Abstract:
A Method and Apparatus for Enhancing the Detection of Weak Emitters provide an enhanced method to eliminate the fake hits of a moving weak signal detection system. The method and apparatus have the abilities stated in the previous U.S. patent application Ser. No.  11/332,801  filed by this author, to do moving detection of weak signals, even in dense urban environments. Secondly, the method and apparatus includes additional antennas and hardware boards, in order to verify authenticity of detected targets. Thirdly, the method and apparatus include appropriate DSP algorithms loaded to program the mission. Fourthly, the method and apparatus are enabled to accurately determine the tangential distance of the target from me vehicles centerline. Finally, the method and apparatus provide the ability to continually discard false targets based upon the information provided by these approaches.

Description:
[0001]    This application is a continuation in part of application Ser. No. 11/332,801, filed Feb. 12, 2006, now pending. 
         [0002]    This application is filed within one year of, and claims priority to Provisional Application Ser. No. 60/898,882, filed Jan. 31, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention relates generally to electronic information surveillance and security systems and, more specifically, to a Method and Apparatus for enhancing the detection of Weak Emitters. 
         [0005]    2. Description of Related Art 
         [0006]    The embodiments of the present invention describe a significant enhancement to systems for detecting the presence and locations of weak emitters. The embodiments describe an enhanced way of detecting weak emitters utilizing the system described by U.S. patent application Ser. No. 11/332,801, by eliminating the false alarms through an innovative Doppler differentiation approach. 
         [0007]    Details disclosed in previously filed U.S. patent application Ser. No. 11/332,801: “Method And Apparatus For Detecting The Presence And Locations Of Radio Controlled Improvised Explosive Devices In Real Time,” are incorporated herein by reference in that the system and method of the present invention builds upon and/or modifies the basic design and operation disclosed in that application. 
         [0008]    What is needed to eliminate the false alarms of a moving weak signals detection system (such as, for example, the “Street Sweeper” system described by patent application Ser. No. 11/332,801) is to augment that prior art system with the following: 1) The replacement of the roof antenna with two antennas, one on the front of the vehicle, and one on the rear, and 2) The addition of delay memory hardware and digital downconverters, and finally 3) The addition unique real-time algorithms, running on the DSP processors of the delayed digital downconverter outputs (these will be described future). 
         [0009]    In conclusion, it is the inventor&#39;s position that no invention formerly developed provides this unique method to reduce the false alarms of moving weak signal detection systems through Doppler differentiation. This invention represents an important enhancement to me prior art method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  shows a drawing of the system invention as it is typically installed inside a vehicle with the additional hardware antennas; 
           [0011]      FIG. 2  is a flowchart depicting the signal processing method employed by the present invention; 
           [0012]      FIGS. 3A and 3B  show graphical depictions of the invention as it is traveling down a roadway and how it&#39;s physical location relative to the weak emitter, equates to the signals that it is receiving from the front and rear antennas; and 
           [0013]      FIGS. 4A and 4B  show the difference between two profiles and how those can be used to further resolve the tangential distance of the detected weak emitter from the centerline midpoint of the vehicle. This additional feature of the invention provides yet another discriminator to weed out false alarms. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0014]    The following description is provided to enable airy person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide a Method and Apparatus for Enhancing the Detection of Weak Emitters. 
         [0015]      FIG. 1  shows a drawing of the system invention as it is typically installed inside a vehicle with the additional hardware antennas (Moving Weak Signal Detection System Vehicle  200 ) The operation of the original moving weak signal detection system design (outlined by patent application no. U/332,801) will not be covered here. Only the augmentation of the embodiments of the present invention will be described in this document. 
         [0016]    As before the vehicle detects the presence of weak emitter energy and logs detected anomalies in its event logs. This original detection is now used as a qualifier stage of identifying anomalies. The embodiments of the invention of this patent application takes all qualified “hits” and performs a more rigorous analysis. 
         [0017]    When a qualifying hit signal is found by the wideband system (that process is defined by patent application Ser. No., 11/332,801), that particular frequency value is passed off to an internal firmware algorithm of the Central Processor  100  that then tasks two Direct Digital Downconverters (DDC&#39;s) to pluck out those signals and digitize them. The process of using DDC&#39;s to pluck out delayed, signals is described by a different previously filed U.S. patent application Ser. No. 10/829,858, entitled “Method And Apparatus For The Intelligent And Automatic Gathering of Sudden Short Duration Communications Signals,” also written by this author. 
