Frame timing synchronization for orthogonal frequency division multiplexing (OFDM)

• US 20070217524A1
• Filed: 03/16/2006
• Published: 09/20/2007
• Est. Priority Date: 03/16/2006
• Status: Active Grant

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: NEC Electronics Corporation (Renesas Electronics Corporation)
• Inventors: Wang, Dong, Zhang, Jinyun
• Granted Patent: US 7,809,097 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2676 Blind, i.e. without using known symbols

Abstract

A frame timing synchronization technique for orthogonal frequency division multiplexing (OFDM) systems is presented. First, a coarse synchronization technique generates a coarse frame timing estimate. The coarse synchronization technique applies a sliding window differentiator to the output of a conventional auto-correlator to mitigate the plateau effect associated with conventional auto-correlation techniques. Second, a fine synchronization technique generates a fine frame timing estimate. The fine synchronization technique uses the coarse frame timing estimate to reduce the number of cross-correlation calculations. Additionally, the fine synchronization technique acquires a fine frame timing estimate based on a signal-to-interference ratio (SIR) metric, which is more robust to multi-paths and pseudo multi-paths caused by cyclic delay diversity (CDD) schemes than conventional cross-correlation synchronization techniques. A fine-tuning technique generates a desired frame timing estimate by searching a first signal path in a searching window around the fine frame timing estimate to further refine frame timing synchronization.

Claims

1. A frame timing synchronization system, comprising:

a coarse frame timing synchronizer, comprising;

an auto-correlator that generates an auto-correlator output signal based on a received signal, and

a sliding window differentiator that generates a sliding window differentiator signal based on the auto-correlator output signal, wherein the coarse frame timing synchronizer detects a peak value of the sliding window differentiator signal and generates a coarse frame timing estimate based on a timing position of the peak value of the sliding window differentiator signal; and

a fine frame timing synchronizer that operates in a window around the coarse frame timing estimate, comprising;

a cross-correlator that generates a cross-correlator output signal based on the received signal, and

a signal-to-interference ratio (SIR) metric calculator that generates a SIR metric signal based on the cross-correlator output signal, wherein the fine frame timing synchronizer detects a peak value of the SIR metric signal and generates a fine frame timing estimate based on a timing position of the peak value of the SIR metric signal.

2. The frame timing synchronization system of claim 1, further comprising a search operator that generates a desired frame timing estimate by searching a window around the fine frame timing estimate.

3. The frame timing synchronization system of claim 1, wherein the sliding window differentiator applies first and second moving average windows to the auto-correlator output signal to generate first and second moving average window output signals and calculates a difference between the first and second moving average window output signals.

4. The frame timing synchronization system of claim 3, wherein the second moving average window is separated from the first moving average window by a predetermined amount.

5. The frame timing synchronization system of claim 4, wherein the predetermined amount corresponds to a length of a training symbol in the received signal.

6. The frame timing synchronization system of claim 5, wherein the received signal includes a plurality of long and short training symbols, and wherein the predetermined amount corresponds to a length of a short training symbol.

7. The frame timing synchronization system of claim 1, wherein the SIR metric calculator compares an amount of signal energy in a signal energy window to an amount of interference energy in an interference window to mitigate an error associated with pseudo multi-paths introduced by a cyclic delay diversity (CDD) scheme.

8. The frame timing synchronization system of claim 1, wherein the fine frame timing synchronizer further comprises a carrier frequency offset compensator that generates a received signal with carrier frequency offset compensation, and wherein the cross-correlator generates the cross-correlator output signal based on the received signal with carrier frequency offset compensation.

9. A coarse frame timing synchronization system, comprising:

an auto-correlator that generates an auto-correlator output signal based on a received signal, and

a sliding window differentiator that generates a differentiator signal by applying first and second moving average windows to the auto-correlator output signal and calculating a difference between first and second moving average window output signals, wherein the coarse frame timing synchronizer generates a coarse frame timing estimate based on a timing position of a peak value of the differentiator signal.

10. The coarse frame timing synchronization system of claim 9, wherein the second moving average window is separated from the first moving average window by a predetermined amount.

11. The coarse frame timing synchronization system of claim 10, wherein the received signal includes a plurality of long and short training symbols, and wherein the predetermined amount corresponds to a length of a short training symbol.

12. The coarse frame timing synchronization system of claim 9, wherein the sliding window differentiator generates the differentiator signal to mitigate an error associated with a plateau of the auto-correlator output signal.

