Direction of arrival angle tracking algorithm for smart antennas

• US 6,483,459 B1
• Filed: 04/05/2001
• Issued: 11/19/2002
• Est. Priority Date: 04/05/2001
• Status: Expired due to Term

• Current Assignee: Buffalo Patents, LLC
• Original Assignee: NeoReach, Inc. (Gobility, Inc.)
• Inventors: Hou, Weiguang, Kwon, Hyuck M.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US09/826,100
• Time in Patent Office: 593 Days
• Field of Search: 342/453, 342/378, 342/380, 342/383, 455/456
• US Class Current: 342/378
• CPC Class Codes: G01S 3/02 using radio waves
• CPC Class Codes: G01S 3/42 the desired condition being maintained automatically

Abstract

Recently, a smart antenna, i.e., a blind adaptive antenna array, has attracted much attention to suppress multiple access interference (MAI) and multipath signals to improve the capacity of a code division multiple access (CDMA) wireless communications system. Most of the smart antenna algorithms either need matrix computation or complex calculations. In this invented direction-of-arrival (DOA) tracking algorithm only 2M complex multiplications are required per snapshot. Further more the DOA tracking algorithm is not sensitive to the mixer phase distortions. Hence the system complexity is reduced since a separate phase calibration is not required for the DOA tracking algorithm. Also the equivalent DOA tracking error due to the mixer phase distortions is derived. Simulation results show that the DOA tracking algorithm in the present invention works effectively under additive white Gaussian (AWGN) as well as Rayleigh fading environments. Also the system employing the invented smart antenna has the same bit error rate (BER) performance as those of other existing smart antennas, however, has less computation burdens and complexity.

Claims

1. A method for acquiring a direction of arrival angle for an incoming spread spectrum signal comprising the steps of:

initializing an estimated direction of arrival angle of an incoming spread spectrum signal;

calculating a weight vector for a smart antenna array based on the estimated direction of arrival angle, the weight vector being matched to an array response vector for the antenna array;

weighting signals received by the smart antenna array with the weight vector to form a weighted output without performing phase calibration;

despreading the weighted output to form a despread output; and

selecting the estimated direction of arrival angle as a direction of arrival angle based upon the despread output.

2. The method of claim 1, wherein the selecting step is performed by comparing the despread output to a threshold.

3. The method of claim 2, further comprising the steps of:

updating the estimated direction of arrival angle if the estimated direction of arrival angle is not selected in the selecting step; and

repeating the updating, calculating, weighting, and despreading steps if the estimated direction of arrival angle is not selected in the selecting step.

4. The method of claim 3, wherein the estimated direction of arrival angle is changed by a step size.

5. The method of claim 4, wherein the step size is approximately one half of a beamwidth of the incoming spread spectrum signal.

6. The method of claim 3, wherein the estimated direction of arrival angle is modified by randomly selecting a new direction of arrival angle within a sector corresponding to the smart antenna array.

7. The method of claim 1, wherein the estimated direction of arrival angle is initialized to correspond to a boundary of a sector in the initializing step.

8. The method of claim 7, further comprising the steps of updating the estimated direction of arrival angle by a step angle and repeating the updating, calculating, weighting, and despreading, steps until the estimated direction of arrival angle has traversed the sector.

9. The method of claim 8, wherein the step angle is approximately one half of a beamwidth of the incoming spread spectrum signal.

10. The method of claim 8, wherein the selecting step is performed by selecting the estimated direction of arrival angle corresponding to the largest despread output from among all estimated direction of arrival angles in the sector.

11. The method of claim 1, wherein the array is linear.

12. The method of claim 11, wherein each element of the weight vector is calculated according to an equation of the form ${\underset{\_}{W}}_M=C$

 

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

-j

 

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2

 

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π



 

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d

 

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Mλ



sin

 



θ

1

where W_M is a weight for Mth element of the array, C is a constant, M is an antenna array element number, λ

is a wavelength of the incoming spread spectrum signal, d is an antenna array element spacing, and θ

₁ is the estimated direction of arrival angle.

13. The method of claim 11, wherein the weight vector is calculated according to an equation of the form $\underset{\_}{W}={\frac{1}{\sqrt{M}}}^{}$

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-j

 

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2

 

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π

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sin

 

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1,…

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d

(M-1)λ

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sin

 

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θ

1]T

wherein W is the weight vector, M is an antenna array element number, λ

is a wavelength of the incoming spread spectrum signal, d is an antenna array element spacing, θ

₁ is the estimated direction of arrival angle, and T is the transpose.

14. The method of claim 1, wherein an imaginary portion of the despread output is not used in the selecting step.

15. The method of claim 1, wherein both a real and an imaginary portion of the despread output is used in the selecting step.

