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 a first Orthogonal Frequency Division Multiplexing (OFDM) symbol from an OFDM signal, the first OFDM symbol comprising a first plurality of Doppler-shifted OFDM subcarriers of a subband;
receiving a second OFDM symbol from the OFDM signal, the second OFDM symbol comprising a second plurality of Doppler-shifted OFDM subcarriers of the subband;
calculating an auto-correlation for the first OFDM symbol;
calculating a respective mutual correlation between the first OFDM symbol and the second OFDM symbol;
calculating an average frequency shift factor based on the auto-correlation and the mutual correlation;
calculating, for each Doppler-shifted OFDM subcarrier of the first OFDM symbol and the second OFDM symbol, 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 said each Doppler-shifted OFDM subcarrier for the frequency synchronization.
2. The method of claim 1 , comprising:
generating, based at least on a part of the first OFDM symbol, the auto-correlation; and
generating, based at least on a part of the second OFDM symbol, the mutual correlation,
wherein the average frequency shift factor comprises an average of a plurality of subcarrier specific frequency shift factor values.
3. The method of claim 2 , wherein the part of the first OFDM symbol is the entire first OFDM symbol and the second part of the second OFDM signal is a repetition of the entire first OFDM symbol.
4. The method of claim 2 , wherein the part of the first OFDM symbol is the entire OFDM symbol and the part of the second OFDM symbol is a cyclic prefix corresponding to the first OFDM symbol.
5. The method of claim 1 , comprising: determining, based at least on a part of the first OFDM symbol, a first length; determining, based at least on a part of the second OFDM symbol, a second length; and wherein the determining is based, at least in part, on the first length and the second length.
6. One or more non-transitory computer-readable storage media embodying logic when executed by a processor is configured to:
receiving a first Orthogonal Frequency Division Multiplexing (OFDM) symbol of an OFDM signal, the first OFDM symbol comprising a first plurality of Doppler-shifted OFDM subcarriers of a subband;
receiving a second OFDM symbol of the OFDM signal, the second OFDM symbol comprising a second plurality of Doppler-shifted OFDM subcarriers of the subband;
calculating an auto-correlation for the first OFDM symbol;
calculating a respective mutual correlation between the first OFDM and the second OFDM symbol;
calculating an average frequency shift factor based on the auto-correlation and the mutual correlation;
calculate, for each Doppler-shifted OFDM subcarrier of the first OFDM symbol and the second OFDM symbol, 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 said Doppler-shifted OFDM subcarrier for the frequency synchronization.
7. The one or more non-transitory computer-readable storage media of claim 6 , comprising logic that when executed by the processor is configured to: generate, based at least on a part of the first OFDM symbol, the auto-correlation; and generate, based at least on a part of the second OFDM symbol, the mutual correlation, wherein the average frequency shift factor comprises and average of a plurality of subcarrier specific frequency shift factor values.
8. The one or more non-transitory computer-readable storage media of claim 7 , wherein the part of the first OFDM symbol is the entire first OFDM symbol and the part of the second OFDM symbol is a repetition of the entire first OFDM symbol.
9. The one or more non-transitory computer-readable storage media of claim 7 , wherein the part of the OFDM symbol is a cyclic prefix of the second OFDM symbol and the part of the second OFDM symbol is the entire second OFDM symbol.
10. 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 on a part of the first OFDM symbol, a first length; and determine, based at least on a part of the second OFDM symbol, 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.
11. A mobile system comprising:
an Orthogonal Frequency Division Multiplexing (OFDM) receiver configured to receive a first OFDM symbol and a second OFDM symbol of an OFDM signal, the first OFDM symbol comprising a first plurality of Doppler-shifted OFDM subcarriers of a subband and the second OFDM symbol comprising a second plurality of Doppler-shifted OFDM subcarriers of the subband;
a subcarrier frequency-shift estimator interoperably coupled to the OFDM receiver, the subcarrier frequency-shift estimator configured to:
calculating an auto-correlation for the first OFDM symbol,
calculating a respective mutual correlation between the first OFDM symbol and the second OFDM symbol, and
calculating an average frequency shift factor based on the auto-correlation and the mutual correlation; 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 of the first OFDM symbol and the second OFDM symbol, 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 said each Doppler-shifted OFDM subcarrier for the frequency synchronization.
12. The system of claim 11 , comprising a correlator configured to: generate, based at least on a part of the first OFDM symbol, the auto-correlation; and generate, based at least on a part of the second OFDM symbol, the mutual correlation, wherein the average frequency shift factor comprises an average of a plurality of subcarrier specific frequency shift factor values.
13. The system of claim 12 , wherein the part of the first OFDM symbol is the entire OFDM symbol and the part of the second OFDM symbol is a repetition of the first OFDM symbol.
14. The system of claim 12 , wherein the part of the first OFDM symbol is a cyclic prefix of the second OFDM symbol and the part of the second OFDM symbol is the entire second OFDM symbol.