Null processing and beam steering receiver apparatus and method

• US 5,317,322 A
• Filed: 06/28/1993
• Issued: 05/31/1994
• Est. Priority Date: 01/06/1992
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Magnavox Electronic Systems Company
• Inventors: Grobert, Paul H.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/083,396
• Time in Patent Office: 337 Days
• Field of Search: 342/378, 342/380, 342/383, 342/194
• US Class Current: 342/378
• CPC Class Codes: G01S 3/06 Means for increasing effective directivity, e.g. by combining signals having differently oriented directivity characteristics or by sharpening the envelope waveform of the signal derived from a rotating or oscillating beam antenna comparing amplitude of signals having differently oriented directivity characteristics to determine direction G01S3/16, G01S3/28

Abstract

A system for processing modulated signals received, together with at least one interference signal, by an array of antenna elements in a communications receiver. The method of the invention includes demodulating the received signals, and processing the demodulated signals to produce an output signal that is substantially free of any interference signals, while at the same time effectively steering the antenna pattern produced by the array of elements, to move any spurious nulls in the pattern away from a source of information signals. This results in avoidance of any cycle slipping problems that might otherwise arise in receiver tracking control loops, and has the added benefit of significantly improving performance as measured by the signal-to-noise ratio.

Claims

1. Signal processing receiver apparatus, comprising:

demodulator means for demodulating a plurality of modulated signals received at a corresponding plurality of antenna array elements, to produce a primary information signal and one or more related auxiliary information signals, all of the information signals containing an interference signal;

weighting means for operating on the one or more auxiliary information signals to produce a corresponding number of intermediate signals; and

summing means for combining the primary information signal and the intermediate signals to produce a sum signal in which the interference signal is substantially nulled out;

wherein the weighting means includes means for adjusting weighting factors applied to the auxiliary information signals, to steer a composite beam formed by the antenna array elements to a direction that enhances reception of the modulated signals, without detracting significantly from nulling of the interference signal;

and wherein the weighting means and the summing means function together to produce simultaneous nulling of the interference signal and steering of the composite beam;

and wherein the means for adjusting the weighting factors to enhance reception of the modulated signals includes adjustable gain means, to ensure that beam steering correction signals do not have an adverse effect on nulling out the interference signal;

and wherein the weighting means includes

means for correlating the sum signal with each of the auxiliary information signals, to produce a corresponding number of product signals,

means for integrating the product signals to product a corresponding number of weighting factors, and

means for multiplying the weighting factors by the corresponding auxiliary information signals to produce the intermediate signals for summing with the primary information signal;

and further comprising;

means for removing any time-varying data components from the demodulated primary information signal, to leave only an essentially non-varying primary information signal;

low-pass filter means, for removing from the demodulated primary information signal any components due to the interference signal; and

additional summing means, for combining the primary signal, free of the interference signal, with the intermediate signals, to produce a beam steering error signal;

and wherein the means for adjusting the weighting factors includes additional correlation means, for correlating the beam steering error signal with each of the auxiliary information signals to produce a second set of product signals, and means for combining the two sets of product signals to product a signal set of weighting factors.

2. Signal processing receiver apparatus as defined in claim 1, wherein:

the adjustable gain means includes means for multiplying the beam steering error signal by a gain factor less than unity, for coupling to the additional correlation means, whereby adjustment of the weighting factors to perform a beam steering function is given less significance than selection of the factors for nulling performance.

3. A signal processing method, comprising the steps of;

receiving modulated signals and at least one interference signal in an array of antenna elements;

demodulating a plurality of modulated signals received by the antenna elements, to produce a primary information signal and one or more related auxiliary information signals, all of the information signals containing an interference signal;

weighing the one or more auxiliary information signals to produce one or more intermediate signals; and

summing together the primary information signal and the one or more intermediate signals to produce a sum signal in which the interference signal is substantially nulled out;

and wherein the step of weighting the auxiliary information signals includes generating a set of weighting factors that will result in nulling of the interference signals, and adjusting the weighting factors to avoid any unwanted nulling of one or more of the information signals;

