COMPENSATION OF BEAMFORMING ERRORS IN A COMMUNICATIONS SYSTEM HAVING WIDELY SPACED ANTENNA ELEMENTS

• US 20100123625A1
• Filed: 11/19/2008
• Published: 05/20/2010
• Est. Priority Date: 11/19/2008
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Roach, John, Minear, Kathleen, Dianic, Allan V., Martin, G. Patrick, Ralston, Lynda Margaret, Adams, William C. JR.
• Granted Patent: US 7,969,358 B2
• Time in Patent Office: Days
• US Class Current: 342/377
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0848 Joint weighting

Abstract

Systems and methods for operating a communications system. The methods involve computing one or more complex weights to be applied to transmit signals and receive signals by beamformers. The complex weights are based at least on configuration data for the communications system. The methods also involve applying a first plurality of weight corrections to the complex weights based on phasing errors occurring in a communication path inclusive of a control system and antenna elements. The methods further involve applying a second plurality of weight corrections to the complex weights based on phase differences at the antenna elements relative to a reference location for the receive signals.

Claims

1. A method for operating a communications system, said communication system comprising a plurality of antenna elements, an array control system having a plurality of beamformers for said plurality of antenna elements, and a plurality of communications links between said control system and said plurality of antenna elements, the method comprising:

computing a plurality of complex weights to be applied to a plurality of transmit signals and a plurality of receive signals by said plurality of beamformers, said plurality of complex weights based at least on configuration data for said communications system;

applying a first plurality of weight corrections to said plurality of complex weights based on phasing errors occurring in a communication path inclusive of said control system and said plurality of antenna elements; and

applying a second plurality of weight corrections to said plurality of complex weights based on phase differences at said plurality of antenna elements relative to a reference location for said plurality of receive signals.

2. The method of claim 1, wherein said applying said first plurality of weights comprises:

determining a first reference signal at a first location along the communication path and a second reference signal at a second location along the communication path, the second reference signal having the same phase as the first reference signal;

determining at the first location a first phase offset using the first reference signal and a first transmit signal of said plurality of transmit signals;

determining at the second location a second phase offset using the second reference signal and a second transmit signal of said plurality of transmit signals; and

adjusting at the second location a phase of a third transmit signal of said plurality of transmit signals using the first and second phase offsets to obtain a modified communication signal;

wherein the first, second, and third transmit signals are the same communication signal obtained at different locations along the communication path.

3. The method of claim 2, wherein said determining a first and second reference signal comprises:

sensing at the first location a forward signal propagated over a transmission media in a forward direction and a reverse signal propagated over the transmission media in a reverse direction opposed from the forward direction, the reverse signal being a reflected version of the forward signal;

determining a first sum signal by adding the forward and reverse signals together and a first difference signal by subtracting the reverse signal from the forward signal;

determining a first exponentiation signal using the first sum signal and a second exponentiation signal using the first difference signal; and

subtracting the first exponentiation signal from the second exponentiation signal to obtain the first or second reference signal.

4. The method of claim 1, wherein said applying said first plurality of weights comprises:

determining a first reference signal at a first location along the communication path and a second reference signal at a second location along the communication path, the second reference signal having the same phase as the first reference signal;

combining at the first location a receive signal of said plurality of receive signals with the first reference signal to obtain a modified communication signal;

determining at the second location a phase offset using the modified communication signal and the second reference signal; and

adjusting at the second location a phase of a modified communication signal using the phase offset to obtain a phase adjusted communication signal.

5. The method of claim 1, wherein said applying said second plurality of weight corrections further comprises:

identifying an actual fractional wavelength value (f_true) for at least one of said received ones of said plurality of signals at each of said plurality of antenna elements;

obtaining a differential distance for each of said plurality of antenna elements relative to a reference location for said plurality of antenna elements based at least on configuration data;

estimating said second plurality of weight corrections based on the estimated phase propagation and f_true.

6. The method of claim 1, further comprising:

calculating a plurality of relative phase center locations for said plurality of antenna elements based on said phase differences; and

updating said configuration based on said plurality of relative phase center locations.

7. The method of claim 6, wherein said calculating comprises:

for each one of said plurality of antenna elements, obtaining a plurality of differential distance vectors relative a reference location for said plurality of antenna elements, each of the plurality of differential distance vectors associated with one of said received ones of said plurality of signals; and

obtaining said plurality of relative phase center locations based on the plurality of differential distance vectors.

8. The method of claim 1, wherein said array control system comprises a model-based control system, wherein said configuration data comprises a computer simulation model for said communications system and model parameter values, and wherein the method further comprises:

comparing a measured value and a modeled value for at least measured output characteristic of said communications system, said modeled value based on said configuration data, and

adjusting said configuration data based on said comparing.