13. A fine frame timing synchronization system, comprising:

a cross-correlator that generates a cross-correlator output signal based on a received signal and a pilot signal, and

a signal-to-interference ratio (SIR) metric calculator that generates a SIR metric signal based on the cross-correlator output signal, wherein the fine frame timing synchronizer generates a fine frame timing estimate based on a timing position of the peak value of the SIR metric signal.

14. The fine frame timing synchronization system of claim 13, further comprising a carrier frequency offset compensator that generates a received signal with carrier frequency offset compensation, wherein the cross-correlator generates the cross-correlator output signal based on the received signal with carrier frequency offset compensation and the pilot signal.

15. The fine frame timing synchronization system of claim 13, wherein the SIR metric calculator compares an amount of signal energy in a signal energy window to an amount of interference energy in an interference window to mitigate an error associated with pseudo multi-paths introduced by a cyclic delay diversity (CDD) scheme.

16. The fine frame timing synchronization system of claim 15, wherein the SIR metric calculator optimizes a length of the signal energy window and a length of the interference window.

17. The fine frame timing synchronization system of claim 15, wherein the SIR metric calculator adjusts a position of the interference window based on a polarity of CDD values associated with the CDD scheme

18. A frame timing synchronization method, comprising:

determining a coarse frame timing estimate, comprising;

generating a sliding window differentiator signal based on an auto-correlator output signal, and

detecting a peak value of the sliding window differentiator signal, wherein a timing position of the peak value of the sliding window differentiator signal corresponds to the coarse frame timing estimate; and

determining a fine frame timing estimate in a window around the coarse frame timing estimate, comprising;

generating a signal-to-interference ratio (SIR) metric signal based on a cross-correlator output signal, and

detecting a peak value of the SIR metric signal, wherein a timing position of the peak value of the SIR metric signal corresponds to the fine frame timing estimate.

19. The method of claim 18, further comprising determining a desired frame timing estimate by searching a window around the fine frame timing estimate.

20. The method of claim 18, wherein the generating a sliding window differentiator signal step comprises:

applying first and second moving average windows to the auto-correlator output signal to generate first and second moving average window output signals, wherein the second moving average window is separated from the first moving average window by a predetermined amount; and

calculating a difference between the first and second moving average window output signals.

21. The method of claim 18, wherein the generating a sliding window differentiator signal step comprises mitigating an error associated with a plateau of the auto-correlator output signal.

22. The method of claim 18, wherein the generating a SIR metric signal step comprises mitigating an error associated with pseudo multi-paths introduced by a cyclic delay diversity (CDD) scheme.

23. The method of claim 22, wherein the generating a SIR metric signal step comprises comparing an amount of signal energy in a signal energy window to an amount of interference energy associated with the multi-paths in an interference window.

24. The method of claim 23, wherein the generating a SIR metric signal step further comprises optimizing a length of the signal energy window and a length of the interference window.

25. A coarse frame timing synchronization method, comprising:

generating an auto-correlator output signal based on a received signal;

applying first and second moving average windows to the auto-correlator output signal to generate first and second moving average window output signals, wherein the second moving average window is separated from the first moving average window by a predetermined amount;

calculating a difference between the first and second moving average window output signals; and

determining a coarse frame timing estimate based on a timing position of a peak value of the calculated difference signal.

26. The method of claim 25, wherein the generating an auto-correlator output signal step comprises calculating a sum of auto-correlated signals received from each of a plurality of receive antennas.

27. A fine frame timing synchronization method, comprising:

generating a cross-correlator output signal based on a received signal and a pilot signal;

calculating a signal-to-interference ratio (SIR) metric signal based on the cross-correlator output signal;

detecting a peak value of the SIR metric signal; and

determining a fine frame timing estimate based on a timing position of the peak value of the SIR metric signal.

28. The method of claim 27, further comprising generating a received signal with carrier frequency offset compensation, wherein the generating a cross-correlator output signal step comprises generating a cross-correlator output signal based on the received signal with carrier frequency offset compensation and the pilot signal.

29. The method of claim 27, wherein the calculating a SIR metric signal step further comprises comparing an amount of signal energy in a signal energy window to an amount of interference energy to mitigate an error associated with pseudo multi-paths introduced by a cyclic delay diversity (CDD) scheme.

30. The method of claim 29, wherein the calculating a SIR metric signal step further comprises optimizing a length of the signal energy window and a length of the interference window.

31. The method of claim 29, wherein the generating a SIR metric signal step further comprises adjusting a position of the interference window based on a polarity of CDD values associated with the CDD scheme.

32. The method of claim 27, wherein the generating a cross-correlator output signal step comprises calculating a sum of cross-correlator output signals based on received signals from each of a plurality of receive antennas.