and wherein the steps of weighting and summing are performed in such a way as to effect simultaneous nulling of the interference signals and beam steering to avoid any unwanted nulling of the information signals;

and wherein the step of adjusting the weighting factors includes applying a gain factor to beam steering correction signals, the gain factor being selected to ensure that beam steering correction signals do not have an adverse effect on nulling out the interference signal;

wherein the step of weighting the auxiliary information signals includes

correlating the sum signal with one or more auxiliary information signals to produce a set of product signal,

integrating each of the set of product signals to produce a set of the weighting factors, and

multiplying the one or more auxiliary information signals by corresponding weighting factors to obtain the intermediate signals;

wherein the step of adjusting the weighting factors includes;

deriving a modified primary information signal that is substantially free of interference and data modulation;

combining the modified primary information signal with the intermediate signals, to produce a beam steering error signal indicative of the degree to a composite antenna beam is being steered toward a source of the information signals;

correlating a selected fraction of the beam steering error signals with the one or more auxiliary information signals to produce a second set of product signals; and

combining the two sets of product signals to produce a single set of weighting factors that results in nulling of beam to avoid alignment of a spurious null with a source of the information signals.

4. Signal processing receiver apparatus, comprising:

demodulator means for demodulating a plurality of modulated signals received at a corresponding plurality of antenna array elements, to produce a primary information signal and one or more related auxiliary information signals, all of the information signals containing an interference signal;

interference nulling means for combining the primary information signal with weighted components derived from the auxiliary information signals, in such a manner that an output information signal is produced substantially free of interference components;

beam steering means for combining the primary information signal with weighted components derived from the auxiliary information signals, in such a manner that a composite antenna beam is steered to maximize the signal power of the received information signals; and

means for combining the interference nulling means and the beam steering means to provide for simultaneous interference nulling and beam steering, wherein the means for combining includes amplifier means with a gain selected to give priority to the interference nulling means, whereby the antenna array produces a pattern that has a null directed to at least one interference signal source and has no spurious nulls aligned with an information signal source;

and wherein;

the interference nulling means and the beam steering means both employ a common weighting means for operating on the one or more auxiliary information signals to produce a corresponding number of intermediate signals;

the interference nulling means has a first summing means for combining the primary information signal and the intermediate signals to produce a first sum signal in which the interference signal is substantially nulled out;

the beam steering means has a second summing means for combining the primary information signal, filtered to remove interference signals, to produce a second sum signal indicative of beam steering error;

the weighting means includes means for correlating the auxiliary information signals with the first sum signal to produce a first set of product signals, and means for correlating the auxiliary information signals with a selected fraction of the second sum signal to produce a second set of product signals; and

the means for combining the interference nulling means and the beam steering means includes integrator means for combining the first ad second sets of products to produce a single set of weighting factors for application to the auxiliary information signals.

5. Signal processing receiver apparatus comprising:

demodulator means for demodulating a plurality of modulated signals received at a corresponding plurality of antenna array elements, to produce a primary information signal and one or more related auxiliary information signals, all of the information signals containing an interference signal;

interference nulling means for combining the primary information signal with weighted components derived from the auxiliary information signals, in such a manner that an output information signal is produced substantially free of interference components;

beam steering means for combining the primary information signal with weighted components derived from the auxiliary information signals, in such a manner that a composite antenna beam is steered to maximize the signal power of the received information signals; and

means for combining the interference nulling means and the mean steering means to provide for simultaneous interference nulling and beam steering, wherein the means for combining includes amplifier means with a gain selected to give priority to the interference nulling means, whereby the antenna array produces a pattern that has a null directed to at least one interference signal source and has no spurious nulls aligned with an information signal source;

and wherein;

the interference nulling means includes means for distinguishing between interference signals and information signals, such that the information signals are not subject to nulling.

6. Signal processing receiver apparatus as defined in claim 5, wherein:

the means for distinguishing between interference signals and information signals includes one or more capacitive components that present a low impedance path to high-frequency interference signals and a high impedance path to low-frequency information signals.

