Abstract:
A target/track assignment method for a combined radar/ADS surveillance environment uses tandem cycles to help the air traffic control system update the order of system tracks, thereby permitting numerous target reports to be processed in real time.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention can be classified to air traffic control, and particularly to a tandem-cycle target/track assignment method in combined radar/ADS surveillance environment. 
     2. Description of the Related Art 
     Future radar/ADS combined surveillance environment includes the following facilities: primary radar, secondary radar, Automatic Dependent Surveillance-Addressing (ADS-A), and Automatic Dependent Surveillance-Broadcast (ADS-B). These facilities&#39; report rates are quite different. For example, ADS-B broadcasts every second and, on the other hand, ADS-A sends reports every 15 to 30 minutes, on average. To eliminate problems which might come with the various report rates, current air traffic control system needs a new target/track assignment method to get the latest surveillance information of an aircraft in real time. 
     In the present invention, a tandem-cycle target/track assignment method is proposed to satisfy this requirement. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a tandem-cycle target/track assignment method in combined radar/ADS surveillance environment so that an air traffic control system can get the latest surveillance information of aircrafts in real time. 
     The method contains the following steps; (A) determine whether the system should run a batch process. If not, go to (B); otherwise go to (G). (B) filter out improper targets; (C) according to system track&#39;s position, velocity, etc., select candidate tracks which might correlate with the reported target; (D) according to the candidate track&#39;s type and correlation conditions, further filter candidate tracks selected in (C) and calculate remaining tracks&#39; likelihood values while correlating them with the reported target. Save all likelihood values of track-target pairs for later processing in (G). If no candidate track can be found, initialize a new track using the reported target; (E) determine when should the system update tracks. If in sequential process, go to (F); otherwise go to (G). (F) select a system track which likelihood value is the highest, update it with the reported target, and then go to (A). (G) If it&#39;s time to run a batch process, use the auction algorithm to select best track-target pairs and update system tracks with their best targets. Then, go to (A). 
     The various objects and advantages of the present invention will be readily understood in the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the flow diagram of the proposed method in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The flow diagram of the tandem-cycle target/track assignment method of the present invention is illustrated in FIG.  1 . The proposed method, when receives a target report, will run the following steps. 
     Step A. If the system is going to run a batch process, go to Step G; otherwise, go to Step B. Note that a system might run a batch process every 4.5 seconds. 
     Step B. filter out the received target if 
     it is a radar test target, 
     its beacon code is invalid, 
     it&#39;s outside system plane, 
     it overloads the system, i.e., the number of targets will exceed system&#39;s maximal capacity, 
     it is not eligible for correlation 
     If the target is filtered out, go to Step A. 
     Step C. select candidate tracks that can reach reported target&#39;s position in a reasonable time. On selecting these candidates, their positions, velocities, headings, turn rates, correlation time, etc. are considered. 
     Step D. Use correlation conditions listed in Table 1 to filter out candidates selected in Step C. Calculate remaining candidate tracks&#39; likelihood values while correlating them with the reported target. On calculating a track&#39;s likelihood value, increase the value when 
     The distance between the candidate track and the target is small, 
     The difference of velocity, heading, or altitude between the candidate track and the target is small. 
     The beacon codes of the candidate track and the target are of the same 
     The aircraft IDs of the candidate track and the target are of the same 
     The candidate track and the target are both reported by the same primary or secondary radar. 
     On the other hand, decrease the value if the target is reported by a primary radar and is in a clutter area. Save likelihood values of all {(candidate track, reported target)} pairs for later processing in Step G. If no candidate track can be found, initiate a new track using the reported target. 
     Step E. According to Table 1, determine when should the reported target update a system track. If the target will update a system track in sequential process, go to Step F; if the target will update a system track in batch process, go to Step G. 
     Step F. Update the system track which likelihood value is the highest. Go to Step A. 
     Step G. If it&#39;s time to run a batch process, use the auction algorithm to determine best track-target pairs for system tracks and update them with their best targets. Go to Step A. 
     Table 2 explains meanings of various track types listed in Table 1. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 track-target correlation conditions and track update time. 
               
