Method and system for an OFDM joint training and frequency tracking system

• US 8,929,197 B2
• Filed: 09/24/2013
• Issued: 01/06/2015
• Est. Priority Date: 08/01/2008
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Kent, Mark
• Primary Examiner(s): MEW, KEVIN D
• Application Number:
  US14/035,713
• Publication Number:
  US 20140023162A1
• Time in Patent Office: 469 Days
• Field of Search: 370203-204, 370/206, 370208-210, 370/252, 370/330, 370/336, 370/503, 370/516
• US Class Current: 370/208
• CPC Class Codes: H04L 27/265 Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators H04L27/26524 takes precedence
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

Aspects of a method and system for an OFDM joint timing and frequency tracking system may include tracking carrier frequency and symbol timing in an Orthogonal Frequency Division Multiplexing (OFDM) signal based on at least a reference symbol set. A receiver frequency and timing may be adjusted based on the tracked carrier frequency and symbol timing. The carrier frequency may be tracked by generating an output signal as a function of a frequency offset Δf, and the symbol timing may be tracked by generating an output signal as a function of a guard time Δt_g. The received OFDM signal may be fast Fourier transformed to generate the reference symbol (RS) set. The receiver frequency and timing may be adjusted coarsely prior to fine adjustment. The coarse receiver frequency and the timing adjustment may be based on processing a primary synchronization signal and a secondary synchronization signal.

Claims

1. A method for processing communication signals, the method comprising:

tracking a carrier frequency and a symbol timing in an Orthogonal Frequency Division Multiplexing (OFDM) signal based on a reference symbol set;

coarsely adjusting a receiver frequency and a receiver timing based on the tracked carrier frequency and the tracked symbol timing, wherein the coarse adjustment includes generating a coarse receiver frequency and a coarse timing adjustment based on a primary synchronization signal and a secondary synchronization signal; and

finely adjusting the receiver frequency and the receiver timing based on the tracked carrier frequency and the tracked symbol timing.

2. The method according to claim 1, wherein the coarse adjustment is performed prior to the fine adjustment.

3. The method according to claim 1, wherein the reference symbol set comprises:

a plurality of time-frequency slots configured to change according to a time-frequency shift and pseudo-noise sequence that modulates the reference symbol set.

4. The method according to claim 1, further comprising:

Fast Fourier Transforming the OFDM signal to generate the reference symbol set.

5. The method according to claim 1, further comprising:

controlling the coarse and fine adjustment of the receiver frequency via a receiver frequency oscillator.

6. The method according to claim 1, further comprising:

controlling the coarse and fine adjustment of the symbol timing via a timing generator.

7. The method according to claim 1, wherein the tracking of the carrier frequency and symbol timing comprises:

comparing an input clock signal to frequency and timing information extracted from the OFDM signal utilizing the reference symbol set to generate frequency error information and timing error information.

8. The method according to claim 7, wherein the tracking of the carrier frequency comprises:

generating an output signal as a function of a frequency offset, the output signal being generated based on the frequency error information.

9. The method according to claim 7, wherein the tracking of the symbol timing comprises:

generating an output signal as a function of a guard time, the output signal being generated based on the timing error information.

10. The method according to claim 7, wherein the tracking of the carrier frequency comprises:

generating an output signal as a function of a frequency offset, the output signal being generated based on the frequency error information; and

wherein the tracking of the symbol timing comprises;

generating an output signal as a function of a guard time, the output signal being generated based on the timing error information.

11. A system for processing communication signals, the system comprising:

a frequency and timing module configured to track a carrier frequency and a symbol timing in an Orthogonal Frequency Division Multiplexing (OFDM) signal based on a reference symbol set; and

a receiver configured to;

coarsely adjust a frequency and a timing of the receiver based on the tracked carrier frequency and the tracked symbol timing, wherein the coarse adjustment includes generating a coarse receiver frequency and a coarse timing adjustment based on a primary synchronization signal and a secondary synchronization signal; and

finely adjust the frequency and the timing of the receiver based on the tracked carrier frequency and the tracked symbol timing.

12. The system according to claim 11, wherein the receiver is configured to perform the coarse adjustment prior to the fine adjustment.

13. The system according to claim 11, wherein the reference symbol set comprises:

a plurality of time-frequency slots configured to change according to a time-frequency shift and pseudo-noise sequence that modulates the reference symbol set.

14. The system according to claim 11, wherein the receiver comprises:

a Fast Fourier Transform module that is configured to Fast Fourier Transform the OFDM signal to generate the reference symbol set.

15. The system according to claim 11, wherein the receiver comprises:

a receiver frequency oscillator, wherein the receiver is further configured to control the coarse and fine adjustment of the receiver frequency utilizing the receiver frequency oscillator.

16. The system according to claim 11, wherein the receiver comprises:

a timing generator, wherein the receiver is farther configured to control the coarse and fine adjustment of the symbol timing utilizing the timing generator.

17. The system according to claim 11, wherein the frequency and timing module is configured to compare an input clock signal to frequency and timing information extracted from the OFDM signal utilizing the reference symbol set to generate frequency error information and timing error information to track the carrier frequency and the symbol timing.

18. The system according to claim 17, wherein the frequency and timing module is configured to generate an output signal based on the frequency error information, the output signal being a function of a frequency offset.

19. The system according to claim 17, wherein the frequency and timing module is configured to generate an output signal based on the timing error information, the output signal being a function of a guard time.

20. A system for processing communication signals, the system comprising:

a frequency and timing module configured to track a carrier frequency and a symbol timing in an Orthogonal Frequency Division Multiplexing (OFDM) signal based on a reference symbol set; and

a receiver configured to;

generate the reference symbol set and provide the reference symbol set to the frequency and timing module, wherein the reference symbol set includes a plurality of time-frequency slots configured to change according to a time-frequency shift and pseudo-noise sequence that modulates the reference symbol set;

coarsely adjust a frequency and a timing of the receiver based on the tracked carrier frequency and the tracked symbol timing; and

finely adjust the frequency and the timing of the receiver based on the tracked carrier frequency and the tracked symbol timing.