System and method for real-time spectrum analysis in a radio device

• US 20040028123A1
• Filed: 04/22/2003
• Published: 02/12/2004
• Est. Priority Date: 04/22/2002
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Sugar, Gary L., Miller, Karl A., Baek, Jong Sup
• Granted Patent: US 7,254,191 B2
• Time in Patent Office: Days
• US Class Current: 375/224
• CPC Class Codes: H04L 1/1664 the supervisory signal being transmitted together with payload signals; piggybacking
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements

Abstract

A real-time spectrum analysis engine (SAGE) that comprises a spectrum analyzer component, a signal detector component, a universal signal synchronizer component and a snapshot buffer component. The spectrum analyzer component generates data representing a real-time spectrogram of a bandwidth of radio frequency (RF) spectrum. The signal detector detects signal pulses in the frequency band and outputs pulse event information entries output, which include the start time, duration, power, center frequency and bandwidth of each detected pulse. The signal detector also provides pulse trigger outputs which may be used to enable/disable the collection of information by the spectrum analyzer and the snapshot buffer components. The snapshot buffer collects a set of raw digital signal samples useful for signal classification and other purposes. The universal signal synchronizer synchronizes to periodic signal sources, useful for instituting schemes to avoid interference with those signals.

Claims

1. A method for generating information pertaining to activity occurring in a radio frequency band, comprising steps of:

a. receiving energy in the radio frequency band in which activity associated with a plurality of signal types may occur; and

b. generating spectrum activity information for activity in the radio frequency band from the received radio frequency energy.

2. The method of claim 1, wherein the step of generating spectrum activity information comprises generating power spectral information from the radio frequency energy received in the radio frequency band.

3. The method of claim 2, and further comprising the step of detecting signal pulses that satisfy one or more characteristics from the power spectral information.

4. The method of claim 3, wherein the step of generating comprises generating signal pulse data including one or more of:

pulse duration, pulse center frequency, pulse bandwidth, for signal pulses detected in the frequency band.

5. The method of claim 3, and further comprising the step of detecting one or more peaks in spectral information obtained from signals received in the frequency band, and wherein the step of detecting signal pulses comprises detecting signal pulses that meet the one or more characteristics from the detected one or more peaks.

6. The method of claim 5, wherein the step of detecting a peak comprises detecting power values above a threshold at a contiguous set of frequency bins.

7. The method of claim 5, wherein the step of detecting a peak comprises detecting power values that exceed the threshold at contiguous Fast Fourier Transform (FFT) frequency bins.

8. The method of claim 6, and further comprising the step of outputting for each detected peak, data including the maximum power value for each peak and frequency bins spanned by the peak.

9. The method of claim 5, wherein the step of detecting signal pulses comprises computing, for each detected peak, signal pulse data comprising one or more of:

pulse bandwidth, center frequency and duration.

10. The method of claim 9, and further comprising the step of displaying information associated with signal pulses detected in the frequency band.

11. The method of claim 9, wherein the step of detecting signal pulses further comprises determining whether the signal pulse data are within one or more ranges for one or more of pulse bandwidth, center frequency and duration.

12. The method of claim 11, and further comprising the step of accumulating signal pulse data for signal pulses determined to fall within the one or more ranges, wherein the accumulated pulse data comprises for each detected signal pulse one or more data selected from the group consisting of:

pulse bandwidth, pulse center frequency, pulse duration, and pulse start time.

13. The method of claim 11, and further comprising configuring the one or more ranges for signals to be detected in the frequency band.

14. The method of claim 12, wherein the step of accumulating comprises accumulating histograms for the one or more signal pulse data.

15. The method of claim 14, wherein the step of accumulating comprises accumulating one or more histograms are selected from the group consisting of:

a center frequency histogram that tracks a percentage of time a given center frequency was observed for detected signal pulses, a bandwidth histogram that tracks the percentage of time a given bandwidth was observed for detected signal pulses, a pulse duration histogram that tracks a percentage of time a given duration or durations was observed for detected signal pulses, a time between pulses histogram that tracks percentage of time that a given time duration or durations was observed between signal pulses and a number of active transmissions histogram that tracks when several different signal pulses simultaneously occur.

16. The method of claim 15, and further comprising the step of displaying information associated with the one or more histograms.