         [0018]    The Front Antenna  28  and Rear Antenna  26  are both connected to the Central Processor  100 . Note that the locations of the two antennas are of extreme importance to this invention (front and rear of the vehicle). 
         [0019]    According to embodiments of the present invention the signals from these two antennas are also connected to delay memory modules. The purpose of this delay memory modules is that after the detection in the wideband system occurs, there is enough time for the Central Processor  100  to allocate the two DDC channels and tune them to the detected frequency. One DDC is allocated to monitor the signals from the front antenna and other one from the rear antenna. Thus it is possible to “go back” in time. The DDC&#39;s then hand off fee signals to DSP chips that use a much more narrowband FFT resolution (as opposed to the wideband FFT approach of the qualification stage. This more narrowband processing of the signals provides a better signal to noise ratio at the signal that was earlier Determined to be interesting by the wideband detector (qualification stage). The resulting FFT bin data streams are then fed to an FPGA where continuous frequency comparisons are performed to determine the maximum Doppler difference between the two signals received between the front and the back antennas. 
         [0020]      FIG. 2  is a flowchart depicting the signal processing method  302 A employed by the present invention. 
         [0021]    As the vehicle  200 A proceeds down the street, the receiver subsystems  102 A-C of the central processor  100  are programmed to scan through a wide range of RF frequencies in synchronous fashion. Again, the operations of the receiver subsystems  102  (hereafter referred to as “Wideband Systems”) are exactly the same as described by U.S. patent application Ser. No. 10/829,858. 
         [0022]    The wideband systems  102 A-C digitize large bandwidths of the RF spectrum for processing. One wideband receiver subsystem  102 A is attached to the rear antenna  26 , one wideband receiver subsystem  102 B is attached to the bottom antenna  18 , and one wideband receiver subsystem  102 C is attached to the front antenna  28 . Every time each receiver subsystem  102 A-C produces a single n-point Fast Fourier Transformation (FFT) frame of information, the flames are sent to an algorithm that quickly compares those frames. An n-point EFT frame is comprised of n number of frequency measurements, or “bins” across the entire bandwidth. 
         [0023]    As the FFT frames are collected from antennaes  302 A, the bins of one of the ambient RF receiver subsystem  102 A, C FFT frames are compared to the corresponding bin of the RCIED receiver subsystem  102 B FFT frame that is taken at the same instant in time  304 A. 
         [0024]    The signals that come in from the wideband receiver subsystems  102 A, C connected to the antennas  26 , 28  will be different man the signals coming from the wideband receiver subsystem  102 B connected to the bottom antenna  18  due to numerous factors. In most cases, the signals from the top antennas  26 , 28  will have higher amplitudes than the signals from the bottom antenna  18  since the bottom antenna is facing towards the ground and thus is more isolated from the surrounding RF environment. The only time the FFT bin amplitudes from the bottom antenna  18  should be higher than the bin amplitudes from the top antennas  26 , 28  will be when a leakage signal from an RCIED is detected underneath (or beside) the vehicle  200 . It is this phenomena that is exploited according to embodiments of the present invention. 
         [0025]    Continuing forward, the system  100  calculates which bins received from the bottom antenna  18  have higher amplitudes than the corresponding top antenna&#39;s  26 , 28  FFT bins  308 . If the bins from the bottom subsystem  102 B are not higher in amplitude than the corresponding bin of the top subsystems  102 A, C, then the next FFT frames are processed  306 A. 
         [0026]    As high-amplitude bins are detected by the system  100 , the system  100  takes those higher bins and labels them as “bins of interest”. These bins of interest, and their respective amplitudes from the bottom antenna only, are then taken to another algorithm that begins to populate “trends”  308  which are finite numerical arrays of the amplitude data from one particular frequency bin number. 
         [0027]    The operational modification of the present method  300 A is that when bins have been seen before, it is considered to be a “Qualifying Event”  309 A. This triggers the Buffered Data to be analyzed and the Doppler profiles are created for each set of buffered data  311 A. These Doppler profiles are then used to determine the tangent position of the emitter and the tangential distance to that detected emitter  313 A. Each element in these trend arrays is a successive frequency measurement (amplitude data from the bottom antenna, for a single bin of interest) over time. 