16. The method of claim 1, wherein the incoming spread spectrum signal is a code division multiple access signal.

17. The method of claim 1, wherein the incoming spread spectrum signal is a pilot channel signal.

18. The method of claim 17, wherein the despread output is multiplied by a pilot symbol pattern.

19. The method of claim 1, wherein the incoming spread spectrum signal is multiplied by a tentative decision feedback bit.

20. The method of claim 1, wherein the signals weighted in the weighting step are collected over a bit period.

21. A method for tracking a direction of arrival angle comprising the steps of:

initializing an estimated direction of arrival angle of an incoming spread spectrum signal;

forming a first trial angle, the first trial angle being spaced apart from the estimated direction of arrival angle by a first angular difference in a first direction;

calculating a first weight vector for a smart antenna array based on the first trial angle, the first weight vector being matched to an array response vector for the antenna array;

weighting signals received by the smart antenna array with the first weight vector to form a first weighted output without performing phase calibration;

despreading the first weighted output to form a first despread output; and

selecting the first trial angle as a new direction of arrival angle based upon the first despread output.

22. The method of claim 21, further comprising the steps of:

forming a second trial angle, the second trial angle being spaced apart from the estimated direction of arrival angle by a second angular difference in a second direction, the second direction being different from the first direction;

calculating a second weight vector for a smart antenna array based on the second trial angle, the second weight vector being matched to an array response vector for the antenna array;

weighting signals received by the smart antenna array with the second weight vector to form a second weighted output; and

despreading the second weighted output to form a second despread output;

wherein the selecting step is performed by selecting the first trial angle as a new estimated direction of arrival angle if the first despread output is larger than the second despread output, selecting the second trial angle as a new estimated direction of arrival angle if the second despread output is larger than the first despread output, and otherwise leaving the estimated direction of arrival angle unchanged.

23. The method of claim 21, further comprising the steps of repeating the forming, calculating, weighting, despreading and selecting steps until a loss of tracking is detected.

24. The method of claim 22, further comprising the steps of repeating the forming, calculating, weighting, despreading and selecting steps until a loss of tracking is detected.

25. The method of claim 21, wherein the selecting step is performed by comparing the first despread output to a threshold.

26. The method of claim 21, wherein the first angular difference is approximately equal to ten percent of an angle error of the smart antenna array.

27. The method of claim 21, wherein the smart antenna array is linear.

28. The method of claim 27, wherein each element of the first weight vector is calculated according to an equation of the form ${\underset{\_}{W}}_M=C$

 

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

-j

 

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2

 

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π

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d

 

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Mλ

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sin

 



θ

1

where W_M is a weight for Mth element of the array, C is a constant, M is an antenna array element number, λ

is a wavelength of the incoming spread spectrum signal, d is an antenna array element spacing, and θ

₁ is the first trial angle.

29. The method of claim 27, wherein the first weight vector is calculated according to an equation of the form $\underset{\_}{W}={\frac{1}{\sqrt{M}}}^{}$

[1,

-j

 



2

 

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π

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dλ

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sin

 

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θ

1,…

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(M-1)λ

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sin

 

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θ

1]T

wherein W is the first weight vector, M is an antenna array element number, λ

is a wavelength of the incoming spread spectrum signal, d is an antenna array element spacing, θ

₁ is the first trial angle, and T is the transpose.

30. The method of claim 21, wherein an imaginary portion of the first despread output is not used in the selecting step.

31. The method of claim 21, wherein both a real and an imaginary portion of the first despread output is used in the selecting step.

32. The method of claim 21, wherein the incoming spread spectrum signal is a code division multiple access signal.

33. The method of claim 21, wherein the incoming spread spectrum signal is a pilot channel signal.

34. The method of claim 33, wherein the despread output is multiplied by a pilot symbol pattern.

35. The method of claim 21, wherein the incoming spread spectrum signal is multiplied by a tentative decision feedback bit.

36. The method of claim 24, wherein a loss of tracking is detected by comparing a bit error rate for the incoming spread spectrum signal to a threshold.

37. The method of claim 24, wherein a loss of tracking is detected by comparing a frame error rate for the incoming spread spectrum signal to a threshold.