17. The method of claim 5, and further comprising the step of storing digital signals representing samples of a received signal when a signal pulse of a particular type is detected.

18. The method of claim 1, wherein the step of receiving comprises receiving radio frequency energy across substantially the entire radio frequency band for a time interval.

19. The method of claim 1, wherein the step of receiving comprises receiving radio frequency energy in a portion of the frequency band for a time interval.

20. The method of claim 19, wherein the step of receiving comprises receiving radio frequency energy in different portions of the radio frequency band over different time intervals.

21. The method of claim 2, wherein the step of generating power spectral information comprises generating power values at a plurality of frequency bins from a digital signal representing radio frequency energy received in the radio frequency band during a time interval.

22. The method of claim 21, and further comprising the step of computing the power at each frequency bin for a time interval.

23. The method of claim 22, and further comprising the step of adding the power at each frequency bin for a current time interval with the power at the corresponding frequency bin for a previous time interval to obtain an average power at each frequency bin.

24. The method of claim 23, and further comprising the step of comparing the power at each frequency bin with a power threshold to obtain a duty count of the number of times that the power at each frequency bin exceeds the power threshold over time intervals.

25. The method of claim 24, and further comprising the step of comparing the power at each frequency bin for a current time interval with the power at the corresponding frequency bin for a previous time interval to track the maximum power in each frequency bin over time intervals.

26. The method of claim 25, and further comprising storing in a memory one or more of:

the average power at each frequency bin, the duty count for each frequency bin and the maximum power for each frequency bin over time intervals.

27. The method of claim 25, and further comprising the step of comparing the power at each frequency bin with a peak threshold over multiple update cycles each of which comprises a plurality time intervals, thereby tracking the number of update cycles during which a certain number of peaks are detected.

28. The method of claim 27, and further comprising the step of storing the number of update cycles during which the certain number of peaks are detected.

29. The method of claim 27, and further comprising displaying the duty count and number of peaks detected.

30. The method of claim 2, and further comprising steps of:

a. detecting from the power spectral information a signal pulse associated with a periodic signal occurring in the frequency band;

b. comparing the occurrence of the signal pulse with a local clock signal;

c. determining a phase error between the occurrence of the signal pulse and a state of the local clock signal; and

d. delaying or advancing the local clock signal by an amount corresponding to the phase error.

31. The method of claim 30, and further comprising the step of continuing to monitor the phase error between the occurrence of the signal pulse and the local clock signal and adjusting a frequency of the local clock signal based on the phase error.

32. The method of claim 31, and further comprising the step of updating the frequency offset over time using a loop filtering process.

33. The method of claim 32, and further comprising the step of updating the frequency offset over time using a second order loop filtering process.

34. The method of claim 2, and further comprising the step of verifying the authenticity of a device operating in the radio frequency band based on the power spectral information obtained when the device emits a signal in the radio frequency band.

35. The method of claim 34, wherein the step of verifying comprises comparing signal pulse characteristics obtained when the device emits a signal with stored signal pulse characteristics that are associated with devices authorized to operate in the radio frequency band.

36. The method of claim 35, wherein the step of verifying comprises comparing signal pulse characteristics associated with the emitted signal with signal pulse characteristics associated with an identifier that matches an identifier contained in the emitted signal and determining that the device is not authorized when the captured signal pulse characteristics do not match the stored signal pulse characteristics for that identifier.

37. The method of claim 1, and further comprising steps of receiving a request for spectrum activity information from an application program interface;

and supplying the spectrum activity information in accordance with the request.

38. The method of claim 37, wherein the step of receiving the request comprises receiving parameters for specifying spectrum activity information to be generated including at least one of:

characteristics of signal pulse types to be detected in the radio frequency band, and portion of the radio frequency band for which spectral power information is to be generated.

39. The method of claim 37, wherein the step of supplying comprises supplying at least one of:

(a) statistics associated with a particular portion of the radio frequency band including one or more of average power level, maximum power level of activity for each of a plurality of frequency bins in the particular portion of the radio frequency band, and a measure of activity in those frequency bins having activity;

(b) signal pulses determined to occur in the frequency band whose center frequency, duration and/or bandwidth fall within ranges;

(c) histograms for one or more of center frequency, duration and bandwidth of signal pulses determined to occur in the radio frequency band over time; and

(d) digital samples of received radio frequency energy when a particular signal pulse type is determined to occur in the frequency band.

