Preamble detection with unknown channel

1. A system, comprising:

a correlation module configured to generate correlation values based on a correlation of modulated signals with a plurality of preamble sequences, wherein the modulated signals include sub-carriers modulated using orthogonal frequency domain multiplexing (OFDM); and

a control module configured to

select a largest correlation value from the correlation values, and

detect one of the preamble sequences in the modulated signals upon determining that a magnitude of the largest correlation value is greater than or equal to a first predetermined threshold,

wherein the control module divides N of the sub-carriers into L bands in response to a channel gain of the sub-carriers not being substantially the same for all of the sub-carriers, where N and L are integers greater than 1, and where each of the L bands includes N/L of the sub-carriers.

2. The system of claim 1 , wherein each of the preamble sequences is different from others of the preamble sequences.

3. The system of claim 1 , wherein the preamble sequences are stored in one of the correlation module and the control module.

4. The system of claim 1 , wherein the control module is configured to identify a segment of a base station that transmitted the modulated signals based on the one of the preamble sequences.

5. The system of claim 1 , wherein every P th one of the sub-carriers is modulated with a preamble bit, where P is an integer greater than or equal to 1.

6. The system of claim 1 , wherein the sub-carriers have a random channel phase.

7. The system of claim 1 , wherein the preamble sequences have a cross-correlation value of less than or equal to a second predetermined threshold.

8. The system of claim 7 , wherein the second predetermined threshold is less than approximately 0.2 for an orthogonal frequency domain multiplexing (OFDM) system using a 1024 fast Fourier transform (FFT) mode.

9. The system of claim 1 , wherein the first predetermined threshold is based on a signal strength of the modulated signals.

10. The system of claim 1 , wherein the modulated signals include a fractional carrier frequency offset (CFO) configured to generate a phase error that is substantially the same in each one of the modulated signals.

11. The system of claim 1 , wherein the modulated signals include an integer carrier frequency offset (CFO) configured to generate a phase error that is substantially the same in each one of the modulated signals.

12. A physical layer module (PHY) comprising:

the system of claim 1 ; and

a transceiver module configured to

communicate with the correlation module and the control module; and

receive the modulated signals.

13. A network device comprising:

the PHY of claim 12 ; and

at least one antenna configured to communicate with the transceiver module.

14. The system of claim 1 , wherein the correlation module is configured to:

correlate symbols in every P th one of the N/L of the sub-carriers in each of the L bands with corresponding symbols in each of the preamble sequences; and

generate intra-band correlation values for each band for each of the preamble sequences,

where P is an integer greater than or equal to 1.

15. The system of claim 14 , wherein the control module is configured to:

generate a band correlation value for each of the L bands and for each of the preamble sequences by adding the intra-band correlation values;

generate a magnitude of each of the band correlation value; and

generate the correlation values by adding the magnitude of each of the band correlation value for each of the preamble sequences.

16. A method, comprising:

receiving modulated signals, wherein the modulated signals include sub-carriers modulated using orthogonal frequency domain multiplexing (OFDM);

dividing N of the sub-carriers into L bands in response to a channel gain of the sub-carriers not being substantially the same for all of the sub-carriers, where N and L are integers greater than 1, and where each of the L bands includes N/L of the sub-carriers;

correlating the modulated signals with a plurality of preamble sequences;

generating correlation values based on the correlating;

selecting a largest correlation value from the correlation values; and

detecting one of the preamble sequences in the modulated signals upon determining that a magnitude of the largest correlation value is greater than or equal to a first predetermined threshold.

17. The method of claim 16 , further comprising storing the preamble sequences, wherein each of the preamble sequences is different from others of the preamble sequences.

18. The method of claim 16 , further comprising identifying a segment of a base station that transmitted the modulated signals based on the one of the preamble sequences.

19. The method of claim 16 , wherein every P th one of the sub-carriers is modulated with a preamble bit, where P is an integer greater than or equal to 1, and wherein the sub-carriers have a random channel phase.

20. The method of claim 16 , wherein the preamble sequences have a cross-correlation value of less than or equal to a second predetermined threshold.

21. The method of claim 20 , further comprising determining that the second predetermined threshold is less than approximately 0.2 for an orthogonal frequency domain multiplexing (OFDM) method using a 1024 fast Fourier transform (FFT) mode.

22. The method of claim 16 , further comprising determining the first predetermined threshold based on a signal strength of the modulated signals.

23. The method of claim 16 , wherein the modulated signals have a fractional carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of the modulated signals.

24. The method of claim 16 , wherein the modulated signals have an integer carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of the modulated signals.

25. The method of claim 16 , further comprising

correlating symbols in every P th one of the N/L of the sub-carriers in each of the L bands with corresponding symbols in each of the preamble sequences; and

generating intra-band correlation values for each band for each of the preamble sequences,

where P is an integer greater than or equal to 1.

26. The method of claim 25 , further comprising:

generating a band correlation value for each of the L bands and for each of the preamble sequences by adding the intra-band correlation values;

generating a magnitude of each of the band correlation value; and

generating the correlation values by adding the magnitude of each of the band correlation value for each of the preamble sequences.

