Digital beam forming for communications systems

• US 7,373,127 B2
• Filed: 04/27/2005
• Issued: 05/13/2008
• Est. Priority Date: 04/27/2005
• Status: Active Grant

• Current Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Reed, John C.
• Primary Examiner(s): VO, NGUYEN THANH
• Application Number:
  US11/115,721
• Publication Number:
  US 20060246863A1
• Time in Patent Office: 1,112 Days
• Field of Search: 455/255, 455259-260, 455/265, 455/303, 455/323, 455/324, 455/272, 455/273, 455/257, 455/276.1, 375/327
• US Class Current: 455/259
• 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 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04B 7/088 using beam selection

Abstract

An antenna-receiver communications system and method is provided to mechanize multibeam mobile antenna-receive subsystems. Digital beam forming for modern wideband mobile communications systems is provided. In an aspect, subsystems can simultaneously receive, acquire, track and output a multiplicity of signals from sources of different locations using a single antenna aperture from a mobile platform. The angle of arrival of a signal of interest is continuously determined. Individual phased array antenna output channels are phased aligned as required by the phased array equation and monopulse signal processing. Angle sensing and beamsteering are separated from antenna channel coherent summation. Thus, the angle sensing and beamsteering functions are not required to be computed at the data rate, but can instead be computed at a rate necessary for the beam acquisition and beam tracking function speed requirements. Signal processing computational load and system cost is reduced as compared to current systems.

Claims

1. A method for a communications system comprising:

shifting a phase of a quadrature down-converter reference signal utilizing a phase adjustment (Ψ

_n) to phase shift an antenna element channel baseband signal for phase aligning the antenna element channel;

maximizing a sum of an array coherent summation equation to determine an input signal angle of arrival wherein φ

_n is set equal to −

Δ

φ

_n for each antenna element channel, wherein the φ

_n and the Δ

φ

_n are terms from the array coherent summation equation given as

$\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>y_n<br><br>\left(t\right)<br><br>w_n<br><br>{\mathrm{e<br><br>}}^{{\mathrm{j\phi <br><br>}}_n}=\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>z<br><br>\left(t\right)<br><br>{\mathrm{e<br><br>}}^{j<br><br>\left[\left({\mathrm{\omega <br><br>}}_1-{\mathrm{\omega <br><br>}}_{\mathrm{lo}}\right)<br><br>t+\mathrm{\Delta <br><br>\varphi <br><br>}<br><br><br><br>n\right]}<br><br>w_n<br><br>{\mathrm{e<br><br>}}^{{\mathrm{j\phi <br><br>}}_n};<br><br>$

and

determining the φ

_n that maximizes the array coherent summation equation,

wherein the Ψ

_n is set to the input signal angle of arrival values, wherein the Ψ

_n is set equal to φ

_n.

2. The method as in claim 1, wherein the phase aligning the antenna element channels comprises one of employing intermediate frequency (IF) digitizing with digital quadrature down conversion and baseband digitizing with analog quadrature down conversion.

3. The method as in claim 1, further comprising repeatedly determining the input signal angle of arrival and repeatedly performing the phase aligning for forming an angle tracking feedback loop to maintain a beam pointing at a communication source.

4. The method as in claim 3, further comprising maintaining a 90 degree steered beam boresight angle of phase corrected channels, coincident with a phased array aperture normal vector, to drive the angle tracking feedback loop.

5. The method as in claim 3, further comprising determining an angle of arrival of a beam summation peak by correlation with a reference curve and verifying that a monopulse peak occurs substantially at a same angle as the summation peak, utilizing at least one of monopulse processing, conical scanning, sequential lobing, adaptive-array systems, and switched-beam systems for angle finding.

6. The method as in claim 1, further comprising varying the quadrature down-converter reference signal frequency parameter to mechanize frequency tracking, frequency locking, and phase locking functions.

7. The method as in claim 1, wherein the maximized sum of the coherent summation equation is employed with one of a linear, planar and conformal array, and wherein antenna channel element spacing is one of uniform and nonuniform.

8. A communications system comprising:

a digital beam forming (DBF) signal processing system including one of intermediate frequency (IF) digitizing with digital quadrature down conversion and baseband digitizing with analog quadrature down conversion,

wherein the DBF system includes a first function to maximize a sum of an array coherent summation equation to determine an input signal angle of arrival, wherein φ

_n is set equal to −

Δ

φ

_n for each antenna element channel, wherein the φ

_n and the Δ

Φ

_n are terms from the array coherent summation equation given as

$\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>y_n<br><br>\left(t\right)<br><br>w_n<br><br>{\mathrm{e<br><br>}}^{{\mathrm{j\phi <br><br>}}_n}=\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>z<br><br>\left(t\right)<br><br>{\mathrm{e<br><br>}}^{j<br><br>\left[\left({\mathrm{\omega <br><br>}}_1-{\mathrm{\omega <br><br>}}_{\mathrm{lo}}\right)<br><br>t+\mathrm{\Delta <br><br>\varphi <br><br>}<br><br><br><br>n\right]}<br><br>w_n<br><br>{\mathrm{e<br><br>}}^{{\mathrm{j\phi <br><br>}}_n};<br><br>$

wherein the DBF system includes a second function to determine the φ

_n that maximizes the array coherent summation equation; and

wherein the DBF system includes a third function to phase align the antenna element channels to accomplish beam steering, wherein element channel baseband signals are shifted in phase by shifting a phase of a quadrature down-converter reference signal with a phase adjustment (Ψ

_n), wherein the Ψ

_n is set to the input signal angle of arrival values, wherein the φ

_n is set equal to the φ

_n for phase alignment.