40. A device for generating information pertaining to activity occurring in a radio frequency band, comprising:

a. a spectrum analyzer that computes power values for radio frequency energy received in at least part of the radio frequency band for a time interval; and

b. a signal detector coupled to the spectrum analyzer that detects signal pulses of radio frequency energy that meet one or more characteristics.

41. The device of claim 40, wherein the signal detector comprises:

a. a peak detector circuit that detects one or more peaks from the power values for a time interval, wherein a peak corresponds to power values above a threshold at a predetermined number of contiguous frequencies; and

b. at least one pulse detector circuit coupled to the peak detector circuit that detects signal pulses that meet one or more characteristics based on one or more peaks detected the peak detector.

42. The device of claim 41, wherein the peak detector circuit comprises a comparator that compares power values at each frequency with a peak threshold to identify which frequencies exceed the peak threshold.

43. The device of claim 42, wherein the peak detector circuit identifies the maximum power value among a set of contiguous frequencies that exceed the peak threshold.

44. The device of claim 43, wherein the pulse detector circuit receives as input information from the peak detector circuit that identifies which frequencies exceed the peak threshold and maximum power value for a set of contiguous frequencies that exceed the peak threshold, and determines whether that information satisfies the one or more characteristics.

45. The device of claim 44, wherein the pulse detector circuit detects a signal pulse from the output of the peak detector circuit if one or more of:

center frequency, duration and bandwidth of the information describing detected peaks from the peak detector circuit are within a corresponding range.

46. The device of claim 45, wherein the pulse detector circuit is configurable to adjust the range for one or more of the center frequency, duration and bandwidth in order declare a signal pulse from the information generated by the peak detector circuit.

47. The device of claim 45, wherein the pulse detector circuit outputs pulse event data for each detected signal pulse including one or more of:

center frequency, bandwidth, start time and duration.

48. The device of claim 47, and further comprising a processor coupled to receive pulse event data output by the pulse detector circuit and to accumulate pulse event data for pulses detected by the pulse detector circuit over time.

49. The device of claim 48, wherein the processor accumulates pulse event data and builds one or more histograms for pulse event data accumulated over time, wherein the one or more histograms are selected from the group consisting of:

a center frequency histogram that tracks a percentage of time a given center frequency was observed for detected signal pulses, a bandwidth histogram that tracks the percentage of time a given bandwidth was observed for detected signal pulses, a pulse duration histogram that tracks a percentage of time a given duration or durations was observed for detected signal pulses, a time between pulses histogram that tracks percentage of time that a given time duration or durations was observed between signal pulses and a number of active transmissions histogram that tracks when several different signal pulses simultaneously occur.

50. The device of claim 41, and comprising a plurality of pulse detector circuits each coupled to receive the output of the peak detector circuit, wherein each pulse detector circuit detects signal pulses that satisfy configurable characteristics based on the output of the peak detector circuit.

51. The device of claim 41, wherein the pulse detector circuit outputs a trigger signal in response to detecting a signal pulse that meets the configurable characteristics.

52. The device of claim 51, and further comprising a memory responsive to the trigger signal that stores digital signals representing samples of radio frequency energy received in the radio frequency band.

53. The device of claim 51, wherein the memory further stores a timestamp signal identifying a time associated with an occurrence of the trigger signal.

54. The device of claim 51, wherein the memory is a first-in-first-out buffer.

55. The device of claim 40, wherein the spectrum analyzer receives as input a digital signal representing activity in at least a portion of the frequency band and comprises a power calculation circuit that computes power values for a plurality of frequency bins for a time interval that are supplied as input to the peak detector.

56. The device of claim 55, wherein the spectrum analyzer computes from the power values for the plurality of frequencies, one or more data selected from the group consisting of:

average power at each frequency bin over time intervals;

a duty count comprising a running sum at each time interval of the number of times the power at each frequency bin exceeds the power threshold;

a maximum power for each frequency bin for a current and prior time intervals; and

a running count of the number of time intervals in which a certain number of peaks have been detected.

57. The device of claim 56, and further comprising a memory for storing the one or more data.

58. The device of claim 57, and further comprising a memory controller coupled to the memory, wherein a pulse detector circuit outputs a trigger signal in response to detecting a certain type of pulse that is coupled to the memory controller to write to the memory the output of the power calculation circuit for one or more time intervals.

