shift values and calculating an average of the plurality of subcarrier-specific frequency-shift values. The method further includes frequency shifting each subcarrier of the plurality of Doppler-shifted OFDM subcarriers by a value based on the determined frequency-shift data multiplied by a frequency index of each subcarrier.
1. A method for frequency synchronization in an OFDM communication system comprising:
receiving an Orthogonal Frequency Division Multiplexing (OFDM) signal comprising a plurality of Doppler-shifted OFDM subcarriers of a subband;
calculating a frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers, thereby yielding a plurality of subcarrier-specific frequency shift factor values;
calculating an average of the plurality of subcarrier-specific frequency shift factor values as the average frequency shift factor corresponding to the plurality of Doppler-shifted OFDM subcarriers;
calculating, for each Doppler-shifted OFDM subcarrier, a frequency offset by multiplying the average frequency shift factor by a frequency index of the each subcarrier, the frequency offset for at least two Doppler-shifted OFDM subcarriers of the subband being different from each other; and
compensating the frequency offset for each Doppler-shifted OFDM subcarrier for the frequency synchronization.
2. The method of claim 1 , comprising:
generating, based at least in part on a first part of the OFDM signal, auto-correlation data; and
generating, based at least in part on a second part of the OFDM signal, mutual correlation data,
wherein the frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers is calculated based, at least in part, on the auto-correlation data and the mutual correlation data.
3. The method of claim 2 , wherein the first part of the OFDM signal is an OFDM symbol and the second part of the OFDM signal is a repetition of the OFDM symbol.
4. The method of claim 2 , wherein the first part of the OFDM signal is an OFDM symbol and the second part of the OFDM signal is a corresponding cyclic prefix.
5. The method of claim 1 , comprising:
generating, based at least in part on a first part of the OFDM signal, first Fourier Transform data; and
generating, based at least in part on a second part of the OFDM signal, second Fourier Transform data,
wherein the frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers is calculated based, at least in part, on the first Fourier Transform data and the second Fourier Transform data.
6. The method of claim 1 , comprising:
determining, based at least in part on a first part of the OFDM signal, a first length;
determining, based at least in part on a second part of the OFDM signal, a second length; and
wherein the determining is based, at least in part, on the first length and the second length.
7. One or more non-transitory computer-readable storage media embodying logic when executed by a processor is configured to:
receive an Orthogonal Frequency Division Multiplexing (OFDM) signal comprising a plurality of Doppler-shifted OFDM subcarriers of a subband;
calculate a frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers, thereby yielding a plurality of subcarrier-specific frequency shift factor values;
calculate an average of the plurality of subcarrier-specific frequency shift factor values as the average frequency shift factor corresponding to the plurality of Doppler-shifted OFDM subcarriers;
calculate, for each Doppler-shifted OFDM subcarrier, a frequency offset by multiplying the average frequency shift factor by a frequency index of the each subcarrier, the frequency offset for at least two Doppler-shifted OFDM subcarriers of the subband being different from each other; and
compensate the frequency offset for each Doppler-shifted OFDM subcarrier for the frequency synchronization.
8. The one or more non-transitory computer-readable storage media of claim 7 , comprising logic that when executed by a processor is configured to:
generate, based at least in part on a first part of the OFDM signal, first Fourier Transform data; and
generate, based at least in part on a second part of the OFDM signal, second Fourier Transform data,
wherein the frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers is calculated based, at least in part, on the first Fourier Transform data and the second Fourier Transform data.
9. The one or more non-transitory computer-readable storage media of claim 7 , comprising logic that when executed by the processor is configured to:
generate, based at least in part on a first part of the OFDM signal, auto-correlation data; and
generate, based at least in part on a second part of the OFDM signal, mutual correlation data,
wherein the frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers is calculated based, at least in part, on the auto-correlation data and the mutual correlation data.
10. The one or more non-transitory computer-readable storage media of claim 9 , wherein the first part of the OFDM signal is an OFDM symbol and the second part of the OFDM signal is a repetition of the OFDM symbol.
11. The one or more non-transitory computer-readable storage media of claim 9 , wherein the first part of the OFDM signal is a cyclic prefix of an OFDM symbol and the second part of the OFDM signal is the OFDM symbol.
12. The one or more non-transitory computer-readable storage media of claim 7 , comprising logic that when executed by the processor is configured to:
determine, based at least in part on a first part of the OFDM signal, a first length; and
determine, based at least in part on a second part of the OFDM signal, a second length,
wherein the frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers is calculated based, at least in part, on the first length and the second length.
13. A mobile system comprising:
an Orthogonal Frequency Division Multiplexing (OFDM) receiver configured to receive an OFDM signal comprising a plurality of Doppler-shifted OFDM subcarriers of a subband;
a subcarrier frequency-shift estimator interoperably coupled to the OFDM receiver, the subcarrier frequency-shift estimator configured to:
calculate a frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers, thereby yielding a plurality of subcarrier-specific frequency shift factor values, and
calculate an average of the plurality of subcarrier-specific frequency shift factor values as the average frequency shift factor corresponding to the plurality of Doppler-shifted OFDM subcarriers; and
a frequency shift bank interoperably coupled to the OFDM receiver and the subcarrier frequency-shift estimator, the frequency shift bank configured to:
calculate, for each Doppler-shifted OFDM subcarrier, a frequency offset by multiplying the average frequency shift factor by a frequency index of the each subcarrier, the frequency offset for at least two Doppler-shifted OFDM subcarriers of the subband being different from each other, and
compensate the frequency offset for each Doppler-shifted OFDM subcarrier for the frequency synchronization.
14. The system of claim 13 , comprising a processor configured to:
generate, based at least in part on a first part of the OFDM signal, first Fourier Transform data; and
generate, based at least in part on a second part of the OFDM signal, second Fourier Transform data,
wherein the frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers is calculated based, at least in part, on the first Fourier Transform data and the second Fourier Transform data.
15. The system of claim 14 , comprising a correlator configured to:
generate, based at least in part on a first part of the OFDM signal, auto-correlation data; and
generate, based at least in part on a second part of the OFDM signal, mutual correlation data,
wherein the frequency shift factor for each Doppler-shifted OFDM subcarrier of the plurality of Doppler-shifted OFDM subcarriers is calculated based, at least in part, on the auto-correlation data and the mutual correlation data.
16. The system of claim 15 , wherein the first part of the OFDM signal is an OFDM symbol and the second part of the OFDM signal is a repetition of the OFDM symbol.
17. The system of claim 15 , wherein the first part of the OFDM signal is a cyclic prefix of an OFDM symbol and the second part of the OFDM signal is the OFDM symbol.