System and method for frequency synchronization of Doppler-shifted subcarriers

• US 10,091,044 B2
• Filed: 07/16/2015
• Issued: 10/02/2018
• Est. Priority Date: 07/17/2014
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Conversant Intellectual Property Management Inc (MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management))
• Inventors: Hu, Hanwu, Ahmadvand, Nima
• Primary Examiner(s): Fotakis, Aristocratis
• Application Number:
  US14/801,146
• Publication Number:
  US 20160020936A1
• Time in Patent Office: 1,174 Days
• CPC Class Codes: H04L 27/26132 using repetition
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2671 Time domain
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2692 with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver

Abstract

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.

Claims

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.