Detection of burst signal transmissions

• US 4,943,974 A
• Filed: 10/21/1988
• Issued: 07/24/1990
• Est. Priority Date: 10/21/1988
• Status: Expired due to Term

• Current Assignee: COMSAT Corporation (Reorganized ISA SA)
• Original Assignee: Geostar Corp.
• Inventors: Motamedi, Masoud
• Primary Examiner(s): Congialosi, Salvatore
• Application Number:
  US07/260,614
• Time in Patent Office: 641 Days
• Field of Search: 375/1, 375/96, 375/102, 375/115
• US Class Current: 375/149
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: H04B 1/70753 Partial phase search
• CPC Class Codes: H04B 2201/70709 with discontinuous detection

Abstract

A method is disclosed for detecting the presence of and synchronizing to burst transmissions which contain repeated acquisition codes. The received signal is applied as an input to a surface acoustic wave (SAW) filter which is matched to detect one repetition of the code. The SAW filter correlation output is sampled at times corresponding to the times of arrival of each repetition of the code. The mean value and variance of the correlation values for each repetition are computed, and the system declares an acquisition when the mean value and variance meet certain criteria.

Claims

1. A method for detecting a burst signal transmission containing a sequence of N acquisition codes occurring at known time intervals, comprising:

receiving said burst signal transmission and comparing successively received portions thereof to a stored acquisition code pattern;

generating a time-varying correlation output having a magnitude proportional to the similarity between the successively received portions of the burst signal transmission and the stored acquisition code pattern;

detecting and measuring peaks in the magnitude of said correlation output;

forming a group of N peak magnitudes occurring at time intervals corresponding to said known time intervals;

computing values proportional to the mean value and variance, respectively, of the group of N peak magnitudes;

comparing the computed values proportional to the mean value and variance to predetermined minimum and maximum values, respectively; and

indicating the presence of a burst signal transmission when the computed value proportional to the mean value exceeds said minimum value and the computed value proportional to the variance is less than said maximum value.

2. The method of claim 1, wherein said acquisition codes are identical to each other.

3. The method of claim 1, wherein said known time intervals are equal to each other.

4. The method of claim 1, wherein said burst signal transmission comprises a digital bit stream modulated on a carrier frequency, and wherein the step of comparing successively received portions of the burst signal transmission to a stored acquisition code pattern is carried out by repeatedly comparing the most recently received bits of the burst signal transmission with stored aacquisition code bits.

5. The method of claim 1, wherein the burst signal transmission comprises a spread spectrum modulated signal.

6. The method of claim 5, wherein the burst signal transmission is modulated by a direct sequence pseudo-noise code.

7. The method of claim 1, wherein said burst signal transmission contains data following said sequence of N acquisition codes, and further comprising the step of demodulating said data following an indication that a burst signal transmission is present.

8. A method for detecting first and second burst signal transmissions arriving in an overlapping manner, each transmission containing a sequence of N acquisition codes occurring at known time intervals, comprising:

receiving each of said first and second burst signal transmissions and comparing successively received portions of each burst signal transmission to a stored acquisition code pattern;

generating a time-varying correlation output having a magnitude proportional to the similarity between the successively received portions of each burst signal transmission and the stored acquisition code pattern;

detecting and measuring peaks in the magnitude of said correlation output;

forming first and second groups of N peak magnitudes, the peak magnitudes of each group occurring at time intervals corresponding to said known time intervals;

computing values proportional to the mean value and variance, respectively, of each such group of N peak magnitudes;

comparing the computed values proportional to the mean value and variance of each group to predetermined minimum and maximum values, respectively; and

indicating the presence of each of said first and second burst signal transmissions when the computed value proportional to the mean value of the corresponding group exceeds said minimum value and the computed value proportional to the variance of said group is less than said maximum value.

9. The method of claim 8, wherein the acquisition codes of each of said first and second transmissions are identical to each other and to the acquisition codes of the other transmission.

10. The method of claim 8, wherein the known time intervals of each of said first and second transmissions are equal to each other and to the known time intervals of the other transmission.

11. The method of claim 8, wherein the predetermined minimum and maximum values are the same for each group of N peak magnitudes.

12. The method of claim 8, wherein said burst transmissions comprise digital bit streams modulated on a carrier frequency, and wherein the step of comparing successively received portions of each burst signal transmission to a stored acquisition code pattern is carried out by repeatedly comparing the most recently received bits of the received signal with stored acquisition code bits.

13. The method of claim 8, wherein the first and second burst signal transmissions comprise spread spectrum modulated signals.

