Abstract:
A Real-time Emitter Locating System and Method is disclosed. The system provides a technique for taking in data sets (lines of bearing) from DF receivers and characterizing those signals with their respective probabilities of error. Then using a unique method, the preferred system applies a recursive processing technique to this continuous stream of data, displaying transmitter positions with significantly less uncertainty. Furthermore, the preferred system is able to perform these functions in real-time. The system is further capable of being fully automated to would reduce the processing time and reduce the necessity of human intervention. Still further, in an alternative embodiment of the present invention the system can be remotely controlled over a communications network and collect whereby locating data from several DF sets can be combined. In this way, a far more efficient EL System can be achieved in which the emitter&#39;s position can be determined more quickly from a centralized command facility. This combination of data filtering and data collection techniques significantly reduces measurement uncertainties and enhances the accuracy of EL systems.

Description:
[0001]    This application is filed within one year of, and claims priority to Provisional Application Serial No. 60/449,442, filed Feb. 2, 2003. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to Emitter Locating Systems and, more specifically, to a Real-time Emitter Locating System and Method  
           [0004]    2. Description of Related Art  
           [0005]    Emitter Location (EL) Systems are used to locate the position of emitting radio transmitters. Presently in the industry today, finding the location of a radio transmitter involves triangulation methods using at least three radio Direction Finding (DF) “Sets”. Inherently though, the DF Sets that comprise EL Systems produce uncertainties in their measurements due to several factors which will be described later. The invention of this disclosure provides a far more accurate method of operating EL Systems than is presently done today.  
           [0006]    As mentioned, present day EL Systems are comprised of multiple radio Direction Finding (DF) Sets which can either be fixed in location, or mobile on a vehicle, ship, aircraft, etc. The invention of this disclosure especially relates to EL Systems employing at least one mobile DF Set. In fact, with the use of the technique and method of this provisional patent, only a single mobile DF Set is required in an EL System. To understand how uncertainties in the DF Set measurements are reduced with this invention, the background of direction finding operations needs to covered.  
           [0007]    The basic components of a DF Set are: (1) a DF antenna array; and (2) a DF receiver/processor (hereafter referred to simply as “DF receiver”). The basic components of an EL System are: (1) at least one DF Set; (2) some device to interpret the streaming Line-Of-Bearing (LOB) data sets from the DF Set; (3) some sensor device to determine the DF Set&#39;s location; and (4) some sensor device to output the DF Set&#39;s orientation relative to true North.  
           [0008]    The major sources of measurement errors in real-world DF Sets are: (1) uncertainties from the DF antenna array due to frequency dependent variations; and (2) received signal reflections (also known as multi-path).  
           [0009]    Typically in a DF Set, a device is attached to the output that collects, interprets, and plots the line-of-bearing (LOB) data. This device is typically a computer which then displays the LOB&#39;s on some sort of map display. The LOBs that are displayed will vary from measurement to measurement depending on the aforementioned uncertainties. Most often in the industry today though, the DF Sets simply take the collected LOB data sets and average them to produce a best guess as to the true LOB to the transmitter. But as mentioned, the resulting LOB invariably has some level of error, which translates to errors in overall determination of the transmitter&#39;s location.  
           [0010]    Another problem with present-day DF Sets is that the calculation of the transmitter&#39;s location is done by a batch process. That is, the output is calculated by taking every single previous measurement and doing an analysis on the entire aggregate set of data. This is a slow process and cannot be done in real time with large sets of data.  
           [0011]    The invention described in this disclosure uses an improved method and technique to collect data from one or multiple DF Sets, and then to intelligently process that data in real time so that overall measurement uncertainties are reduced. Thus the transmitter&#39;s position plotted on a map will be more accurate. It should be reiterated that with the method and technique of this invention, it is possible to determine, and continuously plot on a map, the location of a transmitter by using only a single DF Set. This fact makes this invention further unique.  
           [0012]    In conclusion, insofar as the inventor is aware, no invention formerly developed provides this unique application of methods to significantly reduce EL system measurement uncertainties.  
