Apparatus and method of multiple antenna receiver combining of high data rate wideband packetized wireless communication signals

• US 20050078649A1
• Filed: 10/08/2003
• Published: 04/14/2005
• Est. Priority Date: 10/08/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: Wang, Yi Hsiu, Gilbert, Jeffrey M., Choi, Won-Joon, Tehrani, Ardavan M.
• Granted Patent: US 7,366,089 B2
• Time in Patent Office: Days
• US Class Current: 370/343
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0848 Joint weighting
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

The present invention provides an apparatus and method of multiple antenna receiver combining of high data rate wideband packetized wireless communication signals, where the apparatus includes M receive antennas, receiving M high data rate wideband packetized wireless communication signals, where each of the signals includes N frequency bins. The apparatus, in an exemplary embodiment, includes (1) a joint timing recovery units that perform joint coarse signal timing estimation, joint frequency offset estimation, and joint fine timing estimation on each of the signals, (2) M Fast Fourier Transform units (FFTs) that each convert the digital data for each of the M signals into frequency domain information for each of the N received frequencies and that output Q pilots for each of the signals, where Q is a positive integer, and (3) a combiner that weights and combines the outputs of the M FFTs for each of the N received frequencies.

Claims

1. An apparatus for combining of M high data rate wideband packetized OFDM wireless communication signals (“

M signals”

) to form a combined output signal, wherein at least M receive antennas each receive one of the M signals, wherein each of the M signals includes N frequency bins, and wherein M is an integer greater than or equal to 2 and N is a positive integer, the apparatus comprising;

a joint timing recovery unit that performs joint coarse signal timing estimation and joint frequency offset estimation on digital data corresponding to each of the M signals;

M fast fourier transform (FFT) units that each convert the digital data for one of the M signals into frequency domain information in the form of sub-carrier data for each of N frequency bins for that one M signal and that output the frequency domain information for each of the m signals; and

a combiner that weights and combines the frequency domain information of the M FFT units to thereby generate the combined output signal having reduced circuit impairments and channel effects.

2. The apparatus according to claim 1 further including:

M radio frequency front ends, each having an input coupled to one of the M antennas and outputting analog data corresponding to each of the M signals;

M baseband units, each baseband unit having an input coupled to an output of one of the M radio frequency front ends that inputs the analog data, and having an output that outputs the digital data corresponding to each of the M signals; and

wherein the joint timing recovery unit has a plurality of inputs, each input coupled to the output of one of the M baseband units to receive the digital data corresponding to one of the M signals.

3. The apparatus according to claim 2 wherein the FFT units convert the digital data into the frequency domain.

4. The apparatus according to claim 2 further including an automatic gain control unit, and wherein the automatic gain control unit sends a signal to the joint timing recovery unit indicating a start of the M signals.

5. The apparatus according to claim 1 wherein the joint timing recovery unit that performs joint timing estimation determines a coarse end time for P consecutive Shorts within the M signals.

6. The apparatus of claim 5 wherein P equals 10.

7. The apparatus according to claim 5 wherein the joint timing recovery unit determines the coarse end time using self correlation of some of the P Shorts within the M signals.

8. The apparatus of claim 7 wherein P equals 10.

9. The apparatus according to claim 7 wherein the joint timing recovery unit includes a joint coarse signal time estimation unit that performs the joint coarse signal timing estimation on each of the M signals, the joint coarse signal time estimation unit comprising:

M self-correlation units, wherein each self-correlation unit independently self-correlates the some of the P Shorts in one of the M signals after the automatic gain control unit indicates the start of the M signals and outputs for the one M signal a self correlation signal that is the self-correlation of the P Shorts, wherein P is a positive integer;

M weighting units that weight the self correlation outputs based on the signal strength;

a summer that sums the M weighted self correlation signals to obtain a weighted summed self correlation signal;

a normalizing unit that normalizes the weighted summed self correlation signal, thereby outputting a normalized self correlation signal; and

a coarse timing estimation unit that receives the normalized self correlation signal and obtains, for the M signals, the end time for the P Shorts in the M signals by comparing the normalized self correlation signal power to a threshold.

