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 comprising:
receiving an Orthogonal Frequency Division Multiplexing (OFDM) signal comprising a plurality of Doppler-shifted OFDM subcarriers of a subband;
determining an average frequency shift factor corresponding to the plurality of Doppler-shifted OFDM subcarriers;
wherein determining the average frequency shift factor comprises:
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; and
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; and
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.
2. The method of claim 1 , comprising:
generating, based at least in part on a first part of the OFDM signal, first Fourier Transform data;
generating, based at least in part on a second part of the OFDM signal, second Fourier Transform data; and
wherein the determining is based, at least in part, on the first Fourier Transform data and the second Fourier Transform 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, auto-correlation data;
generating, based at least in part on a second part of the OFDM signal, mutual correlation data; and
wherein the determining is based, at least in part, on the auto-correlation data and the mutual correlation data.
6. The method of claim 5 , 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.
7. The method of claim 5 , 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.
8. 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.
9. The method of claim 8 , wherein the first part of the OFDM signal is a cyclic prefix and the second part of the OFDM signal is an OFDM symbol.
10. The method of claim 1 , wherein determining the average frequency shift factor is performed by a subcarrier frequency-shift estimator.
11. The method of claim 1 , wherein each frequency offset is calculated by a frequency shift bank.
12. 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;
determine an average frequency shift factor corresponding to the plurality of Doppler-shifted OFDM subcarriers;
wherein the determination of the average frequency shift factor comprises:
calculation of 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
calculation of 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
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.
13. The media of claim 12 , 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;
generate, based at least in part on a second part of the OFDM signal, second Fourier Transform data; and
wherein the determination is based, at least in part, on the first Fourier Transform data and the second Fourier Transform data.
14. The media of claim 13 , 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.
15. The media of claim 13 , 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.
16. The media of claim 13 , 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;
generate, based at least in part on a second part of the OFDM signal, mutual correlation data; and
wherein the determination is based, at least in part, on the auto-correlation data and the mutual correlation data.
17. The media of claim 16 , 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.
18. The media of claim 16 , 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.
19. The media of claim 12 , 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;
determine, based at least in part on a second part of the OFDM signal, a second length; and
wherein the determination is based, at least in part, on the first length and the second length.
20. The media of claim 19 , wherein the first part of the OFDM signal is a cyclic prefix and the second part of the OFDM signal is an OFDM symbol.
21. A 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 determine an average frequency shift factor corresponding to the plurality of Doppler-shifted OFDM subcarriers;
wherein the determination of the average frequency shift factor comprises:
calculation of 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
calculation of 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.
22. The system of claim 21 , comprising a processor configured to:
generate, based at least in part on a first part of the OFDM signal, first Fourier Transform data;
generate, based at least in part on a second part of the OFDM signal, second Fourier Transform data; and
wherein the determination is based, at least in part, on the first Fourier Transform data and the second Fourier Transform data.
23. The system of claim 22 , 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.
24. The system of claim 22 , 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.
25. The system of claim 21 , comprising a correlator configured to:
generate, based at least in part on a first part of the OFDM signal, auto-correlation data;
generate, based at least in part on a second part of the OFDM signal, mutual correlation data; and
wherein the determination is based, at least in part, on the auto-correlation data and the mutual correlation data.
26. The system of claim 25 , 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.
27. The system of claim 25 , 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.