Multilateration on Mode S and ATCRBS signals at Atlanta's Hartsfield Airport
January 8, 1998
The ATC community is seeking a way to obtain aircraft ID and improved surveillance on the airport movement area. Surface radars provide good surveillance data, but do not provide ID, may not cover the whole movement area, and suffer from false reflection targets and performance degradations in rain. This report describes an evolutionary technique employing multilateration, TCAS technology, and existing ATCBI transponders to provide the desired surface surveillance information. Five multilateration receiver/transmitters (RTs) based on TCAS units, and a central multilateration computer processor were procured and installed on the highest available buildings on the perimeter of the north side of Atlanta's Hartsfield airport. The resulting coverage was such that there was a 93% probability that a multilateration position would be computed on a given Mode S short squitter emitted from a a target at a randomly selected position on the movement area. Multilateration was performed on ATCRBS targets using replies elicited by whisper shout methods originally developed for TCAS. Measurements showed that whisper shout was successful in degarbling targets that were in close proximity on the movement area. The probability of obtaining an ATCRBS multilateration position in a given one second interval depended on the number of whisper shout interrogations transmitted. The equipment required over 10 interrogations per target per second to obtain per second multilateration update rates on two typical targets of 58% and 83% respectively. This less than anticipated performance was primarily due to the inefficient whisper shout interrogation technique that was used in the test equipment. This can be corrected in next generation equipment. The multilateration accuracy was about 20 feet one sigma, as anticipated from theoretical considerations and previous experience with other equipment. By combining the multilateration data with ASDE data and tracking the results, it would be possible to obtain track reliabilities on the airport surface similar to that obtained elsewhere in the ATC system but update rates of 1Hz as required for surface surveillance and control purposes. The RTs were also capable of receiving Mode S long squitters containing GPS position information. The probability of at least one of the 5RTs receiving a given long squitter was essentially 100% on the movement area.