System and related circuits and methods for detecting and locating illicit cellular telephone use within a facility

• US 20080171560A1
• Filed: 10/16/2007
• Published: 07/17/2008
• Est. Priority Date: 10/17/2006
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Inventors: Horvath, Kenji C., Olbers, Robert L., Liu, Yuan-Min, Reyes, Joseph L., Keimig, John, Nesky, Mark S., Plecas, Craig A.
• Granted Patent: US 8,103,293 B2
• Time in Patent Office: Days
• US Class Current: 455/456.6
• CPC Class Codes: H04W 12/12 Detection or prevention of fraud
• CPC Class Codes: H04W 12/63 Location-dependent; Proximity-dependent
• CPC Class Codes: H04W 48/02 Access restriction performed under specific conditions
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A system for detecting and locating illicit cellular telephone use within a facility includes an array of radio frequency (RF) receivers, each receiver being placed in a predetermined location in the facility, and a central server, the receivers being in electrical communication with the central server. The server commands a group or groups of receivers to tune to a frequency of interest and to perform detailed sample rate measurements of the RF signal level received at the receivers. The array of receivers is organized into a plurality of measurement areas covering widely separated areas of the facility or different buildings of the facility, and the plurality of receivers of a measurement area is organized into a plurality of measurement groups covering areas of approximately uniform RF propagation conditions. Each receiver scans a frequency band of interest non-synchronously and independently of the other receivers in the array. Also, each receiver is preferably a direct-conversion receiver.

Claims

1. A system for detecting and locating illicit cellular telephone use within a facility, which comprises:

an array of radio frequency (RF) receivers, each receiver being placed in a predetermined location in the facility; and

a central server, the receivers being in electrical communication with the central server.

2. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein the server includes software to control system operation and to determine the presence and location of the cellular telephone use, the software having a database of relevant data and detection results of cellular telephone use within the facility.

3. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 2, which further comprises:

a remote platform in electrical communication with the server, the remote platform having client application software situated thereon to support user interaction with the system.

4. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 2, wherein the server includes client application software situated thereon to support user interactions with the system.

5. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 2, wherein the server includes a source location algorithm (SLA) module situated therein, the SLA module performing an iterative search to find a combination of estimated source location and propagation model parameters based on signals received from the array of receivers.

6. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 2, wherein the server commands a group or groups of receivers to tune to a frequency of interest and to perform detailed sample rate measurements of the RF signal level received at the receivers.

7. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein the array of receivers is organized into a plurality of measurement groups covering areas of approximately uniform RF propagation conditions.

8. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein the array of receivers is organized into a plurality of measurement areas covering widely separated areas of the facility or different buildings of the facility, and wherein the plurality of receivers of a measurement area is organized into a plurality of measurement groups covering areas of approximately uniform RF propagation conditions.

9. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 2, wherein the server includes an incident alert services (IAS) module situated thereon, the IAS module notifying the end user that illicit cellular telephone use has been detected.

10. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 2, wherein the system generates an indication to the user of a dynamic radius of uncertainty based on a density of a portion of the array of receivers.

11. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, which further comprises:

a monitor in electrical communication with the server, the monitor displaying a floor plan of the facility and alert indications of cellular telephone use which show the location of cellular telephone use superimposed on the floor plan of the facility, the alert indications being grouped by frequency bands used by the cellular telephones.

12. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 11, wherein the monitor further displays an aggregated location estimate associated with a particular alert indication to determine whether the cellular telephone use is stationary in the facility or is in motion in the facility and to determine the length of time of the cellular telephone use.

13. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 11, wherein the alert indications are displayed on the monitor in groups of frequency bands.

14. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein each receiver includes:

an omni-directional antenna which receives RF signals generated by cellular telephone use;

a switchable RF filter bank in electrical communication with the antenna and designed to reject out-of-band subharmonic and harmonic signals;

a variable attenuator in electrical communication with an output of the RF filter bank to extend the dynamic range of the receiver and to test for the presence of harmonic distortion effects;

a mixer in electrical communication with the RF filter bank to downconvert sidebands of the RF signal received by the antenna;

a local oscillator in electrical communication with the mixer;

a bandpass filter in electrical communication with an output of the mixer which sets the resolution bandwidth of the system;

a detector in electrical communication with an output of the bandpass filter, the detector outputting a voltage proportional to the signal power received thereby, which voltage is proportional to the level of the RF signal received by the antenna; and

a microcontroller in electrical communication with the server, the local oscillator, the filter bank and the attenuator, the microcontroller further converting the output voltage of the detector to a digitized power level measurement.

15. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein each receiver of the array of receivers performs no demodulation.

16. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 8, wherein the receivers of a measurement group are distributed throughout a region in the facility of relatively uniform propagation.

17. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 8, wherein the receivers of the array are separated into different measurement groups based on conditions that do not satisfy a uniform propagation consideration.

18. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 8, wherein the receivers of the array are placed in one measurement group if they are in substantially the same propagation environment.

19. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 8, wherein the system determines the location of cellular telephone use by comparing the signal powers measured by a plurality of measurement groups of receivers and selecting the measurement group of receivers with the highest measured signal power to use in determining the location of the cellular telephone use.

20. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein the array of receivers is located within a predetermined area;

and wherein the system further comprises at least one perimeter receiver, the at least one perimeter receiver being situated outside the predetermined area in which the array of receivers is located, the system comparing the signal level measured by the at least one perimeter receiver to the signal levels measured by the receivers of the array of receivers located within the predetermined area and determining that no illicit cellular telephone use has occurred if the signal level measured by the at least one perimeter receiver is greater than the signal level measured by the receivers of the array of receivers located within the predetermined area.

21. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 20, wherein the receivers of the array of receivers located within the predetermined area have omni-directional antennas, and wherein the at least one perimeter receiver has a hemispherical-pattern antenna.

22. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 20, wherein the predetermined area in which the array of receivers is located defines a perimeter;

and wherein the array of receivers located within the predetermined area includes at least one receiver having at least one of a hemispherical-pattern antenna and a quarter-spherical pattern antenna situated at the perimeter within the predetermined area.

23. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 22, wherein the at least one antenna of the array of antennas having at least one of a hemispherical-pattern antenna and a quarter-spherical pattern antenna includes a hemispherical-pattern antenna;

and wherein the at least one perimeter antenna includes a hemispherical-pattern antenna, the at least one perimeter antenna situated outside the predetermined area being situated in alignment with the at least one perimeter antenna having a hemispherical-pattern antenna and located within the predetermined area.

24. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 11, wherein the monitor displays the cellular telephone frequency band used by a cellular telephone, the alert indication being a geometric shape superimposed on the floor plan of the facility at the location on the floor plan of cellular telephone use.

25. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 24, wherein the geometric shape of the alert indication is displayed on the monitor in one of a plurality of predetermined colors, each color of the predetermined colors representing a frequency band of the cellular telephone use detected by the system, each color of the plurality of colors representing a different frequency band.

26. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 24, wherein the system determines a time series of estimates of the location of cellular telephone use within the facility that is aggregated together and displayed on the monitor by overlapped regions defined by the geometric shape of the alert indication, the brightness and opacity of the overlapped regions being indicative of the location and movement of the cellular telephone use superimposed on the floor plan of the facility.

27. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 26, wherein the system averages signals received by the receivers to reduce the effects of location estimate errors of the cellular telephone use in the facility due to at least one of noise, multipath propagation effects, temporary obstructions in the facility and interference.

28. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 26, wherein the brightness of the geometric shape of the alert indications displayed on the monitor to indicate the estimated location of cellular telephone use is proportional to a level of confidence that the cellular telephone use detected by the system is within the estimated location defined by the geometric shape displayed on the monitor.

29. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 26, wherein the geometric shape of the alert indications is displayed in different predetermined colors, the different predetermined colors indicating the estimated location of cellular telephone use in a facility in time sequence.

30. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein the receivers of the array of receivers are uniformly distributed over a square area, the distance between adjacent receivers defining an inter-receiver spacing equal to the square root of the area divided by the number of receivers in the array.

31. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 30, wherein a respective receiver receiving the strongest signal caused by the cellular telephone use of all of the receivers of the array of receivers has associated therewith a region of uncertainty centered at the respective receiver corresponding to an estimate of the location of the cellular telephone use, the region of uncertainty being bounded by a square, the square having sides which are equal to the square root of the area in which the array of receivers are uniformly distributed divided by the number of receivers in the array.

32. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein the receivers of the array of receivers are non-uniformly distributed over an area, the distance between adjacent receivers defining an irregular spacing;

and wherein a respective receiver receiving the strongest signal caused by the cellular telephone use of all of the receivers of the array of receivers has associated therewith a region of uncertainty corresponding to an estimate of the location of the cellular telephone use, the region of uncertainty being bounded by a circle centered at the respective receiver, the circle having a diameter which is equal to the square root of the area in which the array of receivers are non-uniformly distributed divided by the number of receivers in the array.

37. A method of detecting and locating illicit cellular telephone use within a facility using the system defined by claim 1, which comprises the steps of:

scanning a radio frequency (RF) band of interest to detect the presence of an RF signal within the band of interest by each receiver of the array of receivers independently and non-synchronously with respect to the other receivers in the array of receivers;

detecting the RF signal within the frequency band of interest by at least one receiver of the array of receivers;

determining at least the approximate frequency of the RF signal detected by the at least one receiver of the array of receivers;

performing high-rate measurements at the determined at least approximate frequency of the RF signal by at least some of the receivers of the array of receivers; and

measuring the signal level of the RF signal received by the at least some of the receivers of the array of receivers.

38. A method as defined by claim 37, wherein the RF signal has a pulse width;

and wherein the step of measuring the signal level of the RF signal received by the at least some of the receivers of the array of receivers includes the further step of performing the measuring of the signal level at measurement intervals which are less than the pulse width of the detected RF signal.

39. A system for detecting and locating illicit cellular telephone use within a facility as defined by claim 1, wherein each receiver of the array of the receivers is a direct-conversion receiver, each direct-conversion receiver including:

an antenna;

an RF filter in electrical communication with the antenna;

a variable attenuator in electrical communication with an output of the RF filter;

a mixer in electrical communication with an output of the variable attenuator;

an intermediate frequency (IF) filter in electrical communication with an output of the mixer;

a local oscillator in electrical communication with the mixer; and

a detector in electrical communication with an output of the IF filter;

wherein the variable attenuator is adjustable to increase and decrease the signal level of an RF signal received by the antenna for determining whether the RF signal is a fundamental frequency RF signal or a spurious RF signal caused by harmonic distortion.

40. A method of distinguishing between a fundamental frequency radio frequency (RF) signal and a spurious RF signal caused by harmonic distortion in a direct-conversion receiver as defined by claim 39, which comprises the steps of:

measuring the signal level of the output signal of the detector at a first attenuation setting of the variable attenuator;

changing the attenuation setting of the variable attenuator to a second attenuation setting which is different from the first attenuation setting to cause a change in the signal level of the output signal of the detector;

re-measuring the signal level of the output signal of the detector; and

comparing the change in the attenuation setting from the first attenuation setting to the second attenuation setting with the change in the signal level in the output signal of the detector, thereby determining whether the RF signal received by the direct-conversion receiver is a fundamental frequency RF signal or a spurious RF signal caused by harmonic distortion.

33. A method of allowing a sequence of time-discontinuous or frequency-hopping spread spectrum transmissions from a radio frequency (RF) source to be identified as a single event, which comprises the steps of:

monitoring a plurality of defined frequency bands in which the sequence of transmissions from the RF source is expected to occur;

detecting a first transmission of the sequence of transmissions in a respective frequency band of the plurality of defined frequency bands;

setting a countdown timer to start a preset timeout period;

monitoring the respective frequency band or at least a second transmission occurring in time after the detected first transmission in the sequence of transmissions and occurring in frequency in the respective frequency band;

detecting the at least second transmission if a second transmission occurs;

resetting the countdown timer to restart the preset timeout period if the second transmission occurs in time before the timeout period has ended and not resetting the countdown timer to restart the timeout period if no second transmission occurs or if the second transmission occurs in time after the timeout period has ended; and

identifying the first transmission and the second transmission as being part of the single event if the second transmission occurs in time before the timeout period has ended.

