Abstract:
A simplified multilateration and ADS-B Surveillance System is used, to perform tagging for the FAA Low Cost Ground Surveillance program. This system may also be used as the foundation for a full multilateration system, if a customer wants to upgrade. The present invention uses just one active transmitter/receiver unit as opposed to multiple passive receivers. The present invention captures UF 5 and DF 5 data, thus providing Mode A identification, which then acts as the key to obtaining the call sign from a data fusion packages—thus making it an affordable and marketable product for small to medium-sized airports.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation-In-Part of U.S. patent application Ser. No. 11/541,480 filed on Sep. 29, 2006, and incorporated herein by reference; application Ser. No. 11/541,480 is in turn a Continuation-In-Part of U.S. patent application Ser. No. 11/429,926, filed on May 8, 2006, now U.S. Pat. No. 7,477,193, also incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to aircraft tracking. In particular, the present invention is directed toward a system and method for providing tagging data for aircraft tracking systems. 
     BACKGROUND OF THE INVENTION 
     The National Airspace System (NAS) provides minimal surface surveillance at small to medium airports. The view of the air traffic controller out the window and voice communication with pilots are the primary means of avoiding conflicts and maintaining operational capacity and safety. If visibility is reduced due to weather conditions, then capacity and safety may be severely restricted without some means of surface surveillance. 
     To improve safety at small to medium-sized airports, the Federal Aviation Administration Air Traffic Organization (ATO, See, www.ato.faa.gov) Advanced Technology Development and Prototyping Group is proposing a Low Cost Ground Surveillance (LCGS) system be developed and implemented. 
     This LCGS concept provides scalable and adaptable coverage from user-specified regions to an entire airport movement area. Two different LCGS candidates are under evaluation: the Critical Area Management System (CAMS) and the NOVA 9000 Air Traffic Control System (ATCS). See: http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/operations/td/projects/lcgs/, incorporated herein by reference. 
     CAMS, from Transtech Airport Solutions, Inc. (http://www.transtech-solutions.com/products/asm/airport.html) uses an array of millimeter wave sensors (MWS) distributed throughout the airport movement area to provide coverage of runways, taxiways, and ramp areas. MWS requires no aircraft-installed equipment to operate. The current system installed at Spokane International Airport (GEG), as part of the LCGS evaluation, is integrated with ARTS-IIE. This system can also be integrated with an Optical Identification Sensor (OIS) currently under evaluation. 
     The NOVA 9000 Air Traffic Control System (ATCS) from Park Air Systems of Horten, Norway, uses Terma X-Band radar to provide complete coverage of the airport movement area. It requires no aircraft-installed equipment to operate. The current system installed at GEG is also integrated with ARTS-IIE. 
     Both the CAMS and NOVA systems do not require the use of special equipment in the aircraft, making them well-suited for smaller airport use, where aircraft may only have simple radios and transponders. However, both systems rely upon radars and radar type devices, which may be prone to shading and dead spots in coverage. Moreover, such radar transmitters may be expensive to install, and may require FCC approval and/or may interfere with other radars and radio signals. In addition, while such systems may be able to track aircraft and objects, if they cannot read transponder data from aircraft, they cannot identify aircraft individually (e.g., by registration or flight number) 
     Evers, U.S. Pat. No. 6,211,811, issued Apr. 3, 2001, and incorporated herein by reference, discloses a method and apparatus for improving the surveillance coverage and target identification in a radar based surveillance system. The Evers &#39;811 patent is assigned to the same assignee as the present application and names an inventor in common. 
     The surveillance of the Evers &#39;811 patent provides a means to measure Time Difference of Arrival (TDOA) and decode identification of signal source transmissions. TDOA and identification information received from a minimum of two receiving means is used to supplement non-cooperative surveillance systems (e.g., primary radar, acoustic sensors) with target identification. The system uses a Line Of Position technique to determine position. The system can be implemented as a standalone multilateration surveillance system, which provides signal source position determination when reception is available from a minimum of two receiving means. The system provides position aiding when implemented to supplement non-cooperative surveillance systems. 
     Standalone multilateration systems do not require the use of radio transmitters or radar transmitters in order to track aircraft and other vehicles. Rather, using a plurality of radio receivers, it is possible to track aircraft using aircraft signals ordinarily generated from the aircraft—e.g., transponder signals, radio signals, and the like. From these signals, one can track the position of the aircraft and identify the aircraft as well. However, for smaller aircraft, such transponder signals may only be generated in response to an interrogation signal from a conventional ATC radar. A passive multilateration system may not interrogate aircraft transponders to generate aircraft signal data. 