9. The communications system as in claim 8, wherein a summation function for receiving data sequences from the element channels is situated in a first schematic branch and operates at a rate of an incoming data sampling rate, and wherein a baseband filter, an angle sensing function and a beam steering function are situated in a second schematic branch and operate at a rate independent of the incoming data sampling rate.

10. The communications system as in claim 9, wherein schematically subsequent to the summation function, along the first schematic branch, a digital signal to analog signal function is schematically positioned prior to a baseband signal filter.

11. The communications system as in claim 9, wherein the element channels are present in a multiple number and share an antenna aperture, wherein each of the element channels maintain a dedicated directive beam, and wherein data from each of the element channels is schematically branched to one of quadrature down-converter functions and complex number multiply functions, dedicated to specific element channels, to simultaneously achieve multiple outputs with the DBF system.

12. The communications system as in claim 9, wherein the DBF system forms multiple narrow beams and spatially locks the multiple narrow beams to a multiplicity of far transmitters, and utilizes partially defocused fat beams to receive nearby transmitters.

13. A method of digital beam forming for a communications system comprising:

maximizing a sum of an array coherent summation equation to determine an input signal angle of arrival wherein φ

_n is set equal to −

Δ

φ

_n for each antenna element channel, wherein the φ

_n and the Δ

φ

_n are terms from the array coherent summation equation given as

$\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>y_n<br><br>\left(t\right)<br><br>w_n<br><br>{\mathrm{e<br><br>}}^{{\mathrm{j\phi <br><br>}}_n}=\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>z<br><br>\left(t\right)<br><br>{\mathrm{e<br><br>}}^{j<br><br>\left[\left({\mathrm{\omega <br><br>}}_1-{\mathrm{\omega <br><br>}}_{\mathrm{lo}}\right)<br><br>t+\mathrm{\Delta <br><br>\varphi <br><br>}<br><br><br><br>n\right]}<br><br>w_n<br><br>{\mathrm{e<br><br>}}^{{\mathrm{j\phi <br><br>}}_n};<br><br>$

determining the φ

_n that maximizes the array coherent summation equation;

phase aligning the antenna element channels to accomplish beam steering, wherein element channel baseband signals are shifted in phase by multiplying an in-phase/quadrature modulator (I/Q) output by a complex number having a modulus equal to one, the complex number having a required phase shift Ψ

_n as a phase, wherein the Ψ

_n is set to the input signal angle of arrival values, wherein the Ψ

_n is set equal to the φ

_n for phase alignment; and

situating a summation function for receiving data sequences from element channels in a first schematic branch to operate at a rate of an incoming data sampling rate, and situating a baseband filter, an angle sensing function and a beam steering function in a second schematic branch to operate at a rate independent of the incoming data sampling rate.

14. The method as in claim 13, further comprising performing conversion from a digital signal to analog signal, along the first schematic branch, schematically subsequent to utilizing the summation function and schematically prior to baseband signal filtering.

15. The method as in claim 13, further comprising schematically branching data from each of the element channels to one, of quadrature down-converter functions and complex number multiply functions, dedicated to specific element channels, to simultaneously achieve multiple outputs with a DBF system architecture, and setting multiple element channels to share an antenna aperture, each of the channels having a dedicated directive beam.

16. The method as in claim 13, further comprising forming multiple narrow beams and spatially locking the multiple narrow beams to a multiplicity of far transmitters, and utilizing partially defocused fat beams to receive nearby transmitters.

17. The method as in claim 13, wherein the phase aligning the antenna element channels comprises employing intermediate frequency (IF) digitizing with digital quadrature down conversion.

18. The method as in claim 13, wherein the phase aligning the antenna element channels comprises employing baseband digitizing with analog quadrature down conversion.

19. A method for a communications system comprising:

shifting a phase of a quadrature down-converter reference signal utilizing a phase adjustment (Ψ

_n) to phase shift an antenna element channel baseband signal for phase aligning the antenna element channel;

situating a summation function for receiving data sequences from the element channel in a first schematic branch to operate at a rate of an incoming data sampling rate; and

situating a baseband filter, an angle sensing function and a beam steering function in a second schematic branch to operate at a rate independent of the incoming data sampling rate.

20. The method as in claim 19, wherein the phase aligning the antenna element channels comprises one of employing intermediate frequency (IF) digitizing with digital quadrature down conversion and baseband digitizing with analog quadrature down conversion.

21. The method as in claim 19, further comprising varying the quadrature down-converter reference signal frequency parameter to mechanize frequency tracking, frequency locking, and phase locking functions.