14. The method of claim 13, wherein the first and second burst signal transmissions are modulated by a direct sequence pseudo-noise code.

15. The method of claim 8, wherein each of said first and second burst signal transmissions contains data following said sequence of N acquisition codes, and further comprising the step of demodulating said data following an indication that each of said first and second burst signal transmissions is present.

16. A method for transmitting and receiving burst mode signals, comprising:

transmitting a burst signal containing a sequence of N acquisition codes occurring at predetermined time intervals;

receiving said burst signal transmission and comparing successively received portions thereof to a stored acquisition code pattern;

generating a time-varying correlation output having a magnitude proportional to the similarity between successively received portions of the burst signal transmission and the stored acquisition code pattern;

detecting and measuring peaks in the magnitude of said correlation output;

forming a group of N peak magnitudes occurring at time intervals corresponding to said predetermined time intervals;

computing values proportional to the mean value and variance, respectively, of the group of N peak magnitudes;

comparing the computed values proportional to the mean value and variance to predetermined minimum and maximum values, respectively; and

indicating the presence of a burst signal transmission when the computed value proportional to the mean value exceeds said minimum value and the computed value proportional to the variance is less than said maximum value.

17. The method of claim 16, wherein said acquisition codes are identical to each other.

18. The method of claim 16, wherein said known time intervals are equal to each other.

19. The method of claim 16, wherein said burst signal transmission comprises a digital bit stream modulated on a carrier frequency, and wherein the step of comparing successively received portions of the burst signal transmission to a stored acquisition code pattern is carried out by repeatedly comparing the most recently received bits of the burst signal transmission with stored acquisition code bits.

20. The method of claim 16, wherein the burst signal transmission comprises a spread spectrum modulated signal.

21. The method of claim 20, wherein the burst signal transmission is modulated by a direct sequence pseudo-noise code.

22. The method of claim 16, wherein said burst signal transmission contains data following said sequence of N acquisition codes, and further comprising the step of demodulating said data following an indication that a burst signal transmission is present.

23. A method for transmitting first and second burst signals and for receiving said signals in an overlapping manner, comprising:

transmitting first and second burst signals, each containing a sequence of N acquisition codes occurring at predetermined time intervals;

receiving each of said first and second burst signal transmissions and comparing successively received portions of each burst signal transmission to a stored acquisition code pattern;

generating a time-varying correlation output having a magnitude proportional to the similarity between successively received portions of each burst signal transmission and the stored acquisition code pattern;

detecting and measuring peaks in the magnitude of said correlation output;

forming first and second groups of N peak magnitudes, the peak magnitudes of each group occurring at time intervals corresponding to said predetermined time intervals;

computing values proportional to the mean value and variance, respectively, of each such group of N peak magnitudes;

comparing the computed values proportional to the mean value and variance of each group to predetermined minimum and maximum values, respectively; and

indicating the presence of each of said first and second burst signal transmissions when the computed value proportional to the mean value of the corresponding group exceeds said minimum value and the computed value proportional to the variance of said group is less than said maximum value.

24. The method of claim 23, wherein the acquisition codes of each of said first and second transmissions are identical to each other and to the acquisition codes of the other transmission.

25. The method of claim 23, wherein the predetermined time intervals of each of said first and second transmissions are equal to each other and to the predetermined time intervals of the other transmission.

26. The method of claim 23, wherein the predetermined minimum and maximum values are the same for each group of N peak magnitudes.

27. The method of claim 23, wherein said burst transmissions comprise digital bit streams modulated on a carrier frequency, and wherein the step of comparing successively received portions of each burst signal transmission to a stored acquisition code pattern is carried out by repeatedly comparing the most recently received bits of the received signal with stored acquisition code bits.

28. The method of claim 23, wherein the first and second burst signal transmissions comprise spread spectrum modulated signals.

29. The method of claim 28, wherein the first and second burst signal transmissions are modulated by a direct sequence pseudo-noise code.

30. The method of claim 23, wherein each of said first and second burst signal transmissions contains data following said sequence of N acquisition codes, and further comprising the step of demodulating said data following an indication that each of said first and second burst signal transmissions is present.

31. An acquisition circuit for detecting a burst signal transmission containing a sequence of N acquisition codes occurring at known time intervals, comprising:

first means for generating a correlation output having a magnitude proportional to the similarity between successively received portions of the burst signal transmission and a stored acquisition code pattern;

second means coupled to said first means for detecting and measuring peaks in the magnitude of said correlation output;

third means coupled to said second means for forming a group of N peak magnitudes occurring at time intervals corresponding to said known time intervals, and for computing values proportional to the mean value and variance, respectively, of said group of N peak magnitudes;

fourth means coupled to said third means for comparing the computed values proportional to the mean value and variance to predetermined minimum and maximum values, respectively, and for indicating the presence of a burst signal transmission when the computed value proportional to the mean value exceeds said minimum value and the computed value proportional to the variance is less than said maximum value.