     Multilateration systems may also be used in conjunction with radar systems to provide redundant tracking data, to confirm radar data and serve as backup if radar should fail or a vehicle or aircraft is in an area of no radar coverage. In addition, data from a multilateration system may be fused with radar data to provide an enhanced data stream of robust and redundant tracking and identification data. 
     Different types of data signals may be generated by aircraft for various tracking and collision avoidance systems. The Mode S Transponder has the ability to utilize many different formats to communicate air-to-air and air-to-ground. These formats are separated into “short” messages (56 bits long) and “long” messages (112 bits long). A “UF” message is from the interrogator (can be a ground station or a TCAS—Traffic Collision Avoidance System) to the Mode S transponder. 
     Level 1 is the minimum Mode S Transponder. It has the ability to reply to Mode S interrogations, but it does not have any datalink capability. The message formats used by a Level 1 transponder are all short (56 bit) messages and may include UF messages, which are interrogations to the Transponder. UF messages may include: UF 0—Short Special Surveillance; UF 4—Surveillance, Altitude Request; UF 5—Surveillance, Identity Request; and UF 11—Mode S Only All Call. A “DF” message is a reply from the Mode S transponder to the interrogator, and may include: DF 0—Short Special Surveillance; DF 4—Surveillance, Altitude Reply; DF-5 Surveillance, Identity Reply; and DF 11—All Call Reply. 
     Rannoch Corporation, predecessor to ERA Systems, Inc, assignee of the present invention, worked with NASA on a Small Business Innovation Research project, proposal number 98-1 01.02-9780B entitled “Low-cost Aircraft Identification and Surveillance System” incorporated herein by reference. 
     That system provided a low-cost (i.e., under $300K) 1090 MHz Multilateration/Line of Position (LOP)/Automatic Dependent Surveillance-Broadcast (ADS-B) surface surveillance system, which uses the following cost-saving technology innovations: a two-receiver identification/position determination algorithm, GPS synchronization, and passive Mode A/C multilateration. The system addressed FAA Topic 01 Aviation Safety &amp; Capacity, Subtopic 01.02 Advanced Concepts in Air Traffic Management, by providing low-cost surveillance technology, which can be used to locate and identify traffic operating on the airport surface. This surveillance enhances safety by enabling Air Traffic Control (ATC) to have a situational display of traffic movement, as well as automatic runway incursion detection alerting. The system may be used as an enhancement to primary surface radar (i.e., Airport Surface Detection Equipment or ASDE-3) by providing identification of aircraft targets and providing surveillance position aiding in regions where the radar does not provide reliable coverage. Another application of the system is standalone aircraft surveillance; a low-cost standalone system is needed at airports that have not qualified for any currently fielded surveillance system due to cost-benefits ratio analyses. 
     The multilateration/LOP/ADS-B surface surveillance system has a number of commercial applications: (1) Airport surface surveillance to support runway incursion detection; (2) Airport surface surveillance to support traffic automation for FAA systems such as Surface Movement Advisor; (3) Airport surface surveillance to support NASA&#39;s Dynamic Runway Occupancy Monitoring system; (4) Terminal area surveillance to support Precision Runway Monitoring; and (5) Terminal area surveillance to provide surveillance of ADS-B-equipped aircraft. 
     SUMMARY OF THE INVENTION 
     A need exists in the art to perform low-cost tagging for surface surveillance systems that have Surface Movement Radar and Data Fusion/ATC Displays. The technique of the present invention may be used as a discriminator for follow-on improvements to the FAA Low-Cost Ground Surveillance Program. 
     In the present invention, a single Receive/Transmit (R/T) station automatically tags targets with the help of Surface Movement Radar (SMR). The present invention may be applied as a component of the FAA Low-Cost Ground Surveillance Program, as well as a stand-alone product. 
     In one embodiment of the present invention, a very stripped down unilateration version of ERA&#39;s Multilateration and ADS-B Surveillance System (MSS, see, http://www.sra.com/media/era/mss-by-era.pdf, incorporated herein by reference) is used, to perform tagging for the FAA Low Cost Ground Surveillance program. The cost of such a system may be less than $200,000, making it affordable for small to medium-sized airports. This system may also be used as the foundation for a full MSS system, if a customer wants to upgrade to a multilateration system. 