10. The apparatus according to claim 5 wherein the joint timing recovery unit determines the coarse end time using cross correlation of some of the P Shorts within each of the M signals with a known Short sequence, followed by self correlation of the corresponding cross correlation outputs.

11. The apparatus of claim 10 wherein P equals 10.

12. The apparatus according to claim 10 wherein the joint timing recovery unit includes a joint coarse signal time estimation unit that performs the joint coarse signal timing estimation on each of the M signals, the joint coarse signal time estimation unit further comprises:

M cross-correlation units, wherein each cross-correlation unit independently cross-correlates some of the P Shorts in one of the M signals with a known Short sequence, after the automatic gain control unit indicates the start of the M signals and outputs for each of the M signals a cross-correlation signal;

M self-correlation units, wherein each self-correlation unit is logically coupled to a separate one of the M cross-correlation units and wherein each self-correlation unit independently self-correlates the output of the corresponding cross-correlation unit.

M weighting units that weight the self correlation outputs based on the signal strength;

a summer that sums the M weighted self correlation signals to obtain a weighted summed self correlation signal;

a normalizing unit that normalizes the weighted summed self correlation signal, thereby outputting a normalized self correlation signal; and

a coarse timing estimation unit that receives the normalized self correlation signal and obtains, for the M signals, the end time for the P Shorts in the M signals by comparing the normalized self correlation signal power to a threshold.

13. The apparatus of claim 12 wherein P equals 10.

14. The apparatus according to claim 1 wherein the joint timing recovery unit determines a frequency offset for the M signals.

15. The apparatus according to claim 14 wherein the joint timing recovery unit comprises a joint frequency offset estimation unit that performs the joint frequency offset estimation on the M signals, the joint frequency offset estimation unit comprising:

M self-correlation units, wherein each self-correlation unit independently self-correlates some of the P Shorts in each of the M signals and outputs a self-correlation signal that is the self-correlation output of the some of the P Shorts, wherein P is a positive integer;

M weighting units that weight the self correlation outputs based on the signal strength;

a summer that sums the M weighted self-correlation signals, thereby obtaining a summed self-correlation signal;

a normalizing unit that normalizes the weighted summed self correlation signal, thereby outputting a normalized self correlation signal;

an angle calculator that extracts an angle from the normalized self-correlation signal; and

a coarse frequency offset estimation unit that obtains the frequency offset using the angle.

16. The apparatus of claim 15 wherein P equals 10.

17. The apparatus according to claim 14 wherein the joint timing recovery unit comprises a joint frequency offset estimation unit that performs the joint frequency offset estimation on each of the M signals, the joint frequency offset estimation unit comprising:

M cross-correlation units, wherein each cross-correlation unit independently cross-correlates some of the P Shorts in one of the M signals with a known Short sequence, after the automatic gain control unit indicates the start of the one M signal and outputs for the one M signal a cross-correlation signal;

M self-correlation units, wherein each self-correlation unit is logically coupled to a separate one of the M cross-correlation units and wherein each self-correlation unit independently self-correlates the output of the corresponding cross-correlation output;

M weighting units that weight the self correlation outputs based on the signal strength;

a summer that sums the M weighted self-correlation signals, thereby obtaining a weighted summed self-correlation signal;

a normalizing unit that normalizes the weighted summed self correlation signal, thereby outputting a normalized self correlation signal;

an angle calculator that extracts an angle from the normalized self-correlation signal; and

a coarse frequency offset estimation unit that obtains the frequency offset using the angle.

18. The apparatus according to claim 14 wherein the joint timing recovery unit comprises a joint frequency offset estimation unit that performs the joint frequency offset estimation on the M signals, the joint frequency offset estimation unit comprising:

M self-correlation units, wherein each self-correlation unit independently self-correlates some of the P Shorts in each of the M signals and outputs a self-correlation signal that is the self-correlation output of the some of the P Shorts, wherein P is a positive integer;

M weighting units that weight the self correlation outputs based on the signal strength;

a summer that sums the M weighted self-correlation signals, thereby obtaining a summed self-correlation signal;

an angle calculator that extracts an angle from the weighted summed self correlation signal; and

a coarse frequency offset estimation unit that obtains the frequency offset using the angle.

