Mechanism for extracting hybrid (fh/ds) spread spectrum signals within multi-signal type environment

• US 5,363,401 A
• Filed: 02/25/1993
• Issued: 11/08/1994
• Est. Priority Date: 02/25/1993
• Status: Expired due to Term

• Current Assignee: North South Holdings Incorporated (Spherix Incorporated)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Payne, Edward A., Zahm, Charles L., Andren, Carl F., Lucas, Leonard V.
• Primary Examiner(s): Swann, Tod R.
• Application Number:
  US08/023,264
• Time in Patent Office: 621 Days
• Field of Search: 375/1, 380/34
• US Class Current: 375/131
• CPC Class Codes: H04B 1/692 Hybrid techniques using combinations of two or more spread spectrum techniques
• CPC Class Codes: H04B 1/7102 with transform to frequency domain
• CPC Class Codes: H04B 1/715 Interference-related aspects
• CPC Class Codes: H04B 2001/7152 with means for suppressing interference

Abstract

Identification and extraction of hybrid, frequency-hopped direct sequence pseudo noise (FH/DS), signals from a multiband signal environment is effected by a sequential signal processing technique which examines the distribution of the energy content within a prescribed sub-spectrum window that is iteratively scanned or `slides` across the overall signal spectrum of interest. Based upon this energy content distribution, in particular the extent to which a sub-spectrum window contains energy that exhibits significant conjugate phase symmetry associated with a direct spread signal, the inventive signal processing technique proceeds to emphasize the spectral composition of components of which hybrid signals are comprised and to deemphasize the spectral composition of signals other than those contained in hybrid signals. Potential hybrid signal candidates whose spectral composition has been emphasized are then selectively combined with the deemphasized signals to isolate and identify the hybrid signals.

Claims

1. A method of detecting and identifying hybrid, frequency-hopped direct sequence pseudo noise (FH/DS), signals from a potential multi-signal type environment comprising the steps of:

(a) receiving signals from said from said multi-signal type environment;

(b) processing signals received in step (a) in accordance with a signal processing operator which emphasizes the spectral magnitude of said hybrid signals and deemphasizes the spectral magnitude of signals other than said hybrid signals based upon their differing characteristics;

(c) processing Signals received in step (a) in accordance with a signal processing operator which emphasizes the spectoral magnitude of said signals other than hybrid signals and deemphasizes the magnitude of hybrid signals based on their differing characteristics; and

(d) selectively combining hybrid signals emphasized in step (b) and said signals other than said hybrid signals emphasized in step (c), so as to extract said hybrid signals.

2. A method according to claim 1, wherein step (b) comprises preliminarily normalizing the signal values received in step (a).

3. A method of detecting and identifying hybrid, frequency-hopped direct sequence pseudo noise (FH/DS), signals from a potential multi-signal type environment comprising the steps of:

(a) receiving signals from said from said multi-signal type environment;

(b) processing signals received in step (a) in accordance with a signal processing operator which emphasizes the spectral composition of said hybrid signals and deemphasizes the spectral composition of signals other than said hybrid signals; and

(c) selectively combining hybrid signals emphasized in step (b) and said signals other than said hybrid signals deemphasized in step (b), so as to extract said hybrid signals; and

wherein step (b) comprises processing signals received in step (a) in accordance with a signal emphasis/deemphasis mechanism, which is operative to process signals present within a prescribed frequency spectrum portion of said potential multi-signal type environment, said frequency spectrum portion having a center frequency and a prescribed frequency range above and below said center frequency, said signal emphasis/deemphasis mechanism processing signals within said prescribed frequency spectrum portion of said potential multi-signal type environment by emphasizing signals whose energy content possesses conjugate phase symmetry about said center frequency and deemphasizing signals whose energy content possesses conjugate antisymmetry about said center frequency.

4. A method according to claim 3, wherein step (b) comprises applying said signal emphasis/deemphasis mechanism to successively adjacent frequency spectrum portions of said potential multi-signal type environment, each frequency spectrum portion having a center frequency and a prescribed frequency range above and below said center frequency, so that within a respective frequency spectrum portion said signal emphasis/deemphasis mechanism emphasizes signals whose energy content possesses conjugate phase symmetry about said center frequency and deemphasizes signals whose energy content possesses conjugate antisymmetry about said center frequency.