38. The method of claim 24, wherein a loss of tracking is detected by comparing a signal strength to a threshold.

39. A method for acquiring a direction of arrival angle for an incoming spread spectrum signal comprising the steps of:

initializing an estimated direction of arrival angle of an incoming code division multiple access spread spectrum signal to correspond to a boundary of a sector;

calculating a weight vector for a smart antenna array based on the estimated direction of arrival angle, the weight vector being matched to an array response vector for the antenna array;

weighting signals received by the smart antenna array over a symbol period with the weight vector to form a weighted output without performing phase calibration;

decorrelating the weighted output to form a decorrelated output;

multiplying the decorrelated output by a symbol bit corresponding to a symbol represented by the incoming code division multiple access spread spectrum signal during the symbol period to form a despread output;

changing the estimated direction of arrival angle by a step size approximately equal to one half of a beamwidth of the incoming code division multiple access spread spectrum signal and repeating the calculating, weighting, decorrelating, and multiplying steps for each estimated direction of arrival angle until the sector has been traversed;

selecting the estimated direction of arrival angle corresponding to the largest despread output as the direction of arrival angle.

40. The method of claim 39, wherein the array is linear and the weight vector is calculated according to an equation of the form $\underset{\_}{W}={\frac{1}{\sqrt{M}}}^{}$

[1,

-j

 



2

 

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π



 

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dλ

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sin

 

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θ

1,…



 

,

-j

 

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2

 



π



 



d

(M-1)λ



sin

 



θ

1]T

wherein W is the weight vector, M is an antenna array element number, λ

is a wavelength of the incoming spread spectrum signal, d is an antenna array element spacing, θ

₁ is the estimated direction of arrival angle, and T is the transpose.

41. The method of claim 40, wherein only a real portion of the decorrelated output is multiplied by the symbol bit to form the despread output.

42. The method of claim 41, wherein the incoming spread spectrum signal is a pilot channel signal and the symbol bit corresponds to a pilot symbol pattern.

43. The method of claim 41, wherein the symbol bit corresponds to a tentative decision feedback bit.

44. A method for tracking a direction of arrival angle comprising the steps of:

initializing an estimated direction of arrival angle of an incoming spread spectrum signal to a value within a main lobe of the incoming spread spectrum signal;

forming a first trial angle, the first trial angle being spaced apart from the estimated direction of arrival angle by a step angle in a first direction;

forming a second trial angle, the second trial angle being spaced apart from the estimated direction of arrival angle by the step size in a second direction;

calculating first and second weight vectors for a smart antenna array based on the first and second trial angles, respectively, the weight vectors being matched to an array response vector for the antenna array;

weighting signals received by the smart antenna array during a symbol period with the first and second weight vectors to form a first and second weighted outputs without performing phase calibration;

decorrelating the first and second weighted outputs to form first and second decorrelated outputs;

multiplying a real portion of the first and second decorrelated outputs by a symbol bit corresponding to a symbol represented by the incoming code division multiple access spread spectrum signal during the symbol period to form first and second despread outputs;

selecting the first trial angle as a new estimated direction of arrival angle if the first despread output is larger than the second despread output, selecting the second trial angle as a new estimated direction of arrival angle if the second despread output is larger than the first despread output, and otherwise leaving the estimated direction of arrival angle unchanged; and

repeating the calculating, weighting, decorrelating, multiplying, and selected steps until a loss of tracking is detected.

45. A method for tracking a direction of arrival angle for a signal comprising the steps of:

estimating an estimated direction of arrival angle;

calculating a weight vector for an antenna array comprising a plurality of antenna elements by matching the weight vector to an antenna array response vector based on the estimated direction of arrival angle;

obtaining a signal weighted by the weight vector from the antenna array without performing phase calibration;

updating the estimated direction of arrival angle based on a parameter of the signal.

46. An apparatus for acquiring a direction of arrival angle for an incoming spread spectrum signal, the apparatus comprising:

a processor connectable to a smart antenna array, the processor being configured to perform the steps of

initializing an estimated direction of arrival angle of an incoming spread spectrum signal;

calculating a weight vector for the smart antenna array based on the estimated direction of arrival angle, the weight vector being matched to an array response vector for the antenna array;

weighting signals received by the smart antenna array with the weight vector to form a weighted output without performing phase calibration;

despreading the weighted output to form a despread output; and

selecting the estimated direction of arrival angle as a direction of arrival angle based upon the despread output.

47. The apparatus of claim 46, further comprising a smart antenna array connected to the processor.

48. An apparatus for tracking a direction of arrival angle, the apparatus comprising:

a processor connectable to a smart antenna array, the processor being configured to perform the steps of

initializing an estimated direction of arrival angle of an incoming spread spectrum signal;

forming a first trial angle, the first trial angle being spaced apart from the estimated direction of arrival angle by a first angular difference in a first direction;

calculating a first weight vector for a smart antenna array based on the first trial angle, the first weight vector being matched to an array response vector for the antenna array;

weighting signals received by the smart antenna array with the first weight vector to form a first weighted output without performing phase calibration;

despreading the first weighted output to form a first despread output; and

selecting the first trial angle as a new direction of arrival angle based upon the first despread output.