19. The apparatus according to claim 14 wherein the joint timing recovery unit comprises a joint frequency offset estimation unit that performs the joint frequency offset estimation on each of the M signals, the joint frequency offset estimation unit comprising:

M cross-correlation units, wherein each cross-correlation unit independently cross-correlates some of the P Shorts in one of the M signals with a known Short sequence, after the automatic gain control unit indicates the start of the one M signal and outputs for the one M signal a cross-correlation signal;

M self-correlation units, wherein each self-correlation unit is logically coupled to a separate one of the M cross-correlation units and wherein each self-correlation unit independently self-correlates the output of the corresponding cross-correlation output;

M weighting units that weight the self correlation outputs based on the signal strength;

a summer that sums the M weighted self-correlation signals, thereby obtaining a weighted summed self-correlation signal;

an angle calculator that extracts an angle from the weighted summed self correlation signal; and

a coarse frequency offset estimation unit that obtains the frequency offset using the angle.

20. The apparatus according to claim 1 wherein the joint timing recovery unit also performs joint fine timing estimation.

21. The apparatus according to claim 20 wherein the joint fine timing estimation is peformed by a joint fine timing estimation unit that operates upon a Long training sequence that follows the P Shorts for each of the M signals.

22. The apparatus according to claim 21 wherein the joint fine timing estimation unit estimates a linear phase ramp to determine a fine timing offset for each of the M signals.

23. The apparatus according to claim 1 wherein each of the M FFTs outputs the frequency domain information sequentially.

24. The apparatus according to claim 23 wherein the frequency domain information comprises an amplitude and a phase.

25. The apparatus according to claim 1 wherein the combiner comprises:

a channel estimation unit (CEU) that, for each of the N frequency bins in each of the M signals, receives the outputs of the M FFTs and outputs a channel estimate;

a weight calculator that, for each of the N frequency bins in each of the M signals, receives a corresponding one of the channel estimates from the CEU, receives M RF gains, provides feedback to the CEU, and outputs a weight;

M weight blocks that, for each of the N frequency bins in each of the M signals, receive the weights from the weight calculator, receive sub-carrier data for each of the N frequency bins for each of the M signals, and muliply the sub-carrier data for each of the N frequency bins for each of the M signals with a corresponding weight to obtain weighted sub-carrier data for each of the N frequency bins for each of the M signals;

a summer that sums the weighted sub-carrier data by frequency bin to obtain N weighted sub-carrier data sums;

a pilot tracking unit that, for each of the N frequency bins, receives pilot data from a corresponding pilot frequency bin also output from the summer and outputs pilot tracking information for each of the N frequency bins; and

a channel correction unit that, for each of the N frequency bins, converts the weights from the weight calculator, the corresponding weighted sub-carrier data sum output from the summer, and the pilot tracking information from the pilot tracking unit into the combined output signal.

26. The apparatus according to claim 25 wherein the weights obtained by the weight calculator are updated using decision feedback data.

27. The apparatus according to claim 26 wherein the decision feedback data is obtained from hard decision decoded data symbols.

28. The apparatus according to claim 26 wherein the decision feedback data is obtained from a Viterbi decoder output.

29. The apparatus according to claim 25 wherein each of the M weights is a discretized weight.

30. The apparatus according to claim 29 wherein the discretized weight is represented by a 3-bit binary number.

31. The apparatus according to claim 25 wherein the frequency domain signal is represented by a 12-bit binary number.

32. The apparatus according to claim 25 wherein each of the M weight blocks is a 12-bit×

3-bit multiplier.

33. The apparatus according to claim 1 wherein the signals are packetized 802.11g signals.

34. The apparatus according to claim 1 wherein the packetized OFDM signals are 802.11a signals.

35. The apparatus according to claim 1 wherein the weights used by the combiner are obtained from channel estimates.

36. The apparatus according to claim 35 wherein the weights are updated using decision feedback data.

37. The apparatus according to claim 36 wherein the decision feedback data is obtained from hard decision decoded data symbols.