32. The acquisition circuit of claim 31 wherein said acquisition codes are identical to each other.

33. The acquisition circuit of claim 31, wherein said known time intervals are equal to each other.

34. The acquisition circuit of claim 31, wherein said burst signal transmission comprises a digital bit stream modulated on a carrier frequency, and wherein said first means comprises means for repeatedly comparing the most recently received bits of the received signal with stored acquisition cod bits.

35. The acquisition circuit of claim 31, wherein said first means comprises:

a matched surface acoustic wave filter having an input to which the received signal is applied and an output; and

an envelope detector having an input connected to the output of the surface acoustic wave filter and an output connected to said second means.

36. The acquisition circuit of claim 35, wherein said second means comprises:

a peak detector having an input coupled to the output of said envelope detector and an output; and

an analog-to-digital converter having an analog signal input coupled to the output of said envelope detector, an enable input coupled to the output of the peak detector, and a digital output coupled to the input of said third means.

37. The acquisition circuit of claim 36, wherein said third means comprises a storage and calculation circuit having a digital input coupled to the digital output of the analog-to-digital converter, an enable input coupled to the output of the peak detector, and first and second digital outputs for providing the computed values proportional to the mean value and variance, respectively, to said fourth means.

38. The acquisition circuit of claim 37, wherein said storage and calculation circuit comprises first and second circuit paths, each of said circuit paths having an input coupled to the digital input of the storage and calculation circuit, an output, and a series of N-1 delay stages between said input and said output, each delay stage comprising:

a clocked first-in-first-out (FIFO) register having an input and an output, said FIFO register having a length sufficient to provide a delay equal to the known interval between successive acquisition codes; and

an adder having a first input coupled to the output of the FIFO register, a second input coupled to the digital input of the storage and calculation circuit, and an output;

said delay stages being connected in a manner such that the FIFO register of the first delay stage has its input coupled to the digital input of the storage and calculation circuit, and the FIFO register of each succeeding delay stage has its input coupled to the output of the adder in the immediately preceding delay stage, the output of the adder in the last delay stage providing the output of the corresponding circuit path.

39. The acquisition circuit of claim 38, further comprising:

a first squaring circuit and a multiply-by-N scalar circuit connected in series and interposed between the input of the second circuit path and the inputs of the FIFO register and adder of the first delay stage in the second circuit path;

a second squaring circuit having an input coupled to the output of the first circuit path and an output; and

a subtracter having a first input coupled to the output of the second circuit path, a second input coupled to the output of the second squaring circuit, and an output;

wherein the output of the first circuit path provides the first digital output of the storage and calculation circuit and the output of the subtracter provides the second digital otuput of the storage and calculation circuit.

40. The acquisition circuit of claim 39, further comprising a latch circuit having a digital input coupled to the digital input of the storage and calculation circuit, a digital output coupled to the inputs of the first and second circuit paths, a set input coupled to the enable input of the storage and calculation circuit, and a reset input coupled to a clock signal source.

41. The acquisition circuit of claim 37, wherein said fourth means comprises:

a first comparator having a first input coupled to the first digital output of the storage and calculation circuit, a second input, and an output;

means for applying said predetermined minimum mean value to the second input of said first comparator;

a second comparator having a first input coupled to the second digital output of the storage and calculation circuit, a second input, and an output;

means for applying said predetermined maximum variance value to the second input of said second comparator; and

an AND circuit having first and second inputs coupled to the outputs of the first and second comparators, respectively, and an output, the output of said AND circuit indicating the absence or presence of a burst signal transmission.

42. A receiver for receiving a burst signal transmission containing a sequence of N acquisition codes occurring at known time intervals and followed by data, said receiver comprising an acquisition circuit and a signal processing circuit, said acquisition circuit comprising:

first means for generating a correlation output having a magnitude proportional to the similarity between successively received portions of the burst signal transmission and a stored acquisition code pattern;

second means coupled to said first means for detecting and measuring peaks in the magnitude of said correlation output;

third means coupled to said second means for forming a group of N peak magnitudes occurring at time intervals corresponding to said known time intervals, and for computing values proportional to the mean value and variance, respectively, of said group of N peak magnitudes; and

fourth means coupled to said third means for comparing the computed values proportional to the mean value and variance to predetermined minimum and maximum values, respectively, and for indicating the presence of a burst signal transmission when the computed value proportional to the mean value exceeds said minimum value and the computed value proportional to the variance is less than said maximum value.