         [0028]    If the FFT bins of interest have been seen before, i.e. trends have already been started for those bin numbers, then the new data points are simply placed into the end of those trend&#39;s arrays  312 . If a bin of interest corresponds to a trend that has not been started before, then a new trend is begun  310 . Finally, if existing trends do not have new data to add, that means that the signal amplitude from the bottom antenna  18  have ceased to be higher than the amplitude of the corresponding signals from the top antenna  10  for those particular trend&#39;s bin numbers (i.e. the signal eventually went away or the original trend was started on bad data). In such cases of trend dissipation, the system  100  will conclude that the trend is no longer of interest after the expiration of a specified period of time, as configurable by the system user  312 . 
         [0029]    The next step is to tag each new added element, of each trend, with a “distance tag”  314 . This distance tag number comes from the drive shaft sensor algorithm, and is based upon an input from the drive shaft sensor that includes the sensor data  24 . An algorithm calculates the relative distance the vehicle  200  traveled from when one measurement was taken to the very next. All data elements in an array that were recorded and are older man, for example, 20 meters are discarded  316 . This is because it is necessary to bind the length of the trend arrays for the next stage of the signal processing, which is adjustment, after which comes correlation. 
       Operation 
       [0030]      FIGS. 3A and 3B  show graphical depictions of the invention as it is traveling down a roadway and how it&#39;s physical location relative to the weak emitter, equates to the signals that it is receiving from the front and rear antennas. 
         [0031]    When the vehicle is approaching the emitter, the detected frequency emitted by that target will exhibit a Doppler effect. That is, the wavelengths will slightly compress and the detected frequency will go up slightly by a few Hz. Conversely, when the vehicle passes the emitter, the detected frequency will go slightly down by a few Hz, also due to the Doppler effect. 
         [0032]      FIGS. 4A and 4B  show he difference between two profiles and how those can be used to further resolve the tangential distance of the detected weak emitter from the centerline midpoint of the vehicle. This additional feature of the invention provides yet another discriminator to weed out false alarms. 
         [0033]    This reality is exploited according to embodiments of the present invention. The two data forms are plotted over time. What can be seen by the drawing of  FIG. 4B  is that the detected Doppler shifts will both be identical, but yet offset in time. That is because the Front Antenna  28  will pass the emitter before the Rear Antenna  26  will. The maximum difference in frequencies between the two antennas can only result when the vehicle&#39;s midpoint is perpendicular to the location of the emitter with respect to the midpoint of the vehicle (i.e. the physical separation between the front and rear antennas). Embodiments of the present invention then mark the exact time that this maximum Doppler difference occurred and the central processor can then go back and determine the exact GPS location of the vehicle when that signal was received. This will give the location of the emitter on the roadway. But it will not directly give the distance the emitter is from the vehicle&#39;s centerline motion That calculation is done by a separate algorithm. 
         [0034]    In order to determine the tangential distance of the emitter from the vehicle&#39;s centerline requires a calculation of the vehicle&#39;s velocity when it passed the target 
         [0035]    Again, the drive shaft sensor is used to determine the vehicle&#39;s velocity as it passed by the emitter. An algorithm is installed that calculates the maximum Doppler shift that would have been detected if the emitter was located directly on the cars centerline at the current speed and at the emitter&#39;s frequency. The further away from the centerline that the emitter is located the lower in frequency the Doppler difference signal will be. This will then give an accurate mathematical distance to the emitter&#39;s antenna from the vehicle&#39;s centerline. This calculation allows the system to weed out weak emitters mat are too tar from the vehicle to be considered a threat or “within the sphere of importance”. This will also weed out all other spurious signals that were detected as “interesting” by fee wideband detector. Thus, the invention provides a unique way to eliminate the false alarms and at the same time provides a more accurate way to determine the distance of an emitter&#39;s antenna from the centerline of the moving weak signal detection system vehicle as it drives by. 
       Diagram Reference Numerals 
       [0000]    
       
           14  GPS Antenna 
           16  GPS Signals 
           18  Bottom Flat Antenna 
           20  Weak Signal Energy Tom Bottom Antenna 
           22  Drive Shaft Sensor 
           24  Drive Shaft Signals 
           26  Rear Antenna 
           28  Front Antenna 
           30  Weak Signal Energy from Rear Antenna 
           32  Weak Signal Energy from Front Antenna 
           100  Central Processor 
           200  Moving Weak Signal Detection System Vehicle 
       
     
         [0048]    Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.