System and method for frequency synchronization of doppler-shifted subcarriers

• US 10,498,578 B2
• Filed: 08/30/2018
• Issued: 12/03/2019
• Est. Priority Date: 07/17/2014
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management)
• Inventors: Hu, Hanwu, Ahmadvand, Nima
• Primary Examiner(s): Fotakis, Aristocratis
• Application Number:
  US16/117,215
• Publication Number:
  US 20190013987A1
• Time in Patent Office: 460 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 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.