         SUMMARY OF THE INVENTION  
         [0013]    In light of the aforementioned problems associated with the prior devices and methods, it is an object of the present invention to provide a Real-time Emitter Locating System and Method. The preferred system should provide a technique for taking in data sets (lines of bearing) from DF receivers and characterizing those signals with their respective probabilities of error. Then using a unique method, the preferred system can apply a recursive processing technique to this continuous stream of data, displaying transmitter positions with significantly less uncertainty. Furthermore, the preferred system must be able to perform these functions in real-time. It is a further object that this system is capable of being fully automated which would reduce the processing time and reduce the necessity of human intervention. It is still even further an object that an alternative embodiment of the present invention is to feasibly remote control the system over a network and collect and combine the same information from several DF Sets. In this way, a far more efficient EL System can be achieved in which the emitter&#39;s position can be determined more quickly from a centralized command facility. This combination of data filtering and data collection techniques significantly reduces measurement uncertainties and enhances the accuracy of EL systems.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings, of which:  
         [0015]    [0015]FIG. 1 is a drawing of a typical DF Set;  
         [0016]    [0016]FIG. 2 is a drawing of the configuration of an EL System when employing the method of this invention;  
         [0017]    [0017]FIG. 3 is a drawing of how emitter locating is presently done today with three or more DF Sets;  
         [0018]    [0018]FIG. 4 is a drawing of the technique of this invention for collecting data;  
         [0019]    [0019]FIG. 5 is a flow chart depicting the prior art DF method for locating a transmitter;  
         [0020]    [0020]FIG. 6 depicts the graphical approach employed by the present invention to determine a transmitter&#39;s position point; and  
         [0021]    [0021]FIG. 7 is a flow chart depicting the real-time DF method for locating a transmitter of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    The following description is provided to enable any 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 Real-time Emitter Locating System and Method.  
         [0023]    The present invention can best be understood by initial consideration of FIG. 1. FIG. 1 is a drawing of a typical DF Set  10 . A DF Set  10  is comprised of a DF antenna  16  which is connected to a DF receiver  18 . The DF receiver then outputs LOB data  20 . The output LOB measurements are either raw data, or averaged data.  
         [0024]    [0024]FIG. 2 is a drawing of the configuration of an EL System when employing the method of this invention. A single DF Set has its output LOB&#39;s and quality number data sent to a computer which runs the method of this invention. Other data from a GPS sensor and a Compass are also used. An EL System is comprised of a DF Set which outputs its LOB data to a computer device  26 . The computer also gets DF Set position data  24  from a positioning device  22  (which is often a GPS sensor), as well as DF Set orientation data  25  from a compass device  23 .  
         [0025]    The computer  26  provides the following functions for the EL System: (1) Algorithms on the LOB data sets to reduce measurement uncertainties; (2) DF receiver control; (3) Mapping and LOB histogram displays; (4) Antenna calibration tables; (5) Networking capabilities; and (6) Integrated triangulation functions with other mobile/fixed DF Sets.  
         [0026]    It should be reiterated and understood that present-day DF Sets contain inherent errors in their measurements, which translates to errors in the reported positions of transmitters in EL Systems. Averaging of the DF Set LOB data sets provides a very marginal approach to error correction. In summary, the disadvantages with this prior system and process are that:  
         [0027]    (a) it is still subject to constant inherent uncertainties;  
         [0028]    (b) the averaging methods typically used require full matrix multiplications of the LOB data-sets, which slows the computing process of determining a result;  
         [0029]    (c) the uncertainties in individual DF Set measurements further create errors in multiple DF Set triangulation calculations.  
         [0030]    What is needed therefore in order to fully optimize these EL systems is (1) The enhanced ability to evaluate the measurement data  20  and reduce the overall uncertainties; and (2) An enhanced technique to collect the LOB data. These two things are described in this discription.  
         [0031]    [0031]FIG. 3 is a drawing of how emitter locating is presently done today with three or more DF Sets. The DF Sets are connected through a communications link so the LOB data from each DF Set is used to triangulate the position of the transmitter. The result is a transmitter&#39;s location that sometimes contains large uncertainties.  
         [0032]    [0032]FIG. 4 is a drawing of the technique of this invention for collecting data. In this case, at least one of the DF Sets is mobile. Only one is shown in FIG. 4, the mobile unit can be a part of a larger network of more DF Sets though. The transmitter&#39;s position is calculated much more accurately and in real-time with a combination of data-taking technique and the specialized method to handle the data streams. The result is a transmitter&#39;s location that contains reduced uncertainties and errors and is more accurate.  
         [0033]    The technique of this invention involves the use of a mobile DF Set in a EL System. There may be one or multiple DF Sets used. The first step is for the mobile DF Set to take an LOB measurement of transmitter  12 . This process involves taking the LOB data and the so-called “quality number” reading from the DF receiver. Modem DF receivers now produce a quality number with every LOB output. This quality number value is a metric by which the DF receiver manufacturer estimates the probability that a measurement is accurate. The computer  26  then takes this quality number along with the actual LOB measurement and stores them in memory for future processing.  