7. Signal processing receiver apparatus, comprising:

demodulator means for demodulating a plurality of modulated signals received at a corresponding plurality of antenna array elements, to produce a primary information signal and one or more related auxiliary information signals, all of the information signals containing an interference signal;

interference nulling means for combining the primary information signal with weighted components derived from the auxiliary information signals, in such a manner that an output information signal is produced substantially free of interference components;

beam steering means for combining the primary information signal with weighted components derived from the auxiliary information signals, in such a manner that a composite antenna beam is steered to maximize the signal power of the received information signals; and

means for combining the interference nulling means and the beam steering means to provide for simultaneous interference nulling and beam steering, wherein the means for combining includes amplifier means with a gain selected to give priority to the interference nulling means, whereby the antenna array produces a pattern that has a null directed to at least one interference signal source and has no spurious nulls aligned with an information signal source;

and wherein;

the beam steering means includes means for low-pass filtering the primary information signal to remove substantially all components of the interference signal, and means for removing low-frequency data signals encoded onto the primary information signal, to render the information signal able to pass through the means for low-pass filtering.

8. Signal processing receiver apparatus, comprising:

demodulator means for demodulating a plurality of modulated signals received at a corresponding plurality of antenna array elements, to produce a primary information signal and one or more related auxiliary information signals, all of the information signals containing an interference signal;

weighting means for operating on the one or more auxiliary information signals to produce a corresponding number of intermediate signals; and

summing means for combining the primary information signal and the intermediate signals to produce a sum signal in which the interference signal is substantially nulled out;

wherein the weighting means includes means for adjusting weighting factors applied to the auxiliary information signals, to steer a composite beam formed by the antenna array elements to a direction that enhances reception of the modulated signals, without detracting significantly from nulling of the interference signal, and in a phase lock condition without the presence of a received quadrature signal component;

and wherein the weighting means and the summing means function together to produce simultaneous nulling of the interference signal and steering of the composite beam, in the absence of a received quadrature signal components;

and wherein the means for adjusting the weighting factors to enhance reception of the modulated signals includes adjustable gain means, to ensure that beam steering correction signals do not have an adverse effect on nulling out the interference signal.

9. Signal processing receiver apparatus as defined in claim 8, wherein the means for adjusting weighting factors applied to the auxiliary information signals includes;

means for adjusting a first set of weighting factors used to generate a beamed in-phase (I) signal component; and

means for adjusting a second set of weighting factors used to generate a beamed quadrature (Q) signal component;

and wherein the second set of weighting factors are derived from the first set by cross-strapping with a change of sign.

10. A signal processing method, comprising the steps of:

receiving modulate signals and at least one interference signal in an array of antenna elements;

demodulating a plurality of modulated signals received by the antenna elements, to produce a primary information signal and one or more related auxiliary information signals, all of the information signals contiangn an interference signal;

weighting the one or more auxiliary information signals to produce one or more intermediate signals; and

summing together the primary information signal and the one or more intermediate signals to produce a sum signal in which the interference signal is substantially nulled out;

and wherein the step of weighting the auxiliary information signals includes generating weighting factors that will result in nulling of the interference signal, and adjusting the weighting factors to avoid any unwanted nulling of one or more of the information signals;

and wherein the steps of weighing and summing are performed in such a way as to effect simultaneous nulling of the interference signal and beam steering to avoid any unwanted nulling of the information signals, and in a phase lock condition int eh absence of a received quadrature signal component;

and wherein the step of adjusting the weighting factors includes applying a gain factor to beam steering correction signals, the gain factor being selected to ensure that beam steering correction signals do not have an adverse effect on nulling out the interference signal.

11. A signal processing method as defined in claim 10, wherein the step of adjusting the weighting factors includes:

adjusting a first set of weighting factors used to generate a beamed in-phase (I) signal component; and

adjusting a second set of weighting factors used to generate a beamed quadrature (Q) signal component;

and wherein the second set of weighting factors are derived from the first set by cross-strapping with a change of sign.