Systems and methods for performing initial synchronization in wireless communications systems

1. An apparatus for performing initial synchronization in a wireless device comprising:

a first synchronizer in the wireless device configured to determine approximate timing of a frame boundary for a received signal;

a frequency offset estimator in the wireless device configured to estimate a frequency offset associated with symbol boundaries within the received signal; and

a second synchronizer in the wireless device configured to determine precise timing information of the received signal, wherein the second synchronizer is configured to:

calculate a time domain channel impulse response (CIR) of the received signal, wherein the second synchronizer includes a CIR estimator configured to determine a frequency domain preamble symbol of the received signal and perform an inverse fast Fourier transform (IFFT) on the frequency domain preamble symbol to derive the time domain CIR;

identify a first peak in the calculated time domain CIR; and

determine precise timing information by deriving a timing associated with the identified first peak in the calculated time domain CIR of the received signal.

2. The apparatus of claim 1 , wherein the first synchronizer comprises:

a module configured to downsample the received signal based on a predetermined sampling rate;

a correlator configured to perform auto-correlation across adjacent frames within the downsampled received signal to obtain auto-correlation values;

a combiner configured to combine multiple frame auto-correlation results; and

an edge detector configured to derive timing information associated with the received signal based on the auto-correlation values.

3. The apparatus of claim 2 , wherein the correlator is further configured to normalize the auto-correlation values.

4. The apparatus of claim 2 , wherein the edge detector derives timing information by identifying a maximum value from among the auto-correlation values.

5. The apparatus of claim 1 , wherein the frequency offset estimator comprises:

a cyclic prefix (CP) correlator configured to obtain CP auto-correlation values associated the received signal to determine symbol timing associated with the received signal; and

an estimator configured to determine a frequency offset associated with the received signal based on the determined symbol timing.

6. The apparatus of claim 5 , wherein the correlator is further configured to normalize the auto-correlation values.

7. The apparatus of claim 6 , wherein output from the CP correlator is filtered based on the normalized auto-correlation values to remove interference peaks for interference nulling.

8. The apparatus of claim 7 , wherein the filtering is further based on an adaptive threshold.

9. The apparatus of claim 5 , wherein the CP correlator determines symbol timing by identifying a maximum value from among the CP auto-correlation values.

10. The apparatus of claim 1 , wherein the second synchronizer comprises:

a path identifier configured to detect a first path associated with the time domain CIR based on a maximum energy associated with a path in a multipath environment.

11. The apparatus of claim 1 , wherein to identify the first peak in the calculated CIR, the second synchronizer is further configured to:

identify one or more peak power values in the calculated CIR;

apply windows around the identified peak power values; and

determine the window having a maximum energy, the window containing the identified first peak.

12. A method for performing frame synchronization comprising:

performing a first synchronization to determine approximate timing of a frame boundary associated with a received signal;

based on the approximate timing, estimating frequency offset and symbol boundaries within the frame boundary; and

performing a second synchronization based on the frame boundary and the symbol boundaries, wherein performing a second synchronization comprises:

calculating a time domain channel impulse response (CIR) based on a frequency domain preamble symbol of the received signal, wherein the second synchronization includes determining a frequency domain preamble symbol of the received signal and performing an inverse fast Fourier transform (IFFT) on the frequency domain preamble symbol to derive the time domain CIR;

identifying a first peak in the calculated time domain CIR; and

determining precise timing information by deriving a timing associated with the identified first peak in the calculated time domain CIR of the received signal.

13. The method of claim 12 , wherein performing a first synchronization to determine approximate timing comprises:

downsampling the received signal; and

performing inter-frame auto-correlation on frames within the downsampled received signal to obtain auto-correlation values, wherein inter-frame auto-correlation is performed across adjacent frames within the received signal, and wherein performing inter-frame auto-correlation further comprises:

normalizing the auto-correlation values; and

combining normalized auto-correlation values over multiple frames.

14. The method of claim 13 , further comprising detecting an edge of the received signal based on the normalized auto-correlation values.

15. The method of claim 12 , wherein estimating frequency offset and symbol boundaries within the frame boundary comprises performing cyclic prefix (CP) auto-correlation on the received signal to determine symbol timing associated with the received signal.

16. The method of claim 15 , further comprising:

normalizing the auto-correlation values; and

based on the normalized auto-correlation values, identifying correlation peaks caused by uplink interference and removing the identified correlation peaks.

17. The method of claim 15 , further comprising determining a frequency offset associated with the received signal based on the determined symbol timing.

18. The method of claim 12 , wherein determining a first peak within the CIR comprises identifying a peak within the CIR with a maximum energy.

19. The method of claim 12 , wherein determining a first peak within the CIR further comprises utilizing a predetermined threshold to remove peaks associated with interference paths.

20. A system for performing frame synchronization comprising:

means for performing a first-pass synchronization to determine approximate timing of a frame boundary associated with a received signal;

means for estimating frequency offset and symbol boundaries within the frame boundary based on the approximate timing; and

means for performing a second-pass synchronization based on the frame boundary and the symbol boundaries, wherein means for performing a second synchronization is further configured to:

calculate a time domain channel impulse response (CIR) based on a frequency domain preamble symbol of the received signal, wherein the means for performing a second-pass synchronization includes means for determining a frequency domain preamble symbol of the received signal and means for performing an inverse fast Fourier transform (IFFT) on the frequency domain preamble symbol to derive the time domain CIR;

identify a first peak in the calculated time-domain CIR; and

determine precise timing information by deriving a timing associated with the identified first peak in the calculated time domain CIR of the received signal.

21. The system of claim 20 , further comprising:

means for downsampling the received signal;

means for performing auto-correlation on a plurality of frames within the downsampled received signal to obtain auto-correlation values;

means for normalizing the auto-correlation values;

means for combining normalized auto-correlation values over multiple frames; and

means for detecting an edge of the received signal based on normalized auto-correlation values.

22. The system of claim 20 , further comprising:

means for performing cyclic prefix (CP) auto-correlation on the received signal to determine symbol timing associated with the received signal;

means for normalizing the auto-correlation values and performing interference nulling based on normalized auto-correlation values; and

means for determining a frequency offset associated with the received signal based on the determined symbol timing.