         [0034]    The next step is for the mobile DF Set to move its physical position with respect to the transmitter&#39;s position. While moving, the DF Set is constantly taking in more LOB data and associated quality numbers. This process goes on for as long as required to find the transmitter. The more data that is collected, the higher will be the probability that the triangulated position of the transmitter is where it is expected to be.  
         [0035]    This invention employs a specialized recursive method in the computer to process the LOB data that is continually being stored. The whole process begins after a “cross-over” point is first found. A cross-over point is the intersection between the last best LOB data entry, and the newly arrived LOB; typically a point where two LOB&#39;s cross (a position having a fairly high confidence level).  
         [0036]    This cross-over point, when fixed on a map, is the original triangulated position (hereafter referred to as the “position point”) of the transmitter.  
         [0037]    Next, a new LOB is measured and taken into account. The method calculates the shortest distance between the last best position point, and the newly arrived LOB. This will be a perpendicular vector from the point to the line-of-bearing. The method then calculates a new best guess position point along this vector, taking into account the new LOB&#39;s associated quality number as a weighting. Again, this calculation can be done in real time since the method is recursive, and therefore does not require the recomputing of every single LOB data entry taken up to that point.  
         [0038]    In essence, the method uses a form of feedback control with an expected outcome. This recursive process is the basis of the method&#39;s uniqueness when applied to reducing measurement uncertainties in EL Systems. The measurement update steps of the method are responsible for incorporating every new measurement into the a priori estimate to obtain an improved a posteriori estimate.  
         [0039]    LOB measurements that have a low quality number will be given less weight in the method when calculating the position points. LOB measurements that have a high quality number will be given much more weight in the same method. The method then outputs the “adjusted” output accordingly given the continuous stream of data points. This process will in effect prioritize the higher probability measurements designated by the quality number. Thus, the computer displays to the EL operator a much more accurate fix to the transmitter than can be achieved by simple averaging means of the entire data sets. The method of this invention is a form of statistical filtering.  
         [0040]    This method has the ability to do real-time processing. Simple averaging of values requires more multiplications, thus the old method of averaging is slower and not able to be used in real-time if a large amount of data is used. The newer method of this provisional patent application uses fewer multiplications and thus can be performed by any standard processor and computer. To reiterate, the method&#39;s recursive nature thus makes practical implementations much more feasible than simple averaging, which is designed to operate on all of the data directly for each estimate. This is a unique and distinguishing advantage of the invention when used in EL Systems.  
         [0041]    It is worthy to note that the spreading of position points across an integrated map display gives essentially the size of a “probability field” where the transmitter is most likely to be located. As more position points are calculated that deviate from each other, the probability field can be shown to grow on a map display. Such a display is the topic of another invention described in a provisional patent application entitled: “Technique and Method for Displaying Probabilistic Locations of Transmitters in Emitter Location Systems.” 
         [0042]    [0042]FIG. 5 is a flow chart depicting the prior art DF method for locating a transmitter. As shown, the EL system receives a stream of Line of Bearing and Quality information from at least three DF sets  42 A,  42 B and  42 C; three DF sets is generally the minimum necessary in order to achieve triangulation. Next, the EL system calculates the average Line of Bearing from a particular segment of each DF set  44 A,  44 B and  44 C. These averaged Lines of Bearing from each DF set to the transmitter are then plotted  46  to result in a conclusion by the EL system as to the transmitter&#39;s location  48 . As discussed above, the target problems to be resolved by the present invention is the delay in arriving at the average Line of Bearing for each DF set, the lack of control and understanding of the inherent error in each of the LOB averages, and also the need for three or more active and high-quality DF set LOB signals in order to arrive at any sort of reliable transmitter position. FIG. 6 shows the fundamentals of how the present approach operates.  
         [0043]    [0043]FIG. 6 depicts the graphical approach  50  employed by the present invention to determine a transmitter&#39;s position point. First, the DF set  10  determines that the cross-over point of the transmitter PP( 0 ) has been identified; this point is the transmitter position point at time t=0, and it corresponds to a Line of Bearing from the DF set  10  to the transmitter, known as LOB( 0 ).  
         [0044]    Next, the EL system obtains another Line of Bearing (LOB( 1 )) to the transmitter (PP( 1 )), and constructs a connecting vector  52  that is perpendicular to the current line of bearing (LOB( 1 )), and ends at the last line of bearing (in this case, PP( 0 ), the cross-over point). This method assumes that the higher the quality number associated with LOB( 1 ), the higher the probability that PP( 1 ) actually lies on the connecting vector  52 . This process is repeated, and more LOB&#39;s are obtained, until such time as the EL system determines a high probability of the location of the transmitter.  
