Preamble detection with unknown channel

• US 20070217552A1
• Filed: 12/29/2006
• Published: 09/20/2007
• Est. Priority Date: 03/17/2006
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Lee, Jungwon, Lou, Hui-Ling
• Granted Patent: US 8,031,784 B2
• Time in Patent Office: Days
• US Class Current: 375/343
• 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 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2676 Blind, i.e. without using known symbols
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

A system includes a differential demodulation module and a correlation module. The differential demodulation module differentially demodulates modulated signals to generate differentially demodulated signals. The correlation module correlates the differentially demodulated signals with derived preamble sequences and generates correlation values.

Claims

1. A system, comprising:

a differential demodulation module that differentially demodulates modulated signals to generate differentially demodulated signals; and

a correlation module that correlates said differentially demodulated signals with derived preamble sequences and that generates correlation values.

2. The system of claim 1 wherein said modulated signals include sub-carriers that are modulated using orthogonal frequency domain multiplexing (OFDM).

3. The system of claim 2 wherein every P^th one of said sub-carriers is modulated with a preamble bit, where P is an integer greater than or equal to 1.

4. The system of claim 3 wherein said every P^th one of said sub-carriers has substantially the same channel phase.

5. The system of claim 4 wherein each one of said correlation values has a real part and an imaginary part.

6. The system of claim 5 further comprising a control module that selects one of said correlation values having a largest real part and that detects a preamble sequence in said modulated signals upon determining that said largest real part is greater than or equal to a predetermined threshold.

7. The system of claim 6 wherein said control module identifies a segment of a base station that transmitted said modulated signals based on said preamble sequence.

8. The system of claim 3 wherein said every P^th one of said sub-carriers has substantially the same differential channel phase.

9. The system of claim 8 further comprising a control module that selects a largest correlation value from said correlation values and that detects a preamble sequence in said modulated signals upon determining that a magnitude of said largest correlation value is greater than or equal to a predetermined threshold.

10. The system of claim 9 wherein said control module identifies a segment of a base station that transmitted said modulated signals based on said preamble sequence.

11. The system of claim 3 wherein said differential demodulation module generates said differentially demodulated signals by multiplying a Q^th one of said modulated signals by a complex conjugate of a (Q+P)^th one of said modulated signals, where Q is an integer greater than or equal to 1.

12. The system of claim 1 wherein said derived preamble sequences are derived from preamble sequences, and wherein each of said preamble sequences is different from others of said preamble sequences.

13. The system of claim 12 wherein each bit of one of said derived preamble sequences has a first state when a corresponding bit and a bit adjacent to said corresponding bit in a corresponding one of said preamble sequences have opposite states, and said each bit has a second state when said corresponding bit and said bit adjacent to said corresponding bit have the same state.

14. The system of claim 1 wherein said derived preamble sequences are stored in one of said correlation module and said control module.

15. The system of claim 1 wherein said derived preamble sequences have a cross-correlation value that is less than or equal to a predetermined cross-correlation threshold.

16. The system of claim 15 wherein said predetermined cross-correlation threshold is less than approximately 0.2 for an orthogonal frequency domain multiplexing (OFDM) system using a 1024 fast Fourier transform (FFT) mode.

17. The system of claim 6 wherein said predetermined threshold is based on the signal strength of said modulated signals.

18. The system of claim 9 wherein said predetermined threshold is based on the signal strength of said modulated signals.

19. The system of claim 1 wherein said modulated signals include a fractional carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of said modulated signals.

20. The system of claim 1 wherein said modulated signals include an integer carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of said modulated signals.

21. The system of claim 20 wherein said correlation module correlates said derived preamble sequences with said differentially demodulated signals having said integer CFO.

22. The system of claim 1 wherein said modulated signals include a linearly increasing phase offset generated by a symbol timing offset.

23. The system of claim 9 wherein said control module calculates a symbol timing offset by multiplying a phase angle of said largest correlation value by (N/2π

P), where N is a number of sub-carriers in an N fast Fourier transform (FFT) mode, and where N is an integer greater than 1.