59. The device of claim 40, and further comprising a radio receiver capable of receiving radio frequency energy in the radio frequency band in which activity associated with a plurality of signal types may occur.

60. The device of claim 59, wherein the radio receiver downconverts signals in substantially the entire frequency band for a time interval.

61. The device of claim 59, wherein the radio receiver downconverts signals in a portion of the frequency band, and is tunable to different portions of the frequency band.

62. The device of claim 59, wherein the spectrum analyzer, signal detector and radio receiver reside on a card device having an interface.

63. In combination, the device of claim 62, and a host device coupled to the card device via the interface, wherein the host device comprises a host processor and memory that stores programs that are used to process the output of the spectrum analyzer and signal detector.

64. The device of claim 40, and further comprising a processor coupled to the spectrum analyzer and the signal detector, wherein the processor receives from an application program interface a request for spectrum activity information, and supplies the spectrum activity information to the application program interface.

65. The device of claim 64, wherein the processor generates on the basis of the request at least one configuration parameter for the spectrum analyzer or signal detector including at least one of:

characteristics of signal pulse types to be detected in the radio frequency band, and portion of the radio frequency band for which spectral power information is to be generated.

66. The device of claim 64, wherein the processor generates the spectrum activity information based on the request include at least one of:

(a) statistics associated with a particular portion of the radio frequency band including one or more of average power level, maximum power level of activity for each of a plurality of frequency bins in the particular portion of the radio frequency band, and a measure of activity in those frequency bins having activity;

(b) signal pulses determined to occur in the frequency band whose center frequency, duration and/or bandwidth fall within ranges;

(c) histograms for one or more of center frequency, duration and bandwidth of signal pulses determined to occur in the radio frequency band over time; and

(d) digital samples of received radio frequency energy when a particular signal pulse type is determined to occur in the frequency band.

67. The device of claim 40, wherein the signal detector comprises a pulse detector that detects a signal pulse associated with a periodic signal in the frequency band, and further comprising:

a. a clock module comprising;

i. at least N registers, each of which stores a programmable duration value associated with one of two states of a pulse of the communication signal, where N is equal to 2 times the number of pulses in a cycle of the communication signal;

ii. a down counter driven by a clock signal that counts down with each clock pulse from a value corresponding to the content of one of the N registers;

iii. a mod(N) counter coupled to the down counter that counts up to N−

1 by one in response to the down counter reaching zero and when reaching N−

1, causing content of the next of the N registers to be loaded into the down counter;

b. a processor coupled to the clock module and to the pulse detector, wherein the processor examines the count values of the down counter and the mod(N) counter to measure a phase error between the clock signal used to drive the down counter and the signal pulse of the periodic signal.

68. The device of claim 67, wherein the processor loads the N registers with values based on an expected frequency of one or more signal pulses of the periodic signal.

69. The device of claim 67, wherein the processor generates a phase offset value according to the phase error it measures that is used to load a value into the down counter and the mod(N) counter when those counters count to zero in order to compensate for the phase error.

70. The device of claim 67, wherein the processor continues to monitor the count values of the down counter and the mod(N) counter to measure the phase error and generates a frequency offset value used for advancing or delaying counting of the down counter.

71. The device of claim 67, wherein the processor updates the frequency offset over time using a loop filtering process.

72. A processor readable medium encoded with instructions that, when executed by a processor, cause the processor to perform steps of:

a. computing power spectral information for radio frequency energy received during a time interval in at least part of a radio frequency band in which activity associated with a plurality of signal types may occur; and

b. detecting from the power spectral information signal pulses of radio frequency energy that have meet one or more characteristics.

73. A system that monitors activity in a radio frequency band where signals of multiple types may be occurring, comprising a process for analyzing radio frequency energy occurring in the radio frequency band and accumulating data associated with activity in the radio frequency band, wherein the process is responsive to a request containing parameters associated with spectrum analysis to be performed by the process.

74. A system that monitors activity in a radio frequency band where signals of multiple types may be occurring, comprising:

a. a process that generates spectrum activity information for activity in the radio frequency band based on received radio frequency energy from the radio frequency band;

b. an application program that processes spectrum activity information pertaining to activity in the radio frequency band; and

c. an application programming interface that presents messages the process and returns spectrum activity information to the application program.