43. The receiver of claim 42 wherein said acquisition codes are identical to each other.

44. The receiver of claim 42, wherein said known time intervals are equal to each other.

45. The receiver of claim 42, wherein said burst signal transmission comprises a digital bit stream modulated on a carrier frequency, and wherein said first means comprises means for repeatedly comparing the most recently received bits of the received signal with stored acquisition code bits.

46. The receiver of claim 42, wherein said first means comprises:

a matched surface acoustic wave filter having an input to which the received signal is applied and an output; and

an envelope detector having an input connected to the output of the surface acoustic wave filter and an output connected to said second means.

47. The receiver of claim 46, wherein said second means comprises:

a peak detector having an input coupled to the output of said envelope detector and an output; and

an analog-to-digital converter having an analog signal input coupled to the output of said envelope detector, an enable input coupled to the output of the peak detector, and a digital output coupled to the input of said third means.

48. The receiver of claim 47, wherein said third means comprises a storage and calculation circuit having a digital input coupled to the digital output of the analog-to-digital converter, an enable input coupled to the output of the peak detector, and first and second digital outputs for providing the computed values proportional to the mean value and variance, respectively, to said fourth means.

49. The receiver of claim 48, wherein said storage and calculation circuit comprises first and second circuit paths, each of said circuit paths having an input coupled to the digital input of the storage and calculation circuit, an output, and a series of N-1 delay stages between said input and said output, each delay stage comprising:

a clocked first-in-first-out (FIFO) register having an input and an output, said FIFO register having a length sufficient to provide a delay equal to the known interval between successive acquisition codes; and

an adder having a first input coupled to the output of the FIFO register, a second input coupled to the digital input of the storage and calculation circuit, and an output;

said delay stages being connected in a manner such that the FIFO register of the first delay stage has its input coupled to the digital input of the storage and calculation circuit, and the FIFO register of each succeeding delay stage has its input coupled to the output of the adder in the immediately preceding delay stage, the output of the adder in the last delay stage providing the output of the corresponding circuit path.

50. The receiver of claim 49, further comprising:

a first squaring circuit and a multiply-by-N scalar circuit connected in series and interposed between the input of the second circuit path and the inputs of the FIFO register and adder of the first delay stage in the second circuit path;

a second squaring circuit having an input coupled to the output of the first circuit path and an output; and

a subtracter having a first input coupled to the output of the second circuit path, a second input coupled to the output of the second squaring circuit, and an output;

wherein the output of the first circuit path provides the first digital output of the storage and calculation circuit and the output of the subtracter provides the second digital otuput of the storage and calculation circuit.

51. The receiver of claim 50, further comprising a latch circuit having a digital input coupled to the digital input of the storage and calculation circuit, a digital output coupled to the inputs of the first and second circuit paths, a set input coupled to the enable input of the storage and calculation circuit, and a reset input coupled to a clock signal source.

52. The receiver of claim 48, wherein said fourth means comprises:

a first comparator having a first input coupled to the first digital output of the storage and calculation circuit, a second input, and an output;

means for applying said predetermined minimum mean value to the second input of said first comparator;

a second comparator having a first input coupled to the second digital output of the storage and calculation circuit, a second input, and an output;

means for applying said predetermined maximum variance value to the second input of said second comparator; and

an AND circuit having first and second inputs coupled to the outputs of the first and second comparators, respectively, and an output, the output of said AND circuit indicating the absence or presence of a burst signal transmission.

53. The receiver of claim 42, wherein said signal processing circuit comprises:

a control and switching circuit having a signal input to which the received signal is applied, an enable input coupled to said fourth means, and a plurality of signal outputs; and

a plurality of demodulation circuits, each coupled to a corresponding signal output of said control and switching circuit, for simultaneously demodulating the data contained in a plurality of received signals.

54. A communication system comprising:

a transmitter for transmitting a burst signal transmission containing a sequence of N acquisition codes occurring at predetermined time intervals and followed by data;

a receiver for receiving and detecting said burst signal transmission, said receiver comprising an acquisition circuit and a signal processing circuit, said acquisition circuit comprising;

first means for generating a correlation output having a magnitude proportional to the similarity between successively received portions of the burst signal transmission and a stored acquisition code pattern;

second means coupled to said first means for detecting and measuring peaks in the magnitude of said correlation output;

third means coupled to said second means for forming a group of N peak magnitudes occurring at time intervals corresponding to said predetermined time intervals, and for computing values proportional to the mean value and variance, respectively, of said group of N peak magnitudes; and

fourth means coupled to said third means for comparing the computed values proportional to the mean value and variance to predetermined minimum and maximum values, respectively, and for indicating the presence of a burst signal transmission when the computed value proportional to the mean value exceeds said minimum value and the computed value proportional to the variance is less than said maximum value.