24. The system of claim 23 where N is one of 128, 512, 1024, and 2048.

25. A physical layer module (PHY) comprising the system of claim 1 and further comprising a transceiver module that communicates with said differential demodulation module and that receives said modulated signals.

26. A network device comprising the PHY of claim 25 and further comprising at least one antenna that communicates with said transceiver module.

27. A method, comprising:

differentially demodulating modulated signals;

generating differentially demodulated signals from said modulated signals;

correlating said differentially demodulated signals with derived preamble sequences; and

generating correlation values based on said correlating.

28. The method of claim 27 further comprising differentially demodulating sub-carriers that are included in said modulated signals and that are modulated using orthogonal frequency domain multiplexing (OFDM), wherein every P^th one of said sub-carriers is modulated with a preamble bit, where P is an integer greater than or equal to 1.

29. The method of claim 28 further comprising differentially demodulating said sub-carriers, wherein said every P^th one of said sub-carriers has substantially the same channel phase.

30. The method of claim 29 further comprising determining a real part and an imaginary part of each one of said correlation values.

31. The method of claim 30 further comprising selecting one of said correlation values having a largest real part and detecting a preamble sequence in said modulated signals upon determining that said largest real part is greater than or equal to a predetermined threshold.

32. The method of claim 31 further comprising identifying a segment of a base station that transmitted said modulated signals based on said preamble sequence.

33. The method of claim 28 further comprising differentially demodulating said sub-carriers, wherein said every P^th one of said sub-carriers has substantially the same differential channel phase.

34. The method of claim 33 further comprising selecting a largest correlation value from said correlation values and detecting a preamble sequence in said modulated signals upon determining that a magnitude of said largest correlation value is greater than or equal to a predetermined threshold.

35. The method of claim 34 further comprising identifying a segment of a base station that transmitted said modulated signals based on said preamble sequence.

36. The method of claim 28 further comprising generating said differentially demodulated signals by multiplying a Q^th one of said modulated signals by a complex conjugate of a (Q+P)^th one of said modulated signals, where Q is an integer greater than or equal to 1.

37. The method of claim 27 further comprising deriving said derived preamble sequences from preamble sequences, wherein each of said preamble sequences is different from others of said preamble sequences, and wherein said derived preamble sequences have a cross-correlation value that is less than or equal to a predetermined cross-correlation threshold.

38. The method of claim 37 further comprising generating each bit of one of said derived preamble sequences having a first state when a corresponding bit and a bit adjacent to said corresponding bit in a corresponding one of said preamble sequences have opposite states, and generating said each bit having a second state when said corresponding bit and said bit adjacent to said corresponding bit have the same state.

39. The method of claim 27 further comprising storing said derived preamble sequences.

40. The method of claim 37 further comprising determining that said predetermined cross-correlation threshold is less than approximately 0.2 for an orthogonal frequency domain multiplexing (OFDM) method using a 1024 fast Fourier transform (FFT) mode.

41. The method of claim 31 further comprising determining said predetermined threshold based on the signal strength of said modulated signals.

42. The method of claim 34 further comprising determining said predetermined threshold based on the signal strength of said modulated signals.

43. The method of claim 27 further comprising differentially demodulating said modulated signals having a fractional carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of said modulated signals.

44. The method of claim 27 further comprising differentially demodulating said modulated signals having an integer carrier frequency offset (CFO) that generates a phase error that is substantially the same in each one of said modulated signals.

45. The method of claim 44 further comprising correlating said derived preamble sequences with said differentially demodulated signals having said integer CFO.

46. The method of claim 27 further comprising differentially demodulating said modulated signals having a linearly increasing phase offset generated by a symbol timing offset.

47. The method of claim 34 further comprising calculating a symbol timing offset by multiplying a phase angle of said largest correlation value by (N/2π

P), where N is a number of sub-carriers in an N fast Fourier transform (FFT) mode, and where N is an integer greater than 1.

48. The method of claim 47 where N is one of 128, 512, 1024, and 2048.