34. A method of minimizing the number of steps required to completely measure a contiguous RF (radio frequency) band extending from frequency f₁ to frequency f₂ in a direct-conversion receiver, the direct-conversion receiver downconverting an RF frequency band, centered about an RF center frequency f_c to an IF (intermediate frequency) band centered around zero frequency, the direct-conversion receiver including a local oscillator having a frequency f₀ tuned to f_c, a mixer in electrical communication with the local oscillator, a bandpass IF filter in electrical communication with an output of the mixer and having a low cutoff frequency f_IFL and a high cutoff frequency f_IFH to provide an IF filter passband which extends from f_IFL to f_IFH, and a detector in electrical communication with an output of the bandpass IF filter and providing a detector output filter response, the bandpass IF filter thereby creating a notch in the RF response of the detector extending from (f_c−

f_IFL) to (f_c+f_IFL), which comprises the steps of;

selecting bandpass response corner frequencies such that f_IFH=⅓

f_IFH, whereby each measurement sideband has a bandwidth (f_IFH−

f_IFL) equal to 2 f_IFL, the notch thereby being equal to the bandwidth of either measurement sideband; and

incrementally changing the local oscillator frequency f₀ of the local oscillator in successive steps such that the local oscillator frequency f₀ alternately assumes 2 f_IFL and 6 f_IFL on successive steps.

35. A method of minimizing the number of steps required to completely measure a contiguous RF (radio frequency) band extending from frequency f₁ to frequency f₂ in a direct-conversion receiver, the direct-conversion receiver downconverting an RF frequency band, centered about an RF center frequency f_c to an IF (intermediate frequency) band centered around zero frequency, the direct-conversion receiver including a local oscillator having a frequency f₀ tuned to f_c, a mixer in electrical communication with the local oscillator, a bandpass IF filter in electrical communication with an output of the mixer and having a low cutoff frequency f_IFL and a high cutoff frequency f_IFH to provide an IF filter passband which extends from f_IFL to f_IFH, and a detector for electrical communication with an output of the bandpass IF filter and providing the detector output filter response, the bandpass IF filter thereby creating a notch in the RF response of the detector extending from (f_c−

f_IFL) to (f_c+f_IFL), where the bandwidth f₂−

f₁ of the RF band to be measured is greater than 8 f_IFL, which comprises the steps of;

selecting bandpass response corner frequencies such that f_IFH=⅓

f_IFH, whereby each measurement sideband has a bandwidth (f_IFH−

f_IFL) equal to 2 f_IFL, the notch thereby being equal to the bandwidth of either measurement sideband;

incrementally changing the local oscillator frequency f₀ of the local oscillator in successive steps such that the local oscillator frequency alternately assumes 2 f_IFL and 6 f_IFL on successive steps, in the following substeps;

a) setting the local oscillator frequency to f₀=f₁+3 f_IFL to measure the energy in the sidebands [f₁ to (f₁+2 f_IFL)] and [(f₁+4 f_IFL) to (f₁+6 f_IFL)];

b) incrementing the local oscillator frequency f₀ by 2 f_IFL to measure the energy in the frequencies [(f₁+2 f_IFL) to (f₁+4 f_IFL)] and [(f₁+6 f_IFL) to (f₁+8 f_IFL)];

c) incrementing the local oscillator frequency by 6 f_IFL to measure the frequencies [(f₁+8 f_IFL) to (f₁+10 f_IFL)] and [(f₁+12 f_IFL) to (f₁+14 f_IFL)]; and

d) continuing to incrementally change the local oscillator frequency by 2 f_IFL and 6 f_IFL on alternate successive steps until the contiguous RF band is completely measured.

36. A method as defined by claim 35, wherein the method further minimizes an overlap in the measurement steps required to completely measure the contiguous RF band when (f₂−

f₁) does not equal N times 8 f_IFL, where N is an integer, the step (c) further including the step of;

c1) setting the final two settings of the local oscillator frequency to ensure that the measurement does not extend beyond the upper band edge frequency f₂ by setting the local oscillator frequency to f₀=f₂−

5 f_IFL to measure the frequencies [(f₂−

8 f_IFL) to (f₂−

6 f_IFL)] and [(f₂−

4 f_IFL) to (f₂−

2 f_IFL)], and then setting the local oscillator frequency to f₀=f₂−

3 f_IFL to measure the frequencies [(f₂−

6 f_IFL) to (f₂−

4 f_IFL)] and [(f₂−

2 f_IFL) to f₂] to provide a minimal overlap in the measurements and to ensure that the measurement does not extend beyond the upper band edge frequency f₂.