38. The apparatus according to claim 36 wherein the decision feedback data is obtained from a Viterbi decoder output.

39. The apparatus according to claim 1, further including a transmit beamforming unit.

40. The apparatus according to claim 1, further including a fast antenna switching unit that provides for switching of each of the M FFT units to one of the at least M antennas.

41. The apparatus according to claim 40 wherein the one antenna selected by the fast antenna switching unit is selected based upon largest received power obtained during a first Short preamble period of that one antenna as compared to the other antennas.

52. The method according to claim 1 wherein the frequency domain information is output sequentially.

53. The method according to claim 23 wherein the frequency domain information comprises an amplitude and a phase.

42. A method for combining of M high data rate wideband packetized OFDM wireless communication signals (“

M signals”

) to form a combined output signal, wherein at least M receive antennas each receive one of the M signals, and wherein M is an integer greater than or equal to 2 and N is a positive integer, the method comprising;

performing joint coarse signal timing estimation and joint frequency offset estimation on digital data corresponding to each of the M signals;

converting the digital data for each of the M signals into frequency domain information in the form of sub-carrier data for each of N frequency bins for that each of the M signals and outputting the frequency domain information for each of the M signals; and

weighting and combining the frequency domain information to thereby generate the combined output signal having reduced circuit impairments and channel effects.

43. The method according to claim 42 further including:

obtaining analog data corresponding to each of the M signals;

converting the analog data corresponding to each of the M signals into digital data; and

the step of performing joint coarse signal timing estimation and joint frequency offset estimation on digital data uses the digital data obtained from the step of converting.

44. The method according to claim 43 wherein the step of converting also converts the digital data into at least one converted pilot for each of the M signals;

and wherein the step of weighting and combining uses the at least one converted pilot for each of the M signals to generate the combined output signal.

45. The method according to claim 42 wherein the step of performing joint coarse signal timing estimation and joint frequency offset estimation determines a coarse end time for P consecutive Shorts within each of the M signals.

46. The method according to claim 45 wherein the step of performing joint coarse signal timing estimation and joint frequency offset estimation determines the coarse end time using self correlation of some of the P Shorts within the M signals.

47. The method according to claim 45 wherein the step of performing joint coarse signal timing estimation and joint frequency offset estimation determines the coarse end time using cross correlation of some of the P Shorts within each of the M signals with a known Short sequence, followed by self correlation of the corresponding cross correlation outputs.

48. The method according to claim 42 wherein the step of performing joint coarse signal timing estimation and joint frequency offset estimation determines a frequency offset for the M signals.

49. The method according to claim 42 further including the step of performing joint fine timing estimation.

50. The method according to claim 49 wherein the step of performing joint fine timing estimation operates upon a Long training sequence that follows the P Shorts for each of the M signals.

51. The method according to claim 49 wherein the step of performing joint fine timing estimation estimates a linear phase ramp to determine a fine timing offset for each of the M signals.

54. The method according to claim 42 wherein the signals are packetized 802.11g signals.

55. The method according to claim 42 wherein the packetized OFDM signals are 802.11a signals.

56. The method according to claim 42, further including the step of updating the weights used in the step of weighting and combining.

57. The method according to claim 56 wherein the step of updating the weights includes using newly obtained channel estimates.

58. The method according to claim 57 wherein the step of updating further includes using decision feedback data.

59. The method according to claim 58 wherein the decision feedback data is obtained from hard decision decoded data symbols.

60. The method according to claim 58 wherein the decision feedback data is obtained from a Viterbi decoder output.

61. The method according to claim 56 wherein the step of updating includes using decision feedback data.

62. The method according to claim 61 wherein the decision feedback data is obtained from hard decision decoded data symbols.

63. The method according to claim 61 wherein the decision feedback data is obtained from a Viterbi decoder output.

64. The method according to claim 42, further including the step of selecting one of the at least M antennas.

65. The method according to claim 64 wherein the step of selecting selects the one antenna based upon largest received power obtained during a first Short preamble period of that one antenna as compared to the other antennas.