         [0045]    Three things should be noted: (1) in order to be most effective, the DF set  10  must be exhibit motion relative to the transmitter, so that the LOB&#39;s will change somewhat as more and more readings are taken; (2) there is no need for three or even two DF sets in order to determine a “fix” or actual position for the transmitter with this method; and (3) all position determinations are made “on the fly,” in real-time. Turning to FIG. 7, we can see how the entire method of the present invention executes.  
         [0046]    [0046]FIG. 7 is a flow chart depicting the real-time DF method  54  for locating a transmitter of the present invention.  
         [0047]    First, the EL system receives at least one transmission from a transmitter  56 A. The system will next generate a first Line of Bearing that represents the received transmission from transmitter( 1 )  58 A. Next, the DF set is relocated  60 A (preferably relative to transmitter( 1 )). Another transmission is received from transmitter( 1 )  56 B, and a new Line of Bearing is generated  58 B representing the direction that transmitter( 1 ) was from DF set( 1 ) when the transmission was received. The LOB&#39;s are then analyzed to determine whether or not they cross one another  62 . If they do not, then the implication is that one or both have so much error in them that it would not be advisable to use their data. In this case, DF set( 1 ) is relocated again  60 B, and another transmission is received and LOB generated, until such time as when two sequential LOB&#39;s do cross one another. When two LOB&#39;s cross, a cross-over point in identified  64  at the spacial location of the crossing of the LOB&#39;s—this is the first “Best Guess” at the location of transmitter( 1 ). It should be noted that the operator can simply select a cross-over point manually, in order to expedite the process—while this will effect the initial accuracy of the position locating process, as more sample data is taken, even this error will be resolved.  
         [0048]    Once the cross-over point has been determined  64 , DF set( 1 ) is relocated again  60 C, and another transmission is received from transmitter( 1 )  56 C. Another LOB is generated  58 C representing the direction to transmitter( 1 ) from DF set( 1 ). At this stage, a “connecting vector” (see FIG. 6) is generated from the last “Best Guess” location to the latest LOB  66 . Next, a “New Best Guess” location is generated along the connecting vector, with its proximity to the last best guess being determined by the quality number of the latest transmission (and LOB), weighed against the weight of the last best guess (which is a factor of sample size and quality of the data that led to the last best guess&#39;s location).  
         [0049]    The New Best Guess location will be identified for the user as transmitter( 1 )&#39;s location  70 , updated in real-time (unlike the prior systems). The system  54  then continues to relocate the DF set  60 D and receive transmissions in order to continue to determine the location of transmitter( 1 ).  
         [0050]    It should be understood that no matter how bad the transmission data and resultant LOB&#39;s are, it will not impact the system&#39;s ability to provide a transmitter location to the user, since the “best guess” approach described herein is resilient to erroneous and/or random data.  
         [0051]    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.  
         [0052]    DIAGRAM REFERENCE NUMERALS  
         [0053]    [0053] 10  DF Set  
         [0054]    [0054] 11  EL System  
         [0055]    [0055] 12  Transmitter (Emitter)  
         [0056]    [0056] 14  RF signals  
         [0057]    [0057] 16  DF antenna array  
         [0058]    [0058] 18  DF receiver  
         [0059]    [0059] 20  Line-Of-Bearing (LOB) measurement data and quality number  
         [0060]    [0060] 22  GPS device  
         [0061]    [0061] 23  Compass device  
         [0062]    [0062] 24  DF Set Position data  
         [0063]    [0063] 25  DF Set Orientation data  
         [0064]    [0064] 26  Computer  
         [0065]    [0065] 30  Communications link  
         [0066]    [0066] 32  Triangulated position data plotted on a map display  
         [0067]    [0067] 34  Triangulated position data that has reduced uncertainties, plotted on a map  
         [0068]    [0068] 36  Direction movement vector of mobile DF Set in an EL System  
         [0069]    [0069] 42  Conventional LOB receipt steps  
         [0070]    [0070] 44  Conventional LOB average calculation steps  
         [0071]    [0071] 46  Conventional LOB intersection plotting step  
         [0072]    [0072] 48  Conventional transmitter location determination step  
         [0073]    [0073] 50  and  54  Real-time DF determination method  
         [0074]    [0074] 56 - 70  steps incorporated into the method of the present invention