27. A system, comprising:

correlation means for generating correlation values based on a correlation of modulated signals with a plurality of preamble sequences, wherein the modulated signals include sub-carriers modulated using orthogonal frequency domain multiplexing (OFDM); and

control means for

selecting a largest correlation value from the correlation values, and

detecting one of the preamble sequences in the modulated signals upon determining that a magnitude of the largest correlation value is greater than or equal to a first predetermined threshold,

wherein the control means divides N of the sub-carriers into L bands in response to a channel gain of the sub-carriers not being substantially the same for all of the sub-carriers, where N and L are integers greater than 1, and where each of the L bands includes N/L of the sub-carriers.

28. The system of claim 27 , wherein each of the preamble sequences is different from others of the preamble sequences.

29. The system of claim 27 , wherein the preamble sequences are stored in one of the correlation means and the control means.

30. The system of claim 27 , wherein the control means identifies a segment of a base station that transmitted the modulated signals based on the one of the preamble sequences.

31. The system of claim 27 , wherein every P th one of the sub-carriers is modulated with a preamble bit, where P is an integer greater than or equal to 1.

32. The system of claim 27 , wherein the sub-carriers have a random channel phase.

33. The system of claim 27 , wherein the preamble sequences have a cross-correlation value of less than or equal to a second predetermined threshold.

34. The system of claim 33 , wherein the second predetermined threshold is less than approximately 0.2 for an orthogonal frequency domain multiplexing (OFDM) system using a 1024 fast Fourier transform (FFT) mode.

35. The system of claim 27 , wherein the first predetermined threshold is based on a signal strength of the modulated signals.

36. The system of claim 27 , wherein the modulated signals include a fractional carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of the modulated signals.

37. The system of claim 27 , wherein the modulated signals include an integer carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of the modulated signals.

38. A physical layer means (PHY) comprising:

the system of claim 27 ; and

transceiver means for communicating with the correlation means and the control means and that receives the modulated signals.

39. A network device comprising:

the PHY means of claim 38 ; and

at least one antenna means for communicating with the transceiver means.

40. The system of claim 27 , wherein the correlation means:

correlates symbols in every P th one of the N/L of the sub-carriers in each of the L bands with corresponding symbols in each of the preamble sequences, and

generates intra-band correlation values for each band for each of the preamble sequences,

where P is an integer greater than or equal to 1.

41. The system of claim 40 wherein the control means:

generates a band correlation value for each of the L bands and for each of the preamble sequences by adding the intra-band correlation values;

generates a magnitude of each of the band correlation value; and

generates the correlation values by adding the magnitude of each of the band correlation value for each of the preamble sequences.

42. A computer program stored on a non-transitory computer-readable medium and executable by a processor, the computer program comprising instructions for:

receiving modulated signals, wherein the modulated signals include sub-carriers modulated using orthogonal frequency domain multiplexing (OFDM);

dividing N of the sub-carriers into L bands in response to a channel gain of the sub-carriers not being substantially the same for all of the sub-carriers, where N and L are integers greater than 1, and where each of the L bands includes N/L of the sub-carriers;

correlating the modulated signals with a plurality of preamble sequences;

generating correlation values based on the correlating;

selecting a largest correlation value from the correlation values; and

detecting one of the preamble sequences in the modulated signals upon determining that a magnitude of the largest correlation value is greater than or equal to a first predetermined threshold.

43. The computer program of claim 42 , further comprising instructions for storing the preamble sequences, wherein each of the preamble sequences is different from others of the preamble sequences.

44. The computer program of claim 42 , further comprising instructions for identifying a segment of a base station that transmitted the modulated signals based on the one of the preamble sequences.

45. The computer program of claim 42 , wherein every P th one of the sub-carriers is modulated with a preamble bit, where P is an integer greater than or equal to 1, and wherein the sub-carriers have a random channel phase.

46. The computer program of claim 42 , wherein the preamble sequences have a cross-correlation value of less than or equal to a second predetermined threshold.

47. The computer program of claim 46 , further comprising instructions for determining that the second predetermined threshold is less than approximately 0.2 for an orthogonal frequency domain multiplexing (OFDM) computer program using a 1024 fast Fourier transform (FFT) mode.

48. The computer program of claim 42 , further comprising instructions for determining the first predetermined threshold based on a signal strength of the modulated signals.

49. The computer program of claim 42 , wherein the modulated signals have a fractional carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of the modulated signals.

50. The computer program of claim 42 , wherein the modulated signals have an integer carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of the modulated signals.

51. The computer program of claim 42 , further comprising instructions for:

correlating symbols in every P th one of the N/L of the sub-carriers in each of the L bands with corresponding symbols in each of the preamble sequences; and

generating intra-band correlation values for each band for each of the preamble sequences,

where P is an integer greater than or equal to 1.

52. The computer program of claim 51 , further comprising instructions for:

generating a band correlation value for each of the L bands and for each of the preamble sequences by adding the intra-band correlation values,

generating a magnitude of each of the band correlation value, and

generating the correlation values by adding the magnitude of each of the band correlation value for each of the preamble sequences.