SYSTEM AND METHOD FOR FREQUENCY SYNCHRONIZATION OF DOPPLER-SHIFTED SUBCARRIERS

• US 20200136879A1
• Filed: 10/30/2019
• Published: 04/30/2020
• 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
• Granted Patent: US 10,944,612 B2
• Time in Patent Office: 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 a first Orthogonal Frequency Division Multiplexing (OFDM) signal comprising a first plurality of Doppler-shifted OFDM subcarriers;

receiving a second Orthogonal Frequency Division Multiplexing (OFDM) signal comprising a second plurality of Doppler-shifted OFDM subcarriers of the subband;

calculating an auto-correlation for the first OFDM signal;

calculating a respective mutual correlation between the first OFDM signal and the second OFDM signal;

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 signal and the second OFDM signal, 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 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 average frequency shift factor comprises an average of a plurality of subcarrier specific frequency shirt factor values.

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:

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.

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) signal comprising a first plurality of Doppler-shifted OFDM subcarriers of a subband;

receiving a second Orthogonal Frequency Division Multiplexing (OFDM) signal comprising a second plurality of Doppler-shifted OFDM subcarriers of the subband;

calculating an auto-correlation for the first OFDM signal;

calculating a respective mutual correlation between the first OFDM signal and the second OFDM signal;

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 signal and the second OFDM signal, 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 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 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 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.

9. The one or more non-transitory computer-readable storage media of claim 7, 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.

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 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.

11. A mobile system comprising:

an Orthogonal Frequency Division Multiplexing (OFDM) receiver configured to receive a first OFDM signal comprising a first plurality of Doppler-shifted OFDM subcarriers of a subband and a second OFDM signal 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 signal,

calculating a respective mutual correlation between the first OFDM signal and the second OFDM signal, 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 signal and the second OFDM signal, 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 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 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 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.

14. The system of claim 12, 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.