55. The communication system of claim 54, wherein said acquisition codes are identical to each other.

56. The communication system of claim 54, wherein said predetermined time intervals are equal to each other.

57. The communication system of claim 54, wherein said burst signal transmission comprises a digital bit stream modulated on a carrier frequency, and wherein said first means comprises means for repeatedly comparing the most recently received bits of the received signal with stored acquisition code bits.

58. The communication system of claim 54, wherein said first means comprises:

a matched surface acoustic wave filter having an input to which the received signal is applied and an output; and

an envelope detector having an input connected to the output of the surface acoustic wave filter and an output connected to said second means.

59. The communication system of claim 58, wherein said second means comprises:

a peak detector having an input coupled to the output of said envelope detector and an output; and

an analog-to-digital converter having an analog signal input coupled to the output of said envelope detector, an enable input coupled to the output of the peak detector, and a digital output coupled to the input of said third means.

60. The communication system of claim 59, wherein said third means comprises a storage and calculation circuit having a digital input coupled to the digital output of the analog-to-digital converter, an enable input coupled to the output of the peak detector, and first and second digital outputs for providing the computed values proportional to the mean value and variance, respectively, to said fourth means.

61. The communication system of claim 60, wherein said storage and calculation circuit comprises first and second circuit paths, each of said circuit paths having an input coupled to the digital input of the storage and calculation circuit, an output, and a series of N-1 delay stages between said input and said output, each delay stage comprising:

a clocked first-in-first-out (FIFO) register having an input and an output, said FIFO register having a length sufficient to provide a delay equal to the predetermined interval between successive acquisition codes; and

an adder having a first input coupled to the output of the FIFO register, a second input coupled to the digital input of the storage and calculation circuit, and an output;

said delay stages being connected in a manner such that the FIFO register of the first delay stage has its input coupled to the digital input of the storage and calculation circuit, and the FIFO register of each succeeding delay stage has its input coupled to the output of the adder in the immediately preceding delay stage, the output of the adder in the last delay stage providing the output of the corresponding circuit path.

62. The communication system of claim 61, further comprising:

a first squaring circuit and a multiply-by-N scalar circuit connected in series and interposed between the input of the second circuit path and the inputs of the FIFO register and adder of the first delay stage in the second circuit path;

a second squaring circuit having an input coupled to the output of the first circuit path and an output; and

a subtracter having a first input coupled to the output of the second circuit path, a second input coupled to the output of the second squaring circuit, and an output;

wherein the output of the first circuit path provides the first digital output of the storage and calculation circuit and the output of the subtracter provides the second digital otuput of the storage and calculation circuit.

63. The communication system of claim 62, further comprising a latch circuit having a digital input coupled to the digital input of the storage and calculation circuit, a digital output coupled to the inputs of the first and second circuit paths, a set input coupled to the enable input of the storage and calculation circuit, and a reset input coupled to a clock signal source.

64. The communication system of claim 60, wherein said fourth means comprises:

a first comparator having a first input coupled to the first digital output of the storage and calculation circuit, a second input, and an output;

means for applying said predetermined minimum mean value to the second input of said first comparator;

a second comparator having a first input coupled to the second digital output of the storage and calculation circuit, a second input, and an output;

means for applying said predetermined maximum variance value to the second input of said second comparator; and

an AND circuit having first and second inputs coupled to the outputs of the first and second comparators, respectively, and an output, the output of said AND circuit indicating the absence or presence of a burst signal transmission.

65. The communication system of claim 54, wherein said signal processing circuit comprises:

a control and switching circuit having a signal input to which the received signal is applied, an enable input coupled to said fourth means, and a plurality of signal outputs; and

a plurality of demodulation circuits, each coupled to a corresponding signal output of said control and switching circuit, for simultaneously demodulating the data contained in a plurality of received signals.

66. The communication system of claim 54, wherein said transmitter comprises a remote mobile transmitter.

67. The communication system of claim 54, wherein a plurality of said transmitters are provided.

68. The communication system of claim 54, wherein said burst signal transmission is relayed from the transmitter to the receiver through at least one relay satellite.