     The system of the present invention acquires and periodically updates identification of aircraft that are being tracked by Surface Movement Radar (SMR). Currently, no company makes a system to do this. There are a number of benefits to such a system. First, the system provides identification of ground targets to Air Traffic Control (ATC), which is very important, in terms of safety, workload and reduced communications benefits. Identification of ground targets can be achieved using a full Multilateration (MLAT) system, but such a solution may be too costly for many FAA LCGS airports. Second, a low-cost tagging system may provide a good discriminator for follow-on LCGS systems. 
     The aforementioned Rannoch NASA SBIR demonstrated tagging was feasible. That system, however used two 1090 MHz receivers, instead of a receiver/interrogator as in the present invention. A receiver/interrogator represents an improvement over the earlier system, as it allows the system to interrogate for Mode A identification. Data from a Surface Movement Radar (SMR) and a prototype MLAT system installed in at Hartsfield-Jackson Atlanta Airport (ATL) has been used to demonstrate the present invention. This test showed that it was feasible to use only two receiver sensors to get reliable tagging. Whether two receivers or a receiver/interrogator is used, the tagging technique is similar. When altitude is known, the system determines the Line-of-Position (LOP) of the aircraft transponder. LOP is either a hyperbola or an ellipse or a circle depending on how the system is configured. 
     All technologies have their limitations, and there are instances where the system cannot resolve identification, but this is only for short periods of time. However, as long as the SMR does not drop track, the system can maintain identification on the SMR targets. 
     The present invention builds upon the method set forth in the aforementioned Evers &#39;811 patent, so this class of analysis (SMR to multilateration data mapping) has already been proven. Two main difference between the present invention and the technique in the Evers &#39;8aa patent are: (1) the present invention uses just one active transmitter/receiver unit as opposed to multiple passive receivers, (2) the present invention captures the aforementioned UF 5 and DF 5 data, thus providing Mode A identification, which then acts as the key to obtaining the call sign from a data fusion packages—thus making it an affordable and marketable product for small to medium-sized airports. 
     So the present invention has been demonstrated viable and affordable for smaller airports. Fundamentally, while the existing Low-Cost Surveillance Program (LCGS) is targeting a solution that is 2-3 times less expensive than Rannoch Corporation&#39;s ADS-X system, the present invention provides some key functionality of an LCGS system for significantly reduced cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a first embodiment of the present invention. 
         FIG. 2  is a diagram illustrating the operation of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A need exists in the art to perform low-cost tagging for surface surveillance systems that have Surface Movement Radar and Data Fusion/ATC Displays. The technique of the present invention may be used as a discriminator for follow-on improvements to the FAA Low-Cost Ground Surveillance Program. 
       FIG. 1  is a block diagram of a first embodiment of the present invention. Referring to  FIG. 1 , Surface Movement Radar (SMR)  110  may detect movement of aircraft on the ground using conventional radar techniques. SMR  110  outputs, for example, CAT20 messages  115  to data fusion block  130 . CAT20 messages may comprise multilateration messages as described in the “Eurocontrol Standard Document for Surveillance Data Exchange, Part 14, Category 020” published April, 2008 and incorporated herein by reference. Other types of data messages may be used within the spirit and scope of the present invention. The use of CAT20 messages is by way of example only. 
     Referring again to  FIG. 1 , tagging system  120  also received the CAT20 messages  115  from SMR  110 . Tagging system  120  then populates the ID field in the message payload portion of the CAT20 Messages  115  and provides the tagged messages CAT20 Messages  125  to the Data Fusion System  130 . These tagged CAT20 messages  125  take the position data from the original CAT20 messages  115  and add identifying information as will be described in more detail below. Data fusion block  130  may comprise a Rannoch/ERA data fusion software package for combining different data types to output tracking and identification data for aircraft and ground vehicles. The data fusion system then uses the tagged CAT20 messages either standalone, or in conjunction with messages received directly from the SMR. Note that no Data Fusion modification may be required. 
       FIG. 2  is a diagram illustrating the operation of the present invention. The following describes a unilateration technique using a single co-located Transmitter/Receiver to automatically populate Transponder target IDs with no ADSB for Surface Movement Radar using round-trip TDOA. Referring to  FIG. 2 , the technique of the present invention is described as follows. A single co-located Transmitter-Receiver combination unit  200  can plot a given target position as one of an infinite number of possible points on one or more spheres using Interrogation Round-trip Time Difference of Arrival (TDOA_R), recognizing that these spheres contains a window of error of up to 25 ft in terms of radius relative to the transmitter. The spheres may be degenerated into a plurality of circles on the ground, as illustrated in  FIG. 2  as circles  201 - 206 , if the targets are filtered to include only those transmitting a zero-altitude position. 