             
          
           
               
                 A target 
                   
                   
                 update 
               
               
                 reported by 
                 Track type 
                 Correlation conditions 
                 track in 
               
               
                   
               
               
                 primary 
                 Search, 
                 Track passes the gating in 
                 Batch 
               
               
                 radar 
                 ADS-search 
                 step C. 
                 process 
               
               
                   
                 Beacon, 
                 Track passes the gating in 
               
               
                   
                 accurate 
                 step C and 
               
               
                   
                   
                 (1) track is in coast state; 
               
               
                   
                   
                 (2) target is not in clutter 
               
               
                   
                   
                 area; 
               
               
                   
                   
                 (3) target is reported from 
               
               
                   
                   
                 preferred radar. 
               
               
                   
                 ADS, 
                 Not allowed 
               
               
                   
                 ADS-beacon, 
               
               
                   
                 ADS-accurate 
               
               
                 Secondary 
                 Search 
                 Not allowed 
               
               
                 radar 
                 Beacon, 
                 Track passes the gating in 
               
               
                   
                 ADS-beacon 
                 step C and 
               
               
                   
                   
                 the beacon codes are of 
               
               
                   
                   
                 the same 
               
               
                   
                   
                 Or 
               
               
                   
                   
                 target&#39;s beacon code is 
               
               
                   
                   
                 HIJK or RDOF or EMG. 
               
               
                   
                 Accurate, 
                 Track passes the gating in 
               
               
                   
                 ADS, 
                 step C and 
               
               
                   
                 ADS-search, 
                 track has not correlated 
               
               
                   
                 ADS-accurate 
                 with any beacon target 
               
               
                   
                   
                 or 
               
               
                   
                   
                 the beacon codes are of 
               
               
                   
                   
                 the same 
               
               
                   
                   
                 or 
               
               
                   
                   
                 target&#39;s beacon code is 
               
               
                   
                   
                 HIJK or RDOF or EMG. 
               
               
                 ADS-B 
                 Search 
                 Not allowed 
               
               
                   
                 Beacon, 
                 Track passes the gating in 
                 Sequen- 
               
               
                   
                 Accurate, ADS, 
                 step C and track&#39;s aircraft ID 
                 tial 
               
               
                   
                 ADS-search, 
                 is the same as the target&#39;s 
                 process 
               
               
                   
                 ADS-beacon, 
                 aircraft ID. 
               
               
                   
                 ADS-accurate 
               
               
                 ADS-A 
                 Search 
                 Not allowed 
               
               
                   
                 Beacon, 
                 Track passes the gating in 
               
               
                   
                 Accurate, 
                 step C and track&#39;s aircraft ID 
               
               
                   
                 ADS, 
                 is the same as the target&#39;s 
               
               
                   
                 ADS-search, 
                 aircraft ID. 
               
               
                   
                 ADS-beacon, 
               
               
                   
                 ADS-accurate 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 description of the meanings of various track types 
               
             
          
           
               
                 Track 
                 Meanings 
               
               
                   
               
               
                 Search 
                 The system uses primary radars to track the aircraft 
               
               
                 Beacon 
                 The system uses secondary radars to track the aircraft 
               
               
                 Accurate 
                 The system uses ADS-B data to track the aircraft 
               
               
                 ADS 
                 The system uses ADS-A data to track the aircraft 
               
               
                 ADS-search 
                 The system uses both primary radars and ADS-A to track 
               
               
                   
                 the aircraft 
               
               
                 ADS-beacon 
                 The system uses both secondary radars and ADS-A to 
               
               
                   
                 track the aircraft 
               
               
                 ADS-accurate 
                 The system uses both ADS-A and ADS-B data to track 
               
               
                   
                 the aircraft 
               
               
                   
               
             
          
         
       
     
     Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.