5. A method of detecting and identifying hybrid, frequency-hopped direct sequence pseudo noise (FH/DS), signals from a potential multi-signal type environment comprising the steps of:

(a) receiving signals from said from said multi-signal type environment;

(b) processing signals received in step (a) in accordance with a signal processing operator which emphasizes the spectral composition of said hybrid signals and deemphasizes the spectral composition of signals other than said hybrid signals; and

(c) selectively combining hybrid signals emphasized in step (b) and said signals other than said hybrid signals deemphasized in step (b), so as to extract said hybrid signals; and

wherein said signal emphasis/deemphasis mechanism is operative to multiply signals present in a prescribed frequency range above the center frequency of a respective frequency spectrum portion of said potential multi-signal type environment by signals present in a prescribed frequency range below the center frequency of said respective frequency spectrum portion of said potential multi-signal type environment, thereby emphasizing signals whose energy content possesses conjugate phase symmetry about the center frequency of said respective frequency spectrum portion and deemphasizing signals whose energy content possesses conjugate antisymmetry about the center frequency of said respective frequency spectrum portion.

6. A method according to claim 5, wherein said signal emphasis/deemphasis mechanism is operative to identify as potential hybrid signals within a respective frequency spectrum portion those signals whose products have caused an emphasis of the multiplied signals and to reject as non-hybrid signals within said respective frequency spectrum portion those signals whose products have caused a deemphasis of the multiplied signals.

7. A method according to claim 5, wherein said signal emphasis/deemphasis mechanism is operative to self-multiply signals present at the center frequency of said respective frequency spectrum portion of said potential multi-signal type environment, thereby emphasizing signals at the center frequency of said respective frequency spectrum portion of said potential multi-signal type environment.

8. A method according to claim 7, wherein said signal emphasis/deemphasis mechanism is operative to compare the magnitude of self-multiplied signals present at the center frequency of said respective frequency spectrum portion of said potential multi-signal type environment with the magnitude of the product of signals present in said prescribed frequency range above the center frequency of said respective frequency spectrum portion of said potential multi-signal type environment and signals present in said prescribed frequency range below the center frequency of said respective frequency spectrum portion of said potential multi-signal type environment, and wherein step (c) comprises identifying said self-multiplied signals as being signals other than said hybrid signals in accordance with a prescribed relationship between the magnitude of said self-multiplied signals and said product of signals.

9. A method of detecting and identifying hybrid, frequency-hopped direct sequence pseudo noise (FH/DS), signals from a potential multi-signal type environment comprising the steps of:

(a) receiving signals from said from said multi-signal type environment;

(b) processing signals received in step (a) in accordance with a signal processing operator which emphasizes the spectral composition of said hybrid signals and deemphasizes the spectral composition of signals other than said hybrid signals; and

(c) selectively combining hybrid signals emphasized in step (b) and said signals other than said hybrid signals deemphasized in step (b), so as to extract said hybrid signals; and

wherein step (b) comprises processing signals received in step (a) in accordance with a signal processing operator which emphasizes the spectral composition of signals having conjugate phase symmetry associated with the spread spectrum modulation characteristics of said hybrid signals, and step (c) comprises selectively monitoring the duration of signals processed by step (b) and identifying as hybrid signals those emphasized signals that have a duration no greater than a prescribed hop dwell time associated with frequency-hopped signals.

10. A method according to claim 9, further comprising the step (d) of performing sidelobe suppression of signals that have been selectively combined in step (c).

11. A method of detecting and identifying hybrid, frequency-hopped direct sequence pseudo noise (FH/DS), signals from a potential multi-signal type environment comprising the steps of:

(a) examining the distribution of the energy content within a prescribed sub-spectrum window that is iteratively scanned across a signal spectrum of interest;

(b) emphasizing the spectral composition of components of which hybrid signals are comprised and deemphasizing the spectral composition of signals other than those contained in hybrid signals in accordance with the extent to which sub-spectrum windows examined in step (a) contain energy that exhibit significant conjugate phase symmetry associated with a direct spread signal;

(c) selectively combining signals emphasized and deemphasized in step (b) so as to isolate and identify hybrid signals.