     The embodiment of  FIG. 2  illustrates only one embodiment of the present invention and should not be construed as limiting the present invention in any way. The use of a co-located transmitter and receiver  200  as illustrated in  FIG. 2  has some advantages in ease of installation. However, the transmitter and receiver portions of transmitter/receiver  200  may be located separately without departing from the spirit and scope of the present invention. The receiver portion may or may not be co-located with the interrogator (transmitter) portion. When they are not co-located, the Line of Position may be represented by an ellipse, as opposed to the circle as illustrated in  FIG. 21 . A circle is a special case that falls out of the equation of the ellipse, where the transmitter and receiver are located together. 
     The use of elliptical surveillance is disclosed in parent patent application Ser. No. 11/429,926, (Evers et al.) filed on May 8, 2006, now U.S. Pat. No. 7,477,193, issued Jan. 13, 2009, entitled “Method and System for Elliptical-Based Surveillance,” assigned to the same assignee as the present invention, and incorporated herein by reference. Evers discloses a system for performing elliptical-based and hybrid surveillance using one or more receiving and transmitting elements time synchronized to a common precision time reference. Antennas for transmitting and receiving elements are located at known positions separated from one another. At a given time, one of the transmitting elements transmits an interrogation signal to one or more targets, which respond to the interrogation with a reply transmission, received by one or more receiving elements. The central workstation calculates each target&#39;s ellipse of position with respect to each receiving element, using the interrogator element time of interrogation measurement and each receiving element&#39;s time of arrival measurement for the corresponding reply transmission, and then fuses the elliptical line of positions for each receiving element to compute target positions or augment passive surveillance position. 
     The domain of possible ground positions for a given target can be further reduced by only including targets whose potential TDOA_R falls only on one of the possible ground positions that may be physically occupied in the airport. For example, runways  250 , taxiways  255  and aircraft parking areas  265 . For purposes of the invention, it is presumed that the aircraft are not located off these standard areas. The above filtering technique reduces the number of possible positions for a given target down to only a handful in most airports. 
     These potential positions may be referred to as ‘nests’. Thus, for example, in  FIG. 2 , circle  24  intersects three possible “nests”,  225 ,  230 , and  220 . If a Mode A transponder signal is measured, using TDOA_R techniques from transmitter/receiver  200  places the signal somewhere on circle  204 , then the corresponding aircraft or vehicle may be in one of three possible locations ( 225 ,  230 , and  220 ) in this illustrated example. 
     Tagging system  120  of  FIG. 1  then determines which of the nests are occupied with targets by correlating the nest positions with data feeding in from Surface Movement Radar. In the Examiner of  FIG. 2 , there are three targets,  210 ,  240 , and  235 . The SMR data from SMR  110  of  FIG. 1  provides target positions without providing the target IDs. Once a target position indicates that a unique concentric nest is occupied, tagging system  120  of  FIG. 1  populates the correct nest with the SMR target, thus associating the targets ID with it&#39;s SMR position. In this example, nest  230  corresponds with position of aircraft  240 , and thus Mode A or other the identifying information from the transmitter/receiver  200  may be correlated to the position information of SMR data of aircraft  240 . 
     Upon matching the identified SMR target to its nest, tagging system  120  of  FIG. 1  then continues to track the target by not only using the above method, but also by using the newly determined association. The SMR target is identified only when a unique solution to the matching problem occurs. Thus, for example, if three aircraft occupy the three “nests”  220 ,  230 , and  225  of  FIG. 2 , then unique identification may not be possible, at least momentarily. However, given the dynamic nature of the movement of both the nests and SMR targets, many unique matching opportunities are consistently expected in a relatively small time-frame. It should be noted that this system is inherently capable of recognizing outstanding velocity and acceleration (as would occur on the runway) as heuristics in determining target identification. 
     Implementation of the present invention is as follows. In theory, only a single well-positioned co-located Transmitter/Receiver unit  200  is required. However in practice, it is likely that two such units may be used for enhanced accuracy, coverage, cross-reference, and redundancy. It should be further noted that receiving data from two co-located R/T stations can serve as the first step towards a complete multilateration system and can yield a core set of add-on capabilities. 
     Given the low overhead and installation costs, leasing the system (by charging only for the tagged CAT20 data) becomes a viable option that greatly improves the ability to quickly capture market-share with limited investment. 
     While the preferred embodiment and various alternative embodiments of the invention have been disclosed and described in detail herein, it may be apparent to those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope thereof.