9. The method of claim 8, wherein said comparing comprises computing at least one measured system parameter value from said measured value for said output characteristic and at least one modeled system parameter value said measured value for said output characteristic and evaluating a difference between said measured system parameter value and said modeled system parameter value, and

wherein said adjusting comprises updating said current values for said model parameters to minimize said difference.

10. A communications system comprising:

a plurality of antenna elements,

an array control system having a plurality of beamformers for said plurality of antenna elements and processing element for computing a plurality of complex weights to be applied to a plurality of transmit signals and a plurality of receive signals by a plurality of beamformers, said plurality of complex weights based at least on configuration data for said communications system;

a plurality of communications links between said array control system and said plurality of antenna elements; and

at least one closed loop operator coupled to at least said plurality of antenna elements and said array control system; and

wherein said closed loop operator configured for measuring phasing errors between said control system and said plurality of antenna elements and applying a first plurality of weight corrections for said plurality of complex weights based on said measuring, and

wherein said array control system is further configured for detecting phase differences at said plurality of antenna elements based on received ones of said plurality of signals and relative to a reference location and applying a second plurality of weight corrections to said plurality of complex weights based on said phase differences.

11. The communications system of claim 10, further comprising

at least one reference signal generator configured for determining a first reference signal at a first location along the communication path and a second reference signal at a second location along the communication path, the second reference signal having the same phase as the first reference signal;

wherein the closed loop operator is further configured for determining at the first location a first phase offset using the first reference signal and a first transmit signal of said plurality of transmit signals, determining at the second location a second phase offset using the second reference signal and a second transmit signal of said plurality of transmit signals, and adjusting at the second location a phase of a third transmit signal of said plurality of transmit signals using the first and second phase offsets to obtain a modified communication signal,

the first, second, and third transmit signals are the same communication signal obtained at different locations along the communication path.

12. The communications system of claim 11, wherein the reference signal generator is further configured for:

sensing at the first location a forward signal propagated over a transmission media in a forward direction and a reverse signal propagated over the transmission media in a reverse direction opposed from the forward direction, the reverse signal being a reflected version of the forward signal;

determining a first sum signal by adding the forward and reverse signals together and a first difference signal by subtracting the reverse signal from the forward signal;

determining a first exponentiation signal using the first sum signal and a second exponentiation signal using the first difference signal; and

subtracting the first exponentiation signal from the second exponentiation signal to obtain the first or second reference signal.

13. The communications system of claim 10, further comprising

at least one reference signal generator configured for determining a first reference signal at a first location along the communication path and a second reference signal at a second location along the communication path, the second reference signal having the same phase as the first reference signal;

wherein the closed loop operator is further configured for combining at the first location a receive signal of said plurality of receive signals with the first reference signal to obtain a modified communication signal, determining at the second location a phase offset using the modified communication signal and the second reference signal, and adjusting at the second location a phase of a modified communication signal using the phase offset to obtain a phase adjusted communication signal.

14. The communications system of claim 10, wherein array control system is further configured during said applying said second plurality of weight corrections for:

identifying an actual fractional wavelength value (f_true) for at least one of said received ones of said plurality of signals at each of said plurality of antenna elements;

obtaining a estimated phase propagation for each of said plurality of antenna elements relative to a reference one of said plurality of antenna elements based at least on configuration data;

estimating said second plurality of weight corrections based on the estimated phase propagation and f_true.

15. The communications system of claim 10, wherein said array control system is further configured for:

calculating a plurality of relative phase center locations for said plurality of antenna elements based on said phase differences; and

updating said configuration data based on said plurality of relative phase center locations.

16. The communications system of claim 15, wherein said array control system is further configured during said calculating:

obtaining a plurality of differential distance vectors for each one of said plurality of antenna elements to a reference one of said plurality of antenna elements, each of the plurality of differential distance vectors associated with one of said received ones of said plurality of signals; and

obtaining said plurality of relative phase center locations based on the plurality of differential distance vectors.

17. The communications system of claim 10, wherein said array control system further comprises a model-based control system and a model-based calibration system for calibrating said model-based control system, wherein said configuration data comprises a computer simulation model for said communications system and model parameter values, and wherein the model-based calibration system is configured for:

comparing a measured value and a modeled value for at least measured output characteristic of said communications system, said modeled value based on said configuration data, and

adjusting said configuration data based on said comparing.

18. The communications system of claim 17, wherein said model-based calibration system is further configured during said comparing for computing at least one measured system parameter value from said measured value for said output characteristic and at least one modeled system parameter value said measured value for said output characteristic and evaluating a difference between said measured system parameter value and said modeled system parameter value, and

wherein said model-based calibration system is further configured during adjusting for updating said current values for said model parameters to minimize said difference.