12. A method according to claim 11, further comprising the step (d) of performing sidelobe suppression of signals that have been selectively combined in step (c).

13. A method according to claim 12, wherein step (b) comprises emphasizing the spectral composition of signals having conjugate phase symmetry associated with the spread spectrum modulation characteristics of hybrid signals, and deemphasizing unwanted, interfering narrowband signals by means of a signal processing analyzer, which is operative to cross-multiply and sum the cross-multiply products of signals present in a prescribed frequency range displaced from and located above the center frequency of a respective frequency window by signals present in a prescribed frequency range displaced from and located below the window center frequency.

14. A method according to claim 13, wherein said signal processing analyzer is operative to self-multiply signals at the window center frequency, and wherein step (c) comprises comparing the magnitude of the self-multiplied signals at the window center frequency with the magnitude of the sum of the products of signals present in the ranges above and below the center frequency, and identifying self-multiplied signals as being narrowband signals in accordance with whether or not a ratio of the sum and the self-multiplied product exceeds a prescribed threshold.

15. A method according to claim 14, wherein step (c) further comprises distinguishing non-hopped spread signals from hybrid signals in accordance with the duration of the emphasized spread signals.

16. A method according to claim 15, further comprising the steps of (d) further collapsing energy content of hybrid signals output by step (b) into sharply defined hybrid carrier spectral lines, by subjecting the hybrid signals output by step (b) to sidelobe suppression.

17. A method according to claim 16, wherein step (b) comprises preliminarily normalizing the signal values contents of each prescribed sub-spectrum window.

18. A system for detecting and identifying hybrid, frequency-hopped direct sequence pseudo noise (FH/DS), signals within signals received from a multi-signal type environment comprising:

a fast Fourier transform operator which is coupled to receive said signals received from said multi-signal type environment and output a plurality of signals respectively representative of the energy content within successive subspectrum portions of prescribed frequency spectrum encompassing said multi-signal type environment;

a signal processing operator which is operative to emphasize the spectral composition of components of which hybrid signals are comprised and deemphasize the spectral composition of signals other than those contained in hybrid signals in accordance with the extent to which said subspectrum windows contain energy that exhibit significant conjugate phase symmetry associated with a direct spread signal; and

a hybrid signal identifier which is operative to selectively combine signals emphasized and deemphasized by said signal processing operator so as to isolate and identify hybrid signals within said signals received from said multi-signal type environment.

19. A system according to claim 18, further comprising a sidelobe suppressor coupled to perform sidelobe suppression of signals output by said hybrid signal identifier.

20. A system according to claim 18, wherein said signal processing operator comprises a signal processing analyzer which is operative to emphasize the spectral composition of signals having conjugate phase symmetry associated with the spread spectrum modulation characteristics of hybrid signals, and deemphasize unwanted, interfering narrowband signals by cross-multiplying and summing cross-multiply products of signals present in a prescribed frequency range displaced from and located above the center frequency of a respective frequency window by signals present in a prescribed frequency range displaced from and located below the window center frequency.

21. A system according to claim 20, wherein said signal processing analyzer is operative to self-multiply signals at the window center frequency, and wherein said hybrid signal identifier includes a comparator which is operative to compare the magnitude of the self-multiplied signals at the window center frequency with the magnitude of the sum of the products of signals present in the ranges above and below the center frequency, and to identify self-multiplied signals as being narrowband signals in accordance with whether or not a ratio of the sum and the self-multiplied product exceeds a prescribed threshold.

22. A system according to claim 21, wherein said hybrid signal identifier comprises a timing unit which is operative to distinguish non-hopped spread signals from hybrid signals in accordance with the duration of the emphasized spread signals.

23. A system according to claim 22, further comprising a sidelobe suppressor coupled to perform sidelobe suppression of signals output by said hybrid signal identifier.

24. A system according to claim 22, further comprising a maximum normalizer coupled to the output of said fast Fourier transform operator and is operative to preliminarily normalize the signal values content of each prescribed sub-spectrum window prior to processing thereof by said signal processing operator.